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Technical Report : DEEP OCEAN POWER SYSTEMS

September 1968

NAVAL FACILITIES ENGINEERING COMMAND

NAVAL CIVIL ENGINEERING LABORATORY

Port Hueneme, California

vonGLEARED: FOR-UNEMMIFED-BISTRIBUTION

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DEEP OCEAN POWER SYSTEMS
Technical Report R-597
Y-F015-21-06-001

by

E. Giorgi

ABSTRACT

The objective of a study program on deep ocean power transmission
systems was to determine the technical and economic feasibility of transmitting
electrical power of 30, 100, 300, 1,000, and 3,000 kw to ocean depths of 600,
2,000, 6,000, 10,000, 15,000, and 20,000 feet.

Environmental conditions of the sea and their effects on the elements
of an undersea power system are discussed. Various power system concepts
are developed and evaluated in the report. Design approaches and related
studies used in the selection of the most cost effective system concepts are
presented, as are preliminary designs of a few selected concepts. Recommended
programs for the development of system elements considered beyond the state
of the art are also included.

It was concluded that within the present state of the art (1) 30 to 300
kw of usable AC power can be supplied from in-situ power plants at depths of
600 to 20,000 feet and 1,000 kw at depths of 600 to 2,000 feet; (2) 30 to
3,000 kw of usable AC power can be supplied from surface-tendered power
plants to depths of 600 to 20,000 feet; and (3) 30 to 1,000 kw of usable AC
or DC power can be supplied from shore-based power plants to depths of 600
to 20,000 feet and up to 3,000 kw to depths of 600 to 10,000 feet.

Each transmittal of this document outside the agencies of the U. S. Government
must have prior approval of the Naval Civil Engineering Laboratory.

CLEARED FOR UNLIMITED DISTRICUTICN

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CONTENTS

INTRODUCTION
ENVIRONMENT.

Sea—Air Interface

Ocean Currents

Ocean Bottom Conditions

Bottom Profiles

Slumping .

Temperature and Salinity

Marine Life .

Summary . ae ;
SUBMERGED (IN-SITU) POWER SYSTEMS .

In-Situ Power Sources .
Energy Conversion
Stored Thermal Energy
Chemical Energy .
Nuclear Reactor Energy
Radioisotope Energy
In-Situ Plant Hulls ?
Pressure Vessel Analvets :
Material Selection

Corrosion and Fouling Protection Systran :

Analysis of In-Situ Plant Configuration
Buoyancy Variations
Hydrodynamic Stability . 5
In-Situ Plant Emplacement and Recovery
In-Situ Plant Hardware.

SURFACE POWER SYSTEMS
Surface Power Sources.

Surface Plant Hulls .
Surface Hull Conceate .
Fuel Storage
Wii SYSUIN 6 ee
Upkeep Schedule .

page

Surface Plant Mooring Systems
Dynamic Moor.
Static Moor . ;
Static Multipoint Mooring
Forces Acting on Mooring System
Anchor Holding Power
Mooring System Hardware .

Analysis of Surface Plant Mooring System 5

SHORE-BASED POWER SYSTEMS .
Shore-Based Power Sources .

Shore-Based Generating Plant and Transmission
System.

CABLE SYSTEM
Cable Conductor Material
Cable Insulation Material .
Cable Sheaths and Coverings
Electrical Properties.
Mechanical Properties .
Cable Configuration .
Cable Connectors.

Cable Suspension Systems

ELECTRICAL SYSTEMS

Surface Power Systems

Alternating Current Wests Direet Curent 5

Frequency aii
Voltage Regulation .

AC Distribution System .
Transmission Voltage .
Cable Connectors.
Electrical System Cost .
Protection System

In-Situ Power Systems .

Shore-Based Power Systems.

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DEPLOYMENT CONCEPTS
In-Situ Power Plant Deployment .
Surface Power Plant Deployment
Shore-Based Power Plant Deployment .
SELECTED POWER SYSTEMS .
In-Situ Power Systems .
Surface Power Systems
Shore-Based Power Systems.
CONCLUSIONS .
RECOMMENDED DEVELOPMENT PROGRAMS
Cable Connectors.
Heat Rejection Systems
General Utility Power System .
In-Situ 3,000-kw Power Plant .

APPENDIX — Preliminary Designs of Selected Underwater
Power Systems.

LIST OF SYMBOLS

DISTRIBUTION LIST

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INTRODUCTION

The U.S. Navy has long recognized the importance of the world’s
oceans in military tactical operations. Surprise attack from beneath the sea
is a serious threat to our country, and the Navy is particularly aware of this
problem. This awareness has generated an ever-expanding program of ocean
research.

One of the major obstacles in the development of deep ocean facilities
is the unavailability of reliable electrical power for life support, lighting,
communications during the construction phase, and later, for system opera-
tion as determined by the mission of the facility. A study to determine the
feasibility of providing electrical power to deep ocean installations or load
modules was undertaken at the Naval Civil Engineering Laboratory (NCEL) a
little over a year ago.

The basic study parameters established for the transmission systems
serving deep ocean bottom installations were power levels of 30, 100, 300,
1,000, and 3,000 kw at ocean depths of 600, 2,000, 6,000, 10,000, 15,000,
and 20,000 feet. The transmission systems would be supplied from either
shore-based, surface-tendered (floating), or in-situ power sources. The
Objective of the study was to determine the economic and technical feasibility
limits of deep ocean electrical power systems and to establish preliminary
design criteria for a few selected systems. An evaluation of feasible power
sources was included within the scope of the study program. The study was
accomplished in-house and by contract with Electric Boat Division of General
Dynamics. *

This report presents a discussion of the environmental conditions of
the sea and their effect on the elements of an underwater power system.
Various power system concepts and configurations are developed and
evaluated within established design and environmental constraints. Design
approaches and related parametric studies are discussed for the selection of
the most cost effective system concepts. Preliminary designs of six concepts

* Contract Report CR-68.004, “Conceptual Study of Electrical Power Transmission
Systems to Deep Ocean Installations,’ Contract N62399-67-C-0015, Naval Civil
Engineering Laboratory, Port Hueneme, California, Aug. 1967.

of underwater power systems selected for immediate development are
presented together with budget cost estimates. A recommended research
and development program, based on the findings of this study program, is
included for those system elements considered beyond the current state of
the art.

The constraints and assumptions applied to the study program on
underwater power systems Include

1. Power levels stated shall be at the load module terminal point.

2. Usable power at the load module shall be defined as 480 volts,
3 phase, 60 Hertz, for a single, nondistributed load.

3. The load module shall be assumed to contain such electrical loads,
as lighting systems, motor-driven operational equipment, environmental
control systems, and communications or electronic systems.

4. Protective needs shall be restricted to the power transmission
system and shall not include mission requirements of the load module.

5. Emergency power levels and type of energy source shall be defined
by the power transmission system requirements and not by the mission
requirement of the load module.

The results established in this paper are based on the assumptions and
constraints described above, and are only intended to provide guidance In
making sound management decisions on the future development of underwater
power systems.

ENVIRONMENT

An underwater power transmission system is subject to all ocean
environmental conditions. The effect of sea states, ocean currents, bottom
sediments, temperature variation, salinity, and marine life must be considered
in defining design parameters for power system elements. The selection of
cable routes and sites for underwater structures depends on a knowledge of
bottom profiles and sediment types. Available data and information on the
ocean environment are summarized in this section and evaluated as to their
effect on the underwater power transmission systems and associated elements.

Sea-Air Interface
Surface conditions for a particular area of ocean deployment are

important design parameters in the development of an underwater power
transmission system. Hull shapes for surface-tendered systems, as well as for

mooring and cable support systems, are directly influenced by surface forces.
Therefore, the sea-air interface must be defined to provide a series of design
parameters for the selection of surface hull shapes. Both the average sea state
and the worst sea state expected must be considered.

Winds, gales, and storms depend to a large degree on large, well-defined
regions of high and low pressures. In general, the geographic distribution of
areas of high and low pressure is fairly systematic and does not vary much
between consecutive months. However, there are large seasonal differences
in pressure patterns and prevailing winds between summer and winter months.
Over the oceans, bad weather consisting of widespread cloudiness, precipitation
high surface winds, and turbulence is essentially a phenomenon associated with
rising air Currents or low-pressure conditions. High-pressure areas, which are
regions of descending air or surface divergence, are generally free from bad
weather. Regions which are susceptible to bad weather are the low-pressure
zones near the equator and the western and northern portions of the oceans in
the northern hemisphere, often referred to as the westerlies or migratory lows.

Winds, of course, generate waves on the sea surface, with wave heights
a function of wind velocity and duration. The worst conditions of sea state
and wave forces are described by the Guidance Committee of the Office of
Naval Research in its design recommendations as 150-mph winds and 60-foot
waves. These conditions were applied as design parameters for surface
structures, including mooring and cable support systems, associated with
underwater power transmission systems.

1

Ocean Currents

Surface and subsurface ocean currents vary in velocity, according to
location, reaching an extreme of approximately 5 knots. The average bottom
current velocity, on the other hand, does not exceed 1 knot. Equatorial and
warm currents on the western sides of the oceans, such as the Gulf Stream,
Kuroshio current, East African current, and East Australian coastal current,
have speeds of 2 or 3 knots in general.

From recorded observations of surface currents, two design conditions
were defined for the underwater power transmission systems. The first isa
maximum surface current profile of 6 knots which, in a sense, is the result of
average storm conditions. The second is a surface current profile of 3 knots,
with stronger subsurface currents to a depth of 3,280 feet. Subsurface current
velocities below 3,280 feet are generally agreed to be less than 0.35 knot. At
depths below 12,000 feet, design currents may be assumed to be effectively
zero.

The design current profiles are shown in Figure 1. These curves may
be used with other surface currents of greater or lesser magnitudes by using
the same ratio of decay.

Velocity of Current (knots)
0 1 2 3 4 ‘5 6 {0} 1 2 3 4 5

400

2,000

2,400

Depth Below Surface (ft)

Figure 1. Design current velocity profiles.

Ocean Bottom Conditions

The topography of the ocean bottom to a depth of 6,000 feet includes
continental shelves, most of the continental slopes, shallow areas of mid-ocean
ridges, the borders of atolls and islands, and the tops of some seamounts.
Depths to 20,000 feet encompass the remaining portion of the ocean floors,
with the exception of deep ocean trenches and canyons, which may extend in
depth to more than 35,000 feet. The continental shelves vary from 60 to
1,800 feet in depth and from a scarcely measurable width to greater than 270
miles wide. The average slope of the shelf surface is 0°07’, being somewhat
steeper over the inner than over the outer half. Valleys and canyons that cut
the continental shelf have slopes as steep as any on land. Shelf sediments are
primarily sands, with mud and gravel also common. Sediments of silty clay
with sand layers are found at the bottom of the shelf valleys or basins. Sedi-
ments of the continental slopes are less well known than those on the shelves.
These sediments have a low shear strength that ranges from 0.1 to 15 psi; an
average of 1 psi was considered representative.

Bottom Profiles

Knowledge of the underwater terrain Is vital to the successful
deployment of an underwater power transmission system. Bottom profiling
iS a prerequisite for establishing cable routes and site requirements and for
avoiding potential hazard areas such as steep ledges and narrow valleys.

Since there are great distance-to-depth variations in the ocean bottom
profiles, the actual cable length to reach various design depths was used in
this study. Table 1 illustrates the variations in average distances involved in
reaching the various design depths off of selected coastal regions. A minimum
offshore distance of 21 miles and a maximum of 460 miles is noted in the
table, with a majority of offshore distances of less than 200 miles, only three
distances being greater than 200 miles. Therefore, it appeared feasible to
consider cable lengths at multiples of 10 miles, with specific design lengths of
50 and 100 miles. Design distances of bottom-contoured cable lengths were
established at 10, 50, 100, and 500 miles.

Table 1. Bottom Profiles of Continental Margins

Average Number of Miles From Coast to Reach a Depth of —

600 2,000 6,000 10,000 15,000 20,000
feet feet feet feet feet feet
150

East Coast
175

ae 182 190
West Coast

28
nae 32 55 162
SSN 155 190 208 319
Asia
Seen 72 110 120
Australia

1 Qcean does not reach this depth except in isolated instances. Off the East Coast,
the West Coast, and South Australia the maximum depth is found approximately
3.5 miles from shore.

Slumping

The slumping or sliding of bottom sediments is a potential hazard to
underwater cables and structures. The kind and rate of sedimentation
required to produce an unstable slope occurs only in areas of relatively rapid
sediment accumulation. These areas include deltas and canyon heads in the
inner shelf slopes. The stability of a sedimentary deposit on a given slope
depends basically on the shear strength of the deposit and the rate of increase
of this strength with depth of burial.

The slumping of bottom sediments can jeopardize structures or cables
from either the resultant cascading sediments or turbidity currents. A classic
example of turbidity currents caused by slumping was the submarine landslide
which occurred in the Grand Banks region in 1929 following an earthquake.*
The speed of these turbidity currents has been estimated to be about 50 knots.
It becomes apparent, then, that a thorough bottom survey, including corings,
of the site and above-site slopes should be made to ensure against slumping.

Temperature and Salinity

The range of temperature and salinity in the oceans is anywhere from
about -2°C and 20% to about 30°C and 37%, with some areas having higher
or lower readings. Many of the extreme conditions are found in the Red Sea
and the Persian Gulf. The layers of the ocean are generally classified as:

Troposphere: down to about 300 feet

Thermocline: from a depth of 600 to 984 feet
Subtroposphere: from a depth of 984 feet to about 4,000 feet
Stratosphere: below 4,000 feet

Most of the temperature and salinity variations exist, along with the
strongest currents, in the troposphere. In the stratosphere the temperatures
and salinities are more uniform.

The maximum vertical temperature and salinity gradients are found
between 300 and 600 feet, in the layer between the troposphere and the
thermocline. An exception to the above classification occurs in the subtropics,
where the thermocline is found at a depth of 500 feet at 20 degrees south and
600 feet at 20 degrees north. This layer rises steadily to a depth of 160 feet
at the equator and 10 degrees north. Intensity of the thermocline Is greatest
in the equatorial areas.

Beneath the thermocline, the vertical temperature and salinity gradients
decrease with depth down to the subtroposphere.

* B.C. Heezen and M. Ewing. ‘Turbidity currents and submarine slumps and the Grand
Banks earthquake,” American Journal of Science, 1952, pp. 849-873.

Marine Life

Several types of marine organisms attack various materials used in
underwater power transmission systems. The need for information and data
on the resistance of materials to attack by marine organisms is therefore
important. There is considerable published information on the suitability of
natural organic materials, such as wood, jute, and hemp, for marine use. Some
data are now becoming available on plastics, elastomers, casting resins, and
similar materials.

The highest concentration of marine life is found in intertidal regions
and down to 600 feet, depending on the penetration of sunlight. Beyond
600 feet, to a depth of approximately 4,000 feet, an abundance of animal life
can be found, but plant life is rare. At depths exceeding 4,000 feet, the water
temperature approaches freezing, food is scarce and, therefore, marine life is
rare. Marine life in this zone consists mainly of borers, such as worms, mollusks,
gastropods, hydroids, and sea urchins.

Marine borers are mollusks or crustaceans which bore into a material
for food or shelter. Of the crustaceans, the gribble (Limnoria lignorum) is the
most destructive to cellulose materials. Most borers are found in shallow
depths; however, some boring mollusks have been found down to 11,500 feet.
Records show that the lead sheath of submarine cables were penetrated by
borers at depths of 5,600 feet.

A group of marine organisms attach themselves to exposed surfaces,
resulting in what is commonly termed ‘‘fouling.’” Associated with the fouling
organisms is a microscopic anaerobic bacteria which, because of its sulfate-
reducing character, is predominant in accelerating corrosion and destroying
nonmetallic materials. The bacteria are generally single cell organisms, a large
number of which are heterotrophic, that attack organic matter and use the
carbon as a source of energy. The bacteria play an important role in the
biology of the sea and are found in seawater and sediments from shallow
depths to the deepest areas of the ocean. Submarine cables, mooring lines,
and other power structures are particularly susceptible to deterioration by
bacteria since bacteria are most plentiful in seawater as well as in the first
few inches of bottom sediment.

Summary
An all-encompassing definition of surface conditions of the world’s

major oceans is difficult due to the large variations in weather conditions,
thermodynamics, and prevailing winds which determine the characteristics of

the first 4,000 feet of water. Below this depth, the major oceans conform to
a narrower range of limits. Table 2 presents a summary of critical environ-
mental conditions established as design parameters for the development of
underwater power transmission systems.

Table 2. Summary of Environmental Design Parameters

Surface Conditions

Wine! vellochiv, mex (molt) . .« . so 5 . « . 180

Current velociny, mex knots) ... 6... . 10

WEME NSIC ty ME (NESW) 5 5 sss no a oe 2 CO

Wener weimpermmnea(le) 2 2. 4 6s ee se) | BOA

Salinity (ppt) 35.0 (or 3.5%)

Depth (feet)
= 2,000 6,000 10,000 20,000
64.05

64.25 | 64.68 65.85

Sediment shear strength ere nn seal Mie tie. Ak 22s RR 10
Numerous energy sources and energy conversion systems are available
for power plants located below the surface of the ocean. Power plants for
deep ocean use must function with infrequent, periodic exposure to the
atmosphere. Many of the problems encountered in developing a power plant

Subsurface Conditions

Water temperature,
max (°C)

Density (lb/ft?)

Current velocity
(knots)

cE ee | Conditions

SUBMERGED (IN-SITU) POWER SYSTEMS

In-Situ Power Sources

for use in the ocean are related to combining an energy source with a
conversion system. The energy sources considered in this study for use below
the surface of the ocean are stored thermal energy, chemical energy (including
batteries and fuel cells), nuclear reactor energy, and radioisotope energy.
Storage of energy by mechanical, electrical, and magnetic methods are not of
interest at this time because of their high weight and volume characteristics or
their lack of adequate conceptual and development status.

Efficiencies for energy sources vary with capacity, temperature, and
Operation. In general, the efficiencies of energy sources considered in this
study are

%

Storage batteries(DC). . . .... =. .90

(waitin ANC finversion)). 2. oo « > . 0
Firelicellsi(DG)i 5 eat ea pee eye wrens)

(with AC inversion). . . . . . .40
Chemical and thermal dynamic ... . .30
Nuclear reactordynamic . . .... . .20
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Energy Conversion. The direct conversion of thermal energy to
electric energy can be accomplished by thermoelectric of thermionic devices.
Thermoelectric converters are generally reliable, require little maintenance or
servicing, and are desirable for low-level power sources. However, their
efficiency is extremely low. Large thermoelectric power sources and waste
heat rejection systems would be required for power levels of interest to this
study. Since this system is limited to low voltage and high amperage output,
additional power conversion equipment in pressure hulls may be required.
Therefore, thermoelectric conversion was not considered suitable as an under-
water power source at the desired power levels.

Thermal dynamic conversion systems are numerous and highly
developed. The Brayton, Stirling, and Rankine cycles are the most predomi-
nant types used for thermal dynamic conversion.

The Brayton, or gas-turbine, cycle has the lowest overall efficiency.
However, it is moderately efficient at high temperatures and at the higher
power levels. Brayton systems using oxygen supplied under pressure are more
efficient than systems using air or closed-cycle gas because of the lower
compression power required.

Stirling cycle engines are currently being developed and are
theoretically capable of very high conversion efficiencies. Actual engine
efficiencies in earlier engine tests were about 80% of diesel engines up to
several hundred horsepower. However, improved performance is considered
feasible. An advantage of the Stirling cycle is its inherent low noise level. In
size and weight, it compares with the diesel engine. The use of the Stirling
cycle as a power source for deep ocean applications was not considered
advantageous because of its developmental status and its relatively high cost.

The Rankine, or vapor-turbine, cycle is most commonly used with
steam as the working fluid. This cycle has moderate efficiencies over the
power range of interest and is adaptable to a wide range of thermal energy
input temperatures. For temperatures below 427°C, the Rankine cycle is
more efficient than the Stirling cycle, and an increasing power level favors
the Rankine cycle. Rankine cycle equipment is generally available, although
considerable engineering and design work is required for maximum economy
of weight and space as well as improved efficiencies at low power levels.

Stored Thermal Energy. Stored thermal energy may be used as an
energy source for an underwater power source. The storage material is
charged with thermal energy at the surface and must be periodically recharged.
The weight of energy storage materials is relatively high, the lightest being
lithium hydride. An estimate of the weight for a lithium hydride storage
system, including hardware, is 13 Ib/kw-hr. The overall plant efficiency
would be about 27%. Since lithium hydride has a low density, this storage
material requires a large volume. The material burns and may react violently
with moisture in the presence of air. Hydrogen contamination at high
temperature is also a problem. The developmental status, the volume and
weight units, and the requirement to frequently replenish the thermal energy
at the surface do not make the thermal energy storage system attractive for
underwater use.

Chemical Energy. Electrical power may be produced by utilizing
chemical energy. The two most predominant methods of converting chemical
to electrical energy are by direct conversion and by the generation of thermal
energy, which is then converted to electrical energy. Methods currently
available for direct conversion employ storage batteries and fuel cells. There
are a large number of battery and fuel cell systems in existence; however, only
a few are practical at this time. Virtually all chemical systems, including
batteries, either have oxygen as an initial component or derive oxygen from
chemical compounds.

