Patent ID: 7501830

Claim:
Apparatus for detecting an incipient ground fault that may occur in an electrical propulsion system of a traction vehicle, said electrical propulsion system comprising a plurality of electrical devices, each individual electrical device being potentially subject to an incipient ground fault in at least one electrical phase thereof, said apparatus comprising: a sensor configured to sense a ground leakage signal associated with a ground of the propulsion system; a compensator coupled to the sensor to combine the ground leakage signal and a compensation signal to generate a compensated ground leakage signal; a correlator coupled to the compensator to receive the compensated ground leakage signal, and further coupled to receive at least one signal indicative of a respective energization state of a respective electrical phase for each respective one of the plurality of electrical devices, said correlator configured to individually correlate the compensated ground leakage signal with each received phase energization state signal, and supply an individual correlation signal between the compensated ground leakage signal and each received phase energization state signal, wherein at least one characteristic of the compensation signal is configured to reduce effects expected in the ground leakage signal when a predetermined rate of change of voltage occurs; and a processor coupled to the correlator for processing each of the individual correlation signals supplied by the correlator and extracting a correlation value from the supplied correlation signals, said correlation value being indicative of an incipient ground fault, if any, in a respective phase of one of the plurality of electrical devices.