Insulation coordination studies and selection of lightning arrester for 765kV switchyard

As the Power Transmission System nominal voltages increase, the expected lightning as well as the switching over voltages also increase. One way of handling these over voltages is to design the insulation strength of the equipment and switchgear to withstand the expected over voltages with sufficient safety margin. This directly relates to higher cost of the equipment. The other way is to reduce the expected over voltages at the equipment of substations to a possible level. Lightning Arrester plays a major role in reducing these over voltages to allowable limits under surge conditions. Rating and placement of Lightning Arresters has to be decided properly. This paper presents various essential conditions and practices necessarily to be followed as per standards in selection of lighting arrestors in a 765kV switch yard. The simulation of lightning and switching transients are carried out using PSCAD. Over voltages are mitigated and safety of substation is ensured.