Abstract:In order to solve the over-limit problem of short-circuit current, Sichuan power grid often adopts the scheme of out-series operation. When the line with series compensation（SC）is in out-series operation, the failure of the extension side line will cause impact damage to the series compensation system. At the same time, the existence of SC capacitor bank may cause the line submersible current and transient recovery voltage to exceed the original level when the line is tripped, resulting in heavy breakdown of the fracture after the line tripping, which will cause system overvoltage reclosing failure, delayed fault removal and even damage to the circuitbreaker. A protection coordination method for out-series operation of line with SC is proposed, that is to install a remote transmission device on the side of line with SC to receive the tripping command of adjacent lines so as to achieve the intertrip between adjacent lines and SC lines, which can suppress the potential supply current and transient recovery voltage caused by residual voltage of capacitor after tripping of adjacent lines, and also ensure that the capacitor bank is not damaged by impact. Field tests show that in case of a single-phase transient fault on the extension side, the SC can be bypassed correctly, and the series compensation can be re-opened after the line is overlapped; when the phase-to-phase fault occurs on the extension side, the SC can be bypassed permanently, which meets the engineering application. The research results can provide a certain reference for protection adaptability of out-series operation of series compensated line.