Hobart 9OC24S Operation Manual page 214

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iMOTOR GENERATOR DIVISION
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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
tactor coil is energized, it closes four sets of contacts in the load contactor
(1 LC). Three large sets connect the three generator output phases "A", "B",
and "C" to the load. A smaller set of contacts connect battery power to the
fault sensing devices for use as signaling power. When the main contacts close,
power is supplied from phase "C", to an indicating light (2G) which signals
the operator that power is available at the load (aircraft). A fuse (7FU) pro-
tects the power module (PM) in case of rectifier (3REC) failure.
As the load contactor control switch is released from momentary ON position,
it positions itself automatically in steady (center) ON position, and routes AC
power through another circuit to the rectifier (3REC). AC power is again taken
from the output "C" phase, only this time it comes from the load side of the con-
tactor (1LC). This current is conducted through a resistor (4RES) to the contacts
of the plug-interlock relay (IPIR). The purpose of this relay is to cause the load
contactor to open immediately if the output cable plug is accidentally discon-
nected from the aircraft, or if the plug is not connected to the aircraft prior to
closing the load contactor. 28-V DC power for energizing the (PIR) coil and
closing the contacts is supplied from the aircraft electrical system. If the output
cable plug is properly connected to the aircraft, the (1PIR) contacts should be
closed and allow current to pass to the fuse interlock relay (FIR) contacts. The
function of the (FIR) is to cause the load contactor to open in the event the pro-
tective system fuse (2FU) should "bl ow" and disable
the protective relay system.
The (FIR) contactsare closed when the small contacts in the load contactor
(1 LC) close and supply 12-V DC power to the (FIR) coil. Current is conducted
through the "center" ON contacts of the load contactor control switch to the
rectifier (2RES). From here it follows the original route through the protective
monitor relay to ground. Thus DC holding power is maintained to the load con-
tactor coil (ILC) for as long as the AC circuit, just described, is closed.
'A toggle switch (2S), identified as the "test-bank switch", is provided for
by-passing the plug interlock relay (PIR) when supplying power to a load
bank or aircraft not having a 28-V DC return capability.
D. Protective Monitor System
(1) General
3-l
Page 12
The protective monitor system is designed to protect the aircraft electrical
system, and the generator system, against .any abnormal condition of over-
load, overvoltage , undervoltage, overfrequency, or underfrequency. The
system consists mainly of a group of fault sensing devices and a solid state
protective monitor module. The module receives signals from the sensing
devices and functions to open the load contactor if a fault condition develops.
Twelve-volt DC operating power is supplied to the protective monitor module
and indicating lights continually, however,
fault sensing devices are functional
only ~when the load contactor is CLOSED.
act 30/73