Abstract
High voltage transients in electrical power systems are mainly caused by lightning strikes and switching operations. The high voltage transients above the basic insulation level (BIL) would degrade the electrical insulation of the equipment.In this work, the effect of high voltage impulses on the trend of the surface discharge at the oil-paper interface was investigated. The partial discharge patterns were recorded by the Insulation Condition Monitoring (ICM) system. The HV impulses were generated by a standard 1.2/50 μs HV impulse generator. The measurement results presented in this paper seem to show that surfacedischarge would cause complete breakdown (continuous flashovers) at the oil-paper interface much faster when the test sample is first aged by HV impulses comparedto when it is unaged.
Highlights
High voltage transients in electrical power systems are mainly caused by lightning strikes and switching operations
In power transformer bushing there could be surface discharge at the oil-paper interface initiated from overstressed edges of metal foils
This work compares the trends of surface discharges at the oil-paper interface when oil-impregnated paper used in power transformer bushings are unaged and when they are first aged by HV impulses
Summary
High voltage transients in electrical power systems are mainly caused by lightning strikes and switching operations. This work compares the trends of surface discharges at the oil-paper interface when oil-impregnated paper used in power transformer bushings are unaged and when they are first aged by HV impulses. It consisted of Munksjö Thermo paper layers used in power transformer bushings, rod and plane brass electrodes. The test cell was set in such a way that there would be progressive surface discharges at the oil-paper interface on one side of the electrodes To achieve this as shown in Fig., the HV brass electrode had sharp edges on the sides next to the oil-impregnated paper surface in order to initiate surface discharge . L where, Et is the average tangential electric field stress at the oil-paper interface, L is the length of the surface of the insulation system from the ground electrode to the HV electrode, and U is the applied voltage at the HV electrode; the geometry configuration would result in high average tangential electric field stress (Et) on the side with shorter L as compared to the one with longer L
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