Insulation Capacitance as Diagnostic Marker for Thermally Aged, Low Voltage Electrical Machines

Thermal aging is considered as the principal insulation stress factor in low voltage electrical machines (EMs). Once the insulation reaches its end-of-life, a complete EM out of service can be caused within few operating cycles/hours. In this paper, the strand to strand insulation capacitance (IC) of thermally-stressed windings for low voltage EMs, is experimentally monitored. Its trend is analysed against the cumulative thermal aging with the objective of extrapolating an insulation lifetime prediction tool. The aged specimens are made of a class 200, round enameled magnet wire (modified polyester base coating and polyamide-imide over coating). This wire topology is widely adopted in low voltage EMs employed in aerospace and automotive applications. The outcome of the presented analysis can be either used for diagnostic purposes or for improving the EMs insulation design procedure.