A Novel Technique to Detect AC Machine Turn Insulation Failure Subjected to Steep Front Impulse Waveform

The stator insulation breakdown is a major cause of rotating machine failures. Ground insulation faults are easily detected by classical systems based on leakage current measurements. Also, the stator insulation failure mechanism is now well-known, as it often begins with a local turn-to-turn breakdown. One of the main causes of turn-to-turn insulation failure is due to steep front impulse voltages. Such steep front impulses can be produced due to the operation of vacuum circuit breaker. However the turn-to-turn insulation degradations are more difficult to detect. This paper proposes a new procedure for monitoring the status of the turn-to-turn insulation using the signature of the line to ground leakage current. The winding of 4 kV induction machine stator winding was subjected to turn-toturn and turn-to-ground steep front impulse voltages with rise time of 100 ns. It has been found that the turn-to-ground current is very sensitive to turn-to-turn insulation damage and can be used to assess the insulation integrity of AC machines.