Lightning performance and overvoltage surge studies on a rural distribution line

In an attempt to arrive at an improved understanding of the disturbing influence of lightning upon power distribution lines, a unique project is described involving the construction of a 10km test distribution line together with an automated lightning and surge recording station. Preliminary data are presented from measurements carried out over two full thunderstorm seasons, in respect of direct strokes to the line and induced overvoltage surge characteristics. The majority of lightning disturbances are caused by induction from nearby discharges to ground, are of positive polarity, rarely exceed 100 kV, and are generally accountable in terms of classic electromagnetic field theories of induction. Several bipolar surge records have also been obtained, however, whose characteristics deviate considerably from theoretical prediction, and it is considered that this might be due to the influence of the leader mechanism. It is also found that the direct stroke incidence to the line is considerably greater than anticipated from traditional theory, as is also the frequency of multiple pole flashovers, and it is concluded that further research is required on the attractive effects of lines and of the final stages of the striking process.