Impulse testing and turn insulation deterioration in electric motors

Impulse testing has been an integral part of predictive maintenance of electrical motors for many years. The influence that extensive impulse testing has on a motor is investigated in this paper. The questions investigated are the following: can impulse testing damage healthy or deteriorated insulation? Can weak turn-to-turn insulation be diagnosed with DC resistance, Megger or HiPot tests? Are motors with weak insulation, as proven by impulse testing, able to operate after failing the test? Are motors that show a turn-turn short capable of continued operation? These questions have been investigated by putting a low voltage motor through exhaustive testing rigors, until a failure was induced. Following the failure, additional testing allowed further investigation designed to determine the possible deteriorating effects on turn-turn insulation due to impulse testing beyond the motor's dielectric breakdown.