Time and frequency characteristics of very fast transient overvoltage in ultra high voltage substation

Most work about the measurement of very fast transient overvoltage (VFTO) was carried out in the laboratory and test base. Because of the different GIS arrangement and power capacity, the time and frequency characteristics of VFTO in ultra high voltage (UHV) substation could be different with that obtained in the laboratory and test base. A series of VFTO measurements were carried out in two 1100 kV GIS substations to investigate the characteristics of on-site VFTO. The port-hole sensor based on surface-mounted device was chosen to measure the VFTO for its reliability and wide band-width. The whole measurement system was introduced and the schematic layout of each experiment was given. Measurement results of different switch conditions and measure points were presented for comprehensive understanding of the VFTO characteristics on site. The results indicated that the striking number during one operation was 16 (closing) and 14 (opening), similar to that obtained from test base result. Besides, single strike with front time 5.3 ns and voltage steepness 186.1 kV/ns was recorded, and the steepness was relatively higher than that gained in the test base. Moreover, the spectral analysis based on S transform was investigated to get the duration of different frequency components of VFTO waveform. Compared with the data obtained from the test base, the high frequency components of VFTO were reduced, while the lower frequency components lasted longer. The results provided references for the investigation of the electromagnetic interfere, the insulation coordination, and VFTO mitigation methods.