The statistical calculation of energization overvoltages, case of EGAT 500 kV lines

Normally in EGAT 500 kV lines the shunt reactors are adopted at the line's two terminals. Meanwhile the surge arresters also are installed at the line's two terminals in parallel with the shunt reactors. This paper presents part results of a series of research studies related to the overvoltages in EGAT 500 kV lines. The statistical calculation of 200 times for the energization overvoltages has been carried out. The statistical characteristics of phase-to-earth energization overvoltages in EHV lines have been carefully considered and processed during the simulation calculation while the EMTP was adopted. Results indicated that for 500 kV lines the overvoltages distribution on the line terminals is followed with the normal distribution when there are no surge arresters. However, the overvoltages distribution will no longer follow the normal distribution when the surge arresters are installed at both ends. For the phase-to-earth energization overvoltage the effect of three types of protective devices: surge arrester, closing resistor and shunt reactor have been studied. Results also indicated that under the existing conditions the phase-to-earth energization overvoltages of EGAT 500 kV line are less than 2.0 p.u. while either surge arresters or closing resistor is eliminated. As 1175 kV (2.60 p.u.) has been taken as the systems insulation level, therefore it is possible to consider the elimination of one protective device.