Impulse and fast surge distribution of voltage in 11 kV industrial motor

Insulation failure in a large industrial motor stator winding can occur due to electrical stresses generated by transient over voltages. The voltage distribution in motor winding for transient wave of impulse type or steep fronted type is non-linear. Consequently some turns are more stressed than others. Thus there is a higher probability of failure of those turns which are highly stressed. Estimation of turn to turn and turn to ground voltages is done by considering motor system as an equivalent electrical network. The aim of this paper is to evaluate internal voltage distribution in the winding due to the changes in capacitance and self inductance as well as mutual inductances on voltage magnitude by the application of impulse voltage at HV terminal. In this paper one 11 kV industrial motor winding is modeled and simulated by Electro Magnetic Transient Program (EMTP). The voltage distribution along the first coil and inter turn voltage distribution is presented for incoming wave of standard and non-standard shapes.