A pilot protection method based on energy balance for half-wavelength transmission lines

When the current differential protection is applied to very long transmission lines such as half-wavelength transmission lines, it suffers from the distributed capacitive current as well as from low sensitivity in case of a high-resistance fault. In case of an external fault, the variation of the line storage energy, the distributed resistance energy loss, and the energy injected from both ends of the transmission line satisfy the energy balance equation, and in this case the energy balance is independent of the line length. However, in case of an internal fault, the energy dissipated by the fault resistance breaks the energy balance. Based on the theory of energy balances, this paper proposes a novel pilot protection principle. Compared with the existing long-distance transmission line protection principles, the proposed pilot protection principle has the advantage of not being influenced by the distributed parameters of the long line, and in addition it is suitable for identification of high-resistance grounded faults. A simulation based on EMTDC/PSCAD illustrates the benefits of the proposed approach.