Detecting turn insulation failures in motor coils using ground current signals

This paper proposes a procedure for monitoring the status of the turn-to-turn insulation subjected to steep front impulse voltage using the line-to-ground leakage current as a signature. Medium voltage motor coils with rated voltage of 4kV are tested using steep front impulse voltages with rise time of 100ns. It has been found that the signature of the ground current is unique for a specific coil and it is voltage independent. Moreover, it has been observed that the recorded turn-to-ground current is more sensitive to turn-to-turn insulation damage than the applied impulse voltage waveform. Hence, by analyzing the line-to-ground leakage current the turn-to-turn insulation failures can be assessed.