Novel Airborne Partial Discharge Probe for High Voltage Stator Winding

In this paper, two overlapped signals, airborne partial discharges and electrical RF noises, picked up on metal surface of motor terminal box are analyzed in frequency and time domain. And the novel partial discharge probe called ACP (airborne capacitive probe) is introduced in comparison its characteristic with the commercial TEV (Transient Earth Voltage) sensors. ACP shows the wider frequency band response to airborne partial discharges that spans from 25 MHz to 50 MHz. The probe is magnetically attached on front panel of motor terminal box. Obviously, the key technology is the discrimination scheme to extract only partial discharge pulses from RF noise signals. It is found that the frequency range of airborne induced noise signals on motor front panel spans up to 27 MHz. Based on experimental results at maintenance shop and power plant, we conclude that APDMU (Airborne Partial Discharge Monitoring Unit) could provide the simple instinctive information for the site engineers on insulation health of high voltage stator winding.