General Electric Company

Mohammed Kassem Saleh

Rodney A Lawson

William Robert Pearson

Gautam Sinha

John Earl Bittner

Harold Copeland Sanderson

Michael John Ryan

Bruce Allen Gerritsen

Ivan Elmo Freeman, Jr

The field ground fault detector of the present invention detects a ground fault that occurs in the field circuit and in any associated circuits galvanically connected to the field. The field ground fault detector discerns the ground resistance so that it can be monitored to detect gradual degradation of the ground resistance. The detector estimates the resistance of the ground fault and the location of the ground fault. The detector is able to estimate the location of the ground fault during system operation and during periods of non-operation. The invention utilizes a low frequency square wave oscillator to permit measurement of the ground fault resistance when field voltage is not applied, to insure that there are no blind spots when the field is energized, and to provide a method for estimating the ground fault resistance. The field ground detector can differentiate between ground faults that occur on the AC side form those on the DC side of the Thyristor Bridge.

Apparatus and method for detecting and calculating ground fault resistance

A circuit is provided for use in a synchronous generator excitation system. The circuit comprises a three-phase bridge having six legs. The bridge is connected with an AC power supply. A thyristor is provided in each of the six legs, wherein the thyristors provide a path for a device current. A free wheeling diode functions as a de-excitation means connected in parallel with the three-phase bridge. The free wheeling diode provides a discharge path for a field current.

Full thyristor bridge circuit with free wheeling diode for de-excitation control and stability sensing

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Casa Grande, AZ, United States of America

Mohammed Kassem Saleh