Case Studies Using an Additional Neutral Point PD Sensor for Generator Stator Monitoring

The subject of this paper is to discuss the advantage of using a neutral point partial discharge (PD) sensor, in addition to the phase bus couplers, in order to assess the location of partial discharge sources more precisely. In this context, case studies will be discussed, showing the damage that can occur to bar surface by slot discharges. The related PD measurements show that a distinct amount of such high-energy pulses propagate through the neutral point towards the phase terminals of the other phases. For cases where the PD sources are close to the neutral point, the signal magnitudes and intensity acquired at the neutral point PD sensor are accordingly high. The case studies demonstrate how the typical phase resolved PD patterns from the phase bus couplers and the neutral point sensor, for cases of critical slot PD, allow improved condition assessment with increased reliability.