A considerable number of chemical systems using fuel oil and oxygen
have been proposed and developed. These include closed-cycle diesel, gas
turbine, and steam-gas turbine, known as the Walter cycle. These cycles have

10

been developed primarily to provide power sources for limited shallow-depth
ocean applications for vehicle propulsion. The use of fuel oil results in a
waste product, carbon dioxide, which must either be pumped overboard or
compressed and stored as a liquid. This problem can be avoided by using
hydrogen as fuel.

Hydrogen Is one of the most desirable fuels because of its high energy
content with oxygen and the easily handled waste product (water). Other
fuels are available either as sources of hydrogen or as monopropellants;
however, these systems do not compare with a hydrogen-oxygen system in
terms of weight, volume, cost, safety, handling, and waste product disposal.

The use of hydrogen and oxygen as reactants allows the use of a
mechanical conversion system, such as a turbine-generator, or direct con-
version in a fuel cell. Of these conversion systems, the fuel cell is more
efficient, especially at low power levels. Fuel costs range from a low of about
$0.25/kw-hr for the fuel cell and $0.50/kw-hr for the turbine system.

Some unique problems are encountered in the storage of hydrogen
and oxygen within a submersible hull. Cryogenic and high-pressure methods
are available for storing these reactants. High-pressure gas storage is only
practical when two separate pressure hulls are used, with hull penetrations
made to the power source hull. Cryogenic liquids may be stored in a common
or separate pressure hull.

Cryogenic and high-pressure storage of hydrogen and oxygen
reactants, storage configuration, and methods of transfer to point of usage
were analyzed and evaluated for various power plant concepts included in
the study program. Cryogenic storage within a common power plant
pressure hull was considered the most suitable method since it is the lightest
and requires the least volume. The gaseous transfer method could be
accomplished by using an external heat exchanger to vaporize the liquid.

The power plant’s waste heat or seawater would provide the heat source with
a backup electrical heater to assure gas delivery in the event liquid flow
could not be obtained by the main heat exchanger.

Difficulties and problems associated with the storage and transfer of
liquified gases are numerous. Spherical containers are most efficient for the
cryogenic storage of gases, but in pressure hulls such containers cause con-
siderable loss in usable volume. On the other hand, form-fit containers weigh
more than spherical containers. However, the reduction in size of the pressure
hull by the use of form-fit containers results in an acceptable trade-off.
Another problem encountered with liquified gas is the increase of pressure
due to heat leakage during the holdtime between fueling and power plant
operation. Methods which require further study in solving this problem
include providing a supply of subcooled liquid to the storage container, using

11

the fuel during holdtime, and providing a vent capability. The next major
problem or difficulty would involve the transfer of gas from cryogenically
stored containers. The gas must be delivered at controlled flow rates and
pressures. A suitable control system must, therefore, be developed.

Many fuel cell concepts exist for a wide variety of cell types and fuels.
At present, fuel cell systems are either in development or prototype stages,
with the major effort being applied to the hydrogen-oxygen cell, which is the
most advanced type. Hydrazine-air or oxygen cells have also had considerable
development effort for land applications because of their relatively low cost
and the availability of their fuel supply.

Hydrogen-oxygen cells are of primary interest for underwater power
systems because of their high efficiency, high energy content, and easily
handled waste product (water), as well as the availability of their reactants
(hydrogen and oxygen) from numerous chemical compounds. The hydrogen-
oxygen fuel cell power source is lighter than the hydrazine-air type, but
requires a pressure hull enclosure. The hydrazine-air cell has potential as an
off-hull, pressure-compensated system which would then provide the lightest
power source.

The application of hydrogen-oxygen fuel cells as submerged power
plants will require a major design and engineering effort. The technical
feasibility of fuel cells and the handling of cryogenic reactants has been
established for surface and space applications, but the ocean environment
presents many problems to be resolved for safe, reliable, and maintenance-
free deep ocean fuel cell power sources. Therefore, the feasibility of
utilizing suitable fuel cells for deep ocean applications is not apparent at this
time, and fuel cells were excluded from the study program.

Lead-acid and silver-zinc battery systems are suitable for submerged
use. Both types are in production and have been successfully tested down to
the required depth of 20,000 feet. Nickel-cadmium and silver-cadmium
batteries are more expensive and offer no advantages. Batteries may be
enclosed in pressure hulls or in oil-filled pressure-compensated systems. The
selection of enclosure depends on the depth of power plant submergence, on
the cost of obtaining buoyancy and on safety. For the unattended system
where explosions due to hydrogen gassing are possible, the pressure-
compensated system was selected since it is safer, lighter, and less costly.

Batteries alone have a limited energy capacity as the main power
source. However, they can function effectively as emergency or auxiliary
power sources. The disadvantages of battery systems are the need for
inverters for converting DC to AC, the varying output voltage, and the losses
involved in multiple energy conversions.

Table 3 presents comparative data for lead-acid and silver-zinc
pressure-compensated battery systems. The lead-acid system is more sensitive
to temperature, has a higher initial cost because of the buoyancy material
required, has a lower replacement frequency, lower battery cost, has approxi-
mately five times the deep discharge cycle life, and is three times as heavy as
the silver-zinc system. The effects of many variables will result in considerable
variation in the cost of the battery system.

Nuclear Reactor Energy. There have been many proposals for
underwater power systems which produce electrical power from nuclear
energy by means of various fluid and conversion systems. Reactor systems
are generally classified by their coolant, namely, gas, liquid metal, organic,
pressurized water, or boiling water. A comparison of the various systems
with the same overall performance characteristics has shown relatively little
variation in total weight, space, and cost. Gas-cooled reactors tend to be
larger and heavier and require more complex emergency cooling systems than
other reactors. They must be designed against water flooding, which causes
a nuclear excursion. Their primary application has been for very large, sta-
tionary, land power plants. Liquid metal plants are primarily small and
lightweight, have a very short life, and are used for space applications. The
liquid metals are highly reactive and corrosive in contact with water. Water
leakage will probably result in a total plant loss. Although the plant is
designed for unmanned operation, shielding must be provided for test opera-
tion and maintenance. Boiling water systems eliminate the need for steam
operators by using a direct cycle with higher efficiency; however, weight
savings are questionable. Primary applications are experimental and are for
large land-based stationary power plants. Organic coolants have poor heat
transfer characteristics and require more complex systems with increased
overall plant weights.

A pressurized water-cooled reactor was considered the most suitable
reactor system for a submerged power plant in the immediate future. The
reactor has several advantages. The concept of a pressurized water reactor Is
well tested and will require a minimum amount of development effort for
this application. Besides being a long-life power source, such a reactor is
highly reliable and safe. The use of a liquid coolant is most adaptable for
providing decay heat removal systems that require no power. In addition,
since the coolant retains virtually no radioactivity within a short interval after
shutdown, shielding is minimized. The coolant system is readily sealed to
minimize loss of coolant and eliminate radioactive carry-over to conversion
equipment. The pressurized water coolant provides a fluid which is common
to both reactor and conversion systems, thus making for simplicity of
design.

13

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14

The pressurized water-cooled reactor with a steam conversion system
has seen extensive application in submersibles. However, major problems
encountered in the use of this power plant below the ocean surface include
design and fabrication problems relating to equipment size, orientation,
pressure hull limitations, and waste heat removal. Additional problems that
must be considered are those related to transportation, deployment, and
operation. These difficulties will increase with both power level and operating
depths.

The wide range of power levels
established for this study program
resulted in the establishment of two
power plant arrangements, or concepts, feacionand
based on power level. The 30-kw, 100- electrical plant
kw, and 300-kw plants are arranged in eee
a vertical cylinder, as shown in Figure
2.* Reactors are generally designed to
occupy a vertical cylindrical space for
safety requirements of gravity rod
insertion, natural convection heat

removal, and refueling. Turbine-

generator equipment, which is located conversion
machinery

in the conversion machinery area, Is
normally designed for horizontal
orientation to achieve long-life \ Shield deck NRQQQQQAAD
performance. The vertical cylinder
arrangement is suitable for deployment
but not for transportation by towing.
The plant can readily be designed for
nearly horizontal towing and vertical
operation. The reactor location at the
bottom places the reactor core at a
maximum distance from accessible
areas. The shielded water tank, with
large areas exposed to the sea, provides

* A concept for a 30-kw power plant was
developed under contract to Gulf-General
Atomic Inc. and is contained in Contract
Report No. CR68.011, “TRIGA Oceano-
graphic Power Supply for a Manned

Underwater Station.” (In process of Figure 2. In-situ power plant arrangement
publication.) for 30, 100, and 300 kw.

15

asink for other power plant cooling requirements. The relatively small
diameter of the cylinder also reduces the area of shielding necessary for
personnel occupancy. The conversion machinery located immediately above
the reactor is close to the heat source and attenuates radiation to the control
area. The control area is at the maximum distance from radioactive sources in
the cylinder. The vertical cylinder arrangement is, in general, preferable for
deployment on the ocean bottom due to its hydrodynamic characteristics, its
small area of contact with the bottom, and its stability.

This conceptual arrangement is designed on the basis that a single
turbine generator set will be used for the 30-kw or 100-kw plant. The 300-kw
plant will probably require two 150-kw horizontal units to fit within the hull
diameter, or one single vertical unit, or a high-speed, high-frequency unit.
Since a 300-kw plant will require a larger hull for heat transfer than the 30-kw
or 100-kw plant adequate space is available for any of the three alternative
300-kw arrangements. A steam turbine generator in the low power-level range
with compact size, low weight, and good performance is not an off-the-shelf
item.

Waste heat is transferred from the power plant primarily by the turbine
exhaust steam condensing directly on the inside surface of the pressure hull.
There are many problem areas to be resolved and experimental data that must
be obtained to ensure the feasibility of the hull as a heat transfer surface. The
provision and testing of reliable protective coatings are required on the
seawater side of the hull for high thermal conductivity and high resistance to
fouling.

There are two other heat removal systems within the power plant
which do not appear to pose any development problems. The freshwater
machinery-cooling system rejects its heat to the shield water, and an air
conditioning system for the plant control systems rejects the heat through
the hull via direct contact with plastic channels bonded to the hull.

The 1,000-kw and 3,000-kw plants are arranged in a horizontal
cylinder, as illustrated in Figure 3. This arrangement would have features
similar to the smaller plants. Some additional problems are noted for the
larger plants. A vertical arrangement is possible at shallow depths, but there
is little difference in plant size or cost between the vertical and horizontal
arrangements for the large plants. However, to ensure adequate natural con-
vection heat transfer from the core, a high-power reactor is generally oriented
permanently in one direction once it has been operated. It must also be
transported in the same orientation.

At these power levels, the pressure hull required to house the
equipment is inadequate as a sufficient heat transfer area. The conventional
method for removing waste heat from the hull is to use a heat exchanger piped

16

to the sea through hull penetrations. However, the technology has not yet
been developed that would allow the hull penetrations required for adequate
heat removal at the high power levels for depths of 6,000 feet and more.

In addition to the feasibility of fabricating pressure hulls of adequate
size to enclose the power plant equipment, a suitable technique for heat
removal must be developed for large submersible power plants. Because of
the major developmental effort that would thus be required, the larger
power plants of 1,000 and 3,000 kw at depths of 6,000 feet and over were
eliminated from further consideration in this study program.

A potential means of meeting large power loads |s to use several small
power sources. However, some of the technical problems involved in
paralleling multiple units are related to electrical characteristics, deployment,
and retrieval. In addition, the cost would be very great for multiple units.

conversion
machinery

reactor and
electrical plant
control

Ld

Figure 3. In-situ power plant arrangement for 1,000 and 3,000 kw.

The physical parameters of pressure hulls for various reactor power
plants at operating depths of interest are shown in Table 4. Minimum
diameters have been estimated for the reactor based on obtaining access to
the pressure hull for hull inspection and maintenance (painting). For carbon
steel hulls, these diameters vary from 9 feet for the 30-kw plant to 21 feet
for the 3,000-kw plant. Two factors which will significantly modify these
dimensions are the type of material in the pressure hull and the extensive use
of iron shielding to suppress neutron flux levels and reduce activation of the
pressure hull. The high-strength steels, HY 80 and HY 130, which contain
nickel with cobalt impurities, are not the most effective for shielding. HY 180
steel contains almost 5% cobalt and requires diameters approximately 2 feet
larger than the lower strength steels. Material activation is of importance in
the design of the pressure hull.

17/

A major consideration in the design of the reactor plant is the
refueling cycle, which may have a significant effect on cost. In addition to
the direct cost of the refueling operation, there are costs for retrieving and
transporting the power plant to a refueling site, providing refueling facilities,
and being without the plant during refueling operations. Full-power refueling
cycles based on full-time operation range from more than 10 years for 30 kw
to about 1 year for 3,000 kw, depending on the particular plant selected.
Selecting larger reactors for smaller power plants can generally extend the
refueling cycle, but this must be traded off against increased acquisition costs,
weight, and size. A larger refueling cycle is also possible by increasing the
efficiency of converting thermal energy to electric energy.

Radioisotope Energy. The radioisotope power supply considered for
the study program employs a steam Rankine cycle conversion system for
obtaining electrical power from the heat produced by the decay of radio-
isotope fuel. Only the 30-kw power level was investigated because of the
high fuel inventory cost, estimated at $70,000/kw, and fuel use cost, estimated
at $12,000/kw/yr. The break-even power level is dependent on many factors,
but in general is substantially less than 100 kw. For larger radioisotope plants,
extrapolation from the figures for the 30-kw plant should provide a reasonable
estimate since the major investment and operating costs are either due to the
fuel or proportional to it.

The 30-kw radioisotope power plant of interest here is completely
self-contained within its own pressure hull. The hull is equipped with cable
connections for supplying power and for start, stop, or monitoring functions,
as required. The plant is self-regulating and has a nearly constant output
voltage and frequency from no load to full load. Table 5 presents tentative
system data on the plant.

At the 30-kw power level, the minimum size of the pressure hull is
determined by the requirement for adequate hull area for the transfer of
waste heat. Each hull is sized to provide adequate heat transfer for operation
at all depths from 600 feet to its design depth and at a maximum ambient
temperature for each depth. Heat is transferred from the power plant hull to
the sea by natural convection for both reliability and safety.

The 30-kw radioisotope power plant is estimated to weigh 14,000
pounds, including all machining and shielding. Radiation levels at the outer
surface of the pressure hull are limited to 200 milliroentgens/hour maximum,
with considerably lower levels for access and maintenance.

Spherical pressure hulls will result in a minimum hull weight-to-
displacement ratio. However, the hull shape is not critical. For design
considerations and feasibility of fabrication, it appears that hull shapes made
of ring-reinforced cylindrical sections and hemispherical heads would be
desirable.

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19

Table 5. Tentative Data for the Radioisotope System

General

ISOWOS 2 5 o 2 o
Refueling cycle (years)

Initial fuel loading (kw) . Le Pte Beare eae

Fuel loading, end of refueling cycle (kw) . . . . 200,000
Electrical foowwarr (Kw, Met) . o 5 6 5 5 6 6 5 0 OA
Overall thermal efficiency (%) . ..... ... 16

Steam Cycle

Turbine inlet pressure (psia)

Turbine inlet temperature (CC) .
Condenser saturation temperature (°C) .
Thermal efficiency at turbine shaft (%) .

Radioisotope power plants would have limited application in
underwater power systems because of the large volume per unit of energy
available. At the higher power levels of interest to the study program, nuclear
power plants were preferred for submerged power systems.

In-Situ Plant Hulls

Hull designs for in-situ plants depend on the hydrodynamic
characteristics of the deployment and recovery method selected. The in-situ
power source and associated energy conversion equipment could be incorpo-
rated into a pressure hull as a power module for deployment to the operational
depths. The load module, which was assumed to contain conventional opera-
tional systems, as described earlier, could be deployed completely independent
of the power module. However, since wet connectors required to mate the
power module with the load module in the deployed state do not exist, both
modules must be deployed together, preferably on a common foundation.
Mating the two modules at the surface with long cables and then deploying
each module separately was considered hazardous to mission reliability.

Safety was considered of prime importance to ensure the integrity of
the entire system. A stress and material analysis of the in-situ power plant
pressure hull was required to determine the most cost effective hull for the

20

depths under consideration. A configuration analysis of the load module was
also required to compare all possible deployment concepts. A detailed
investigation of the hydrodynamic phenomena influencing the submerged
station was necessary to establish methods of deployment and recovery.

Pressure hulls for in-situ plants would be constructed in a manner
similar to existing submersible hulls. The only two pressure hull shapes
worthy of consideration for the depths under study are the sphere and the
cylinder. The shape selected depends on both the mission definition and
efficient space utilization. Relative volume effectiveness of the two shapes
is 53% for spheres, 59% for horizontal cylinders, and 93% for vertical
cylinders.

Pressure Vessel Analysis. There are two modes of failure which must
be considered for thin shells subjected to external pressures: collapse by
yielding and collapse by buckling. Minimum factors of safety applied to
these failure modes were established at 1.5 and 2.0, respectively, with local
stresses limited to 3/4 of the yield stress at operating depth.

The following equation was used for computing the collapse of spheres
by yielding: *

Z2hoy
te Tg,

The basic equation used for computing the collapse of spheres by buckling
was

h 2
Pas = 0.86 Es E+ (eo

or for elastic buckling

h 2
P., = oste (a)
Rio

where E =modulus of elasticity
E, =secant modulus of elasticity
E, = tangent modulus of elasticity

h = shell thickness, in.

* The reader is referred to the list of symbols on the foldout page at the end of this
report.

21

Pop = critical buckling pressure, psi

Py = critical yielding pressure, psi

Rio = local outside radius of a spherical shell, in.

o, =yield stress, psi

The equations governing the collapse of cylinder shells are considerably
more complex than for spheres. A method developed by General Dynamics*
was used to analyze the collapse by yielding of a cylinder and hemispherical
cylinder heads. This method calculates outer fiber, midfiber, and inner fiber
stresses at frames and midbay as well as deflections and local stresses.

Computations were made for two types of collapse of a cylinder by
buckling. Lobar buckling was approximated by

h 5/2
2.42E 2a

a Te
(1 - ys) 7 Da (0.45) (2 ah)

PL

Buckling by instability was approximated by

PL = Eh Sasi alu Othe tay Oe + (ie DED
a (" eae m8 £ ey R?
2
where P, = lobar buckling, psi
E = modulus of elasticity
h = shell thickness, in.
a = nominal outside shell radius, in.
Bb == ~Poisson’s ratio
n = number of lobes
m =a/L
L = effective length of cylinder, in.
| = moment of inertia of shell frame
R= = radius of frame-shell section, in. »

* General Dynamics, Electrical Boat Division. ‘‘Circular Cylindrical Shell with Bulkheads
and Intermediate Stiffeners Subjected to Hydrostatic Pressure.”’

22

The above computations are considered conservative for nominal
pressure hull collapse loads. However, a detailed analysis of the final structure
design for a submersible hull is required before definitive collapse pressures
can be defined.

Material Selection. The selection of materials for in-situ plant pressure
hulls depends on submergence depth, size, cost, and weight-to-displacement
ratio. HTS and HY 80 steels were selected for hulls at depths of 600 to
2,000 feet, HY 130 steel for hulls at depths of 6,000 to 15,000 feet, and
HY 180 steel for hulls at depths of 15,000 tc 20,000 feet. As stronger
material becomes available, a reevaluation of the material selection should be
made for these depths.

Corrosion and Fouling Protection Systems. A 5-year or more
no-maintenance mission was established for the in-situ plant pressure hull.
To meet this requirement, very high quality corrosion protection systems
are required. Paint coating systems, metallized coatings, antifouling paints,
and cathodic protection systems were considered. The preferred systems
selected for a 5-year no-maintenance life include the following.

1. Paint coating systems consisting of zinc-based primers followed by
several coats of vinyl or straight epoxy paints, with one or two
coats of copper-base antifouling paint on the outer surface.

2. Metallized coating systems consisting of 3 to 5 mils of flame-sprayed
aluminum sealed with a combination of vinyl! sealing and top coating
paints and finished with a full wet coat of organotin antifouling
paint.

3. Cupronickle plating systems for steel hulls applied by explosive or
roll bonding or flame spraying to provide a corrosion-resistant sur-
face with inherent antifouling characteristics.

For long life, supplementary cathodic protection should be provided
in areas where noble metal is concentrated or where stray electrical currents
can occur. Both sacrificial zinc anode and impressed current systems can
serve this purpose. The preferred protective coatings would have to be
analyzed further to determine their relative heat transfer characteristics on
pressure hulls used as heat exchangers.

Analysis of In-Situ Plant Configuration
Several constraints, assumptions, and requirements dictate the

configuration or arrangement of the in-situ power plant and its deployment.
Since it was established that the load module would be deployed with the

23

power module, additional assumptions must be made. For the purposes of
this study, the load module is assumed to have the same volume as but less
weight than the power module. It was also assumed that the load module
was contained in a single cylindrical or spherical pressure hull. If the load
was inhabited, personnel shielding and personnel transfer chambers, which
add weight and volume to the load module, would have to be considered.

Several arrangements were considered for the power and load module
configurations. The conceptual arrangements included power plant and load
modules side by side, load module mounted atop the power plant (piggy
back), load module remotely located from power module, and load module
and power module in a common pressure hull. Figure 4 illustrates some of
the conceptual arrangements considered in this study.

