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The IS200EGDMH1A is an Exciter De-Excitation board manufactured and designed by GE as part of the EX2100 Series used in Excitation Control Systems.

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 ensureoperation 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.

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 immediately.

The stored field energy must be dissipated through some other means.

SCR De-excitation Module (EDEX)

For customers requiring a rapid de-excitation, an SCR de-excitation module is provided.

In the EDEX module, an SCR is fired to provide a conduction path through the field discharge resistor (or inductor) for the field current to flow and dissipate the field energy.