Inter turn and turn to ground voltages due to fast surges in a 6.6 kV industrial motor coil

Failure of many large industrial motors is caused by voltage surges experienced by turn insulation in the windings. The turn insulations are subjected to high voltage due to fast surges appearing across the line end of the coil. The voltage distribution in motor winding for transient wave of fast surges is non-linear. In order to examine the voltage distribution, the L and C parameters of 6.6 kV industrial motor are calculated and an equivalent circuit is formulated. Electromagnetic Transient Program (EMTP™) is applied to calculate voltage distribution in the winding. Surges of different shapes, 0.1/5 μs, 0.2/2 μs and 0.3/3 μs are applied across the first coil with peak voltage specified in accordance with international standard. The results are compared with the voltage distribution due to standard lightning over voltage.