This paper proposes a self-adaptive principle of current differential protection for AC transmission line in AC-DC hybrid power grid. By analyzing the post-fault transient characteristics of inverter-side AC current with commutation failure occurred, the principle is proposed by using the promoted instantaneous energy ratio of currents from line terminals. The principle eliminates the influence of commutation failure by constructing instantaneous energy of terminal currents using trigonometric method. Besides, based on the feature that zero-sequence network of inverter AC system is isolated from DC system, the principle promotes the sensibility in high resistance-ground fault situations by constructing self-adaptive criterion with promoted instantaneous energy of zero-sequence AC current. PSCAD/EMTDC simulations are provided to verify the reliability of proposed principle and the results show that the novel principle is unaffected from commutation failure and is suitable for AC transmission line protection in AC-DC hybrid grid.
Keywords AC-DC hybrid grid, commutation failure, selfadaptive, current differential protection, promoted instantaneous energy