Effect of Temperature on RPDIV of Enamel Twisted Pair under Repetitive Impulse Voltage Application with Different Rise Time

An increase in the capacitance of the stator winding of an inverter-fed motor increases the rise time of repetitive impulse voltage. It has been reported that partial discharge inception voltage (PDIV) of the windings decreases as the rise time increases. This paper deals with the effect of the rise time on PDIV of enamel twisted pair samples simulating the insulation system of the windings of inverter-fed motors under repetitive impulse voltage and high temperature environment. PDs were detected by a 10 mm diameter loop antenna sensor (LS) with a high-pass filter (395~3200 MHz), and repetitive PDIV (RPDIV) was measured using an automatic PD measurement system. Temperature dependence of RPDIV of the twisted pair sample with varying the rise time tr of the impulse voltage waveform. It was found that RPDIV at room temperature is almost the same regardless of tr, while in the high temperature region above 100 °C RPDIV decreases remarkably with increasing temperature and tr. The decrease in RPDIV with temperature rise can be interpreted in terms of the decrease in gas density with the temperature increase at the wedge-shaped gap formed by the twisted pair sample. In addition, a significant decrease in RPDIV was found to appear with increase in tr in the high temperature region. The result is considered to be caused by increase in the probability of initial electron supply for triggering discharge with increase in tr.