Development and evaluation of small loop sensor for detecting electromagnetic field caused by partial discharges in simulated insulation system of inverter-fed rotating machine

This paper deals with development of small loop antenna sensors with 10 mm in diameter for detecting electromagnetic (EM) waves emitted by partial discharges in the insulation system of inverter-fed motors. Partial discharges (PD) were generated with a pair of crossed enamel wires under ac voltage at 10 kHz for examining various fundamental properties of the small loop sensors; i.e. the frequency response, the distance dependence from the PD source to the sensor. The sensitivity of the small loop sensor was also measured. As a result, it was found that the developed small loop antenna allows detection of EM waves over the frequency range up to 4 GHz and can detect PD current pulse with its peak magnitude as small as 12.6pC. It is also suggested that the array of the developed loop sensors can be applied for PD localization in practical rotating machines under the so-called repetitive voltage impulse. It was found that the developed loop sensor can be also applied to detect and locate the PD source.