Abstract
An average wave front time of the large lightning current, such as over 50kA, is 4_??_5 μs in summer and about 16μs in winter, respectively. In case lightning hits a transmission line, the wave shapes of the tower top voltage are much different in winter from the summer ones, because of the large difference in the current wave front time. Little published data is available on the analysis of the tower top voltage caused by lightning with the longer wave front time, such as longer than 6μs. The authors calculated tower top voltage using EMTP, and found the important phenomena. (1)The wave shape of the tower top voltage is “a leniently rising impulse” in case of the winter lightning. The flashover voltage of an airgap for these kinds of impulse voltage is not proportional to the gap length. (2)The effect of the tower footing resistance to “restrain the occurrence of backflashover” is very much larger in winter as compared with summer. (3)The results of analysis give indispensable factors on the estimation of probability of flashovers caused by winter lightning.
