Lightning overvoltages on a DC transmission line, calculated based on measured bipolar lightning strokes

Abstract

A key principle of insulation coordination is to compare the stress which could potentially be applied to equipment when it is in service with its withstand level. The withstand level is known based on standard tests. For AC systems an important knowledge exists at international level and numerous reference documents are available. In addition, the IEC 60,071 has standardized the rated impulse withstand voltage to be used for equipment and proposed for each value of highest voltage for equipment preferential values regarding impulse withstand voltage. The situation is not the same for DC systems. Less experience has been shared within the international community and there is no standardization of the withstand voltage. In addition, with regard to AC lines their structure is different. All these elements lead to a careful reassessment of hypotheses, which are usually accepted as valid when performing AC system insulation coordination studies. In this paper, the influence of lightning current shape on overvoltage is examined. A 500 kV bipolar DC overhead line is considered. The overvoltages due to bipolar lightning strokes based on measurements are calculated. Measurements available in literature have been used. These overvoltages are compared with calculations based on the use of the CIGRE wave shape as it is usually the case when performing insulation coordination studies and analyzed from an insulation coordination point of view.