Sensitivity characteristics of partial discharge electromagnetic sensor located in stator core

Repetitive partial discharge inception voltage (RPDIV) measurement is indispensable for inverter-fed motor when testing according to IEC 60034-18-41 IS. Our previous study showed sensitivity comparison between kinds of electromagnetic (EM) sensors and a partial discharge (PD) measuring device in an actual motor core. This paper deals with an influence of the position and distance of EM sensor on the sensitivity of detected EM wave to quantitatively evaluate RPDIV. Results revealed that the detected signal attenuation is affected by not only the distance between the PD source and the sensor location but also the existence of the actual core. Furthermore, RPDIV provided by a loop sensor located at 135° around the circumference direction from the bottom of the core was estimated by 10% higher than that determined with a reference LS located just above the PD source which was placed at the bottom of the core. Namely, it is indicated that employing EM wave sensor to detect PD can result in estimating higher RPDIV than actual one. In other words, a correction is necessary for estimating precise RPDIV by multiplying a given factor depending on the size of the core and the location of the EM sensor to measure RPDIV.