Sizing of surge arresters for 400kV Substation — A case study

Every year there are several million lightning discharges occur over world. In power system perspective, lightning is one of the most serious causes of over-voltages. These over-voltages may cause flashovers and serious damage to the equipment and thereby imperil the supply of power to customers. Much of the power equipment in use today is susceptible to damage or service interruption due to striking of lightning and switching operation in transmission. Hence, it is very essential to select the electrical strength of the equipment, so that the resulting voltage stresses do not cause damage to the equipment insulation or affect continuity of service. It is recommended to use protective devices like surge arresters to save the equipment from insulation breakdown. Location, number and size of the surge arresters are important in controlling the lightning over voltages. PSCAD/EMTDC software tool was used to investigate overvoltage phenomena due to lightning surge. This paper starts with a brief introduction to lightning strokes and selection of surge arresters. The method of sizing the lightning arrester is illustrated through the simulation results, discussion and interpretation of the results of arrester sizing carried out for a typical 4×100 MW, 400 kV Substation. The technical particulars of the surge arrester are finalized. It is also verified that the proposed location and number of surge arresters are adequate to meet the requirement of customer´s technical specification.