IS200EGDMH1A

IS200EGDMH1A is an Exciter Ground Detector Module manufactured and designed by General Electric as part of the EX2100 Series used in Excitation Control Systems. It mounts in the Exciter Power Backplane rack as a double slot, double height (6U) form factor board (EPBP). The field ground detector measures the resistance in the field between any point in the field circuit of the generator and the ground, whether it is on the ac or dc side. A redundant system will have three EGDMs, but a simplex system will have one. In order to communicate with the EGDM(s), EXAM, the attenuator module, measures the voltage across the ground sensing resistor. The High Voltage Module, which is housed in the Auxiliary Panel, has the EXAM module mounted in it.

EGDM and Attenuator Module Mounting

The trio of EGDM boards is set up as Controller (C), Master 1 (M1), and Master 2 (M2) in a redundant control (M2). A group of program pins on the P2 connector control each EGDM's setup. The DSPX transmits data to EGDM C via the EISB in the controller rack about which the master delivers the driving signal to the sensing resistor in the Attenuator Module. When C receives this data through the fiber-optic link, depending on whether M2 is the selected driver or M1 is the selected master, C either powers or empowers the relay in the Attenuator Module. A differential signal that identifies the selected master is simultaneously transmitted to M1 and M2.

This signal selects the test command source on each module and activates the signal generator on the active master (M1, M2, and C). The active master now gets an oscillator signal from the DSPX via the EISB across the fiber optic link, which it transforms into a positive or negative 50-volt signal. This square wave voltage is applied to one end of the sense resistor after being transmitted via cable to the EXAM module.

The Sense Resistor in the EXAM module sends an attenuated (10:1) differential signal to the signal conditioner. A straightforward unity gain differential amplifier with a high common-mode rejection ratio serves as the signal conditioner, which is followed by an A-to-D converter (Voltage Controlled Oscillator VCO). A fiber optic transmitter is fed by the VCO. Due to the high common-mode voltage at the sense resistor, the signal conditioner circuitry is powered by an isolated power source to protect worker and equipment safety. When instructed to do so by the control section, the signal conditioner grounds the bridge side of the attenuated Sense Resistor and uses this information to determine the power amplifier output level.