Patent ID: 7498819

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 and a direct current (dc) bus, each individual electrical device being potentially subject to an incipient ground fault in at least one electrical phase thereof, said apparatus comprising: a first sensor configured to sense a ground leakage signal associated with a ground of the propulsion system; a second sensor configured to sense a voltage difference across a positive rail and a negative rail of the direct current bus; a correlator coupled to the first 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, 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; a processor coupled to the correlator for processing each of the individual correlation signals supplied by the correlator and extract a correlation value from the supplied correlation signals, said correlation value, when outside a threshold range, being indicative of an incipient ground fault in a respective phase of one of the plurality of electrical devices; and a module for dynamically adjusting the threshold range for detecting an incipient ground fault, the adjusting based on a magnitude and/or a rate of change of the magnitude of the sensed voltage difference across the positive and negative rails of the direct current bus.