Identification of Simultaneously Active PD Sources in Stator Insulation Using Variable Frequency Excitation

In this paper, a few combinations of PD sources that occur in stator insulation are studied at variable excitation frequencies in the range of (50-0.1) Hz. These combinations tend to complicate the identification of PD sources at power frequency PD measurements, whereas PD measurement at variable excitation frequency for the same combinations has shown positive results. PRPD pattern, pulse phase distribution and PD parameters like peak apparent charge magnitude, integrated charge per cycle and the ratio of positive and negative integrated charge per cycle are used for analysis. From the studies carried out on 6.6 kV rated stator coils, results obtained indicate that PD measurements at variable excitation frequency are helpful in PD source identification when multiple PD sources are active.