Numerical Evaluation of Melting and Breaking Conditions of Strands due to AC Arc Discharge Generated between Wires in 66kV Overhead Transmission Line

Abstract

In March 2011, the earthquake off the Pacific coast of Tohoku caused a power line and a ground wire in 66kV overhead transmission line to shake heavily. That led a flashover and an AC arc discharge between the power line (TACSR 240mm²) and the ground wire (AC 70mm²), where the current and the duration of the ground fault was 596A and 0.47s, respectively. Consequently, the power line strands (aluminum strands) were melted and 0 out of 30 strands was broken, and the ground wire strands (aluminum-clad steel strands) were melted and 5 out of 7 strands were broken due to the arc of the ground fault. In this paper, numerical evaluations of melting and breaking conditions of strands of the power line and the ground wire were carried out and the calculation results were compared with the conditions observed in the actual line and wire. As a result, the calculated number of broken strands of the power line was 0, which was agreed with that of the actual line. On the other hand, the calculated number of broken strands of the ground wire was 3-4, which was less than that of the actual wire. It is considered that non-broken but partially-melted 1-2 out of 7 strands in calculations were broken due to an arc jet spouted from the arc spot on the melted strands, and the added tension because of the ground wire shaking as well as the normal tension in the actual field.