Analysis of overvoltages in overhead ground wires of extra high voltage (EHV) power transmission line under single-phase-to-ground faults

Abstract

Abstract Overhead ground wires (GW) of extra high voltage (EHV) power transmission lines, apart from lightning-induced overvoltage protection are frequently used for carrier-current communication. In this case the ground wires are suspended on insulators, the dielectric strength of which should be sufficient for the line operational conditions. The insulation level is defined from the condition of the single-line-to-ground (SLG) fault, thus insulator protecting spark gaps should not be flashed-over during such conditions — in order to maintain continuity of the communication channel along the line. Overvoltages during such faults depend on many parameters such as fault place, fault angle, pre-fault load etc. Therefore, designers should investigate the problem for determination of the worst-case scenario. In this paper, dependence of the overvoltages on 750 kV power transmission line ground wires upon the SLG fault place and pre-fault load of the line in transient and steady states is investigated. The analysis was performed by using dynamic arc model incorporated into the EMTP program. The provided simulations show that adequately introduced primary and secondary arc models are decisive factors for an accurate simulation of the electromagnetic phenomena in the EHV transmission lines during an arc crossing-over (here the primary arc plays an important role) and during so called dead-time, when the secondary arc takes place. This paper gives some recommendations for the insulator strings coordination in the 750 kV earth wires on the basis of computer simulation results.