Hobart 9OC24S Operation Manual page 213

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4. BI,I~a
OPERATION, MAINTENANCE, AND OVERHAUL MANUAL, TM-240A
SELF-PROPELLED GENERATOR SET, SPEC. NO. 5381A
(b) Theory of operation
A detailed theory of operation is contained in Operation and Maintenance
Manual No. TM-232, in Chapter 8.
Since the regulator should not be re-
paired by operators or maintenance personnel, the complicated theory of
operation is not explained here. See l-l, Para. 5, E , (8) for a description
and brief theory of operation. See 2-3, Para. 3, B, (2) for voltage regu-
lator adjustment procedures.
Three current transformers (4CT, 5CT, and 6CT, Figure 2) detect the mag-
nitude and power factor of current flowing through the output power cables
("A",
"B", and "C") and feed a signal into the voltage regulator (REG).
The regulator interprets the signals and alters its output signal to the
exciter field to compensate for any voltage drop in the cables. Fixed,
loading resistors (5RES, 6RES, and 7RES) are connected across the current
transformer.
(2) Manual voltage regulation
When generator output is control led manually, the automatic voltage regulator
is by-passed by the automatic-manual switch (1s) and DC power is supplied to
the exciter field (2FLD) through a rectifier (2REC) and a rheostat (IRH). The
rectifier converts AC generator output to DC for excitation of the exciter
field (2FLD). E xcitation is controlled as required by manually adjusting the
rheostat (1RH).
C. Generator Output Control System
, (1) General
The generator output control system consists of those parts required to close
the output load contactor (switch) and maintain it in a closed position until
it is opened by the operator or by actuation of one of the protective devices.
(2) Theory of operation (See Figure 2)
It is not possible to close the output load contactor unless the generator is
running and producing a normal output of 115 V AC because the output control
system receives its inital power from a point in the "C" output phase on the
generator side of the load contactor. Placing the load ccntactor control
switch (5s) in momentary ON position allows alternating current to flow
through the switch to the rectifier (3REC). Here a portion of the AC power
is converted to DC for energization of the load contactor coil (ILC). Alter-
nating current is conducted from the rectifier to ground through the normally
closed contacts of a relay in the protective monitor (PM). As the load con-
Ott 30/73
3-l
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