Research on Induced Over-voltage Caused by Lightning Strike on Top of UHV Transmission Towers

Lighting strike is one of the major causes of over-voltage in the electrical power system. As the development of power system, especially the constructing of UHV transmission including AC 1000kV and DC 800kV, the formula for calculating lighting induced over-voltage commended by the national electrical code is no more appropriate now. Therefore new formula and waveform function should be deduced in light of the reality so the lightning protection calculation and design can be on certified basis. In this paper induced over-voltage caused by direct lightning strike on top of UHV transmission tower and its waveform are studied. Several computational methods for calculating induced over-voltage, such as Regulation Method, Loop Voltage Method, and Field Cancellation Method are theoretically analyzed. The Field Cancellation Method is introduced in detail, and based on the method the author developed simulation software. Further, the paper discusses the effect of the following parameters on waveform and crest value of lighting induced over-voltage: propagation velocity, length of upward leader, lightning current peak value, the ground-resistance. With the resultant data, the author deduces the peak value formula and the wave shape function of the lightning-induced over-voltage by curve fitting. The formula and the function can be used to calculate the lightning induced over-voltage individually or be embedded into the EMTP-ATP program to calculate the lightning surge over-voltage.