Patent ID: 7498820

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 correlator coupled to the sensor to receive the 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, wherein said at least one signal indicative of the respective energization state of a respective electrical phase is configured to be modified during a time interval when a predetermined rate of change of voltage is expected, said predetermined rate of change of voltage being sufficient to cause an effect in the characteristics of the ground leakage signal, said correlator configured to individually correlate the ground leakage signal with each received phase energization state signal and supply an individual correlation signal between the ground leakage signal and each received phase energization state signal; 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.