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Gate Pulse Amplifiers (egpa Board) - GE EX2100 User Manual

Excitation control.
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EDCF provides dc current
and voltage feedback
To dc Breaker,
Shunt, and
Generator Field +
Ac power
Input
J1
The gate pulse amplifiers
directly control the SCRs.
2-6 Chapter 2 Functional Description
Current Shunt
A dc shunt provides the bridge output current feedback signal. The mV output signal
is input to a differential amplifier on the EDCF board. The amplifier output voltage
controls the frequency of an oscillator, which generates a fiber-optic signal sent to
the control module. The bridge output voltage feedback signal is generated in a
similar way.
FU1B
FU1A
SCR1
Snubber 1
Snubber 4
SCR4
FU4A
FU4B
Gen. Field -
J4
J2
Gate Driver Inputs from EGPA Board
Figure 2-3. Power Bridge

Gate Pulse Amplifiers (EGPA Board)

The EGPA board interfaces the control to the Power Bridge. EGPA takes the gate
commands from the ESEL board in the controller, and generates the gate firing
pulses for six SCRs (Silicon Controlled Rectifiers). It is also the interface for current
conduction feedback, and bridge airflow and temperature monitoring.
On a new exciter, an RTD is used to monitor the temperature and generate alarms
instead of the Klixon switches. Additional switches actuated by fan rotation monitor
cooling air flow across the bridge. On an exciter controls only retrofit, the exciter
may have provisions for accepting feedback from two thermal switches mounted
on the SCR heatsink assemblies. One thermal switch opens at the alarm level
(170 F (76 C)) and the other at the trip level (190 F (87 C)). These switches
are wired to the EGPA board and may require retrofitting into the existing bridge. If
either switch opens, a bridge overtemperature alarm is generated. If both switches
open, a fault and a trip are generated.
FU2A
FU2B
SCR2
Snubber 2
Snubber 5
SCR5
FU5A
FU5B
J3
J5
FU3A
FU3B
SCR3
Snubber 3
Snubber 6
SCR6
FU6A
FU6B
J6
GEH-6632 EX2100 User's Guide

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