Experimental Study on the Relationship between Transient Enclosure Voltage and Very Fast Transient Overvoltage
Transient enclosure voltage (TEV), generated during gas insulated switchgear (GIS) disconnector operations, may raise the issue of shock hazard and electromagnetic interference to secondary equipment. Malfunctions of SF6 gas density relay caused by TEV have been reported in switching tests of ultra-high voltage substation in China. Previous studies generally defined TEV as the voltage wave which is created by the voltage collapse across disconnector contacts at striking, then propagates on the enclosure, and regarded it as a special case of very fast transient overvoltage (VFTO). However, whether there is a quantitative relationship between TEV and VFTO is still controversial. Moreover, less work has been done on TEV experimental study compared with modelling and simulation study, because of difficulties in TEV accurate measurement. The purpose of this paper is to obtain the relationship between TEV and VFTO, based on the on-site experimental measurement results, and to provide a simple method to estimate the possible maximum TEV in a GIS substation. In this paper, on-site measuring experiments were conducted at Wuhan ultra-high voltage AC test base, firstly. According to IEC 61321-1, TEV measurement and VFTO measurement were based on a resistive impedance voltage divider and a porthole-type capacitive voltage divider, respectively. The waveforms during disconnector operations were recorded by self-developed measurement systems. Secondly, the relationship between TEV and VFTO was analyzed. A synchronous triggering device was employed to provide a comparison from the perspective of time. Pearson correlation coefficient and Spearman rank correlation coefficient were used to compare the TEV magnitude and the corresponding VFTO magnitude. It is shown that TEV pulse voltage is directly proportional to the corresponding VFTO breakdown voltage. Finally, a method to obtain the largest TEV magnitude through a small amount of on-site measurements was proposed. Coefficient k which was defined as the ratio of TEV pulse voltage and VFTO breakdown voltage, was used to present the TEV distribution in the test circuit and to estimate the maximum TEV at a certain point. This study validates the TEV transmission line theory and a quantitative relationship between TEV and VFTO from the experimental view. These results provide insights into TEV measurement and theoretical analysis, and better understandings of TEV simulation and corresponding electromagnetic compatibility design.