Event Analysis of Insulation Breakdown of 220kV Line-Breaker Caused by Multiple Lightning Shielding Failure

In this paper, a multiple lightning shielding failure occurred on a 220kV transmission line in Tianjin was discussed. Due to the low thermal capacity of overhead ground wire, broken-line fault occured when short-circuit current flow through the overhead ground wire caused by the flashover of line insulator. Meanwhile, since the multiple lightning shielding occurred after the line breaker opened. Then the breaker insulation breakdown occured subsequently. To prevent the transmission line from lightning trip which is mostly caused by lightning stroke, the influencing factors of the performance are analyzed, including operating characteristic of relay protection, thermal capacity of transmission line, insulation system of breaker. It is found that the circuit breaker is broken down when the insulation strength has not been fully recovered, which makes the breaker unable to cut off the fault current and circuit breaker failure protection trips the 220kV busbar.