Lightning Transient Analysis of a 69kV Transmission Line with Externally Gapped Line Surge Arrester under Normal Open Circuit Breaker System

摘要

Determining the optimum location for installation of the transmission line arrester to achieve the desired outage rate of the power line system is really not a simple task. If no externally gapped line surge arrester (EGLA) is installed on the transmission line, it is well known that a lightning stroke direct to a phase conductor usually causes insulator flashover. It is also a fact that EGLA installed on every phase of every tower will effectively protect insulator from flashover when a lightning directly strikes to the ground wire or phase conductor. Therefore EGLA is a effective solution to improve lightning protection performance of overhead transmission lines. The lightning overvoltage is the main reason which causes the overhead transmission line outage. Usually, the Air-Breaker Switch (ABS) or Gas Circuit Breaker (GCB) is designed with normal open due to system power flow conditions, where a lightning strikes overhead transmission lines at the outlet of substation, even EGLAs are installed on every phase of every tower of the transmission line, flashover may still occurs at the arc horn of post insulator of ABS, or even a burning accident of GCB occurs. So there were several times that transmission line outage happened in Taiwan Power Company (TPC) till now and caused system voltage sag, which influenced the power supply quality, especially in the Science Park. This paper presents the analysis of lightning surges transient overvoltage in a 69kV transmission line regarding the above conditions. Based on the actual system information, the distributed parameter model is adopted to build a 69kV transmission network by EMTP-ATP for simulations, where the major criteria suggested by IEEE and IEC standards are used to assess the level of insulation coordination of a 69kV circuit breaker with normal open condition.