Analysis of turn insulation degradation under voltage surge stress

摘要

The turn insulation of multiturn coils is often involved in machine failures. Until now, there has been no type test for detecting the long-term performance of turn insulation. The purpose of this study is to establish an aging test that will sufficiently stress the turn insulation, in order to evaluate and compare the degradation of both turn insulation types: coils with dedicated turn insulation and coils without dedicated turn insulation. Two aging tests were performed on new 13.8 kV coils with dedicated turn insulation. A group of four coils was submitted to 200 surges at 5.8 pu while another group of four coils was submitted to a 2,000 surges at the same voltage. Afterwards, both groups of coils were submitted to an impulse breakdown voltage IBDV test and compared to IBDV on new coils. On coils without dedicated turn insulation, a group of three coils was submitted to 200 surges at 5.8 pu while another group of three coils was submitted to 200 surges at 4.0 pu. Afterwards, both groups were submitted to IBDV test and compared to IBDV on new coils. No sign of induced aging was observed in the turn insulation system under repetitive surges. However, it was observed that IBDV can reveal defects or differences within a same group of coils. To compare coils with and without dedicated turn insulation, dimensions and number of turns need to be the same.