Effects of lightning strikes on 20 kV earthcables

Recently appeared defects on high voltage cables made an urgent evaluation of the impact of lightning strikes necessary. Sometimes overvoltages between the copper wire screen of the cable and earth causes damage to the oversheath. Field measurements with a classification of the voltage impulses at the copper wire screen have been made to evaluate the number of events. Additionally, a numerical model was developed to study the effects of atmospheric discharges on underground power cables with emphasis to the influence on the oversheath. This numerical method was also applied to estimate the effectiveness of different protection arrangements. This contribution presents evaluation methods for overvoltages of power cables and a model used firstly for calculating the stress caused by differential voltages and secondly to determinate the influence of protection measures