Prediction of impulse distribution in double section coils of stator windings of high voltage motors

This paper describes a computer model for surge distribution studies in the stator windings of high voltage motors. Due to switching operations, HV motors encounter steep-fronted impulses which get distributed nonlinearly within the winding. This nonlinearity in distribution gives rise to high localised stresses in the insulation system of the windings. Especially the integrity of interturn insulation becomes critical. A convenient and accurate method was designed to evaluate the adequacy of the insulation system for impulses. The model was validated against actually measured values on double section (two stack) 11 kV motor coils for 0.2/0.8 μs and 1.2/50 μs impulse voltages. This paper interturn voltage stresses in two stack coils are discussed in particular