Ageing study on enameled magnet wires through statistical analysis of conventional partial discharge magnitudes and repetition rate

As a result of the use of inverted-fed drives, enameled magnet wires of induction motors are suffering from partial discharge (PD) activity. This is a clear ageing mechanism for the machines which leads to unexpected failures in these systems. Ageing characterization of this insulation system is essential for these applications. In this paper, several statistical PD quantities which account for PD magnitude and repetition rate are studied in ageing processes of twisted pairs of enameled magnet wires. The resulting ageing curves have been adjusted to several mathematical functions in order to check if any clear tendency is detected.

I. Introduction

Inverter-fed AC motors are subjected to different electrical stresses which can degrade the enamel of their magnet wires. The uneven distribution of steep-fronted voltage pulses and the impedance mismatch between cable and motor ([1]) has led to unexpected partial discharge (PD) activity on these insulation systems only prepared for low-voltage applications ([2]).