Effects of lightning punctures on the core-shield voltage of buried cable

A common form of lightning-induced cable damage occurs when a lightning surge travels down the shield of a cable, inducing large voltages between the cable core and the shield and leading to possible insulation breakdown and arcing. The magnitude of this core-shield voltage is a function of how quickly the lightning current is shunted to the surrounding soil, either through a ground or by puncturing the protective jacket of the cable. Core-shield voltages are calculated for various combinations of cable length, cable diameter, soil conductivity, lightning pulse shape, and resistance of the cable jacket to puncturing and compared with results obtained by assuming that the cable jacket is punctured along its entire length. This latter assumption, the “bare shield” model, has generally been used to predict core-shield voltages. We have found that the “bare shield” model can lead to a significant underestimation of the core-shield voltage, particularly for small diameter cables with long distances between grounds (on the order of 10 kilometers). We present curves that provide an estimate of the peak core-shield voltage for a cable in which the jacket punctures for a portion of its length.