Effect of electrical and thermo-mechanical stresses on the surge capability of MV form-wound AC stator coils

This paper investigates the surge (turn-to-turn) capability of form-wound AC stator coils after subjecting them to electrical and thermal stresses imposed by voltage endurance (VE) and thermal cycling tests. Medium voltage (MV) form-wound stator coils rated at 4.0, 10, and 13.8 kV were surge tested up to 5.0 pu or higher 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. The third set of sample coils were subjected to VE and thermal cycling tests before surge testing. Surge testing was performed in accordance with IEEE Std 522. The surge 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.