The in-situ plant configuration would be selected on the basis of
power level, load module dimensions, load module weight, and load module
mission. The power level effect is determined by the requirement for vertical
cylinder or horizontal cylinder pressure hulls. A limitation on the selection
of a configuration can be made by considering the weight of the load module.
To avoid requirements for trimming, the load module could be situated side-
by-side with the power module if the weights are identical. If the weights
are not equal, then the load module (assumed the lightest) could be mounted
atop the power module. The arrangement selected must maintain the overall
center of gravity within limits governing hydrodynamic stability and must
resist overturning moments. The mission of the load module and the orienta-
tion of the load module relative to the ocean bottom have a definite effect
on the selection of the in-situ plant configuration.

Buoyancy Variations. Variations of buoyancy with depth must be
evaluated before a final in-situ plant configuration is selected. These changes
in buoyancy are dependent on the physical environment in which the plant
operates and the characteristics of the pressure hull and its materials. Since

B = dV
it follows that
AB = dAV + VAd + AdAV

where B = buoyancy
d =density, Ib/ft?
V =volume, in.?

A =a discrete change to the particular factor

24

The volumetric change (AV) is dependent on changes in pressure and
temperature that the hull experiences in going from the surface to some
depth. Thus

K

Oo

Av = AV, + AV, = Vo( + eu

where AV, = change in volume due to pressure

AV, = change in volume due to temperature

<
|

= jnitial volume at zero pressure

a
a
I

change in pressure
K, = effective bulk modulus of the hull = P/(V/V,)

@,, = volumetric coefficient of thermal expansion for the hull
and its material

At =change in temperature

An accurate determination of bulk modulus (K,) requires volumetric
calculations based on changes in hull dimensions due to pressure effects. The
value of the bulk modulus used for configurations under consideration was
4x 10° psi.

The coefficient of thermal expansion for the hull is dependent on the
hull material and was taken as 0.117 x 10°7/°C for steel. The maximum
temperature change applied to the analysis was 11.7°C.

The change in density is also dependent on pressure and temperature
changes plus the effects of salinity variations. Two methods were used in the
buoyancy analysis to determine the change in density. In the first method
density was determined from

Nie 62.42
Vv
ame 62.42 AV
‘ a2
where d =density, Ib/ft?
v = specific volume

AV =change in volume

25

Ag

\\

The change in specific volume for seawater as a result of the changes due to
temperature, salinity, and pressure was determined from

Av = AV, + AV

p
where AN Ot
AW. = AAI.
Q@, = coefficient of thermal expansion
At =temperature change
Av =change in specific volume
K, = effective bulk modulus

In the second method the change in density due to temperature and salinity
was determined from changes in specific gravity, or

Ad,, = 64.176 (AP)

64.42 AV,

and M3
2
Vv
The above analysis demonstrates that a submerged object will gain

buoyancy during descent. This behavior results in a decreasing velocity as the
plant descends to the bottom and allows it to return to the surface by
jettisoning diving weight. The change in buoyancy establishes the amount of
diving weight required and presupposes that the plant without this diving
weight is neutrally buoyant near the surface.

Hydrodynamic Stability. A careful study of the plant’s hydrodynamic
characteristics was required to achieve both hydrostatic and dynamic stability
and to properly configure an in-situ plant for successful deployment. A
detailed analysis of the equations of motion of vertically rising or falling
bodies in a fluid established velocity and displacement history curves and
determined the drag coefficient and amount of ballasting required for neutral
buoyancy at the bottom.*

For the plant to be hydrostatically stable, the center of gravity must
be below the center of buoyancy to assure that the plant will not capsize. The
center of gravity of the plant should also be ahead of the hydrodynamic
neutral point. Consequently, it may be necessary to add stabilizing devices
(fins) at the upper end of the plant in descent and at the lower end in ascent.

* Contract Report CR-68.004, op. cit.

27

The investigation of the complete equations of motion would require
a complete knowledge of the coefficients representing hydrodynamic forces
and moments. Since the in-situ plants under study may have irregular or
unconventional forms, model tests should be undertaken to more accurately
establish hydrodynamic characteristics for validating the final design.

In-Situ Plant Emplacement and Recovery. The emplacement and
recovery of an in-situ power plant is cost!y and risky. For this reason, these
operations are extremely important and deserve detailed analysis and careful
planning.

Emplacement and recovery concepts considered for analysis were free
descent and ascent, forced descent and ascent, guided descent and ascent, and
combinations of these concepts.

The concept of free descent and ascent is based on a free, powerless
descent using negative buoyancy. The prime disadvantage of this concept is
that the bottom positioning during free descent is somewhat random.

Figure 5 illustrates how buoyancy, net downward force, and descent velocity
may be expected to vary with velocity.

A free descent begins with the in-situ plant on the surface and rigged
for free descent (stabilizers rigged, proper trim, etc.). A set of tanks may be
flooded to cancel a small amount of reserve surface buoyancy. The plant then
will take on negative buoyancy and sink. As the plant sinks, two parameters
change: seawater density increases with pressure and external pressure Causes
the pressure hull to contract, thereby reducing total displacement. The net
effect causes the plant to become slightly more buoyant with a proportionate
decrease in net downward force, which causes the plant to gradually slow
down. With proper negative buoyancy, the plant should begin its descent at
about 3 to 4 fps and approach the bottom at 1 to 2 fps. A hanging weight
suspended 100 to 200 feet below the plant will make the initial contact with
the bottom and the plant will immediately decelerate to a stop. The plant
could be positioned at the bottom by mechanical means such as a power
winch. If the plant is to be positioned on the bottom, a foundation analysis
will be required. Temperature variations encountered during descent and
while the plant is positioned at the bottom will affect the plant's buoyancy.
These variations must be factored into the final in-situ plant pressure hull
design. Water absorption and fouling should also be considered for an extended
deployment time. The plant may be surfaced by free ascent. Prior to ascent,
the stabilizers must be rigged at the bottom, the trim adjusted, and the plant
must then be released completely from hanging weights. As the plant ascends
it is opposed by drag and gravitational forces and will reach its terminal
velocity when the net buoyancy forces, and therefore the velocity, decrease.
A terminal velocity of 3 to 4 fps is expected. Once on the surface, the surface
tanks can be blown for reserve buoyancy to keep the plant stable.

28

sea surface

anchors hit bottom

= i + Buoyancy Net Downward Force Descent Velocity
1

(a) Free descent.

sea surface
fe
=
Q
o
a
drag force
sea bottom
Buoyancy Net Downward Force Descent Velocity
(b) Free ascent.
sea surface
a descent curves f
z= ascent i
i curves
aD !
= !
sea bottom
'
— | + Buoyanc Net Downward Force Descent Velocit
1! y v7 /
'

(c) Forced descent and restrained ascent.

Figure 5. Hydrodynamic profiles of buoyancy, force, and velocity.

29

Forced descent and ascent can be accomplished by using the tension
in a wire rope to pull the positively buoyant plant down. Tension may be
induced by a winch in the plant or on the surface of the plant. The effective
drum diameter will increase as the plant descends which, with constant
torque applied, will cause the plant to slow down with depth. The analysis
begins with the plant on the surface and rigged for forced descent by the
winch-down method. The winch and rope must be contained below the
plant’s center of gravity. Reserve buoyancy tanks and stabilizers were not
included in this analysis. The rope would be level-wound on the drum and
monitored for constant tension. Loss of tension would indicate that the
plant is sinking, which requires dropping emergency ballast for more positive
buoyancy. As the plant descends, it experiences the same buoyancy
variations as the free descending plant. A bottom-sensing device would
provide a signal to decelerate the winch for bottoming. A certain amount of
tension must always be maintained in the winch rope during and after
deceleration. Temperature variations would also affect this method of
deployment. The plant would surface by reversing the winch operation. The
advantage of the forced descent method is that it allows the plant to be
positioned on the desired site. A free ascent must be provided for emergencies.
Should a winch failure occur, the winch, drum, and cable would be jettisoned
to remove the anchor restraint. If the load module becomes flooded and the
power module is not flooded, the load module could be jettisoned.

In a guided descent the in-situ plant slides down a vertical guide rope
in a ballasted descent. The rope would be anchored at the desired bottom
location. A hanging weight slows the descending station by actuating a brake
on the guide rope. The plant surfaces by dropping ballast in a free ascent.
The magnitude and rate at the brake is applied when bottoming Is critical
because the rope could break. For this reason, the guided descent was not
given further consideration.

In-Situ Plant Hardware. Base legs for the in-situ plant would provide
stabilizing surfaces during descent and ascent, a broad base when the plant is
on the bottom, large bearing areas for soft bottoms, and a means for plant
leveling. The legs could also be used to house TV cameras and lighting. Each
leg would consist of a stiffened A-frame made from light pipe sections hinged
to the plant base. Brakes would be fitted to drums mounted on the hinge pin
to control the leg attitude and to absorb moments resulting from leg reactions.
Leg rotation (down) is accomplished by releasing the brakes. Although the
operation does not require it, the legs could be elevated by using a motor-
driven worm gear in each hinge. Large pads could be fitted at the end of each
leg. The pads would consist of a snow-shoe base to provide support in soft
bottoms. The entire pad is connected to the leg end by a pin, permitting it to

30

assume an appropriate attitude with the bottom topography and leg
orientation. The pads would have sufficient area to reduce bearing pressures
to less than 1/2 psi in currents up to 1 knot. The torque and thrust at the
brake drum and hinge pins amount to 17,500 ft/Ib and 18,000 pounds,
respectively, when a single leg resists a current of 1 knot.

Main ballast tanks would be used to provide free-board when the plant
is on the surface. Flooding the tanks on the surface would provide the proper
buoyancy for diving. The tanks could be located in the foundation area of the
in-situ plant.

The use of a shaped diving weight has significant advantages. |n mud
bottoms, the diving weight should have a small projected area to allow pene-
tration into the mud, and the shape should also resist pulling out once in the
mud. For hard bottoms, the diving weight should make use of flukes or
claw-like protrusions. No retrieval system is necessary for the diving weights.

A free descent winch would be provided to control the rope length
between the hanging weight (diving or velocity control) and the plant. Once
the hanging weight is resting on the ocean bottom, the winch is used to bring
the plant into its operational position.

The forced descent and ascent winch could be powered by a
submersible electric motor through a gear drive. The drum could be sized to
handle a length of rope slightly larger than the depth of operations. The
winch could have constant-tension, level-wind capability in each direction.
The entire winch and drum assembly could be considered jettisonable ballast.

Syntactic flotation material could be utilized to achieve overall trim
and stability and to make components positively buoyant so that they will
return to the surface if jettisoned. Two types of flotation material are
available. The first type is capable of withstanding hydrostatic pressures up
to 4,500 psig and the second type can withstand pressures up to 10,000 psig.
Flotation material may be cast in modular blocks to facilitate buoyancy
distribution in the plant. The in-situ plant must be in trim and balance with
respect to major ballast and flotation material before it can be deployed from
a shore base to an operational site.

SURFACE POWER SYSTEMS
Surface Power Sources
Any power plant that has unlimited access to the earth’s atmosphere

can employ virtually any energy source and energy conversion system.
Economically, however, the selection is limited to the use of the hydrocarbon

3]

(fossil) fuels with internal combustion engines and steam or gas turbines. The
specific selection of fuels and conversion system will depend on such factors
as power level, efficiency, fuel logistics, system availability, and operating
cost.

The liquid and gaseous fluid were considered the best suited for power
levels of 30 to 3,000 kw because they require a minimum of handling or
processing equipment. Fuel oils are generally the most readily available at
the lowest cost. Further, the fluid fuels may be used with all conversion
systems and will not influence the selection of any one conversion system.

The diesel engine was preferred to the steam or gas turbine as a prime
mover for practically all the criteria established for the study program. Spark
ignition engines were not considered because of their low efficiency and the
requirement for highly volatile fuels. The diesel-driven generator system is
approximately twice as efficient as the steam or gas turbine for the power
range of 30 to 3,000 kw, with overall efficiencies of 17% at 30 kw, 27% at
100 kw and 30% from 300 to 3,000 kw. Increased efficiency results in sub-
stantially lower fuel cost and has a large effect on logistics support. The
diesel engine also has a lower acquisition cost and is readily available in a wide
range of capacities to match system requirements.

Steam and gas turbines are generally restricted to higher power levels
because of poor performance and because of their limited availability at the
low power levels. The gas turbine weighs less than the diesel engine, but this
advantage is quickly offset by the increased weight of fuel that must be pro-
vided for the gas turbine. The steam plant is generally larger and heavier and,
for the power levels of interest, less efficient than the diesel system. Reactor
power sources were not specifically considered for applications other than the
in-situ power plants since they are not economically competitive with fossil-
fueled systems at the power levels of interest.

The diesel engine may be employed as the shore-based or ocean surface
power plant for the 30 kw to 3,000 kw power levels. Table 6 presents typical
data for diesel engine generator sets over the range of interest for the surface
power systems, with transmission losses limited to approximately 5%. Shore-
based systems with long transmission lines will require correspondingly larger
power plants.

A single engine generator set results In a minimum of complexity
in instrumentation and control and is the most economical installation.
However, reliability of the load module may require redundant equipment.
Life expectancy of a diesel generator is estimated at 20 years, with programmed
preventive maintenance. For ocean surface power plants the major maintenance
cycles can be scheduled to coincide with hull or buoy maintenance.

32

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Major systems required for the diesel power plant are fuel, air, intake,
exhaust, waste heat removal, engine control and instrumentation, electrical
power control and instrumentation, and engine starting. Seawater cooling
can be used with plants equipped with a freshwater loop to protect the equip-
ment against seawater contamination.

A wide variety of commercial equipment is available for diesel power
plants and will not substantially change the power plant design data. Present
equipment is capable of maintaining a steady-state voltage regulation of 1% at
the low power levels and a much narrower limit at the high power levels.
Steady-state frequency can be held within 3% with standard speed-governing
equipment and within 1/2% with electronic frequency-sensing equipment.

Surface Plant Hulls

The selection of hull shapes for surface-tendered generator plants was
based on the following considerations: continuous operation under extreme
weather conditions; unattended deployments for long periods of time; and
safety of the generator plant, associated systems, and load module. The
environmental sea-air conditions established previously required the surface
plant to withstand 150-mph winds, 60-foot waves (breaking), and 10-knot
ocean currents.

Since the surface plant is to be unmanned, all systems must be
automated. For example, trim and compensation systems for the surface
hull would be controlled by radio or other suitable means. Safety is of the
utmost importance to protect the integrity of the entire system and to assure
continuity in the supply of electrical power

Surface Hull Concepts. The use of a floating instrument platform
(FLIP) type ship was considered as a surface plant hull. Although it would
provide an excellent surface plant, it was eliminated from further analysis
because of excessive cost. Similarly, use of a Fleet submarine was eliminated
due to high cost. Nomad-type buoys were investigated, but such buoys
exhibit resonant motion, which would be detrimental to a surface plant. The
possibility of using a submerged surface plant to eliminate the effects of the
sea-air interface was also investigated. Such a plant would have to be sub-
merged at least 100 to 200 feet, requiring a snorkel mast of equivalent height.
A snorkel mast of this height was not considered structurally feasible, and if
it were it would induce surface effects on the submerged plant. The snorkel
mast could be seriously damaged by refueling or by other vessels. The
submerged plant would also have a higher hull cost and a higher deployment
cost. For these reasons, it was also eliminated from further investigation.

34

The surface power plant
containment hulls selected for study
were unmanned, double-hull, thick-
disc, surface-following steel structures
of modular construction. Three basic
hull designs were established for the
five power levels selected for the study
program. The hulls are not space
limited and, therefore, eliminate
arrangement problems. Snorkel
systems are included with all hull
designs. Modular construction permits
the complete interchange of machinery

space to eliminate at-sea overhaul and _
increase reliability. A typical configu- SS

ration of a thick-disc hull for a surface

power plant is illustrated in Figure 6.

The hulls selected have been scaled to

approximately the same proportions Figure 6. Configuration of a thick-disc hull

: : for a surface power plant.
as the dimensions of the General
Dynamic monster buoy.* Since the
structural design is available, the
thick-disc hull would provide optimum performance at minimum cost. Table 7
summarizes all the characteristics of the thick-disc hull. Machinery weight, hull
weight, reserve buoyancy capacity, usable interior volume, fuel storage and
trim system capacities, hull characteristics, and typical fuel replenishment are
all defined in the table. The reserve buoyancy capacity for larger plants was
reduced to allow for a larger on-board fuel supply. This added fuel supply
would provide a more reasonable refueling cycle for the larger plants. All
surface hulls were sized to carry an additional 50,000-pound external load
imposed by the underwater transmission cable. The trim system was sized to
compensate for variations of the external load.

A welded, double-hull construction from low carbon steel was
recommended for the surface hulls. The external skin should be fabricated
from 1/4-inch plate of higher strength steel. An entrance hatch, air intake
and exhaust stacks, navigational lights, and radio antenna would be supported
or contained in the snorkel mast. All surfaces of the hull would be painted
with corrosion-resistant coatings for protection against the ocean environment,
leakage, flooding, and condensation.

* A. R. Devereaux and F. Jennings. ‘The monster buoy,’’ Geomarine Technology,
April 1966.

35

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Fuel Storage. Transportation is the variable factor in fuel costs, which
vary in proportion to the quantity of fuel and the distance of delivery. The
number of surface hulls serviced affects the cost of fuel. For distant surface
hulls, fuel costs can be a significant percentage of the total operating cost.
Optimum quantities for delivery would be 150,000 gallons. Quantities larger
than this require tanker-size ships. Typically, delivery costs are 0.4 cents per
gallon for a 90-mile delivery and 1.1 cents per gallon for a 240-mile delivery.
These delivery distances would represent the average distances necessary to
reach depths of GOO to 6,000 feet, respectively. The largest surface hull
considered had a fuel capacity of 65,000 gallons.

The fuel storage capacities of a surface hull, shown in Table 7, were
obtained by trading off reserve buoyancy capacity, hull diameter, and height.
The maximum proportion of diameter and height for surface hulls was
established at 55-1/2 feet by 11-1/2 feet; these values are based on values
scaled from the monster buoy to maintain good hydrodynamic characteristics.

Trim System. An automatic trim system was recommended to trim
the surface hulls as fuel is consumed. An emergency system is also incorpo-
rated and is capable of pumping overboard all fuel and seawater ballast and
securing all engines in the event of serious flooding or collision. This
emergency system requires air banks and compressors which would normally
be required for the larger generator plants. The trim system would also
compensate for variations of the external transmission cable loading.

Upkeep Schedule. A major factor in deploying a surface hull is the
laying and installation of the multipoint mooring system. It is not considered
feasible after deployment to take the hull up periodically for overhaul or
component replacement. For this reason, a mean-time-between-overhaul
was established at 5 years for the surface plant hull. This may not be con-
sistent with machinery overhaul within the plant; however, the machinery
can be interchanged with overhauled equipment. This arrangement Is
preferred to at-sea overhaul or lengthy maintenance of the machinery.

Surface Plant Mooring Systems

The forces and phenomena involved in mooring thick-disc hulls for
surface-tendered power plants were defined and analyzed. Once the mooring
requirements were established, mooring system configurations were developed
and evaluated for the most cost effective systems. An investigation of mooring
systems, forces acting on mooring systems, and auxiliary mooring equipment
and components were all included in the analysis.

Si

Dynamic Moor. A dynamic moor consists of propulsion devices
which will permit forces to be applied to the hull in any direction to keep it
in a stationary position against forces of wind and sea. The dynamic moor
requires an automatic sensing device which will accurately locate and hold
the hull with respect to the desired position on the bottom.

A dynamic mooring system is relatively costly because of manning
and logistics problems, and its reliability for use with underwater power
systems is questionable. For these reasons the dynamic moor was not inves-
tigated further. As the state of the art of this mooring technique advances, a
reevaluation would be recommended.

Static Moor. A static moor consists of a wire rope or chain connecting
the surface hull to a device on the ocean bottom which is capable of develop-
ing an anchoring or holding force. Several anchoring devices are available, the
most common of which is the fluke anchor. Three types of static mooring
systems were considered: the simple catenary, the taut line, and the com-
pound catenary. They are illustrated in Figure 7.

The chief disadvantage of a simple catenary is the extremely long scope
required for great depths. On the other hand, a taut mooring line requires an
anchoring device capable of developing a large vertical component of force.
Such an anchoring device would have to be fixed to the bottom by grouting.
Because techniques for emplacing a fixed anchor were considered developmental
the taut mooring line was not considered further in the study program.

A four-point compound catenary mooring line was selected for the
surface plant mooring system because it would provide reasonable scope
requirements and adequate holding power by means of a fluke-type anchor.

