Separation of Partial Discharge Signals and Disturbances Under Impulse Voltage Stress Based on Cross-Correlation

Abstract:
Partial discharge measurements are an important tool for assessing the quality of electrical insulation systems. Most commonly partial discharge measurements are carried out under AC or DC voltage stress. Due to the increased usage of power electronic components, e.g. in pulse-width-modulated drives, the insulation system of electric motors is subject not only to AC but also to transient voltage stress. The transient voltage results in an uneven stress distribution within the motor coils, which can lead to partial discharge inception. Accordingly, test procedures using transient voltage waveforms are advisable but at the same time constitute a challenge regarding the interpretation due to the transient displacement current which can be mistaken as partial discharges. The present investigation introduces an analysis procedure based on the signal form of the measured events during testing using cross-correlation. Measured transient events are compared to measured basis functions, which represent different signal sources. The result is a correlation function, the coefficients of which yield information on whether the analysed signal results from the same source as the applied basis function. A procedure for evaluation is proposed, experimentally verified and influencing factors are discussed.