Hobart 9OC24S Operation Manual page 212

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HOBART BROTHERS COMPANY
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OPERATION, MAINTENANCE, AND OVERHAUL MANUAL, TM-240A
SELF-PROPELLED GENERATOR SET, SPEC. NO. 5381A
3. 400-Hz Generator System (See Figure 2)
A. Generator
(1) General
As stated earlier , the generator is a 400-Hz, three-phase, brush less type, with
a built-in exciter. A six-diode rectifier (1REC) converts exciter AC output
to DC for excitation of the generator field (1FLD).
Generator output voltage
is controlled by an adjustable voltage'regulator (REG) which can vary exciter
field (2FLD) power to control and regulate excitation of the generator field
(1FLD). Output voltage may also be controlled manually by switching control
of the exciter field (2FLD)
f rom the voltage
regulator (REG) to a rheostat (1RH).
Direct current for field excitation is then supplied by a rectifier (2REC) and con-
trolled manually by the rheostat (1RH).
(2) Theory of generator operation (see Figure 2)
The generator rotor, which contains the revolving field (lFLD), must be driven
at exactly 2400 RPM to produce 400-Hz (cycles-per-second) output power.
The
main purpose of the electric-hydraulic governor, described above, is to main-
tain this generator speed under all operating conditions. At initial start-up of
the generator, the exciter field (2FLD) must be polarized by momentarily apply-
ing 12 V DC across the input terminals (Ref. 2-3, Para. 2, A, (15). To make
the generator functional after a start-up, the operating mode switch (3s) must be
placed in GEN position. In this position the switch connects 12-V DC power to
the excitation-deenergization relay (EDR) coil which closes the relay contacts
(E DR, Figure 2) to connect
phases "B" and "C" to the voltage regulator (REG).
The regulator converts AC input to DC and supplies it to the exciter field (2FLD)
through two ballast resistors (1RES and 2RES). The exciter revolving field (1EXC)
supplies excitation through the rectifier (1REC) to the generator revolving field
(1FLD) to produce AC current in the three-phase generator windings (GEN).
B. Voltage Regulation
(1) Automatic voltage regulation
(a) General
The voltage regulator is a solid state,
electronic device, designed to pro-
vide field excitation power for the rotary exciter and to automatically
regulate generator output voltage by varying the exciter field power as
required.
3-1
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