Static Multipoint Mooring. A four-point moor may be considered as
a system of two 2-point moors lying in normal planes. An elevation of one
plane of a typical four-point moor is illustrated in Figure 8. The anchor
spacing would be equal to X + (S - Y) + 22 and the thick-disc hull neutral
position equal to 1/2[X + (S- Y)] +, where & is the horizontal distance
between the hull and any intermediate cantenary support buoys. Figure 9 is
a plan view of the excursion boundary for a four-point moor. This envelope
is circumscribed by the maximum horizontal projection (X) of each mooring
leg. The path of the relaxed leg (S - Y) is also shown. To prevent the moor-
ing ropes from dragging back over themselves, X should not overlap S - ¥ at
any location. When an excursion force (F) is applied colinearly to any single
mooring leg, the moor is holding in its weakest condition; the strongest
condition occurs when an excursion force is at 45 degrees to the hull. The
maximum excursion for a four-point moor was determined from the equation

Go = AD 2 (Sey)

38

anchor

surface plant

(a) Simple catenary mooring line.

anchor

surface plant

(b) Taut mooring line.

anchor

surface plant

chain segment B

(c) Compound catenary mooring line.

chain segment A

Figure 7. Static mooring systems.

39

=< 150 x 10°

anchor spacing = X+(S-Y)+2 Q

ae

neutral position
of buoy

+ [x+ts-¥] +Q

Figure 8. Elevation view of one plane of a typical four-point moor.

Figure 10 illustrates a three-point mooring system excursion envelope.
The shaded area represents the slack rope in excess of (S - Y) that can be laid
on the bottom. This slack would cause the wire rope to foul, kink, and
entangle. Accordingly, the three-point moor was not considered further in
the study.

Forces Acting On Mooring System. The weight of the mooring system,
which increases in proportion to the anchoring holding power and the depth,
must be supported by the surface hull. If the hull is not large enough for
supporting the weight, an intermediate catenary support buoy must be used
to support the weight of each mooring leg segment. The support buoys must
withstand sea pressures at depths corresponding to the 60-foot wave height
expected. The forces acting upon a moored surface hull are created by wind,
waves, and ocean currents. Surface conditions established for the study pro-
gram were 150-mph winds, 10-knot currents, and 60-foot-high breaking waves.

Wind not only applies force to the hull structure above the surface but
creates waves and currents as well. Model tests were conducted at the David
Taylor Model Basin to estimate the force on a moored hull from wind at
various velocities. These wind forces were extrapolated from the scale model
to the full-size hulls used in the study.

40

extreme force oe

vector polygon

Figure 9. Four-point mooring system excursion.

Figure 10. Three-point mooring system excursion.

41

The basic formulas used for wind and current are similar, but because
of the higher specific gravity for water, the forces induced by even the slowest
currents are significant. Surface plant hulls, which were established as sym-
metrical, exhibit an optimum aspect to any direction of the ocean current.

The wave forces that act on a moored surface hull fluctuate and are
caused by three characteristics of a wave. First, the oncoming wave heave
the hull upward. Second, the wave causes the hull to slide down its slope.
Third, the wave subjects the hull to the increased velocity of the water
caused by the orbital motion as the wave crest forms. Wave forces are
periodic, causing the mooring leg and anchor system to react very much like
a weight on aspring. The problem of analyzing the transitory force on the
mooring leg when disturbed by the wave force is complex, and any solution
is peculiar to a given sea-air condition. The possible conditions which may
exist are infinite. For this reason, wave forces are usually neglected when
moors are designed, but a sufficient safety factor is allowed for environmental
conditions.

Anchor Holding Power. A fluke-shaped anchor was selected for use
with the mooring system. The important parameter in the shape of the fluke
is the moment of the fluke about the trunnion. The greater the first moment
of the fluke area, the greater the anchor’s holding power.

The maximum angle which the fluke makes with the shanks affects
the holding power of an anchor in any type of ocean bottom. The optimum
fluke angle is not the same for all types of bottom. Past tests have indicated
that maximum holding power is attained in a mud bottom when the fluke
angle is approximately 50 degrees, whereas in a sand bottom the optimum
angle would be about 26 degrees. Figure 11 illustrates the effects of fluke
angle on the holding power of an anchor.

The maximum anchor holding power is also developed when the pull
extended is parallel to the bottom. If the anchor end of the mooring leg
rises so that the angle of pull (that is, the angle of the mooring leg tangent at
the anchor) begins to exceed critical values, the flukes of the anchor tend to
break out of the bottom. Figure 12 illustrates the effect of the angle of pull
on the anchor’s holding power. A few hundred feet of chain and a clump
are generally attached to the anchor shank to help hold it on the bottom
and maintain the desired shank angle. Figure 13 illustrates the effect of
anchor drag upon holding power.

Mooring System Hardware. Conventional anchors are established
pieces of hardware with proven reliability. Table 8 gives the holding power
and weights of various conventional anchors. Development work is currently
progressing to create new and better anchors. In the past, anchors have been
pulled over the bottom to make them dig in; however, this method may not

42

suffice for surface plant mooring systems. Alternative methods would be to
grout the anchor into the bottom or use explosives to drive it in. The
advantages of these methods are high reliability and holding power that

is not directionally dependent. However, the state of the art in deploying
grouted pile anchors at depths of interest is not sufficiently advanced for use
on the surface plant mooring system.

Table 8. Holding Power and Weight of Conventional Anchors

Maximum Holding
Power in Sand
(Ib)

Type of
Anchor

LWT 75,000

Bal 106,000

wedge block

LWT
wedge block

LWT
wedge block

EBIEES 80,000

175,000

430,000

Conventional anchors of the LWT wedge block design were selected
for the surface plant mooring system. An electronic device that can be
attached to the anchor is available to determine when the anchor has dug
into the bottom.

Wire rope manufacturers and the petroleum industry are significantly
advancing the state of the art of undersea wire rope. Stainless steel wire rope
in underwater applications is susceptible to chloride stress corrosion. Stainless
steel ropes have failed as early as 4 to 5 months after deployment. Programs
to use plain steel and zinc-coated steel indicate that maximum deployment
time for these ropes is 3 years. Cathodic protection for deep ocean applica-
tions is developmental and not available. For purposes of the study, a
polyurethane-clad, three-strand, torque-balanced steel rope was selected for
a 5-year deployment life. Swivels must be provided for terminating the ends
of the wire rope so that end fixing can be avoided. Figure 14 is a conceptional
sketch showing a method for attaching a wire rope to a terminal swivel socket.
Many wire rope moorings are suspected of fatigue failure. Therefore, vibra-
tion dampers should be provided on the terminal swivel.

43

Actual Holding Power
Maximum Holding Power

Fluke Angle (degrees)

Figure 11. Effects of fluke angle on holding power.

Deep sea synthetic mooring rope, such as dacron, nylon, and
polypropylene, is currently available in various types. All synthetic fibers
creep under load. For a 5-year life, this creep will not present a problem if
the working strength is kept below 25% of breaking strength for nylon and
30% for dacron. However, short-term loading equivalent to 90% of breaking
strength is not unrealistic. Synthetic rope is susceptible to failure if a
significant portion of its fibers are abraded. This requires that the line not be
allowed to lie on the bottom or pass over jagged crevices. Synthetic rope
failures usually occur near splices and connections. Therefore, care must be

44

taken in the proper design and application of juncture techniques. The
elongation of synthetic rope is caused by the braiding and plaiting of the
rope. New developments in synthetic fiber may soon eliminate the elonga-
tion problem. Polyurethane coverings on the rope would eliminate the
problem of fish bites. Because synthetic ropes do not appear to be well
enough advanced for deep sea mooring systems, they were not selected for
use on the surface plant mooring system.

Two types of chains are feasible for use on surface plant mooring
systems: 1020 carbon steel and 8620 high-strength steel alloy chain. The
latter was chosen because of Its high reliability. It was recommended that
the chain be proof-tested at half the breaking strength and rated at half the
proof-test value.

1.0

0.8

9
(o>)

Actual Holding Power
Maximum Holding Power
i
L

0.2

Angle of Mooring Leg Tangent at Anchor (degrees)

Figure 12. Effect of angle of anchor pull on holding power.

45

Drag Force

Maximum Holding Power

Anchor Drag Distance (ft)

Figure 13. Effect of anchor drag on holding power.

swivel socket neoprene

vibration damper

Figure 14. Method of attaching wire rope to a terminal swivel socket.

46

Catenary support buoys should be manufactured from A-212
normalized steel plate, with internal structural members and ribs fabricated
from A-36 silicone steel. The buoys’ surfaces must be coated for protection
from corrosion. The buoys should be provided with leak detectors having an
alarm circuit connected to the surface plant alarm system. Automatic bilge
pumps operated from batteries should be provided for support buoys. A
circumferential pipe structure should be provided to protect the buoys from
collision by ocean vessels. Navigational lights on suitable masts would be
required.

Analysis of Surface Plant Mooring System. The sizing of mooring
systems for the surface plant is determined by the mooring leg holding force
required. Computed component drag forces for each power level at the
selected depths are shown in Table 9. Wind and drag forces were combined
into a total drag force for each condition. The required mooring leg holding
power of 150,000 pounds was assumed. The difference between maximum
holding power and the total drag force represents the wave force allowance.
The ratio of wave force allowance to maximum holding power was established
at 0.6 for the smallest hull-power-depth combination and 0.15 for the largest.

Once the required holding power of 150,000 pounds has been
assumed, it is possible to trigonometrically compute the limiting angle and
magnitude of the vertical component of force for standard wire rope sizes.

A vertical component of force at any point in a catenary is equal to the total
weight of the leg suspended beneath it. Thus, a smaller wire rope Is required
to support the leg below any given point. Use of a larger wire rope size for
the entire length of the rope will increase the scope required.

In acompound catenary arrangment, the size of the mooring legs
was determined by establishing nomographs and alignment charts to provide
data which would otherwise be obtained from trial and error solutions.

It is characteristic of the catenary that for mooring legs of equal
weight and bottom angle, the angle at the top will remain constant regardless
of weight distribution along its length. The weight distribution will affect
the scope, and accumulating leg weight into a clump will significantly change
the scope. From a cost effective standpoint, wire rope at $5 per foot can be
replaced with equivalent clump weight worth $0.35 per foot for developing
the same holding power. The clump weight is limited by the capacity of the
deploying winch and by the vertical force component of the wire rope tension.

A typical anchor-chain-clump configuration was elected for the
bottom of each mooring leg based on the required holding power. !t is com-
prised of a 25,000-pound LWT wedge block anchor, one shot of 1-1/2-inch
chain, a clump ranging from 25 to 100 kips, two additional shots of 1-1/2-
inch chain, and a scope of wire rope.

47

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Figure 15 isa mooring leg selection chart showing depth versus the
S/Y ratio for various wire and clump sizes considered. This chart will enable
one to select a wire-clump configuration that results in the shortest scope at
aselected depth. Figure 16 was plotted to show the total horizontal projec-
tion as a faction of the vertical projection for the mooring system configurations
considered. Figure 17 was plotted to illustrate mooring leg wire rope weight as
a fraction of depth.

The results of the mooring system analysis indicate that the weight of
each mooring leg will require catenary support buoys. Catenary support buoys
should be located approximately 1,000 feet from the surface power plant to
provide a constant holding force on the plant.

Table 10 presents a summary of mooring leg data for the surface plant
mooring systems at depths of 600, 2,000, 6,000, 10,000, 15,000, and 20,000
feet.

SHORE-BASED POWER SYSTEMS
Shore-Based Power Sources

The power sources discussed earlier for surface power systems are also
suitable for use in shore-based systems. As in the case with surface systems,
diesel engine generator sets were considered the most cost effective power
plants for shore-based systems. The diesel engine generator sets would be self-
contained at the 30-kw to 300-kw power levels, with conventional radiators
for cooling and battery starting systems. Heat exchanger and cooling tower
installations with compressed air starting would be required for diesel engine
generator sets at the 1,000-kw to 3,000-kw power levels.

Shore-Based Generating Plant and Transmission System

The basic components of the shore-based power plants would be
housed in a steel-framed, corrugated-steel-clad building. They include a
diesel-electric generating plant, with all of the required auxiliaries, handling
equipment, plant services, and monitoring and control equipment. Interme-
diate and high-voltage transmission cables would be used for transmission
over distances of 10, 50, 100, and 500 nautical miles. |n some cases, DC
transmission is used. These DC systems require converters or rectifiers at the
shore-based plant and the equivalent inverter at the load module end. The
load module will be equipped with subsystems similar to those required with
the surface-tendered plant, with the exception of the DC inversion equipment
required when transmission from the shore-based plant is at direct current. In
addition to the inverter, the load module requires a bank of static capacitors
to provide the reactive component for the capacitor and the blocking voltage

49

to stop the inverter if this becomes necessary. The static capacitors are
pressure-compensated and are mounted outside the hull. Weights, volumes,
and dimensions were not given for the shore plant, since these factors are not
critical for this facility.

CABLE SYSTEM

The primary consideration in the selection of a cable system for use
in an underwater power transmission system is the reliability of its elements.
The cable, connectors, and support system must withstand the ocean
environment—that is, must be resistant to corrosion, erosion, marine fouling,
and water absorption—for the useful life of the power transmission system.

Cable Conductor Material

Two basic conductor materials were considered: aluminum and
copper. The conductivity of aluminum is 60% that of copper and would,
therefore, require a cross-sectional area approximately 1.6 times larger than
copper for the same current-carrying capacity. The tensile strength of
aluminum is 24,000 to 29,000 psi and that of copper 50,000 to 70,000 psi.
The modulus of elasticity of aluminum is 10 x 10© and that of copper
17x 10°, Aluminum has a high contact resistance due to the oxidation of
its surface and exhibits a tendency to “‘creep” because of its high coefficient
of thermal expansion. Because of these qualities, aluminum was eliminated
as a conductor material from the study program.

Cable Insulation Material

The primary factors used in determining the selection of insulation
material for underwater cables are voltage stability and life, resistance to
moisture, resistance to temperature, dielectric properties, and flexibility.
Resistance to ionization or corona and mechanical strength are of secondary
importance.

Of the available materials, polyethylene combines excellent electrical
characteristics with outstanding stability of both electrical and physical prop-
erties during long periods of exposure in seawater. Rubber and rubber-like
insulation materials require tinned conductors to prevent a detrimental
chemical reaction between the insulation and conductor. Rubber materials
have a higher water absorption rate than polyethylene. Varnished cambric
and impregnated papers have a long life, but require a continuous lead covering
for underwater use. Lead coverings would make the total weight of the cable
impractical for this installation. Polyethylene was, therefore, selected for the
cable insulation material.

50

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51

Depth (thousands of ft)

35

30

@. 1-1/2 in.

Figure 15. Mooring leg selection chart.

52

4.0

1-3/8 in.

5.0

Vertical Projection (ft)

40
Distance of Maximum Horizontal Projection (ft)

Figure 16. Maximum horizontal projection of mooring leg.

Cable Sheaths and Coverings

Submarine cables usually have a water-resistant covering over their
insulation as added protection. Neoprene or polyethylene may be used for
this purpose. Where additional mechanical strength and abrasion resistance
is required, the cable covering is wrapped with armor wire of bronze, copper,
stainless steel, or galvanized steel. An additional covering is applied to pro-
tect the armor from the sea environment. High-strength galvanized steel with
polyethylene covering was selected as the armor material.

Electrical Properties

The use of either three single-conductor cables or a single three-
conductor cable is feasible for an underwater power transmission system. The
costs involved in deploying three single-conductor cables are greater than those
involved in deploying one three-conductor cable. In addition, three single
conductors have a higher reactance than one three-conductor cable. Off-the-
shelf three-conductor cables with standard conductor wires were considered
in the study.

53

Depth (thousands of ft)

40

35

30

25

20

Wire Cost (thousands of dollars)

250

re) 1-3/4 in., starting

wire size

O No clump

Q 5,000-Ib chain + 25,000-Ib clump
0 5,000-Ib chain + 50,000-Ib clump
@ 5,000-Ib chain + 75,000-Ib clump
V7 _ 5,000-Ib chain + 100,000-Ib clump

50 100 150 200
Wire Weight in Water (Ib)

Figure 17. Weight and cost of mooring leg wire rope.

54

250

Electrical conductors must be shielded to provide symmetrical radial
voltage stress distribution within the insulation and to eliminate tangential
and longitudinal voltage stress on the insulation surface. Tangential and
longitudinal voltage stress causes surface cracking and discharge to ground.
Shielding maintains a zero potential on the surface of the cable for the safety
of personnel and provides protection against lightning and switching surges.
The shield should be of conduction tape or wire material for increased fault
current capacity. Copper was selected for the shielding material, with the
shielding applied to each conductor of the three-conductor cable.

Since each conductor of the cable would be shielded and grounded at
both ends, the first order of faults, if they occurred, would be phase to ground.
The important factor to consider in grounding a cable system is to detect
ground faults and effectively clear the faulted section from the source of
power. In the absence of an effective way to detect low ground currents, the
system should be effectively grounded to provide faults of greater magnitudes
for faster actuation of the system’s protective equipment.

Splicing of the three-conductor power transmission cable was not
considered necessary since the cable would connect directly to the power
source and the load module. The splicing, if required, would be by special
undersea connectors.

Mechanical Properties

The most important consideration in planning cable deployment for
minimum risk of damage is the selection of the cable route. Studies of cable
fauit records indicate that many of the deep sea cable breaks occur where
cables pass over seamounts, canyons, and areas susceptible to turbidity
currents.

Table 11 illustrates the frequency of cable casualties as compiled by
Bell Telephone Laboratories. Approximately 50% of the cable damage is
attributed to breaks caused by fishing trawlers and a majority of these in
depths less than 1,800 feet.

The fundamental requirement in cable laying is to deposit sufficient
lengths of cable commensurate with the irregularities of the ocean bottom.
The most detailed knowledge of the bottom typography and of cable-laying
techniques is required to avoid introducing dangerous cable suspensions and
laying excess cable slack.

55

Table 11. Causes of Cable Breaks

No. of Breaks % of Total Breaks

Trawler
Chafe-corrosion
Kink

Biological

No report

Electrical maintenance

Other (ship anchor, kink, etc.)

Unknown

1 Data derived from Western Union Cable History Study, British Continental
Shelf (Allen, 1962) and includes break data for years 1930-1960.

2 Data derived from a compilation of break history of telegraph cables at all
depths in the North and South Atlantic Ocean. Period covered is 1959-1962.

Cable Configuration

The cable configuration defined by various trade-offs is a multiple
cable, concentric-stranded copper conductor that is insulated with poly-
ethylene, shielded, and protected by armor and jacket to meet the conditions
of the ocean environment. A typical cross section of the marine cable
selected is illustrated in Figure 18. Table 12 presents physical characteristics
of selected marine cables.

Cable Connectors

There are several mechanical and electrical problem areas associated
with underwater cable connectors and penetrations for the transmission of
electrical power to loads encapsulated in a pressure hull. The mechanical
problems involve watertightness, mating or connecting and disconnecting
underwater, material compatibility, and strength. The ability to achieve the
current-carrying capacity at the required voltage with minimum contact
resistance through the connector is the major electrical problem to be
resolved.

56

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57

=

S09 OMONOODPwWDH =

. Condauctor

. Extruded strand shielding

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Tape

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. Fill waterproof jute

. Binder mylar tape

. Polyethylene jacket

. High-strength galvanized steel armor
. High-density polyethylene jacket
over each armor wire

SCOMNDAD ER WN =

Figure 18. Typical cross section of selected marine cable.

One of the first devices used for sealing a cable penetration on a deep
submergence pressure hull was a 1.1-inch-diameter, four-conductor cable sealed
with a stuffing box design. The packing was composed of four or five layers
of flax packing pressurized from both ends of the stuffing box with gland nuts.
The seal was successful down to about 3,000 feet.

Primary and secondary cable seals are mandatory requirements for all
submersibles. The primary seal is located outboard of the pressure hull and
the secondary seal is located inboard of the hull. With respect to primary
cable seals, the use of watertight connectors is recommended. The connectors
would provide a positive water dam in case the cable is damaged or severed.
Connectors also satisfy the secondary cable seal requirement by providing a
positive water dam inboard of the pressure hull. The use of connectors for
hull penetrations allows the testing of such fittings under pressure prior to
deployment and provides junction points for the cable conductors. This
eliminates the need for junction boxes and provides a test point for checking
circuits served by the connectors.

Figure 19 shows a multiple-conductor hull fitting which has been
used on Navy submarines. This fitting will withstand nominal shock loadings.
As noted, the outboard watertight connectors are located radially around
the body of the fitting to accommodate a maximum number of cables.

58

cover

Z USN ue

primary seal water

We dam receptacle

CLL LI

wires

Outboard

Inboard
seal ring
ae retainer nut
slip ring
secondary seal water
weld

dam receptacle

Figure 19. Multiple-connector hull fitting for submarines.

The approximate availability of dry electrical connectors for under-
water power systems as function of voltage and amperage rating is presented
in Figure 20. An extremely small power level area can be satisfied with pre-
sently available connectors. A significant program, therefore, will be required
for the development of underwater connectors suitable for use at high power
levels.

Cable Suspension Systems

In the study program, the analysis of cable suspension systems was
based on the assumption that the cable is affected by its own weight and
the trace configuration it assumes when deployed. The suspension system
was primarily studied for use with surface-tendered power units.

The length of cable, which determines the cable weight, is a function
of the depth of the load module and the excursion of the surface unit. The
excursion of the surface unit depends, in turn, on the environment in which
it is placed. Since the environment could not be predicted, the cables were
chosen to include those lengths which might be required to reach depths of
600, 2,000, 6,000, 10,000, 15,000, and 20,000 feet.

