An equivalent circuit for calculation of interturn voltage distribution of stator windings in the presence of slot discharges

In modern epoxy-mica insulated rotating machines inter-turn insulation breakdown and slot discharges has been the two major cause of electrical failure. In this paper, a distributed high frequency equivalent circuit is proposed which is capable of simulating turn to ground, inter-turn and screen point potentials along the machine winding. Screen potentials may be large enough to cause discharges across the slot wall. The equivalent circuit is based on distributed resistance, inductance and capacitance type ladder network. Transient responses of the machine winding for steep fronted impulse, surge step input, PWM waveform, and steady state high frequency oscillation are presented. Effects of corona screen resistivity and location of loose earth contact on corona screen potentials are also shown in the paper. The proposed model can be very useful in the design of machine insulation.