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OM-2032 / Operation and Maintenance Manual
100D20 / Generator Sets
h. Power Module Panel Assembly
The power module panel assembly (Fig. 13) , or "contactor panel", is located at the right front of the
machine behind the control box and is accessible by opening the left front door. The panel
assembly provides a means of connecting and disconnecting generator output to and from the load
(aircraft) .
(1) Load contactor
The load contactor (6, Fig. 13) is a sealed unit which contains a magnetic operating coil and
four sets of contacts. The three larger contacts conduct three-phase AC generator output. A
smaller contact set is connected in the protective monitor circuit and supplies 12-VDC power
used by sensing relays to signal the protective monitor when a fault occurs. Three-phase,
400-Hz generator output power is conducted to the load contactor by 2/0 cables which pass
through 3 sets of current transformers (3, 4, and 9) .
NOTE: This contactor may be replaced by the old style contactor used in earlier 60 and 90 kVA
machines, (part no. 75GH-566 [Hartman No. A-874C]) in stock.
(2) Current transformers
a. Ammeter current transformers
Three current transformers (4) lower the output load current to a lesser value of definite
ratio (250-A to 5-A) which operates the ammeter (7, Fig. 8) movement without damage.
The ammeter pointer indicates the true load current value rather than the meter movement
current.
b. Line-drop current transformers
Three current transformers (4) , lower the output load current to a lesser value of definite ratio
(250-A to 5-A) which operates the ammeter (7, Fig. 8) , in conjunction with the burden
resistors (8, Fig. 13) , detect the magnitude and power factor of current flowing from
generator to load. They feed a signal to the voltage regulator which interprets the signal and
alters the exciter field current as required to maintain a constant predetermined voltage at
the load. (See Voltage Regulator Manual No. TM-759).
c. Overload current transformers
Three overload current transformers (3) , in conjunction with burden resistors (1) , monitor the
output load current in each of the three output phases, and supply a reduced value current
signal to the overload module (7) .
(3) Overload module
The overload module (7) is a solid-state device designed to interpret a signal from transformers
(3) and to send a signal to the protective monitor module (4, Fig. 9) when an overload
condition exists in any generator output phase. A pull-apart electrical connector is mounted on
the over- load module to provide quick-disconnect facilities for all wiring to the module. The
overload module is equipped with a hermetically-sealed, reed-type relay. Relay contacts are
normally open.
The solid-state circuitry is designed to close the relay contacts when output current in ANY
phase reaches 125% of normal, rated output capacity. The closed relay sends a signal to the
protective monitor. This signal "gates" the overload SCR (silicon-controlled rectifier) in the
protective monitor and interrupts the load contactor to open.
The following is a list of overload module characteristics:
NOTE: The overload protective system will function when any phase carries 123% to 127% of rated
current.
At 125% load the device will function in 5 minutes.
At 150% load the device will function in 16 seconds.
NOTE: All times are plus or minus 25% and are nonadjustable.
Chapter 1-1
Page 22
March 31/94 Revised
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