To limit the length of cable required, the center of excursion for the
surface unit should be placed directly over the load module. However, it has
to be assumed that the surface unit travels through its excursion limits for an
unknown number of cycles during its deployment. This cycling causes a

59

wrap-up of cable because both ends of the cable are fixed. To avoid this
cable wrap-up, the excursion of the surface unit should be beyond the center-
line of the load module. Thus, the surface unit should never pass above the
vertical centerline of the module.

Two methods can be used to provide the cable with added strength.
The first is to provide armor or wire wrapping. The second Is to provide a
separate cable to which the power cable is attached. If in each case the
material used for strength is the same and an equivalent area can be applied,
then it is advantageous to use armor. Armor can be placed on the cable
during manufacture. Original estimates were made for a standard, available
submarine cable with galvanized steel armor. Such a cable would have an
ultimate strength of 60,000 to 70,000 psi. A higher strength armor with an
ultimate strength of 250,000 pounds can be used, but the cost rises sharply.
The added cost of this armor is reduced for extended depths because the
high-strength armor reduces the amount of support which must be supplied
by buoyancy devices.

A safety factor of 2, based on the ultimate strength for the standard
armor and for the high-strength armor, was used in determining the unsupported
cable length. This provides an allowable working stress of 30,000 psi for the
standard armor and 125,000 psi for the high-strength armor.

There is a restriction on the weight that a surface plant can support
which, for the purpose of the study, was established at 50,000 pounds.
Therefore, even if the supporting strength of the cable can exceed this
loading, some system has to be employed to reduce the cable load below
50,000 pounds. Buoyancy devices can be added either completely throughout
or at discrete points in the cable system. Adding buoyancy material to the
cable during manufacture or during deployment is not considered a practical
solution to the provision of natural buoyancy for cables in the undersea
environment. Therefore, the use of the discrete buoyancy system was pre-
ferred.

Optimizing a cable support system requires definite knowledge of the
actual techniques used for the installation of any given number and type of
buoyancy devices. The number of buoyancy units can be kept at a minimum
by so placing them along the cable length that the weight of the cable hanging
below results in a maximum allowable working stress in the cable. A factor
of 1.3 was used in determining the effective net buoyant force necessary to
maintain the cable in a generally vertical attitude, resist ocean current drag
; forces, and account for the load component of the surface cable between the
surface unit and the first buoy.

60

1,000

100

Amperes

10

preliminary engineering
and limited testing

projected state
of the art

development

100 1,000 10,000
Volts

Figure 20. Availability of dry electrical connectors.

Two basic types of buoys were investigated for the cable support
system: hollow buoyancy spheres and homogeneous buoyancy materials.
Various materials with acceptable weight-to-buoyancy ratios, such as glass-
reinforced plastics, glass, and titanium, are considered to be in the development
stage and were eliminated. Of the readily available materials, aluminum alloy
7079-T6 was selected because of its high yield strength, lightness, and suit-
ability for the marine environment. The sphere buoys must be fabricated with
a mechanical joint at the equator because the material has poor welding
characteristics. Hemispheres with a diameter of up to 84 inches are presently
available. This size was used as maximum to avoid unnecessary development
costs. At all depths multiple spheres must be used to support the selected
cable sizes.

61

A syntactic foam material weighing 44 |b/ft® in air was considered for
buoyancy floats. This foam is available and has well-established properties.

Typical buoy configurations used in the study are shown in Figure 21.
Each of the configurations is shaped like a clam shell to minimize drag forces
on the buoyancy units.

Figure 22 shows the support requirements for a representative number
of cables at their respective depths. The number of aluminum spheres required
for each float device is noted in Figure 22.

Both the syntactic float and aluminum sphere float are considered to
be within the present state of the art and can be procured in a reasonable
time. Aluminum spheres were considered the most cost effective buoys for
the cable support system.

There are two cable suspension configurations suitable for an
underwater power transmission system—namely, a taut line configuration
and a normal catenary configuration. A taut line configuration is shown in
Figure 23. One or more buoys are suspended along the cable length. The
total buoyancy of the buoys is greater than the displacement weight of the
cable so that a positive vertical force is generated along the cable. Attached
to the uppermost buoy is a pendant cable which is attached to the surface
unit. The uppermost buoy was placed at a 2,000-foot depth for all concepts
evaluated.

When the surface unit excursion is at its minimum point, it was
assumed that the pendant cable is hanging essentially vertical, with one end
supported by the surface unit and the other end by the upper-most buoy at
2,000 feet. For a load module at a 20,000-foot depth, the length of the
pendant cable was postulated to approach 20,000 feet. With this length the
pendant cable would hang to about 11,000 feet when the surface unit is above
the load module. The minimum excursion point in an actual design must be
displaced a horizontal distance from the vertical centerline of the load module
to prevent the cable from entangling with the mooring legs or wrapping around
itself.

A catenary configuration is shown in Figure 24. As noted, the
buoyancy units are spaced along the cable at discrete points to maintain safe
tensile levels in the cable armor. The surface unit excursion poses no serious
problem in catenary configuration. However, as the surface unit moves from
its maximum excursion point, the cable will abrade on the bottom. To pre-
vent this, a buoyancy unit must be installed so that at the innermost portion
of the excursion the total depth of cable is less than that of the load module.
With a load module at 20,000 feet, the surface excursion is approximately
18,000 feet. Allowing the innermost portion of the excursion range to be
directly above the load module, the buoyancy unit would be placed some
7,000 feet above the bottom.

62

power cable
plastic fairing
(clam shell)

SIEBUE aluminum 7079-T6 pressure

spheres (bolted hemispheres)

Bisphere Quintsphere
Trisphere length to diameter = 4to 1 Hexsphere length to diameter = 5to 1
Quadsphere Heptsphere

(a) Aluminum sphere.

power cable

sleeve

molded syntactic foam reinforcement

diameter

3-diameters (avg)

(b) Homogeneous material.

Figure 21. Buoyancy support configurations.

63

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64

excursion limits coe
surface

surface unit

pendant cable

taut line cable

low drag cable

load module
ocean bottom

Figure 23. Taut cable support system.

The above configurations are based on the assumption that the total
cable suspension system is slightly negatively buoyant. If it is made positively
buoyant, the cable system will probably broach the surface during the excur-
sion of the surface unit and be subjected to surface conditions as well as to the
possibility of becoming entangled with the mooring system.

Both the taut line and the catenary system suffer from the fact that If
the cable is lost at any point below the attachment to the last support buoy,
the cable complex will descend to the bottom. The cable would have a higher
probability of falling on the load module with the taut line system. Suspension
systems for underwater cables will require careful analysis during system design.

ELECTRICAL SYSTEMS
Surface Power Systems
The electrical system for each load at each depth considered for

analysis in the study program included the generated voltage, step-up primary
transformer, transmission line, and protective equipment. A load power

65

factor of 0.85 lagging was selected for analysis. Stability problems due to
system synchronization were not investigated since only a single generating
source was considered. Circuit stability was limited to the ability of the
system to respond from no load to full load and vice versa. To establish
circuit protection requirements, loads under steady-state voltage and
transients caused by a fault condition were evaluated.

Early in the study it was established that overall electrical character-
istics could not be clearly defined that would be suitable for all lengths of
transmission cable under consideration. Therefore, an analysis was initiated
for moderate cable lengths of 600 to 30,000 feet which would be applicable
to surface power sources.

Alternating Current Versus Direct Current. The design constraint
established for the study program required the delivery of 480-volt, 3-phase
60-Hertz AC power to the load module. For a DC transmission system, this
constraint would require additional transformation, conversion, or inversion
equipment at each end of the transmission cable. The primary advantage of
using DC is the reduction in cable size for an equivalent power level. In
addition, transmission cable losses are substantially reduced with DC. For
loads over the distance of 600 to 30,000 feet, it was determined that the
savings in transmission losses and cable size would not be offset by the
additional cost of DC terminal equipment at each end of the transmission
cable.

For each voltage level, AC costs were found to be less than DC for
cable lengths of 600 to 30,000 feet. Therefore, an AC transmission system
was considered optimum for moderate cable lengths because of simplicity,
reliability, availability of hardware (including control devices), and low
acquisition cost.

Frequency. Transmission frequencies above and below 60 Hertz were
evaluated in the study. As frequency increases, the impedance of the trans-
mission cable also increases, requiring a larger and heavier cable for a given
power level and cable length. In addition, frequency conversion equipment
would be required.

The total impedance of the transmission cable decreases with
decreasing frequency down to the DC resistance at zero (DC) frequency. A
reduction in cable sizes is possible, but this advantage is quickly offset by
limited availability of low-frequency equipment for the load module. The
requirement for conversion equipment at the load module results in added
costs for a hull to house the equipment. Consequently, the 60-Hertz
frequency was selected as the optimum AC power transmission frequency
for cable lengths of 600 to 30,000 feet.

66

excursion limits

surface unit

surface

Power cable

low drag buoy

load module

Figure 24. Catenary cable support system.

Voltage Regulation. A voltage variation limit of plus or minus 5% was
established as a design constraint to obviate the need for additional voltage
regulation equipment in the load module. In case of constant power demand,
voltage regulation equipment can be added at the power source end. However,
this criterion is not practical since any load module will have an average load
and a peak load, either of which may vary as much as 50%. The allowable
voltage drop for a circuit depends on the required regulation or the current-
carrying capacity of the cable. The required voltage regulation would be
obtained by limiting the voltage drop in the cable system to 5%.

AC Distribution System. The selection between single-phase and
three-phase power was based on the power demand, equipment availability,
reliability, and losses. In a single-phase circuit, the power delivered is pulsat-
ing and, when the current and voltage are in phase (unity power factor), zero
power is deliverd twice in each cycle.

67

The same pulsations take place in a three-phase system in each of the
phases, but each phase of a three-phase circuit is separated by 120 electrical
degrees. When one phase is delivering zero power, the other two are supply-
ing the power requirements. Line losses are less in a three-phase circuit than
in a single-phase circuit. Three-phase circuits may be as much as 40% more
efficient. Conductor size and weight would be less for the three-phase circuit
for the same power level and cable length. A three-phase system was therefore
selected as the most cost effective for distributing AC power.

Transmission Voltage. Transmission voltage is the most significant
electrical characteristic to be resolved since it will produce the most variation
in the cost and versatility of the basic electrical system. Incremental trans-
mission voltages of 480, 600, 2,400, 4,160, and 13,800 volts were considered
appropriate for the study for cable lengths of 600 to 30,000 feet. Higher
voltages were only considered appropriate for long transmission cables in
excess of 10 miles, as required for shore-based plants.

At each selected transmission voltage, the components and equipment
of the basic electrical system were added to the cable to arrive at an
acquisition cost. The acquisition cost was then compared for each possible
combination of transmission voltage, power level, and cable length. The
acquisition cost was used in this trade-off on the assumption that engineering
and deployment costs were the same for each voltage selected. The 5%
maximum voltage drop in the transmission cable created limitations in the
cost analysis of the selected voltage levels.

Cable Connectors. The availability of connectors with respect to
voltage level and pin sizes was investigated in the selection of the most cost
effective transmission voltage. Wet connectors suitable for underwater mating
are nonexistent, and only a limited number of dry connectors are available for
underwater use at the power levels of interest.

In an effort to reduce the number and types of connectors required
for the power transmission system, a study was conducted on the effects of
combining the secondary transformation and distribution equipment within
the load module. This concept would require high-voltage connectors and
hull fittings on the load module but would eliminate multiple sets of connectors
and hull fittings required on a separate hull for transformation and distribution
equipment. The separate pressure hull would also be eliminated. Consequently,
it was determined that it is most cost effective to transmit the higher voltages
directly to the load module. With this concept, additional weight and volume
requirements would be imposed on the load module.

Electrical System Cost. A cost analysis was conducted on the
acquisition cost of the basic electrical system versus transmission voltage.
The costs of engineering, packaging, and protective circuits were considered

68

constant for the analysis. In addition to the costs of electrical equipment,
the cost of cable support systems was considered. This cost, a direct function
of the size of the cable and its overall length, favors the selection of higher
voltage. For cable lengths of 600 to 2,000 feet, the cost of the suspension
system must include additional buoyant support to maintain the cable in a
vertical orientation. Therefore, a cost constant was assigned to the cable
suspension systems.

An analysis of the two armor strengths included in the study indicates
that the 125,000-psi armor costs about twice as much as the 30,000-psi armor
and provides a cable load capability four times greater than that of the
30,000-psi armor. The results of the analysis indicate that the most cost
effective cable support system would be 30,000-psi armor for cable lengths
of 600 to 10,000 feet and 125,000-psi armor for cable lengths of 15,000
feet or greater.

Table 13 presents the most cost effective transmission voltages
selected as a function of power level and cable length. The voltages indicated
in Table 13 are acceptable for applications requiring long-term usage at a
specific power level and installation. However, for general utility purposes,

a block of power level conditions at various cable lengths can be selected and
satisfied by one or two specific transmission voltages.

Table 13. Selected Transmission Voltages for Various Cable Lengths

C
Poe teval able Lengths (ft)

i) seal 1,000 | 2,000 | 6,000 | 10,000 | 15,000 | 20,000 | 30,000

4,160 | 4,160
4,160 | 4,160

Protection System. The protection of electrical systems can be
extremely complex. For this study, a constraint was established which
limited the electrical protection to the underwater power transmission
systems, excluding the load module or the specific safety needs of the mis-
sion.

For faults within the generation area, such as a generator or prime
mover failure, it was determined that the generator plant would shut down
while at the same time the emergency power system would be activated if
available. All other faults on the transmission cable or at the load module

69

would be referred to the main reclosing circuit breaker at the power
generating plant. The circuit recloser would complete one, two, or three
reclosures before lockout to allow for transient conditions. The generator
would be kept in operation during the reclosing operation but would be
shut down at the time lockout occurs. The plant would also shut down

on loss of control power. Standard differential and overcurrent relay pro-
tection would be provided for the generator plant. The transmission cable
and load module faults would be referred by a carrier current scheme to the
main reclosing circuit breaker for isolation.

The two modes of operation considered for the protection system
were cascade and selective tripping. The selective system was not considered
beyond a preliminary stage because of the added weight and space require-
ments.

A cascade protective scheme was therefore selected for the transmission
system. Faults in the cascade system would be detected anywhere in the power
transmission system up to and including the load module transformer. Loads
connected on the secondary of the load module transformer would be pro-
vided with adequate protection with automatic, multiple-state reclosers. Both
the load protection and reclosing equipment have to be coordinated with the
transmission system for proper operation.

An unattended load module and generating plant, as envisioned in the
study, would constantly display their condition and have a provision for
periodic inspection. Some form of control is also necessary to allow an
inspector or operator to operate (close or open) a circuit breaker remotely,
depending on conditions noted on the display board. An alarm system
connected to an established monitoring point is also required to alert plant
operators of trip functions and problem indicators (high water temperature,
low lubricating oil, etc.). A carrier system would be employed for this
purpose.

In addition to providing a transfer trip function and indication, the
carrier system would provide an overall differential circuit around the entire
transmission line. Any faults in the cable would be detected by this differential
zone which would, in turn, trip a differential relay located at the generator
plant. Differential relays would be provided for the generator and transformer
at the generator plant. Activating the differential relay would trip the main
reclosing circuit breaker independent of the carrier system.

Control power would be provided by a control power transformer
which would be connected ahead of the main breaker on the generator output.
Thus, control power would always be available regardless of fault conditions,
providing the generator is operating normally. The control system would
automatically switch to emergency control power source should loss of the
primary control power occur. A loss of both power sources would cause the
generator plant to shut down.

70

A power transformer would be required for the plant auxiliary
services and a rectifier for battery changing. The batteries provide emergency
control power for relays, instrumentation, and tripping power for the main
breaker.

The generator prime movers would have a full complement of
mechanical and electrical indicating and protective devices.

In-Situ Power Systems

The preceding discussion on the electrical power transmission system
for the selected power levels and cable lengths concerns surface plant facilities.
In the in-situ facilities, the power module and the load module may be sepa-
rated by less than 100 feet because wet connectors do not exist. Asa result,
the in-situ power module and the load module must be electrically connected
prior to emplacement.

The operationat philosophy of the protection system for in-situ plants
is similar to that described earlier for surface plants. On a permanent fault,
the load module Is electrically isolated from the in-situ power module. The
reactor then goes through a controlled shutdown. When the primary source
fails, power for the load module is derived from batteries. In an in-situ facility,
there is no external station to which fault information can be monitored, nor
are there means to provide a remote corrective capability.

The mode of operation selected as the most cost effective for the
in-situ system is to provide protective devices, instrumentation, and main
circuit breaker in the power module, with redundant protective and control
devices located in the load module for corrective action performed by an
operator. The power module for all power levels and ocean depths would
also contain the reactor, steam turbine, and generator. Only critical mechan-
ical problems and electrical failures will shut down the in-situ plant by
energizing various protective relays. All relays, main breaker, switchgear,
and monitoring devices are located in the power module. All functions and
ability to close or open the main breaker are carried back to the load module
by a control cable.

Shore-Based Power Systems

For the shore-based system, the maximum length of circuit that
could be tolerated while maintaining a 15% maximum voltage drop was
considered for loads of 30, 100, 300, 1,000, and 3,000 kw at nominal
voltages of 5 kv, 15 kv, and 34.5 kv, with a brief evaluation at 69 kv and
115 kv. The maximum incremental distances of 10, 50, 100, and 500

71

nautical miles were chosen as representative distances to reach the depths
selected for the study. Table 14 presents the selected AC or DC voltages
and includes all electrical costs, including costs for transformers, switchgear,
and conversion and inversion equipment. No system is shown for the
3,000-kw power level at 500 miles. This distance and power level must be
reached at a voltage level not considered practical with the present cable

technology.

Table 14. Selected Voltages

Power Level

Cable Lengths (miles)

4,160 AC
4,160 AC
13,800 AC
13,800 AC
13,800 AC

13,800 DC
13,800 DC
13,800 DC
34,500 DC
34,500 AC

13,800 DC
13,800 DC
34,500 DC
34,500 DC
34,500 DC

34,500 DC
34,500 DC
34,500 DC
34,500 DC

For shore-based plants, the available cable sizes are limited. The
maximum size of a three-conductor cable is determined by the maximum
diameter of the three conductors, the insulation requirements for the voltage
level, and the limitations of the cable manufacturing process. The minimum
cable conductor size required for each voltage level would be dictated by
voltage stress considerations.

Voltage stress in a cable may be defined as the electrical pressure on
a unit thickness of insulation material and is usually expressed in volts per
mil thickness. The average value of voltage stress was determined by
dividing the voltage across the insulation by the insulation thickness in mils.
Voltage stress is not uniform in all parts of the insulation wall and is greatest
at the conductor-insulation interface. Voltage stress in any point of a cable
may be found by

Voltage

ees Bl
0 Saree, DE

72

where S, = stress in volts per mil at a point in the insulation 7 mils from
the cylindrical axis of the cable

D, = outside diameter of insulation in mils
D, = inside diameter of insulation in mils

T = point in the cable insulation measured from the cylindrical
axis of the cable

Using the above formula, the maximum stress will occur at the conductor
surface (7 = D,/2), or

_ 0.868 Volt
vmax D,
d log D5

The voltage levels considered for transmission of power from shore-
based plants were 5 kv, 15 kv, 34.5 kv, 69 kv, and 115 kv. At 69 kv and
115 kv, single-conductor cables are recommended. The three-conductor
cables rated for these voltage levels at the selected power levels and cable
lengths exceed current manufacturing capabilities. Further, the single-
conductor cables for 69 kv or 115 kv require a cable separation from 90 to
600 feet, depending on retrieval, maintenance, and repair requirements.
This would require multiple passes with a cable-laying vessel, resulting in
excessive deployment costs. For the larger cable lengths (500 miles), the
inductive and capacitive reactances would cause a changing current of many
times the load current. In addition, the size and weight of transformers at
69 kv and 115 kv required in the load module would be prohibitive when
related to the added size and cost of the load module. Therefore, the 69 kv
and 115 kv were eliminated from the study.

A trade-off analysis was made of AC versus DC power transmission
systems for shore-based plants. The cost of engineering and deploying the
AC and DC systems was assumed to be equal for purposes of this analysis.
The three items considered to have a major influence in a cost effective
analysis of the two systems were cable costs, DC conversion and inversion
equipment, and the cost of the containment hull needed to house the DC
inversion equipment in the load module.

A DC transmission system has distinct advantages over an AC system
when related to transmission cable requirements at the voltage and power
levels considered in this trade-off. The DC transmission cable has practically
no changing current, no ionic motion in the insulation, no induced current

S

73

in the cable sheath, and no skin effect, all of which are prevalent in an AC
transmission cable. Further, the DC transmission system may require only
one cable if the sea is used as a return circuit; however, the hazards involved
with so using the sea must be thoroughly investigated. Thus, the effective
power transmitted in a DC cable is greater than that transmitted by AC for
the same circuit conditions, resulting in reduced cable costs.

A DC transmission system does have some restricting factors. There
is no easy way of transferring DC voltages except by AC methods at the
converter and inverter ends of the transmission system. Inversion equipment
requires a leading power factor which must be supplied by AC static or
synchronous capacitors. Mercury arc valves have been used as conversion
equipment for DC; however, this equipment requires clean room housing,
degassing facilities, and rebuilding approximately every 5 years. The mercury
arc equipment is expected to be replaced by high-voltage DC solid-state
conversion equipment in the near future.

