IS200EDEXG1ADA GE De-Excitation Card
Description:
IS200EDEXG1A is GE EX2100 series De-Excitation Card, it is installed in the auxiliary cabinet. The auxiliary cabinet is located next to the power conversion cabinet and containsmodules to protect the generator and provide startup dc power. Modules for filteringthe incoming ac power, for de-excitation, shaft voltage suppression, and fieldflashing are mounted in this cabinet.

During any shutdown, the energy stored in the generator field must be dissipated. In a normal shutdown, a stop is initiated by an operator. The bridge is fired at retard limit and sufficient time is allowed for the field to decay before the field contactors are opened. During an abort stop (trip), the field contactors are opened immediatelyThe stored field energy must be dissipated through some other means.

For customers requiring a rapid de-excitation, an SCR de-excitation module isprovided. In the IS200EDEXG1A module, an SCR is fired to provide a conduction paththrough the field discharge resistor (or inductor) for the field current to flow anddissipate the field energy.

IS200EDEXG1A has dual independent firing control circuits. Each isactivated by a parallel combination of auxiliary contacts representing the status ofthe field contactor(s), bridge ac supply breaker, and exciter bridge operating stateAny one of these paths can gate the de-excitation SCR which does not conductunless the field voltage is inverted. If neither firing control circuit can fire the SCR, itis fired on overvoltage when the anode to gate voltage on the SCR exceeds the breakover voltage of the breakover diode string connected between the anode and gateDe-excitation modules can be paralleled for larger excitation systems.