Statistical analysis on measured lightning overvoltage surges in a 110 kV air-insulated substation

The wide variety of lightning stroke characteristics and the modifying effects of power system components result in a diversity of intrusive lightning voltage waveshapes that stress transformers. These are not the traditional standard lightning impulses with a waveshape of 1.2/50 μs. Therefore the applicability of the standard lightning impulse voltage to power transformer testing has been questioned, and the overvoltage used in the test on transformers should be in accordance with the lightning overvoltage measured in the field. In this study, a lightning overvoltage monitoring system was installed in a 110 kV air-insulated substation, and the lightning overvoltages from 2007 to 2012 have been measured. Analysis was conducted on the measured data, which indicated that bidirectional oscillatory lightning waveforms rose up in the measured overvoltages. Using the energy method, the bidirectional oscillatory lightning waveform was reformulated into double exponential waveform, and the characteristic parameters, such as peak amplitude, front time and tail time, of the measured data were statistically analysed.