Effect of Surge Wave Reflection Inside a Motor On Voltage Distribution Across Stator Windings

A study was conducted to evaluate the need for surge protection of large motors in NGL plants. Power system analysis indicated that motor winding insulation can withstand lightning and switching surges. Motor surge protection was not installed as a result. The investigation of subsequent failure of four 21,000 HP motors indicated that motor winding failures occurred due to high magnitude switching surges. The test results of winding insulation surge withstand level and voltage distribution across coils are presented. The repetitive insulation failure of the second coil in all four motors is explained.