New principle of distance protection for asymmetric short circuit of the transmission line of inverter renewable energy station

Because the output current of the renewable energy grid-connected inverter has the traits of weak amplitude feed and controlled phase angle, compared with the traditional AC system, the ability of the distance protection to withstand the transition resistance in the renewable energy access AC power grid is reduced, and the risk of incorrect protection action is aggravated. Therefore, in order to solve the problem of adaptability decline of backup protection, this paper proposes a new principle of distance protection based on the method of solving the additional impedance phase. Firstly, in accordance with the well-known impedance model, combined with the boundary conditions of the sequence network after the asymmetric fault of the AC line, and then using the nature of the new energy side open circuit in the negative sequence network, an additional impedance phase solution method based on the normalization of the negative sequence network is proposed. On this basis, the sine theorem is used to calculate the fault distance, and finally a new protection principle is constructed. Compared with the traditional ratio amplitude distance protection, this principle has a strong ability to withstand transition resistance, and can withstand a maximum of 200 Ω transition resistance when single-phase grounding, which addresses the issue where the proposed distance protection principle is negatively impacted by transition resistance as a result of renewable energy's weak feed characteristics.