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Full text of "The history and development of the Patapsco underwater generator / by P.M. Lasswell."

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The Underwater Generator near Ellicott City was unusual 
in that all of the equipment wes placed in the hollow center 
of the dam. The generator was constructed for the Patapsco 
Electric and Manufacturing Company hut later, when sold to the 
Baltimore Electric '-nd Power Company, it was remodeled and 
operated for several years. This station is a good example of 
the cost of progress, for almost as soon as it was constructed, 
a new type of generator was invented which replaced the old 
horizontal type which had "been installed, and consequently the 
dam was abandoned after shout six years service. The project 
however served to show that a power house built inside of a 
dam is possible^ although not always practical. 


In 181? Edward Gray end several fr-iends combined to 
organize the Union Manufacturing Company and a cotton mill was 
"built "by this company on the Patapsco River near the Ellicott 
Mills, the locality now known as Ellicott City, The mill 
carried on prosperously for many years until it was practically 
destroyed in the flood of 1868. Due to this damage and also to 
the foreign competition in cotton manufacturing the mill never 
reopened and was sold to the Patapsco Electric and Manufacturing 
Company about 1900. 

The old mill was converted into a generating station 
for electrical power with a capacity of 680 h.p. of which 380 h.p. 
was generated by water power &nd the remainder by a steam 
turbine. The electrical equipment consisted of one 240 kw. 
Stanley Generator and one 150 kw. Allis Chalmers Generator, 
Both generators were 2200 volt, 3 phase, 60 cycle alternators^ 
and transformers were used to step up the voltage to the 11000 
volts required for transmission. In 1906 the company decided 
to erect a new power plant two miles further down stream and to 
use the old plant as a sub station. 

The designer and builder of the new dam and power plant 
was the Ambursen Hydraulic Construction Company of Boston while 
Newton and Painter of Baltimore were the Electrical Engineers, 
It "'ps finally decided to build one of the most unique power 


plants in this vicinity and at the time of its construction 
much comment was made upon it "because of its unusual design; 
the dam "being of hollow construction, the water wheels e nd 
generators being housed within the dem itself. The reasons 
for this unusual construction were primarily of cost but also 
of location. The Patapsco Electric and Manufacturing Co, 
wps only a small concern and did not have the capital to 
finance the building of an expensive structure. The river 
has very low "banks further upstream and a high dam would cause 
the baclrwr ter to overflow into Ellicott City and would cover 
much more land. A submerged power house also secures the highest 
obtainable hydraulic efficiency of available flow and fall and 
it represents greatest economy in power house construction for 
the 8 mount of material is no more than for the dam alone. The 
underwater plant may also be used the year round as the water 
will not freeze as far down as the inlet which is six feet below 
the surface of the water. 

T'-e water was taken through trash racks into short 
penstocks connecting to the wheel casing. The discharge was 
vertically downward below the floor of the power plant into the 

The dam has a total length of 220 feet and is 40 feet 
wide at the base. The height of the dam from normal tail water 
to the crest is 26.5 feet. At each end the buttresses a nd deck 
of the dam rise ten feet above the spillway as a protection from 
floods and to afford convenient entrances to the interior of the 
dam. The spillway is 168 feet long and was provided with anchor 


bolts so that if at any time it was desireable, flash "boards 
could be bolted to them and the available head increased two 
feet. The backwater extend? about one mile with an average 
width of about five hundred feet. The dam is built of re- 
inforced concrete and the deck is supported by nineteen but- 
tresses twenty four inches thick at the bottom and sixteen in- 
ches thick at the top which are placed twelve feet apart. The 
edgep of the buttresses and of the openings were reinforced with 
three quarter inch corrugated iron rods in groups of three. The 
shell of the dam is eighteen inches thick at the bottom and 
tapers to ten inches at the top. The deck is concrete reinforced 
with three quarter inch corrugated iron bars at graduated distances 
down to four and one half inch centers. The apron extends only 
half way down from the crown, the remaining down stream portion 
being entirely open and provided with portholes similar in 
construction to those used on shipboard to admit light, but 
when a heavy flow of water was going over the dam, or it was 
muddy the interior was nearly dark except for artifical light. 

Only one hundred and eight feet of the dam was used for 
housing the power plant. This part of the dam was protected 
from possible moisture by four inch walls of f erro-inclave 
entirely separated from the structure of the dam itself. The 
waste water going over the crest of the dam is carried on the 
apron of the spillway to within sixteen feet of the tail water. 
This apron causes the water to fall about twenty feet from the 
down stream side of the dam and as the river bed is quite rocky 
at this point, no appreciable pitting has taken place even today. 


A fish ladder is placed at one side of the dam as 
required "by law. This ladder is about two hundred feet long 
and has the proper slope and fins so that the fish can easily 
go from the tailwater to that above the dam. The fish reach 
water above the dam "by jumping from fin to fin of the fish 
ladder until they reach the top. 


The power equipment originally consisted of two 
thirty four inch horizontal Leffel water wheels fitted with 
Woodward governors arranged so that either governor could 
control both wheels "'hen the generators were operated in 
parallel. Each turbine ran at 240 r.p.m, and was direct 
connected to an Allis Chalmers 300 kw. 11000 volt three 
phase 60 cycle alternator. Each alternator was provided 
with a 125 volt exciter belted to the shaft. The part of the 
dam used as power house was 108 feet long, 10 feet high, and 
27 feet wide except at the buttresses where the width was 
18 feet. A concrete steel floor was built t.t a proper eleva- 
tion above the lower pool between buttresses, the latter 
being increased in section below the floor. 

