Research On Relay Protection Of UHV AC Double-circuit Transmission Line

As the influence of the distributed capacitance of the UHV transmission line, the sensitivity of differential current protection reduced badly and even can not be used, miss-trip of distance protection may occur when fault occurs at the end of the line. According to the problem of differential current protection, a new principle of differential current protection of UHV transmission line based on the Bergeron model is proposed; Aiming at the problem of pilot distance protection, this paper analyzes and deduces novel calculation formulas of distance protection for parallel transmission line based on distributed parameter model and six sequence component and uses it in fault component distance relay. To improve its resistance tolerance and prevent the relay from"in-phase"problem caused by high fault resistance, we propose a novel type relay with high-speed and high-resistance-tolerance characteristics and its concrete implementation scheme. The scheme can ensure operating speed for low-resistance faults near the start of the protected zone and correct action for high-resistance faults. Simulation has confirmed that the protection scheme is security. Finaly, a configuration scheme of main protection and backup protection of UHV parallel transmission line is presented.