Comparison of Transient Response of 11 kV Motor For a Single Coil and Double Coil Connected in Series

Failure of motor insulation is now recognized as one of the reasons for the failure of industrial motors. The line end coil of the winding is the most likely site for such problems since for fast surges it bears almost up to 100 percent peak magnitude for a few ${\mu}\sec$. During this period, the distribution of voltage across the coil of 11 kV motor is non-linear. The present paper describes the technique for calculation of turn-ground and inter-turn voltage distribution in the motor winding during the transient condition. Previous authors have reported the distribution of transient voltage in a single coil of the motor only. Present work reports the distribution in two coils connected in series. For this, an equivalent circuit model is prepared and implemented in EMTP. The model parameters are calculated from the coil geometry and standard formulas. It discusses the simulated results. This method can help full in understanding the design withstand capability of motor insulation for high stress.