Equivalent traveling waves based current differential protection of EHV/UHV transmission lines

Current differential protection is one of the most important primary protections of extra/ultra-high-voltage (EHV/UHV) transmission lines. Despite its wide application, there exist major adverse factors of synchronization misalignment, current transformer (CT) saturation and line capacitive charging current, which may lead to a mal-operation. To solve these problems, a new current differential protection method, based on the concept of equivalent traveling wave (ETW), is proposed. The protection method is immune to CT saturation and line capacitive charging current, operates at an ultra-high speed, and does not require synchronized sampling. In the protection method, wavelet transform modulus maxima (WTMM) are used to reconstruct the current ETWs and thus reduce the communication traffic to an appropriate level. The reconstructed ETWs are then used to establish the percentage restraint operation criterion. Besides, a blocking method is implemented to avoid possible mal-operation when an external fault occurs on a line that forms a parallel path but has no mutual coupling with the protected line. Extensive simulations verify that the proposed protection method can serve as a secure and reliable primary protection for non-, shunt-, or series-compensated transmission lines with high sensitivity, even on internal high-resistance faults.