The DC transmission system has a lower cable cost than an equivalent
AC system but requires special transformers and converter-inverter equipment
at each end. A careful trade-off was therefore required before appropriate
transmission systems from shore-based plants could be selected for the given
circuit requirements.

Figure 25 shows a preliminary system selection and indicates that
DC is the most cost effective system for cable lengths of 50 to 500 miles for
the given power levels. AC is the most cost effective for all loads up to 10
miles and for a 3,000-kw load at 10 and 50 miles.

Power Level
(kw)
30 DC DC
100 DC DC
300 pc pc
1,000 DC DC
3,000 DC as
SSS
10 miles 50 miles 100 miles 500 miles

Figure 25. AC—DC system selection.

74

Voltage regulation of selected power transmission systems for shore-
based plants is of major importance because of the long cable lengths. Voltage
regulation for AC systems is affected the most by changing currents. Normally,
the AC voltages at each end of the system are kept within desired limits by
automatic tap changers on the transformers provided.

DC high voltage is normally regulated by controlling the rectifier firing
angle to produce the required DC current and by operating the inverter with
the maximum firing angle necessary for safe commutation.

The protection system for shore-based generator plants will be similar
to that of the surface plant system. Where DC transmission is required, the
protection system must also protect the DC equipment, which includes con-
verter, DC transmission cable, and inverter. The AC transformers at either
end of the DC system are protected with a differential relay circuit similar to
the surface plant arrangement. The inverter equipment would have failure
detectors, voltage sensors, and monitoring and control devices to cover such
conditions as commutation failure, pulse synchronization, and fire-through.
The converter or rectifier would also be similarly protected. All DC faults
are referred to the AC systems at both ends of the DC link. The protection
system should provide a means to differentiate between DC cable faults,
inverter faults, and load module faults.

DEPLOYMENT CONCEPTS

The deployment of the three underwater power transmission systems,
in-situ, Surface-tendered, and shore-based, involves unique problems in the
emplacement of cable in the deep ocean. Some of the major problems include
induced cable oscillations due to ship or hull motion, high cable loading on
storage drums, twist induced in long cables, and the placement and recovery
of the large modules and associated components.

A route and site survey is of utmost importance in obtaining data for
the design and deployment of an underwater power system. A bottom survey
should be conducted to determine topography, sediment characteristics,
temperature, and current profiles. Sediment information would also be
required to determine the correct anchoring configuration. Temperature
and current profiles are necessary to define the temperature effects on
structures and materials as well as the current forces which cables and
structures may be subjected to.

5)

In-Situ Power Plant Deployment

The emplacement of the in-situ plant includes two modules, the power
plant and the load module, which are rigidly coupled to a common base with
either negative or positive buoyancy, depending on the mission. However,
each module is positively buoyant and is provided with a safe method of
separating from the base or from the other module in an emergency. The
base has provisions for a ballast system. A wire rope and winch-down system
are also included in the base for controlled descent and ascent.

The power plant and the load module would be connected together
with the power and control cables at the surface prior to submergence. The
in-situ plant is emplaced on the bottom by towing the preassembled system
to the work site. The anchor is lowered to the bottom by heavy-lift ship,
and the plant complex is trimmed out to the required buoyancy. Descent of
the plant is accomplished by winching down against the positive buoyancy.
A system of leveling legs and minor anchor blocks may be used for leveling
when the system nears the bottom. In an emergency, the power unit may be
shut down and the power cable disconnected (by explosive or mechanical
means) to allow the power module to ascend upon release from the base.
Retrieval of this power plant would involve the reversal of the deployment
steps.

When it is impractical to deploy the two modules together on a
common base, precaution must be taken in the handling of the power cable.
If the two modules are deployed without a common base and are connected
with a short link coupling, inherent cable fouling problems may occur. If
the mission requires the two modules to be separated by a working radius
greater than the depth of submergence, then deployment Is greatly facilitated
since the emplacement techniques used for the surface-tendered plant could
be utilized.

Surface Power Plant Deployment

The sequence of deploying a surface-tendered power source and its
related power cable is the establishment of the moor, emplacement of the
surface power plant, and the connection and emplacement of the load
module. Equipment and components required include a winch, specialized
heavy lift equipment or modifications to a ship for the winch, and sensing
and control devices. Flotation devices may also be used, particularly for
the deeper depths. The mooring deployment vessels and equipment should
have the capability of installing one leg of the moor without having to be
resupplied with cable during the installation. A minimum of three deploy-

76

ment ships are envisioned, with one ship having heavy-lift capacity, one
ship acting as a termination and collection point of the mooring legs, and
one ship acting as a wire rope or cable supply and assist ship. A fourth ship,
such as a seagoing tug, may be required for moor tensioning and intership
transfer.

On arrival at the mooring site, the three ships take a position over
the site of the first mooring leg anchor. Then the anchor is lowered in a
controlled manner, keeping a constant rate of tension on the wire rope to
place the anchor as opposed to dropping it. The use of a battery-operated
bottom-sensing device attached to the anchor serves to indicate depth and
anchor position relative to the bottom. A scheme using a different frequency
for the sensing device on each anchor would provide an accurate positioning
system.

An example of an anchoring system is shown in Figure 8. The anchor,
a single shot of chain, a clump, and at least two additional shots of chain are
attached to steel wire rope and deployed the full scope length. The wire rope
is then connected to the terminal swivel socket and to the catenary support
buoy. A nylon mooring line is attached to the terminal rig. This nylon
mooring line is connected to a second ship at the central position of the
moor, which would also be the location of the surface plant. Tension is kept
by the second ship while the mooring legs are deployed 180 degrees apart.
An estimate of mooring time per leg is 1 day to depths of 6,000 feet and 2
or 3 days per leg to depths greater than 6,000 feet. On completion of the
deployment of the mooring system the surface plant hull js towed to the
ship at the plant site. The nylon mooring lines are transferred from the
ship to the hull by divers. This involves passing the lines through hawsepipes
to the termination points (bits) on the deck of the hull. If required, a winch
is used to pretension the lines.

The load module is deployed by positioning it relative to the bottom
and slightly off-center along a bisector of the mooring legs. The ship that
lays the power cable is brought alongside and the power cable is connected
to the load module. The submergence of the load module and the paying
out of the power cable from the ship storage drum are synchronized. On
completion of the deployment of the load module the power cable is trans-
ferred and connected to the surface plant.

Two basic modes of load module emplacement are available: the
free-fall technique and the tethered concept described earlier for the in-situ
plant emplacement. The free-fall technique was not considered suitable for
this emplacement. The second scheme involves tethering at the surface or at
the bottom and winching down from the deployment ship. A surface-tethered
emplacement uses a cable attached to the deployment vessel and is winched

Ui,

down with negative buoyancy. This method provides a controlled and precise
method of placement but is hazardous should the tethering cable fail. A
module tethered at the bottom and winched down against positive buoyancy
provides the best controlled mode with maximum safety. A nylon or poly-
propylene rope should be used for the winching operation because of the
neutral buoyancy.

Shore-Based Power Plant Deployment

The emplacement of a shore-based power plant for an underwater
power system involves three phases of effort—namely, construction of the
power site, deployment of the power cable, and deployment of the load
module. Deployment of the cable would be initiated at the power site and
would end at the load module site at sea. Emplacement of the load module
at the bottom would be accomplished last. The power cable would be
connected to the load module while the module is on the surface over the
deployment site. This would enable the complete check-out of the power
system before the load module is submerged. Further, this method would
assure that the proper amount of cable had been deployed to place the load
module at the operational site.

The cable-laying procedure is basically the same as used for submarine
power cables, except in deep water where a cable not capable of supporting
itself must be deployed using buoyancy devices. A bottom topography survey
is required to establish a cable route, to determine the correct cable length
required, and to locate hazardous areas. A cable-laying ship having the
required cable storage and handling capacities would be used for cable
emplacement. The cable would be layed seaward from the shore with the
surf and tidal zone section of the cable buried or placed in ducts 6 feet
below the low tide level. Bottom cable laying may be done from a ship
having spinal-wound cable tanks, providing the recommended cable tension
is maintained by the winches on the ship. Table 15 lists the cable-laying
capacities of ships which can be used for the cable emplacement.

When the cable becomes so long that it can no longer support its
own weight, cable buoyancy must be provided. A state-of-the-art buoyancy
system that could be used to give maximum buoyancy control is 42-Ib/ft?
aviation gasoline. Syntactic foam increases net buoyancy by 2% due to Its
relative incompressibility and temperature independence. Aviation gasoline
decreases in buoyancy by about 8% at a depth of 20,000 feet due to com-
pressibility and temperature effects.

78

Table 15. Cable Ship Data

Volume of Nautical Miles of
Cable Tanks 1.25-Inch-Diam
(ft?) Cable?

No. of Cable
Tanks

LCV

LSM

LSIF

USS Neptune
USS Aeolis

USS Thor
USACS A. J. Meyer
SS Salemum

SS Long Lines
SS Mercury

SS Neptune

SS Marcel Bayard

6,937
10,395
15,777
30,116
43,385
43,385
48,000
22,354

139,000

106,740

222,500
77,333

BPOWNWRPWWWNDN

1AII the ships except the LCV, LSM, and LST are equipped with
automatic tensioning devices to compensate for sea conditions.

2Ship loaded at 80% cable capacity.

Varying ratios of syntactic and aviation gasoline can be used to
achieve negative, positive, or neutral buoyancy. The floats may or may not
have release mechanisms to enable them to return to the surface. A retrievable
flotation system would use rubberized fiber bags containing a mixture of
aviation gas and syntactic foam; upon reaching the bottom the bags would
be released by an imploding glass ball or spring-loaded trip mechanism.

It is important that the power cable be allowed to relax as the load
module is emplaced. Cable stored in the tanks twists as it is deployed. The
twist is tolerable when the cable is laid on the bottom, since the surrounding
friction forces tend to secure the cable. However, in open water, the cable
would tend to coil. One way which could be used to solve this problem is to
unwind the cable from the tank in a tangential manner. Proper techniques
in applying cable armoring would also relieve the problem. The cable twist
problem during cable-laying operations must be investigated thoroughly in
the final design of underwater power systems.

79

Figure 26 illustrates two methods of submerging the load module
from the surface. An untethered descent requires an outward force through
the arc of deployment, as shown in Figure 26a. Figure 26b illustrates a
precisely positioned, self-submerged (by winching) load module emplace-
ment.

SELECTED POWER SYSTEMS

The evaluations, analyses, and optimization processes described
heretofore provide the basis for selecting the most cost effective concepts
of the following underwater power systems:

1. 30-, 100-, and 300-kw in-situ power plants for load modules
deployed at depths of 600, 2,000, 6,000, 10,000, 15,000, and
20,000 feet; 1,000- and 3,000-kw in-situ power plants for load
modules deployed at depths of 600 and 2,000 feet.

2. 30-, 100-, 300-, 1,000-, and 3,000-kw surface-tendered power
plants for load modules deployed at depths of 600, 2,000, 6,000,
10,000, 15,000, and 20,000 feet.

3. 30-, 100-, 300-, and 2,000-kw shore-based power plants for load
modules deployed at distances of 10, 50, 100, and 500 miles from
shore; 3,000-kw shore-based power plants for load modules deployed
at distances of 10, 50, and 100 miles from shore.

The preliminary designs for six of these power systems are given in the
Appendix.

The cost estimates presented for the recommended systems are for
engineering, construction, and testing. Cost of development programs or
advanced engineering for the power cable connectors, system deployment,
property acquisition for shore-based plants, transportation, and site prepa-
ration are not included. Likewise, the cost of the common base for the
in-situ plant is not included.

In-Situ Power Systems

A reactor power plant was chosen for all the selected in-situ power
systems. This plant will provide an in-situ power system with a reasonably
long life. Cost data for the in-situ power systems are presented in Table 16.
Operational costs are difficult to define without more complete data on
Operating schedules and power profiles, both of which influence refueling

80

costs. Investment and maintenance costs range from $150,000 to $500,000
per year for 30-kw to 300-kw plants, and estimated yearly fuel costs range
from $25,000 for the 30-kw plant to $1,000,000 for the 3,000-kw power
plant. Maintenance and investment costs are related to power level and
operating depth, whereas fuel costs depend primarily on the core size or
energy available, refueling operational costs, and core costs.

Table 16. Estimated Costs of In-Situ Power Sources

(Values are in millions of dollars and include the cost of
syntactic foam for flotation.)

f
Power Level Diepian (0)

iy) | 600 | 2,000 | 6,000 | 10,000 | 15,000 | 20,000

Note: Dashes indicate that the power plant concept was not defined
because of the major developmental effort required.

For loads of 30 to 300 kw, a 3-phase, 60-Hertz, 480-volt transmission
link was selected between the in-situ power and load modules. A 3-phase,
60-Hertz, 4,160-volt transmission link was selected for loads of 1,000 and
3,000 kw. A transformer would be required in the load module at the higher
transmission voltage.

Table 17 summarizes the cable and connector requirements for the
recommended in-situ power systems. As indicated in the table, there is no
restriction on connectors for loads of 30 and 300 kw. However, at the 300-
kw power level, two 1/0 AWG conductors would be used in lieu of the 4/0
AWG shown since no connectors are available with 4/0 AWG pin size. A
connector is available for the 4,160-volt and 1,000-kw load but requires some
engineering and testing prior to use. For the 4,160-volt and 3,000-kw load,
connectors are not available; therefore, three 1/0 AWG conductors per phase
are recommended.

81

load module

tension

flotation

devices eae

|
|
ene

negative buoyancy

(a) Surface tethered.

load module

tension

anchor

(b) Bottom tethered.

Figure 26. Load module deployment.

82

Table 17. Cable and Connector Requirements
for In-Situ Plants

Transmitted Conductor | Connector Recommended
Voltage Size Available Transmission Method

6 AWG optional
4 AWG optional
4/0 AWG two 1/0 AWG cables

4 AWG requires engineering
300 MCM three 1/0 AWG cables

The hull of the in-situ power plant would serve as a heat transfer area.
The internal equipment of the plant includes a typical pressurized water-cooled
reactor and shielding as a primary system. The secondary system includes the
steam turbine generator system. The turbine steam exhaust would be con-
densed and the waste heat removed by contact with the steel pressure hull for
loads up to 300 kw. For loads of 1,000 kw and above, standard condensing
techniques would require the use of hull penetrations to provide seawater
cooling for the condenser.

Surface Power Systems

A 3-phase, 60-Hertz, AC electrical system was selected for each of the
surface-tendered power plants. A diesel generator was selected as the power-
generating equipment for surface-tendered plants. Control and instrumentation
signals from the load module would be transmitted by carrier over the power
cable. A 24-kw/hr manchex plante battery complete with battery charger
was selected for the emergency power source.

The cable system selected included a three-conductor power transmission
cable, cable support system, watertight connectors, and pressure hull penetra-
tions. High-strength galvanized steel wire armor was selected for the cable.
Conductor sizing was based on the smallest size that would transmit the
required power at no greater than 5% voltage drop. A maximum cable load to
be supported by the surface plant hull was established at 50,000 pounds.

The budget cost estimates for the surface power systems are given in
Table 18.

83

Table 18. Estimated Costs of Surface Power Sources

(Values are in thousands of dollars.)

f
Power Level Diefsidn (i)

(kw)

2,000 6,000 | 10,000 | 15,000 | 20,000

12291 || 1,631.8 || 184-1 || 1/8279) | Zea) || SSO), 1
1,439.2 | 1,609.1 | 1,847.1 | 2,142.4 | 2,549.4 | 3,263.6
ipesto0 |) 1,708.1 | 12612 | 2.28.4) | ZVSs8) | 445.9)
ANS | ZILA! || ZOOS |) ZASISYS) || SSSA? || ZOOS
2,619:0 | 2,775.3) | 3,010.2 || 3/4233 | 3/824°5 | 4;660!6

Shore-Based Power Systems

In most cases, a DC electrical system was selected for the shore-based
power systems. A DC system requires conversion or rectifiers at the shore-
based plant and inversion equipment at the load module end. Shore-based
power systems require the same load module subsystems as surface-tendered
plants, with the addition of the DC inversion equipment and a bank of
capacitors. The capacitors would provide blocking voltage to stop the
inverter if this becomes necessary and would be mounted on the outside of
the module in a pressure-compensated configuration. Table 19 presents the
voltage levels, loads, frequency, conductor sizes, and losses for the shore-
based power systems.

Physical characteristics of the shore plant were not investigated since
those factors are not critical for this facility. The diesel generators are
self-contained in the 30-kw to 300-kw power levels. The 1,000-kw and
3,000-kw diesel generators require cooling tower and compressed air starting
systems. No system was selected for the 3,000-kw load at 500 miles. The
protective system for the shore-based power system would be similar to that
of the surface plant system. Cost estimates for the shore-based power systems
are given in Table 20.

A power generating plant was purposely included in the shore-based
power systems to provide a ‘‘worst case’’ cost effectiveness analysis. Electrical
power services available at the shore sites should be utilized if sufficient power
is available.

84

Table 19. Selected Cable Systems for Shore-Based Plant

Transmission Voltage Full Load
Distance Level Frequency | Wire Size Losses
(miles) (kv) (kw)

6 AWG
ne 4 AWG
AC 2 AWG

2 AWG

4/0 AWG

2 AWG
2 AWG
1/0 AWG
1 AWG
1 AWG

2 AWG
1/0 AWG
1 AWG
2/0 AWG
350 MCM

1 AWG
1 AWG
4/0 AWG

600 MCM
1

1 A 3,000-kw load at 500 miles cannot be reached at the voltages
considered.

85

Table 20. Estimated Costs of Shore-Based Power Sources

(Values are in thousands of dollars.)

Cable Length (miles)

Power Level
(kw)

CONCLUSIONS

1. The most serious problem associated with the development of underwater
power systems for power levels of 30 to 3,000 kw at depths of 600 to
20,000 feet is the limitation of watertight cable connectors.

2. In-situ power plants can supply 30 to 300 kw of usable AC power at
depths of 600 to 20,000 feet and 1,000 to 3,000 kw at depths of 600 to
2,000 feet within the current state of the art.

3. Surface power plants can supply 30 to 3,000 kw of usable AC power to
depths of 600 to 20,000 feet within the current state of the art and, except
for underwater connectors, without technical limitations.

4. Shore-based power plants can supply 30 to 1,000 kw of usable AC or DC
power to depths of 600 to 20,000 feet and 3,000 kw at depths of 600 to
10,000 feet within the current state of the art and, except for underwater
connectors, without technical limitations.

5. In-situ power plants are not economically competitive with either shore-
based or surface-tendered power plants except for restrictive undersea missions.

6. Surface-tendered power systems are most cost effective for all selected
power levels and ocean depths more than 50 miles from shore.

7. Shore-based power systems are most cost effective for all selected power
levels and cable lengths of 10 to 50 miles.

86

8. The water-cooled nuclear reactor is the most cost effective power plant
for the in-situ power system that operates at power levels greater than 30 kw.

9. The diesel engine generator is the most cost effective power plant for both
the surface and shore-based power systems.

10. AC power transmission is more cost effective for distances up to 10 miles
between power source and load module; distances from 10 to 500 miles
involve trade-offs; and beyond 500 miles, DC power transmission is more
cost effective.

11. The most cost effective generated voltage is 480 volts, 3 phase, 60 Hertz
for loads of 30, 100, and 300 kw and 4,160 volts, 3 phase, GO Hertz for loads
of 1,000 to 3,000 kw.

12. An armored, polyethylene-insulated and jacketed, three-conductor cable
provides the most reliable transmission cable for all deep ocean power systems.

13. A four-point mooring system is the most reliable method of mooring a
surface plant.

RECOMMENDED DEVELOPMENT PROGRAMS

As a consequence of the study program on underwater power systems,
several development or “high risk’’ areas were identified. These development
areas are necessary to complete the preliminary design of selected power
systems (see the Appendix). The establishment of a development program
for the “high risk’’ areas would greatly improve the cost effectiveness of the
selected systems.

Cable Connectors

The surface-tendered and the shore-based underwater power systems
require two different connectors for each system—one at the power plant
and one at the load module. For the in-situ power systems, two connectors
are also required, but both would be identical.

Connectors can be characterized as two basic types, wet and dry. The
dry connector is essentially an electrical device that provides the necessary
continuity between a cable and a particular module. In a dry connector,
water or moisture are not allowed to enter the connection point. Therefore,
the connection must be made ina relatively dry atmosphere and, In the case
of underwater systems, connections must be made prior to emplacement of
the cable or modules. A wet connector has the same capabilities as the dry

87

connector, but it enables an electrical connection to be made in the ocean.
This feature offers a tremendous advantage in the emplacement of under-
water power system elements.

A wide range of connectors are available so that power levels up to
1,000 kw can be handled. However, this is not true for connectors to be
used with the higher voltages selected in the study program. Figure 20
illustrates the availability of dry connectors for underwater power systems.
Connectors suitable for a power level of 100 kw could be made available by
preliminary engineering and limited testing. Connectors in the 3,000-kw
range are not available and would require substantial development effort.

