Observation of current waveshapes of lightning strokes on transmission towers

Considerable cost reductions have been achieved through rationalizing insulation design for substation equipment based on the application of high-performance surge arresters and improvement in analysis techniques. For further rationalization in insulation design and cost reduction, it is important to evaluate the lightning stroke current waveshape in detail. Some studies to observe current waveshapes have been conducted before, but they were ones conducted on independent towers and do not provide many data in a large-current region. So, we have been observing lightning stroke currents larger than 9 kA on 60 transmission towers (mainly 500 kV lines) since 1994. In this paper, we present some lightning parameters for insulation design of substations, drawn from current waveshape data, which have been collected so far. In addition, we report on the relationships among the peak value, the front steepness and the front duration, which heavily affect the insulation design of substations.