The water was fed to the turbines through steel p 
pipes passing through the upstream spillway shell and dis- 
charged by draft tubes into the base of the dam, dropping 
into a well sunk some three feet below the river bed. The 
intake ^as about six feet below the crest of the spillway so 
that the trash racks were kept clear of drift wood. The 
trash racks were ten and one half feet and the flumes to the 


turbines seven feet in diameter. Two waste gates were placed 
near the "bottom of the dam, trie water from these passing under 
t v e floor of the power house. The flow through the feed pipe 
was controlled by a valve operating from the turbine chamber. 

T v ie switchboard which was located at one end of the 
power house was built by the General Electric Company. As the 
two exciters wee arranged to be operated in parallel an auto- 
matic regulator waa used for controlling the voltage of the 
generators. Polyphase indicating wattmeters were provided; one 
for indicating the street service and the other the total load. 
The leads o the generators and for the commercial and street 
feeders were fitted with distant control, oil circuit breakers, 
with disconnecting switches. 

At this time ( 1907-1913 ) the plant supplied electricity 
for Ellieott City, Catonsville, Irvington, Carroll, Halethorp, 
Arbutus, St. Denis, Elkridge, and a part of West Baltimore. 


The dam was purchased from the Patapsco Electric and 
Manufacturing Com;, any in 1913 along with its entire electric 
system and business by the Consolidated Gas and Electric Light 
and Power Company of Baltimore. The new owners found the dam 
to be greatly in need of repair and construction was begun 
immediately on the repairs. 

The Patapsco carries a large amount of sand and debris 

down during its freshets and this material had accumulated 

rapidly in the pond above the dam. It was found that neither 

of the waste gates was operative. Wooden gates for the two water 


'■"heels had "been installed by the operators but they were also 
out of commission. Two small sluice gates had been originally 
installed and one had been blasted away and the opening coTered 
with planking, and a second was broken and inoperative, A third 
sluice gate of w.oden construction had been installed and was also 
broken, ?o that the sediment had remained undisturbed in the 
pond and had accumulated to a depth of over twenty feet and had 
partially obstructed the water flow through the openings to the 
water wheels. This condition resulted inlowering the effective 
head on the water wheels and decreasing their output. 

The problem of how to empty the pond unaer these 
conditions wsa solved by cutting away a large portion of the old 
wooden sluice gate by working underneath the power house floor, 
boring holes through the gate, which was twelve inches thick ana 
then chiseling between these holes. After a section of the gate 
was removed the mud still prevented any flow of water. An 
opening in the power house floor, which had been made to give 
access to the gate, was provided with a hinged hatch which could 
be quickly closed, and finally a number of dynamite blasts were 
discharged in the deposit after having been placed through an 
iron pipe thrust down to a position near the opening. These 
blasts started a small flow of water, and after seeping for a 
time the mud deposit gave way and the water flow commenced with 
a tremendous rush. For about six hours the process continued 
and masses of sediment weighing many tons slipped from the 
banks and melted under the heavy flow of water, 

When the pond was emptied it was seen that the trash 


rack on wheel number one was broken allowing sticks and other 
debris to enter the water wheel and impede its action. While 
the pond, emptied } new, properly designed,, head gates and sluice 
gate? were installed. The gates were purchased from the 
Coldwell- Wilcox Compeny. The two head gates were construted 
with openings seven feet by seven feet, each gate consisted of 
a heavy iron ess ting forming the base, and a heavily ribbed 
iron g?te. The gates were operated from motor driven pedestals 
mounted in concrete houses well above the crest of the dam. The 
motors for operating these head gates were three phase commutator 
type. The gates h^d heavy bronze facing to prevent rust and 
bronze shafts were also used for the same reasun/ 

In 1924, operation of the plant was stopped for 
several reasons; first, the plant at Holtwood or McCalls Ferry 
w; 8 so much larger that the ten thousand kwh. obtained from 
this plant was almost negligible. Secondly, the power equip- 
ment had never been replaced and was becoming worn; also a 
new type of vertical turbine had come into use which was more 
efficient than the horizontal type used in the plant; also 
about 8 mile up the river a paper mill had been built and the 
considerable increase in trash hampered the efficient operation 
of the plant. Several years later, during one of the spring 
freshets, water backed up from some obstruction down stream 
and entered the dam around the windows washing in much dirt. 

The plant has been permanently sealed up, and according 
to Mr. Baily of the Power Company, has become the abooe of 


snakes. Thus the former wonder generating station of the 
Patapsco has "become merely an old unused dam for its unusual 
features are unnoticed by the casual observer. 


Albrittsin, II. C. 
Bailey, J. 

Ko ester, P. 

Loizeaux, A.S. 

Reynolds, A 


Engineering Magizine 

Electrical World 

Industrial Power Department , 
Baltimore Power Company. 

Industrial Power Department, 

Baltimore Power Company. 
Hydroelectric Deyelopments and Engineering 
Water Power Plant at Ilchester. 
Librarian of Baltimore Power Company. 
Hydroelectric Practice. 

September 1910 

August 3, 1907 

■j. Thh Dam aku Smllvva* 


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