Conference Agenda

A novel classification tool has been developed to analyze partial discharge patterns. This technique integrates features from the Peak Phase Dispersion Analysis (PPDA) Cross and the PPDA Cactus. It is intended to classify partial discharge patterns, including internal, slot, surface, and corona discharges. The PPDA Cross automatically generates key metrics, including the peak partial discharge (PD), the dispersion phase angle of the largest PD cluster, and the median phase angle of that cluster. On the other hand, the PPDA Cactus method clarifies the vertical characteristics of the phase-resolved partial discharge (PRPD) pattern in relation to the phase angle. This tool can simultaneously detect partial discharge signals from three-phase stator windings. A technique called three-phase signal discrimination (TPSD) has been introduced to improve measurement accuracy. This technique differentiates phase-related PD, external noise, and phase-to-phase PD, allowing PRPD data collection specific to each phase. Additionally, the instrument includes an innovative partial discharge sensor called the wide frequency band current transformer (WFBCT), which functions within a frequency range of 300 kHz to 60 MHz. This capability allows for acquiring PRPD patterns in voltage peak mode (VPM) and charge integration mode (CIM) under IEC60270.

The Insulation Resistance and Polarization Index test is routinely used to determine the condition of salient pole hydro generator field winding insulation. The current applicable IEEE standard, 43-2013 “IEEE Recommended Practice for Testing Insulation Resistance of Rotating Machinery” notes that the Polarization Index test is not applicable to salient pole machines with strip-on-edge windings. A 2021 Electrical Insulation Conference Paper described the author’s experience with Polarization Index testing of strip-on-edge field windings over a 20-year period; this paper continues the effort to share hydrogenerator owner experience on this subject. The paper will briefly review the test theory as applied to strip-on-edge windings and test results reporting, and present several case studies in which the polarization index test results provided actionable information used to make decisions related to whether the salient pole generator field winding insulation was suitable for operation or testing at higher voltage. A brief discussion of possible minimum Polarization Index limits for salient pole strip-on-edge field windings is included.

To demonstrate the consistency of partial discharge (PD) measurements, a comparative study was carried out using two different PD instruments on several 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 a matter of debate. Proper use and understanding of the instruments are essential for obtaining reproductible PD results. Therefore, the main objective of this comparative study was to evaluate the effect of different parameters that can influence PD measurements, and to validate the reproducibility from one PD instrument to another. PD measurements were carried out in the laboratory on individual coils using capacitive couplers and an electromagnetic probe. Various parameters were studied, such as the impact of the value of the capacitive coupler, 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 capacitive coupler and those obtained using the electromagnetic probe. Analysis of the Phase Resolved Partial Discharge (PRPD) pattern analysis in each case was also very similar between the two PD instruments.