The recommended development program was divided into a series
of phases. A milestone chart, program schedule, and budget costs for the
connector development program are given in Figure 27. Phase | of the con-
nector development would encompass concept formulation and trade-off
analysis. Four types of connectors suggested for development were pressure-
compensated and not-pressure-compensated connectors for both the dry and
wet connector designs. The connectors would be suitable for 4,160 volts
and loads of 300, 1,000, and 3,000 kw and for 13,800 volts and 3,000 kw.
Final design approaches would be studied to evaluate the most cost effective
connectors and to establish the validity of specific connector concepts
developed. Phase || would involve the design, fabrication, and testing of
prototype dry connectors for the selected designs established in phase |.
A 4,000-volt, 50-ampere connection would be developed for depths as great
as 20,000 feet. In phase II| a prototype 4,000-volt, 50-ampere wet connector
and a prototype 4,000-volt, 160-ampere dry connector would be developed
and tested. Phase IV is the same as phase II! except that the prototype
connectors would be for higher power levels. A 4,000-volt, 200-ampere
wet connector and a 4,000-volt, 500-ampere dry connector would be
developed. In phase V a prototype 13,800-volt, 150-ampere dry connector
and a prototype 4,000-volt, 500-ampere wet connector would be developed
and tested. Phase VI would produce the final design of the entire family of
connectors for underwater power systems.

Heat Rejection Systems

An in-situ reactor power plant using a secondary steam turbine
generator as the energy conversion system requires a significant heat removal
capability. Heat removal could be accomplished by the use of circulating
seawater through appropriate hull penetrations or by condensing the steam
on the normally cooler pressure hull. The advantage of the first method is
that a theoretically unlimited heat removal capability would be provided.

88

Phase |

Concept formulation and

! 6
trade-off analysis I 9*
Phase |] Wl 9
Design and test prototype 4,000-volt, 50-amp IV 6
dry connector
Phase II] v 2
Vi [Bye

Develop and test prototype connectors

Phase 1V
Develop and test prototype connectors

Phase V

Develop and test prototype connectors

However, such a method suffers from such significant disadvantages as the

requirements for hull penetrations, high pressure piping systems, and internal
heat exchangers, as well as the excessive weight of transition forgings for the
hull penetrations. There is also the possibility of sediment clogging with the
plants resting on or near the ocean bottom. At present pressure hull penetra-

tions 3 inches in diameter have the capability of withstanding pressures as

great as those found at 3,000-foot depths. The second method of heat

removal—condensing steam on the pressure hull—would reduce the high

risk design of hull penetrations and the sediment clogging problems, but its
limited heat removal capability would make necessary an oversized hull or

the provision of finned surfaces with external or internal circulating techniques.

Months After Contract Award
ie} 2 4 Oo 8 10 12 14 6 18 2) 2 ew 23 2 eH)

a. Wet type, 4,000 volts, 50 amps

b. Dry type, 4,000 volts, 160 amps 5 Gant 3
n be concurren

a. Wet type, 4,000 volts, 200 amps
b. Dry type, 4,000 volts, 500 amps

a. Wet type, 4,000 volts, 500 amps
b. Dry type, 13,800 volts, 150 amps

Final design; review and evaluation of
specifications, material selections and
test requirements

OD 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Months After Contract Award

Figure 27. Milestone chart for cable connector development program.

89

Time (months)

*** Conclusion type task at end

Cost ($1,000)

70
200
100

80
150
100

* Can start 3 to 5 months after start of phase |

A three-phase development program was suggested to advance the
state of the art in heat rejection systems for in-situ reactor power plants. A
milestone chart, budget costs, and program schedules for the heat rejection
systems development are shown in Figure 28. Phase | would entail a concept
formulation and trade-off analysis to develop criteria for the selection of the
most promising heat rejection designs. Two concept approaches to be
evaluated would be circulating seawater through hull penetrations and heat
removal through the hull structure. Effective ranges of both concepts would
be established to show the feasible upper limit of the hull transfer and the
lower limit of the seawater circulating systems.

Months After Contract Award
0 2 4 6 8 10 12 14

select most efficient heat rejection systems

Phase |

Concept formulation
and trade-off analysis

concepts acceptable for
final design process

stress analysis

Phase II

Hull heat rejection concept,
development study

pipe stress analysis; pipe compression techniques

Phase III

Hull penetration concept,
development study

Cost ($1,000)

65
95

* Can be concurrent

6 8
Months After Contract Award

Figure 28. Milestone chart for heat rejection system development program.

90

Phase || would include concept development studies for the most
promising hull heat rejection system selected in phase |. Sufficient stress
analysis would determine the adequacy of hulls with thermal stresses applied.
In addition, the upper limit of effectiveness of this approach would be
established, with sufficient details developed to initiate the final design
process.

Phase ||| is similar to phase || except the most promising seawater
circulating system and hull penetration schemes would be analyzed. A stress
analysis of the transition forgings for the hull penetrations and a pipe stress
analysis would be conducted to minimize the weight of the high pressure
piping and forgings. The parameters developed would define cost effective
limits of the hull penetration—seawater-circulation concept. Here, as in
phase ||, the goal would be to extend the state of the art of in-situ power
plant heat rejection systems and to provide sufficient details for initiation
of the final design process.

General Utility Power System

A development program for an underwater utility power transmission
system was recommended as a result of the underwater power systems study
program. The development program would involve three phases. The
estimated budget costs and a milestone chart for the general utility under-
water power systems are shown in Figure 29.

In phase | concepts of a 30-kw to 100-kw general utility power
transmission system would be developed for depths of GOO to 10,000 feet.
The concepts would provide a secondary power distribution module to
serve several dissimilar loads and the necessary primary power conditioning
equipment for adaptation to either the surface or the in-situ power plants.

In phase |! additional concepts for a 100-kw to 300-kw general
utility power transmission system would be developed. The concepts would
provide primary conditioning equipment and a secondary power distribution
module to serve several dissimilar loads from an in-situ reactor plant only. A
maximum transmission cable length of 6,000 feet would be considered.

The adaptation and modification of the recommended systems to
the available power sources constitute phase ||! of the development program.

The recommended development program for each system described
above would include a definition of all major equipment, its availability, a
potential schedule of major milestones in its development and construction,
placement and recovery techniques, and logistics support.

With this development program, the underwater general utility power
transmission systems would provide the current needs of underwater load
modules with total power requirements of 30 to 300 kw down to 10,000 feet.

91

Months After Contract Award
(0) 2 4 6 8 10 12

Phase | for adaptation to either surface power

lant or in-situ power plant
Concept development, 30-kw P P

to 100-kw system

Phase I! for adaptation to in-situ

reactor power plant
Concept development, 100-kw

to 300-kw system

Phase II

Adaptation and modification to
proposed power sources available

Phase Time (months) Cost ($1,000)
I 60
ll 6 85
Il 3 35
(0) 2 4 6 8 10 12

Months After Contract Award

Figure 29. Milestone chart for general utility power system development program.

Development of the secondary power distribution module, including
pressure containment hull and penetrations for cable connectors, would be
assigned the highest priority of all the elements associated with the develop-
ment of the general utility power system.

In-Situ 3,000-kw Power Plant

It became apparent during the course of the study that reactor power
systems with a 1,000-kw to 3,000-kw electrical power output could not be
readily adapted to depths of 6,000 to 20,000 feet. There are numerous
problems associated with the physical size and weight of large reactor plants,
such as hull design and materials, buoyancy, heat transfer techniques, place-

Q2

14

14

ment and recovery, and logistics. A separate study was therefore considered
necessary to formulate concepts for large in-situ reactor plants when an
application becomes apparent and defined in greater detail. Sufficient
definitive information was not available in this study to establish cost and
time schedules for the development program.

93

Appendix

PRELIMINARY DESIGNS OF SELECTED
UNDERWATER POWER SYSTEMS

SELECTED SYSTEMS

The underwater power systems selected for preliminary design were:

1. 100-kw in-situ power systems emplaced on the ocean floor at
depths of 600 feet and 6,000 feet.

2. 30-kw surface-tendered power systems for supplying power to
ocean depths of 600 feet and 6,000 feet.

3. 300-kw shore-based power systems for cable lengths of 10 miles
and 50 miles.

100-kw Nuclear Reactor In-Situ Power System

The in-situ plant selected for a preliminary engineering analysis
consists of a power module, a load module, a foundation, and auxiliary equip-
ment, as illustrated in Figure A-1. Trim and ballast components, as well as
winches, would be provided as the required auxiliary equipment.

A design concept of a
100-kw in-situ power plant
module is shown in Figure
A-2. The plant consists of a
nuclear steam generator and a
Rankine cycle turbine genera-
tor system rated for 100-kw
net power. The steam genera-
tor selected was based on
General Atomics TOPS-300
power supply. It features
light water cooling in a pres-
surized primary coolant loop.
The secondary steam system
provides steam on load demand
to a high-speed turbine which
would be geared to a 60-Hertz
electric generator.

Figure A-1. In-situ nuclear reactor power
plant.

94

watertight access hatch

main electrical cable

enetration 2 et ee
e air conditioning

eater B unit space
electrical power distribution Pp

and control panels

external framing

reactor instrumentation
and control panels

deck

turbine generator set and
auxiliary systems

shield deck

hatch shield deck

7a a” “0 0°@ © OO

reactor systems equipment-
condenser, pumps, feed pumps,
demineralizer, etc.

reactor power unit

platform deck
steam condenser
(inner cylinder)

shielding water

Figure A-2. Preliminary design of a 100-kw in-situ power plant.

95

The pressure hull for an in-situ power plant would be cylindrical, with
external frames and hemispherical heads on each end. External frames allow
smooth internal surfaces for use as a heat exchanger. The top hemispherical
head would be used for all the electrical penetrations and an access hatch.
Main power, plant monitoring and control, and battery cable penetrations
would be required, with a number of spare or blank penetrations provided
for power and instrumentation. The access hatch would be large enough to
accept a small submersible for underwater servicing or maintenance of the
power plant. An alternative to the access hatch could be a bolted hemispher-
ical top, which would make it easier to replace large equipment and refuel the
reactor. However, a more complete analysis of these two methods in terms
of equipment size would be required if replacement or refueling was defined
as a plant requirement.

The pressure hull for the 600-foot depth has been estimated as
1/2-inch HTS steel plate and for the 6,000-foot depth as 1-5/8-inch HY 130
steel plate. Typical hull designs are shown in Figure A-3. These hull estimates
allowed for factors of safety of at least 1.5 on yeilding and 2.0 on buckling.
An increased hull weight of 10% was included in the plant design to allow the
use of the hull as a heat exchanger. The hull would be used for condensing
steam.

The arrangement of the power plant is the same for both operating
depths, 600 and 6,000 feet. The characteristics of the load module were
undefined. Preliminary characteristics of a 100-kw plant are listed In
Table A-1. The plants would normally operate with the axis oriented ver-
tically. However, full power could be obtained with the plant at 15 degrees
from the vertical. The plant could be transported in nearly the horizontal
position.

Table A-1. Characteristics of Preliminary In-Situ Power Plant

Outside i
O ti Weight (Ib)
eee Diam, Less Hull weiner Displacement | Buoyancy
Frames Material 5 (Ib) (Ib)
(ft) (ft) Hull | Machinery Total

600 10 36-1/2 HTS | 34,000} 122,000 156,000 166,500 +10,500
6,000 10 36-1/2 | HY 130] 93,000 | 122,000 215,000 166,500 —48,500

96

[ Sin. = (~ 78in.

5ft0in. Rio

rib spacing 18 in. HTS

1/2 in. (a) 600-foot depth. R = 5 ft Oin.

pee] opie

5 ftOin. Rig

rib spacing 12 in. HY 130
R = 5ftOin.
(b) 6,000-foot depth.

Figure A-3. Typical pressure hull designs.

97

The lower portion of the plant would contain the reactor, its auxiliary
systems, shielding, the secondary system condensate and feed pumps, and the
freshwater cooling system. The midsection would contain the turbine genera-
tor and its auxiliary systems. A shield deck separates the midsection from the
lower compartment, through which there is limited access while the plant is
operating. The upper level would contain all the electrical and electronic
equipment, the power plant control equipment and enclosures, the primary
distribution equipment, and the transmission control and instrumentation
circuits. An air conditioning unit would be provided for temperature and
humidity control of the upper compartment. Cable penetrations through the
hull and the access hatch would be located in the upper compartment.

An inner cylinder would be provided in the lower reactor compartment
to form asteam condenser. This cylinder supports nearly all the equipment in
the midsection and meets the hull only through a flexible skirt at the upper
end of the inner cylinder. The bottom end of the cylinder would be fastened
to the shield tank structure. This arrangement would prevent pressure hull
deflections from disturbing the equipment. The deck above the cylinder is
connected to the shield deck by stanchions.

The inner cylinder provides a structure on which the complete plant
may be assembled, tested, and installed within the pressure hull without
disassembly. Prior to installation, the reactor operating time and power level
should be limited to the amount of residual radiation which would not pro-
hibit handling during installation. For subsequent refueling or maintenance,
the inner cylinder with the two deck levels may be detached and removed
as a unit.

The maximum radiation levels established for the in-situ plants are
presented in Figure A-4. These levels would allow limited personnel access
to the area above the shield deck for servicing the plant while it is operating
at full power. Since occupancy times can only be predicted, the maximum
permitted radiation levels established may be lower than necessary. A pri-
mary shield would be provided by lead and shield water tank. This would
allow limited access to the exterior of the pressure hull after the reactor is
shut down (30 days). Dose rates during operation would be high in the
water surrounding the reactor compartment. A protective screen would be
required around the reactor compartment at shallow depths where divers
may have access.

Requirements for a special containment vessel for this power plant
were not firmly established. Such a vessel would protect the pressure hull
from overstress due to thermal gradients resulting from secondary steam,
primary coolant relief valve lifting, or primary coolant system leakage. The
containment vessel would also provide additional protection against the

98

release of fission products. The thermal stress gradient across the hull was

not calculated, but if a containment vessel were required, the inner cylinder
could be closed off at the upper end. This would result in increased fabrication
complexities. Even without the containment vessel, there would be three
barriers to the release of fission products: fuel element clodding, primary
coolant pressure vessel, and pressure hull. Therefore, a special containment
vessel would not be required.

all dose rates for full power
operation unless otherwise
indicated: 6 mrem/hr

(occupancy time, 2 hr/day)

power plant control

24 mrem/hr
(occupancy time, 1/2 hr/day)

machinery space

DGAIGGGPGIDS SST
ae

shield deck

not accessible

maximum contact dose rates:
500 mrem/hr, 24 hours after
shutdown; 150 mrem/hr, 30
hours after shutdown

reactor space

Figure A-4. Maximum radiation levels for in-situ power plants.

The power conversion system would have a single turbine generator
with a main steam system, condensate and feed system, auxiliary steam equip-
ment, make-up water system, and purification system. The power conversion

99

system flow diagram is shown in Figure A-6. Superheated steam would be
obtained from dual, full-capacity, once-through steam generators. Steam
would flow through a stop valve and would be controlled by a throttle valve
which is governor-regulated to control the turbine speed. The stop valve
would be closed automatically to protect against overpressure, overspeed, or
loss of lubrication. Exhaust steam would be condensed by an annular hull
condenser and recycled through a full-flow demineralizer to maintain purity
for the once-through steam system. Power conversion system data for the
preliminary design are shown in Table A-2. Figure A-6 shows the full-power
heat balance for the power conversion system.

Table A-2. Data for Preliminary Power Conversion System

General

Electric power (net), kw .
Overall efficiency, %
Thermal power, kw .

Steam Cycle

Turbine inlet pressure, psia .

Turbine inlet temperature, OC .
Turbine inlet superheat, °C .

Turbine exhaust pressure, psia .
Turbine steam flow, lb/hr . . . . .
Turbine steam consumption, |b/bhp-hr

Turbine

Speed, rpm (estimate) .
States (estimate) .
Efficiency, %

Thermal efficiency, % .

Generator

Type drive

Speed, rpm .
Power, kw
Voltage, volts .
Frequency, Hertz.
Phases .

100

to electrical control
a and distribution to primary
pressure a overpressure ceolantisystem
release alll O trip

throttle E>
oO a
Dk] bk turbine @)

q Xt Stearn annular hull
pressure dump condenser
reducer 4 ><] \
steam generator auxiliary i!
><]
(once-through type) steam system i es
sudden loss additives
of load

NAAAAAAAAAAAAAAAN
ASSASSSSSSAAAAOSASY

\ \Z
L\ L\
condensate
pumps (*) (L)
surge oYLoY
tank O
p<
hotwell level
7A control

feed pumps q va

freshwater LS ere |
Gr-tf] ae
D Met) > low-pressure
> AS V full flow aaah

| drains
demineralizer label a
| eae ty

Figure A-5. Preliminary power plant conversion system.

Legend:
Steam
— Vater
# = flow rate, lb/hr

P = pressure, psia
Zee Q = heat, Btu/hr
1,

auxiliary steam system (air H = enthalpy, Btu/Ib

ejectors, gland exhaust, etc.)

steam

[| generator
generator

115 kw

2,560#

2,660# 1,065H
| 113H 6
condenser 2.43(10) Q
| : nor 3.3P
| makeup
| 2,660#
ent) Be, 113H
condensate pump
feed pump

Figure A-6. Preliminary full-power heat balance.

101

The annular condenser would be formed by making a space between
the pressure hull and the inner cylinder. A 3/4-inch annular condenser would
allow for pressure hull deflections of 5/32 inch. The lower end may be rig-
idly attached, but the upper end should be attached with a flexible seal to the
hull to avoid loading the inner cylinder with sea pressure deflections of the
pressure hull. The hull condenser would be adequate sized for plants at depths
of 600 and 6,000 feet where the ambient seawater is 249°C. However, for
29°C seawater, the plant at 6,000 feet would have to operate at about 2/3 of
full power, and the plant at 600 feet would provide full power at 29°C.

The freshwater cooling system, shown in Figure A-7, would provide
cooling for the air ejecter and gland exhaust condenser, air and lubricating
oil cooler for the turbine-generator set, reactor plant auxiliary systems, and
machinery spaces. Freshwater would be circulated through a water cooler
heat exchanger and then circulated to the various coolers. Heat would be
transferred from the freshwater to the shield water by a shield water circu-
lating system and then finally rejected from the shield water through the
pressure hull. The total freshwater heat load was estimated to be less than
250,000 Btu/hr. The shield water heat load was estimated to be less than
300,000 Btu/hr.

pressure hull shield tank
expansion tank

air and lubricating oil cooler
for the turbine-generator set

49{009 Jayemysey

freshwater air ejecter and gland
circulation pumps exhaust condenser

shield water
circulation pumps

Figure A-7. Preliminary freshwater cooling system.

102

A relatively warm interior is possible when the pressure hull is used
for heat transfer. However, humidity would be high because of the water and
steam systems. The upper level would be thermally insulated from the rest of
the plant to maintain a reasonable temperature and humidity for the electronic
and control equipment. An air conditioning unit that uses a forced convection
cooler with water circulating against the hull could be used for the upper level
area.

A pressure-compensated battery supply located outside the pressure
hull would supply power for plant start-up, monitoring and standby, deploy-
ment and recovery operations, and emergency power. Batteries would provide
power for navigational lights and signalling devices during deployment and
recovery. The total battery power requirement was estimated not to exceed
15 kw-hr, with about 5 kw-hr allowed for plant start-up. A battery charging
system was included to automatically maintain the batteries at full charge.

The turbine generator plant would deliver 100-kw, 480-volt, 3-phase,
60-Hertz power for the 600- and 6,000-foot depths. The transmission cable
between the power module and the load module of the in-situ system would
be a three-conductor, shielded, grounded, neutral, armored cable. Conductor
size would be 4 AWG. Duplicate monitoring and control of the power plant
would be provided in both the power module and in the load module. A
multiconductor control cable would be provided between the two modules.

The protective system for the in-situ power system would include
standard differential relay circuitry for the generator, a differential zone for
the cable transmission between modules, and circuit protection for the control
power as well as the generator exciter circuits. The philosophy of operation
would be to keep the system in operation until loss of equipment Is inevitable,
at which time it will shut down. Loss of control power would also shut the
plant down.

A forced descent-ascent concept was selected for emplacement of the
in-situ power system. The anchor would be located on the bottom by using
soundings in conjunction with a leveling device or by the more elaborate
method of using a remote television camera mounted on the anchor cable.
The camera method would probably be used at the 600-foot depth; the
bottom leveling device and surface soundings at the 6,000-foot depth.

Once the anchor has been set on the bottom site, deployment of the
in-situ plant would begin by placing the plant's primary and secondary systems
in a remotely actuated start-up mode. Final ballast and trim adjustment
would be made, and descent stabilizers would be rigged for descent. The
descent may be initiated by flooding the main ballast tanks, but the winch-
down method would be used for the actual descent. A bottom-sensing
weight would begin to decelerate the descent velocity 150 to 200 feet above
the bottom. When the plant is on the bottom, a triggering device would trip
the winch switch to stop the winch operation.

103

Emergency ascent is based on
retrieving as much of the in-situ plant
as possible. The winch would also
be used for ascent. However, if the
batteries fail or the winch becomes
inoperative, the free ascent method,
described earlier, would be made. In
the preliminary design, the power
module would be jettisoned for free
ascent, leaving the load module and
base in situ. The ascent rate of the
power module must be controlled to
avoid having the module jump out of
water when it surfaces. Figure A-8
illustrates the emergency ascent
method selected.

The major milestone chart
and budget cost estimates for the
100-kw in-situ power systems are
shown in Figure A-9. The milestone
schedule would be the same for both
depths of 600 and 6,000 feet. The
costs of transportation deployment
and common base for the power and
load modules are not included in
the estimates.

