In-Depth Analysis of Partial Discharge Measurements Performed with Two Different Instruments on Individual Stator Coils

To demonstrate the consistency of partial discharge (PD) measurements, a comparative study was carried out using two different PD instruments on five individual coils of various designs. Although PD measurements on individual bars and coils have been performed for many years, the quantification as well as reproducibility of the results are still being questioned by the industry. Proper use and understanding of the instruments are essential for obtaining reproductible PD results. Therefore, the main objective of this comparative study was to assess the effect of different parameters that can influence PD measurements, and to validate the reproducibility of two commercially available PD instruments. PD measurements were carried out in the laboratory on individual coils using coupling capacitors and an electromagnetic probe. Various parameters were studied, such as the impact of the value of the coupling capacitor, the frequency bandwidth, the amplitude of the calibrating pulse and the connection to the coil terminals. The results presented in this paper reveal close correlations between the two PD instruments, both for PD results obtained using the coupling capacitor and those obtained using the electromagnetic probe. Analysis was based on PD amplitude values and correlated with the Phase Resolved Partial Discharge (PRPD) pattern.