this provides for losses and the capability to maintain
tages of light weight, quick starting, and acceptance of
constant speed at full load. The engine must also be
load without the usual warmup period. A disadvantage
equipped with a governor to maintain a constant out-
is their high fuel consumption rate.
put when the generator is connected to a varying load.
2-27. Power Distribution
Diesel and gasoline engines are used as prime movers.
a General. As previously indicated, most DCS
Stations have at least two separate power sources, pri-
(1) Diesel Engines. Both low-speed and high-&
mary power and auxiliary power. These two power
diesel engines are used as prime movers. High-speed
sources must be selectable; that is, switching and other
necessary mechanisms must be provided to permit
diesel engines can be installed at less cost than the low-
speed, heavy-duty diesel engine, but not operated or
station personnel to select the desired source. Change-
over must be fast, in fact, it should be possible to
maintained as economically.
(2) Gasoline Engines. Gasoline engines are used as
change power sources without any break in the power
supply to the communications equipment. When pri-
prime movers to drive generators of limited capacity
mary power fails without warning, this may not be
to supply power on an intermittent or purely auxiliary
basis. They should not be used to drive generators to
possible, but activation of the auxiliary power and con-
nection to the communication should comply with the
supply power continuously or over extended periods of
prescribed standards. In addition to the power change-
time, because the useful life of a gasoline engine in
over requirements, normal operation requires that the
continuous service is relatively short. The initial cost
power demands within the station be balanced among
of a gasoline engine is much less than that of a diesel
the phases of *phase primary power supplies.
engine, but maintenance costs are higher.
b. Switchboards and Automatic Transfer Panels.
(3) Gas Turbines. Gas turbines have the advan-
Figure 2-10. Double bus arrangement and automatic transfer panel, wiring diagram.