IS200EDEXG1B Exciter De-Excitation Module

This model is located in an auxiliary cabinet and has a silicon-controlled rectifier (SCR) de-excitation mode. In the SCR de-excitation module, the SCR is fired when a conduction path is needed, once the SCR has been fired it will make a path through the field discharge inductor and will allow the field current to flux and disperse the field energy. If for any reason the SCR is not able to be fired then it will fire on overvoltage, firing on overvoltage will occur when the anode to gate voltage surpasses the break overvoltage of the break-over diode string which is connected between the gate and anode functions. 

The GEH-6632 EX2100 Excitation Control User’s Guide is the best manual to use for information on the installation and function of the IS200EDEXG1B model.

IS200EDCFG1BAA

IS200EDEXG1B is an exciter De-Excitation Control Board designed and developed by GE. The EDEX is the de-excitation module’s main board. When an emergency shutdown occurs and the field breaker or contactors open, this module removes stored energy from the generator field. To ensure operation in the event of a power outage, EDEX includes SCR firing, conduction sense feedback, and voltage retention. On the EXTB board, EMIO initiates de-excitation. The EXTB board activates the 41dc contactor (MDA/MDB) or breaker, then transfers de-excitation signals from the auxiliary contacts to the EDEX’s SCR firing circuits. EDEX boards are classified into two types. Group 1 is for SCR de-excitation, while Group 2 is for diode de-excitation.

IS200EDEXG1B Functional Description

• Two firing commands are received through the EXTB and activate the firing circuit with redundant control. When the circuit is activated, it generates a high frequency square wave that is connected to the SCR gate and causes conduction.
• If this circuit fails or is delayed, the gate is activated by a self-firing circuit. This circuit consists of a break-over diode network connected to the SCR gate and controlled by the SCR anode voltage.

Voltage Hold Up Circuit

• In the event of a total power failure, EDEX retains voltage on the positive and negative 24 V dc lines so that it can fire the SCR.
• The voltage hold up circuitry also provides voltage for wetting the external de- excitation contacts. This ensures that the firing command is available for de-excitation in the event of a power outage.