Extensive engineering effort is anticipated for solving heat transfer
problems and for protecting the hull surfaces against the environment. Some
testing may be necessary to evaluate the heat transfer characteristics of selected
protective coatings.

Figure A-8. Emergency ascent.

30-kw Diesel Electric Surface Power System

A standard commercial 30-kw diesel electric power plant would be
installed in a surface hull similar to the General Dynamic monster buoy. The
hull (buoy) —41 feet in diameter and 7-1/2 feet high overall—would be equip-
ped with a 20-foot-high, 5-foot-diameter mast and stack. The buoy would
have a double hull, the outer hull being circular and the inner hull being square.
An egg-crate structure between the inner and outer hulls would serve to stiffen
the hulls and provide a baffled fuel storage area with a minimum of fuel agi-
tation. Four vertical hawsepipes would traverse the fuel storage area, allowing
passage of the mooring lines.

104

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105

The surface plant hull would use a modular arrangement of the
power plant and components. Three compartments would be provided
in the power plant module. The largest would contain the power plant,
a separate compartment would contain the electrical and electronic equip-
ment, and the third compartment would contain the oil handling and filtering
equipment. Any of the major units could be hoisted out of the buoy or
surface hull without disturbing the mooring system. The provision was made
to avoid abandoning the moor for equipment replacements. The generator
plant could be replaced with a 100-kw unit if needed in the future. The
only difference as the result of this exchange is that a shorter refueling cycle
is required. This eliminates the need for establishing a new moor. Existing
cables would have adequate capacity to serve the higher load. Figures A-10
through A-12 show the surface plant hull arrangement.

1. Engine and generator
compartment

2. Electrical and electronic
control compartment

3. Oil handling and oil

filtering compartment

Figure A-10. Surface power plant hull.

106

Hull
. Fuel oil storage

Mast

. Snorkel induction

. Snorkel exhaust

. Navigational lights

. Whip antenna

. Power module 5
. Hawsehole

OMDNOANRwWN =

Figure A-11. Cutaway of surface power plant hull.

The power plant is a turbocharged diesel generator. The unit is
self-contained, with necessary engine accessories and protective devices. A
shell-and-tube-type heat exchanger is provided for the diesel engine, with
seawater in the tubes and freshwater in the shell. The freshwater system
cools the engine. Engine intake air is taken from the engine room at
ambient conditions. An additional 3,000-cfm fan is provided to ventilate
the engine room. An exhaust muffler is provided between the engine and
a plenum leading to the exhaust stack. Batteries are used for starting the
engine.

107

1. Mooring line 6. Power plant

2. Hawsepipe 7. Inner hull

3. Steel rope 8. Outer hull

4. Exhaust 9. Power cable

5. Air intake 10. Swivel connector

Figure A-12. Cross section of surface power plant hull.

The generator is rated for 50-kw continuous or 60-kw intermittent,
60-Hertz, 480-volt, 3-phase, AC power output. Voltage regulation was
established at 1% bandwidth of steady-state voltage, with a maximum
steady-state frequency variation of 0.5%. The no-load to full-load recovery
time was set at 4 seconds with an isochronous governor. The same generator
plant is used for the 600-foot-deep and the 6,000-foot-deep transmission
systems. Table A-3 lists the characteristics of the diesel generator.

The electrical systems selected for the surface-tendered power system
were 480 volts, 3 phase, 60 Hertz for 600-foot depths and 4,160 volts,

3 phase, 60 Hertz for 6,000-foot depths. The 480-volt generator plant out-
put will be transmitted directly to the load module. The 4,160-volt system
will generate power at 480 volts, which will be stepped-up to 4,160 volts
with a dry transformer; the power will then be transmitted to the load
module at 4,160 volts.

Both the 480-volt and 4,160-volt systems will utilize the same type
of cable, with the insulation level at 5,000 volts. The conductor size selected
for both systems is6 AWG. The 480-volt system at 600 feet will require
915 feet of cable, and the 4,160-volt system at 6,000 feet will require
11,790 feet of cable. These cable lengths would limit the voltage drop to
within 5%.

108

Table A-3. Characteristics of 30-kw Diesel Generator for 600-Foot-Deep
and 6,000-Foot-Deep Surface Power Plant

Diesel Engine (Turbocharged and Aftercooled)

Rating. . . . . . . . 50kwat 1,800 rpm, continuous
60 kw at 1,800 rpm, intermittent

Approximate volume. . . 6 feet longx 3 feet wide x 3-1/2 feet high (63 ft3)

Approximate weight . . 2,400 pounds

Governor. . . . . . . 0.5% speed control

Heat exchanger . . single-pass shell and tube

Capacity . . . . . . . 5,000 Btu/min
Generator (Splash Proof)

Voltage . . .. . . . 480volts at 60 Hertz, 3 phase

Rating. . . . . . . . 50kwat 70°C, continuous, with 25% overload
capability for 2 hours

Regulation 1% steady state

Attached Accessories

Turbocharger and aftercooler

Detached Accessories

Heat exchanger

Generator and exciter

Heat exchanger pump

Air filter Exhaust muffler

Alarms and gages

Lubricating oil pump and filter (self bypassing)
Fuel oil pump and filter (self bypassing)

water pump

A cascade-type protection system was recommended because of savings
of weight and volume in the load module. The carrier system was provided for
transfer of trip functions, data recordings, and system-condition displaying.
Communications to the surface could also be provided by carrier.

109

A four-point moor would be provided for the surface plant hull. The
four wire rope moorings enter the bottom of the hull close enough to the
center to retain the desirable characteristics of a single-point moor but far
enough outboard to prevent rotation and the consequent twisting of the power
cable. A four-point moor reduces the excursion limits of the surface hull and
therefore reduces the length of power cable required. The moors entering the
bottom of the hull would prevent the hull from towing under in high sea states.
Figure A-13 illustrates a four-point mooring attachment to the surface hull.

Three ships would be
required to set the four-point
mooring system: a heavy lift
ship (HLS), a supply ship (SS),
and a station-keeping ship
(SKS). The HLS or the SS
could be used to tow the sur- 1. Hawsehole
face plant hull to the site. On :s Nes oe
arrival at the site, the SKS
would establish and record
the site geography for compar-
ison to a prior site survey and
would position itself at the
center of the moor. The SS
would take a position at 90
degrees to the SKS while the
HLS would position itself
over the first leg. The HLS
would first lower the anchor
slowly. When the anchor has
bottomed, the HLS would
then proceed slowly toward
the SKS to bottom the anchor
clump. When the clump bot-
toms, the HLS proceeds to
the location of the catenary
support buoy, paying out the
remaining mooring leg. The
anchor would then be set and
the support buoy emplaced. The HLS then continues toward the SKS to lay
the synthetic mooring line for the first leg. This procedure would be repeated
for the other three mooring legs. On completion of the mooring system
emplacement, the mooring lines would be transferred from the SKS to the

Figure A-13. Four-point moor accommodations
on surface buoy.

110

surface plant hull by transferring one mooring line at a time. The mooring
lines would be pretensioned from winches in the surface hull. It is estimated
that each mooring leg could be set in 1 day.

Requirements for the four-point moor are shown in Figure A-14. As
noted, the excursion limit, vertical and horizontal components, and scope
developed for each leg, are given for the 600-foot depth and for the 6,000-foot
depth. The moor geometry for the two depths is shown in Figures A-15 and
A-16. Installation details of the catenary support buoy and mooring leg riser
are shown in Figure A-17. The anchor, clump weight, and mooring leg details
are shown in Figure A-18.

A major milestone chart and estimated budget costs for installation of
a 30-kw, surface-tendered power plant system for 600-foot and 6,000-foot
depths are presented in Figure A-19. These cost estimates do not include cost
of development programs, transportation, and deployment, since the load
module mission and site are undefined.

buoy buoy

Emax = '-417xe
for a four-point moor

When Y = 600 ft When Y = 6,000 ft
S = 1,590 ft S = 10,300 ft

X = 1,350 ft X = 8,600 ft

e = 370ft e = 4,300 ft

e = 523 ft Cmax = 6,093 ft

Figure A-14. Basic configuration of four-point moor.

300-kw Shore-Based Diesel Generator System
The 300-kw shore-based power plant selected for preliminary design

is illustrated in Figure A-20. The selected transmission distance was estab-
lished at 50 miles. This system includes a diesel generator plant and auxiliary

111

support facilities. The diesel generator is housed in a corrugated steel building
equipped with a 10-ton bridge crane for installation and maintenance require-
ments. All equipment associated with the diesel generator system is housed in
the same building. The switchgear and transformer equipment are located in

a single location and oriented to facilitate surveillance during plant operation.

®@ anchor

Cmax = 1.417[X -(S-Y)]

x = 1,350 ft

Ss = 1,590

Y = 600 ft

@ = support buoy
load module
ae maximum excursion

anchor
® support buoy @ @ support buoy

surface-tendered buoy

support buoy

Maximum excursion = 523 ft
Scale: 1/2 in. = 500 ft

anchor

Figure A-15. Moor geometry for 600-foot depth.

112

anchor

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open socket

closed socket —*—

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ty
150 ft long

4 closed socket Soe

—=—_—_—— closed socket
‘ bolt-type chain
shackle ——_ 3-in. x 12-in.-1D ground ring

——_—__——— Miller swivel
wi Pepa open socket

mooring line riser

ire rope (length to
suit installation) ———>—

bolt-type chain shackle

mooring line

Miller swivel ae oo open socket

3-in. x 12-in.-ID ground ring

lower catenary leg ~a

Figure A-17. Installation details for the catenary support buoy.

114

: catenary leg
wire rope __ x
closed socket ———_—

chain termination assembly —————=

; Pear-shaped detachable link (bald type) ee D shots) et/2ansehain
2 ae Bolt-type chain shackle :
termination i ‘ SS
assembly Miller Swivel Z

i ic round ring
Bolt: type chain shackle groun SS
bolt-type chain shackle

_.— clump weight,
57,000-85,000 Ib

SE 1 shot, 1-1/2-in. chain

anchor shackle

25,000-Ib LWT wedge
block anchor

Figure A-18. Details of the mooring leg.

The shore-based facility could also include a water tower and, if
remote monitoring of the plant is necessary, a microwave link. This link
would transmit plant conditions and could provide a voice channel. A closed
circuit television system could also be incorporated to monitor the plant
conditions.

Diesel fuel would be stored underground adjacent to the diesel
generator building. The fuel pump, filter, and day tank would be located
inside the building in one shallow drain basin area.

Power would be transmitted to the load module by cable. This cable
would originate at the generator building and extend to the sea via an
underground duct. A carrier system would be provided for monitoring,
communications, and control functions between the load module and the
shore-based plant.

The self-contained diesel generator would be rated for 300-kw
continuous operation. The engine would be equipped with supercharger or
scavenging blower for reduced operating temperatures and higher efficiencies.
Engine sensors would be provided to indicate cooling water temperature,
lubricating oil pressure, and engine overspeed. A freshwater cooling system
would be provided with a forced convection radiator requiring a minimum
air flow of 29,000 cfm. Radiant heat from the engine and generator was
expected to approximate 7,500 Btu/min.

115

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116

Figure A-20. Shore-based power plant.

Fuel consumption necessary to transmit 300 kw 50 miles was
approximated to be 7% higher than that necessary to transmit 300 kw
10 miles.

The drip-proof generator would have a remote alarm to indicate
overtemperature conditions. The generator output rating would be 300 kw
continuous, 4,160 volts, 3 phase, 60 Hertz. A steady-state voltage regulation
of 0.25% was considered possible with a generator of this capacity. The diesel
engine generator characteristics are listed in Table A-4.

The shore-based plant could supply a load of 300 kw at distances of
10 to 50 miles at 13,800 volts. For the 10-mile distance it was recommended
that a 13,800-volt AC system be used, but for the 50-mile distance a
13,800-volt DC system was preferred. Since a 300-kw plant for a 50-mile
load was selected for preliminary design, a transformer for stepping-up the
generated voltage of 4,160 volts to 13,800 volts, as well as conversion equip-
ment to provide DC transmission power, must be provided at the shore plant.
Inversion equipment would be required in the load module. A two-conductor,
shielded, armored cable with 1/0 AWG conductors would be used for the
power transmission cable.

WAY

Table A-4. Characteristics of Shore-Based 300-kw Diesel
Engine Generator

Diesel Engine

Rens 6 0 6 co ow 5 MOOMWeL 1,200 Kann, continuous
550 kw at 1,200 rpm, intermittent

Approximate volume . 14 feet long x 5 feet wide x 7 feet high (490 ft?)

Approximate weight . . . 21,000 pounds

Gowann@Ps o o o o 6 o OAM

Cooling c «a 6 56 5 o oc Radiator, forced convection, 29,000 cfm

Generator (Drip-Proof)

500 kw at TOXG, continuous

Rating -

WOMEGS os 0 “oo 6 4 4,160 volts at 60 Hertz, 3 phase

Regulation . . . . . . 0.25% steady state

Attached Accessories Detached Accessories

Supercharger or scavenging blower Air filter and silencer

Radiator

Generator and exciter

Lubricating oil pump and filter (self bypassing) Exhaust muffler

Fuel oil pump and filter (self bypassing) Alarms and gages

Water pump

Cooling fan

118

The deployment and emplacement of the 10-mile, three-conductor,
15-kv power cable from a shore-based power source to a load module on the
ocean floor involve many factors, such as bottom conditions, depths, and
tide and current data, which have an effect on the type and size of the cable
ship required. An intermediate landing craft was selected as an excellent
vessel for an emplacement of the 10-mile cable.

The diameter of the cable is approximately 3 inches and the weight
of the cable is estimated at 7 |b/ft. The cable would be furnished in one
continuous length, with a termination and connector on the load module
end. The shore end would be capped and sealed. The cable would be loaded
at the manufacturer's plant and the cable ship dispatched to the emplacement
location.

It is assumed that the load module would be transported and lowered
from a separate vessel. Therefore, at arrival on site the cable ship would float
the cable end on the surface (using inflatable floats and a towing craft) to the
module-carrying vessel. The cable would then be hoisted on board and the
necessary electrical connections made.

The load module would then be placed overboard and jowered to the
bottom, with the cable ship paying out cable and standing well clear of the
module-lowering vessel. When the module is on the bottom, the lowering
line is slipped and retrieved and the cable ship then proceeds to the shore
landing, paying out cable en route. This general principle is utilized in either
shallow or deep water.

The method of landing the shore end may vary somewhat, depending
upon the nature of the site. If possible, the landing craft can work well into
shallow water. When beached, or nearly so, the cable ship floats the shore
end into the site. If the slope of the landing area is steep enough, the ship
may be able to beach out near the waterline. In this instance, a bight, or
the end can be passed ashore. Once the cable is ashore, it is led to the termi-
nal box, cut, and anchored in place. Trenching is recommended in surf and
beach areas for protection of the cable. For installing a 50-mile length of
power cable, the general procedure would be as noted above. The only major
change would be utilizing a larger ship, such as a landing ship tank, to
adequately cope with the increased weight of cable involved.

A major-milestone chart and budget cost estimates for the 300-kw,
50-mile, shore-based power system are presented in Figure A-21. Costs for
transportation, deployment, property acquisition, site preparation, and
development programs were not included in the estimates.

Worst-case conditions were assumed for the preliminary design of the
shore-based power system. The availability of electrical power at the shore
site would, of course, reduce budget costs for this system.

119

Months After Contract Award
(0) 2 4 6 & WO Ww 4 WG Ws 2) 22 Bel a 3} eh) Sh ey

contract award, design,

conceptual development manufacture, test
engineering 300-kw power source

| I
contract plans and specifications

preparation

design freeze
engineering drawings

work authorization

connector development (if required)

Procure diesel generator

procure power cable

procure electrical components

eee ere a TR

procure auxiliary components
|
procure transmission equipment

|
procure building materials

land acquisition
building construction

install diesel generato’ ==
1 !

install auxiliary equipment 1Sreghs
' \ I
install electrical equipment
' t

'
install transmission equipment

GE install cable
I
system testing

Gl deploy system

site testing

(¢) 2 4 6 & 10 Ve 14 18 i 20) 2 2b 2 23 30 2 &
Months After Contract Award

Budget Cost Estimates

600 Feet 6,000 Feet
Conceptual development engineering 50 50
Contract guidance plans and specification 80 80
preparation
Detail design, manufacturing, and test 1.25* 2.8*

*|ndicates millions of dollars; all others in thousands of dollars.

Figure A-21. Milestone chart and budget cost estimates for 300-kw shore-based power system.

120

LIST OF SYMBOLS

Nominal outside shell radius, in. S
Buoyancy
Outside diameter of insulation in mils

Inside diameter of insulation in mils

5 Oo

Density, lb/ft

AV,
Change in density due to pressure

AV,
Change in density due to temperature and
salinity Avis
modulus of elasticity Y
Secant modulus of elasticity X
Tangent modulus of elasticity Y
Excursion, ft Oey
Excursion force, !b

Oy
Shell thickness, in.

iu
Moment of inertia of shell frame

@

Effective bulk modulus of the hull = P/(V/V,)
Effective length of cylinder, in.

Horizontal distance between hull and any
intermediate catenary support buoys, ft

a/L

Number of lobes

Pressure

Lobar buckling pressure, psi

Critical buckling pressure, psi

Critical yielding pressure, psi

Radius of frame-shell section, in.

Local outside radius of a spherical shell, in.

Scope of mooring leg, ft -

121

Stress in volts per mil at a point in the insulation
T mils from the cylindrical axis

Temperature
Volume, in.3
Initial volume at zero pressure

Change in volume due to pressure, AP/K,
Change in volume due to temperature
ow, At

Specific volume

Horizontal projection of mooring leg, ft

Vertical projection of mooring leg, ft

Volumetric coefficient of thermal expansion for
the hull and its material

Yield stress, psi
Poisson's ratio

Point in the cable insulation measured from the
cylindrical axis of the cable

ea

r

e

DISTRIBUTION LIST

SNDL No. of Total
Code Activities Copies

1 20 Defense Documentation Center
FKAIC 1 10 Naval Facilities Engineering Command
FKNI 13 13 NAVFAC Engineering Field Divisions
FKN5 9 9 Public Works Centers
FA25 1 1 Public Works Center

15 15 RDT&E Liaison Officers at NAVFAC

Engineering Field Divisions and
Construction Battalion Centers

234 234 NCEL Special Distribution List No. 9

for Government Activities interested in
reports on Deep Ocean Studies

123

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Unclassified
Secunty Classification

DOCUMENT CONTROL DATA-R&D

(Security classification of title, body of abstract and indexing annotation must be entered when the overall report is classified)

ORIGINATING ACTIVITY (Corporate author) 2a. REPORT SECURITY CLASSIFICATION

Naval Civil Engineering Laboratory Unclassified
Port Hueneme, California 93041

REPORT TITLE

DEEP OCEAN POWER SYSTEMS

DESCRIPTIVE NOTES (Type of report and inclusive dates)

Not final; July 1965 to December 1967

AUTHOR(S) (First name, middle initial, last name)

E. Giorgi

6- REPORT DATE 7a. TOTAL NO. OF PAGES 7b. NO. OF REFS
September 1968 123 10)

Ba. CONTRACT OR GRANT NO. 948. ORIGINATOR’S REPORT NUMBER(S)

. PROJECT NO Y-F015-21-06-001 TR-597

9b. OTHER REPORT NO(S) (Any other numbers that may be assigned
this report)

DISTRIBUTION STATEMENT

Each transmittal of this document var the agencies of the U. S. Government must have prior approval

of the Naval Civil Engineering Laborato

LEARED FOR UNLIMITED DISTRiauTIGN

SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY

Naval Facilities Engineering Command
Washington, D.C.

- ABSTRACT

The objective of a study program on deep ocean power transmission systems was to determine
the technical and economic feasibility of transmitting electrical power of 30, 100, 300, 1,000, and 3,000
kw to ocean depths of 600, 2,000, 6,000, 10,000, 15,000, and 20,000 feet.

Environmental conditions of the sea and their effects on the elements of an undersea power
system are discussed. Various power system concepts are developed and evaluated in the report. Design
approaches and related studies used in the selection of the most cost effective system concepts are
presented, as are preliminary designs of a few selected concepts. Recommended programs for the
development of system elements considered beyond the state of the art are also included.

It was concluded that within the present state of the art (1) 30 to 300 kw of usable AC power
can be supplied from in-situ power plants at depths of 600 to 20,000 feet and 1,000 kw at depths of
600 to 2,000 feet; (2) 30 to 3,000 kw of usable AC power can be supplied from surface-tendered power
plants to depths of 600 to 20,000 feet; and (3) 30 to 1,000 kw of usable AC or DC power can be supplied
from shore-based power plants to depths of 600 to 20,000 feet and up to 3,000 kw to depths of 600 to
10,000 feet.

FORM (PAGE 1)
DD 1 NOV P| 4 TS Unclassified

S/N 0101-807-6801 Security Classification

Unclassified
Security Classification

KEY WORDS

Deep ocean power systems

In-situ power sources

Surface power sources

Shore-based power sources

D D eae 4 73 (BACK) Unclassified

(PAGE 2) Security Classification

ocean pow
Civil Engin
ot. R597.

em
eering L
Sept S