h. Overvoltage module
The overvoltage relay
(2)
is a solid-state protective device on a printed circuit board. A normally
closed relay in the circuit is wired into the load contactor coil circuit. An overvoltage condition causes
the relay contacts to open, which in turn prevents the contactor from closing, or opens the load
contactor and discontinues the power delivery. The overvoltage module is adjusted to trip at 32 to 34
volts DC in 2 to 10 seconds.
i. Resistor and diode assembly
This network, which is mounted on a terminal strip behind the control panel, protects the load
contactor hold circuit against excessive current draw when the generator is delivering power.
j. Excitation rectifiers
Two diode bridge rectifiers, CR418 and CR418,
(3, Fig. 4)
convert an AC voltage from the generator
armature to the DC voltage needed for the generator revolving field.
k. Voltage sensing relay
Voltage sensing relay K406
(5, Fig. 4)
is a safety device which automatically opens the grounding
circuit of the revolving field to prevent excessive voltage build-up if the push-to-build-up-voltage
switch is held in too long, or if it is pushed in after voltage is built up.
9. Contactor
The load contactor, which is mounted behind the control panel on the fuel tank support, provides a safe
and convenient means of connecting and disconnecting the generator from the load. Initial power for
closing the load contactor is supplied by the generator through the spring-loaded momentary contacts of
the contactor control switch
(11, Figure 3)
. Holding power, to keep the contactor closed, passes through
the normally open auxiliary contacts in the load contactor.
10. Output Terminals
The output terminal panel is mounted inside the unit just behind the control panel. The positive terminal
is the A2 terminal of the load contactor, and the negative terminal is to the right of the load contactor.
11. Rectifier Assembly
This assembly consists of two aluminum heat sinks with twelve diodes on each heat sink. The rectifier
assembly converts the AC output of the generator to 28.5 VDC.
12. Ammeter Shunt
The ammeter shunt is connected in the generator’s negative output circuit. It supplies a small voltage
proportional to output current for operation of the generator ammeter
(5, Fig. 3)
and for sensing output
current for the current limit circuit of the voltage regulator
(1, Fig. 4)
. This shunt is mounted on the
negative heat sink of the rectifier assembly
(6, Fig. 2)
.
OM-2063 / Operation and Maintenance Manual
Jet-Ex 4D / Specs 7003A-3 and 7003B-3 / Generator Sets
Dec 31/92
Chapter 1-2
Page 9