Abstract
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.
Highlights
The reliability and availability of electrical machines (EMs) can be compromised by failures of electrical nature [1]
This indicates that the inception of partial discharge (PD), which is definitely happening when the specimens are excited with 500 V, causes an insulation capacitance (IC) increment
This phenomenon can be justified by analysing the physics of PD
Summary
The reliability and availability of EMs can be compromised by failures of electrical nature [1]. Stator failures, originated by insulation breakdown, are among the main causes of low voltage EMs outage [2]. Traditional EMs design procedures aim in addressing this challenging issue (i.e. insulation degradation) by over-engineering the insulation, namely employing higher grade/thermal class than the one required by the application. This design approach, which works perfectly fine for EMs employed in industrial/household applications, can no further be implemented for high performance EMs employed in mobile applications, such as aerospace [5, 6] and automotive [7]. For these EMs any minimum weight improvement is of crucial importance [6, 8]
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