Electric Traction

1625

Electric Wiring

used by the street and interurban railways ex-
cept that the construction is heavier, and ;
adapted to permit higher operating speeds, j
Both alternating current and direct current j
energy supply systems have proved entirely
satisfactory. The high voltage alternating:
current system simplifies the problem of power i
distribution, and with transformer equipment j
on the rolling stock the motors are operated at
voltages lower than that of the contact line.
Use of direct current simplifies the design of
rolling stock but necessitates a more compli-
cated transmission system to feed the contact j
lines. The two schemes most generally favored
at the present time are the 11,000 volt single
phase alternating current and the 3000 volt
direct current. It appears likely that the elec-
trification projects undertaken in the near
future will follow either one of these two sys-
tems.

Locomotives and Multiple Unit Cars.—For
operation on electrified railroad systems the
design of electric locomotives and multiple
unit cars is similar in principle to that of urban
and interurban electric rail cars. The special
designs developed by the different railroads,
however, vary greatly in detail. In general the
electric locomotive drives are of two distinct
types—geared and gearless. In the geared
locomotives the motors may be mounted in a
manner similar to that used on an electric car.
A few designs have the motors mounted on the
locomotive frame and connected through flex-
ible links carried by the gears. Some of the
gearless locomotives have the armatures
mounted directly on the driving axles, the lo-
comotive frame carrying the field coils. A
modification of this design has the armatures
carried on quills concentric with the axles and
connected to them through springs. Still
another type of gearless locomotive has the
motors mounted in the cab and connected to
the driving wheels by means of cranks and con-
necting rods. Multiple unit cars for electrified
steam railroad service are heavier than those
for street railway and rapid transit service,
but do not differ greatly in other respects. For
operation on alternating current systems both
electric locomotives and multiple unit cars are
equipped with alternating current motors and
transformers to step down the high tension
current to a suitable operating voltage.

The Trolley Bus,—For rendering service'
where tragic is comparatively light the 'trolley
bus* has been developed in recent years. The
trolley bus may best be described as a street
car on rubber tires operating over ordinary
pavement. The wheels are driven by small

high speed eleciric motors "which derive their
energy from overhead contact win,? as do the
motors of *Jic {.r-jiiey car. TIic control equip-
ment for the mt-turs is essentially the same as
that for an electric rail car. The braking ar-
rangement, on the other harul, resembles that
of a gasoline motur bus. Since the vehicle
operates vrithout tracks it is pruvided with a
steering mechanism, which also is similar to
that of a gasoline motor bus. The absence of
tracks necessitates the use of double trolley
wire, one positive and one negative and double
trolley poles on the vehicle. Its advantages
are moderate initial cost, low operating cost,
relatively high speeds and quiet operation.
Other Electric Vehicles.—Certain other ve-
hicles, such as the electric storage battery car,
the gasoline electric bus, the gasoline electric
and the Diesel electric rail car utilize electric
motors to drive their wheels. As they do not
obtain their electrical energy from a remote
generating station they should not be classi-
fied under the head of electric traction. The
gasoline electric bus is a modification of the
ordinary motor bus. Instead of having me-
chanical transmission of power from the engine
to the wheels, this type of vehicle has a small
electric generator connected to the engine to
supply energy to electric motors \vhich actuate
the wheels. The gasoline electric rail car and
the Diesel electric rail car are similar in prin-
ciple to the gasoline electric bus, in that the
engine drives a generator which supplies
energy for the operation of motors geared to
the wheels.
See ACCUMULATORS; DYNAMO AND MOTOR;
RAILROADS; SUBWAYS.
Bibliography.—Street Railway Journal, Oct.
8, 1924 (Historical issue); Electric Rail-way
Journd, Sept. 19, 1931 (Historical issue);
Electric Traction for Railway Trains, E. P.
Burch; Electric Railway Transportation, Blake
& Jackson; Electric Railway Handbook, A. S.
Richey, Handbook of modern electric railway
methods and practices (American Electric Rail-
way Association); Electric Traction, A. T.
Dover; The Electric Railway, A. M. Buck.
Electric Transmission, See Electric
Power Transmission.
Electric Units. See Units; Ampere;
Coulomb; Dyne; Erg; Farad; Henry;
Joule; Ohm; Volt; Watt.
Electric Welding. See Electrometallur-i
gy-
Electric Wiring of Houses. The three
most important factors to consider when plan-
ning to wire a new house are (i) protection,
(2) convenience or flexibility, and (3) economy