Bridge and Protection Boards and Modules
Bridge control passes through
EGPA. One EGPA is required
EDEX is usually controlled by
EXTB, but can initiate de-
excitation if control fails.
EGDM and EXAM work
together to detect field ground
EX2100 User's Guide GEH-6632
The exciter bridge and protection boards are as follows:
IS200EGPA Exciter Gate Pulse Amplifier board (EGPA)
IS200EXCS Conduction Sensor board (EXCS)
IS200EDEX Exciter De-Excitation board (EDEX)
IS200EGDM Exciter Field Ground Detector Module (EGDM)
IS200EXAM Exciter Attenuator Module (EXAM)
The EGPA board interfaces the control to the power bridge. EGPA takes the six gate
commands from the ESEL and controls the gate firing of up to six SCRs on the
bridge. It is also the interface for current conduction feedback, and the bridge airflow
and temperature monitoring.
A nominal 125 V dc power source from EPDM supplies an on-board dc/dc converter
that provides power for SCR gating over the full range of input supply voltage. LEDs
provide visual indication of the status of the output firing, currents into the bridge,
gate power supply, line filter, cooling fan rotation, and bridge temperature and alarm
or fault conditions. For more information refer to Chapter 4 and GEI-100461.
The EXCS board has four conduction sensors. It is used to detect the presence of
current in the bus. The output is a logic signal.
The EDEX board is the main board in the de-excitation module. EDEX provides de-
excitation SCR firing, conduction sense feedback, and voltage retention to ensure
operation in the event of a power failure. EMIO initiates de-excitation on the EXTB
board. The EXTB board opens the 41 dc contactor (41A/41B) or breaker, and then
transfers de-excitation signals from the auxiliary contacts to SCR firing circuits on
the EDEX. There are two types of EDEX. Group 1 board is designed for SCR de-
excitation, Group 2 is designed for diode de-excitation. For more information refer
to Chapter 4 and GEI-100466.
The EGDM is a double slot, double height (6U) form factor board that mounts in the
Exciter Power Backplane rack (EPBP). A simplex system has one EGDM, while a
redundant system has three. EGDM detects field leakage resistance from any point
in the field circuit of the generator to ground, either on the ac or dc side. The field
ground detector applies a low frequency square wave to the sense resistor connected
to the field circuit. EXAM, the attenuator module located in the Auxiliary Panel,
senses the voltage across the ground resistor and sends the signal to the EGDM
through a nine-conductor cable.
Chapter 3 Printed Wiring Boards Overview 3-7