A Partial Discharge Measurement Technique for Applied Square Pulse Voltage with 50 NS Rise Times

Abstract

During the fabrication of solid electrical insulation, small cavities known as micro voids may form in the material. As electrical stress increases in this micro void, the breakdown probability also increases. This type of electrical breakdown is commonly known as partial discharge. Magnitudes of partial discharge currents are typically small but enough to cause degradation of the electrical insulation. To study degradation for fast-rise time voltage square pulse train, partial discharge measurement is needed. In current studies, partial discharge pulse widths have been measured in the range of nanoseconds. The best approach for measurement at ultra wide band frequencies is a bridge type measurement system, to reduce external noise and improve sensitivity to PD currents. The bridge configuration can be used with samples instead of one sample and one coupling capacitor. Identically created samples will have a close match for impedance and frequency response. This type of bridge also helps to reduce other sources of measured current such as the high displacement currents due to fast rise time square pulse voltage on the samples. Further improvement includes simultaneous measurements using a “linked” bridge configuration, where bridges share a common sample. A directly connected measurement current shunt should be used for high sensitivity with a uniform ultra wide band frequency response. Post-measurement digital signal processing (DSP) algorithms will perform the task of pulse discrimination and time delay from the pulse front. This research presents a method to improve the measurement of partial discharge when applied voltage is non-sinusoidal, with high frequency components. The improvements are apparent when square pulse voltage rise times are less than 50 ns. Ultra wide band measurements of physical samples will be performed for short time duration with a digital storage oscilloscope. A DSP algorithm is used to filter residual noise from the partial discharge current. The presented measurement technique for samples for this study is an original approach. Sample results demonstrate the effectiveness of the technique