Vacuum Pressure Impregnated High Voltage Motor Embedded with Capacitive Slot Couplers

On-line partial discharge monitoring system has become one of the major tools for maintaining stator winding of high voltage motors from incipient failure. High voltage motors are typically produced through the VPI (vacuum pressure impregnation) process. Thereafter, on-line PD (partial discharge) sensors, such as high voltage coupling capacitors, are connected to high voltage feeders in a terminal box. However, the installation of external PD sensors requires extra cost and intensive work. Moreover, noise elimination and PD signal attenuation issues have been the major technical difficulties for on-line PD monitoring of stator winding. To overcome this limitation, a 6.6 kV VPI motor embedded with PD sensors and a capacitive slot coupler (CSC) has been developed, that can successfully operate in a power plant. In this study, PD monitoring scheme using CSC sensor was proposed based on both laboratory and plant site experiments. For safety measures, CSC sensors were inserted between stator core and bottom stator winding prior to the VPI process. PD monitoring system, PDM6ES (partial discharge monitoring with 6 embedded sensors), was also fabricated to monitor phase resolved partial discharge (PRPD) spectra simultaneously using 6 CSC sensors in two frequency bands. Finally, PRPD spectra were compared with the results obtained from a conventional PD detector.