Power transmission lines are the widest section of the power systems and the lightning is the most dangerous natural phenomenon disturbing their normal operation. To prevent direct lightning stroke to the phase conductors, it is normally to use ground wires. These wires almost protect phase conductors from direct lightning stroke, but lightning stroke to these wires, may lead to back flashover. The insulation coordination based on lightning overvoltages for power systems is a competitive issue worldwide. Lightning can be considered the main cause of decreasing the power systems reliabilities. Lightning phenomena strikes the transmission lines ground conductors or seldom the phases conductors causing travelling overvoltages waves towards the GIS substations. These travelling overvoltages waves may cause serious problems in the substation insulation unless the proper design is pre-intended accordingly. To understand precisely the insulation coordination complex problems inside the GIS substation, it is essentially required to analyze the power systems using a simulation model. For this purpose, a simulation model for the entire system consisting of overhead lines, transformer, surge arresters, and earth grid has been developed in (EMTP/MATLAB). The current work is based on a typical power system outdoor 500/220 kV GIS substation located at west of Cairo-Egypt. Different scenarios of lightning strokes over the ground/phases conductors of ingoing and outgoing power lines are simulated. Back flashover (BFO) and the effective parameters are investigated to minimize its occurring probability. Different methods are proposed to decrease this probability with presenting the surge overvoltages at different locations. Effects of different surge arrester arrangements are investigated. Finally, the obtained simulation results of insulation coordination inside the GIS substation have compared with similar work exhibiting a very high convergence. |
