Surge withstand capability of electrically and thermo-mechanically aged turn insulation of medium voltage form-wound AC stator coils

This paper investigates the surge (turn-to-turn) withstand capability of form-wound AC stator coils after subjecting them to electrical and thermal stresses imposed by voltage endurance (VE) and/or thermal cycling tests. Medium voltage (MV) form wound stator coils rated at 4.0, 10, and 13.8 kV were surge tested to failure after they were aged under VE testing in accordance with IEEE Std. 1553. Another set of sample coils rated at 3.3 kV were subjected to thermal cycling following the procedure of IEEE Std. 1310 and were then surge tested-to-failure. A third set of sample coils were subjected to the VE and thermal cycling tests before surge testing. Surge testing was performed in accordance with IEEE Std. 522 until the failure point is reached. The surge failure levels and waveforms for each sample coil were carefully analyzed to investigate the adverse effect of electrical and thermal stresses on the surge capability of the sample coils.