Failure mechanism of the interturn insulation of low voltage electric machines fed by pulse controlled inverters

When induction machines are fed by fast switching inverters, their interturn insulation is electrically more stressed than in the conventional feed. When inverters are used steep voltage pulses of high repetition frequency occur. This can cause partial discharges (PDs) leading to insulation failure. The PD inception voltage and velocity of the resulting electrical ageing depend on the voltage characteristic, insulation design and temperature. These relations were investigated using laboratory models of interturn insulation, semiconductor-based pulse generator and as PD detector an UV-sensitive photo multiplier tube