New method for live line measuring the zero-sequence distribution parameters for partial parallel double-circuit transmission lines

• A universal zero-sequence distributed parameter measurement method for transmission lines. • This method is suitable for partial parallel transmission lines without symmetric simplification. • This method is suitable for both power outage measurement and live line measurement. • This new method is verified by PSCAD and field test in two transmission lines. • First successful application of non full phase operation to live line measure parameters of 500 kV transmission lines. Accurate measurement of the transmission line parameters is essential for the stable operation of the power system. However, the existing methods are limited in their engineering applicability due to the assumption of parameter symmetry. The solution method for transmission line equations based on Laplace transform also leads to significant complexity in derivation and poor generalizability. To overcome these limitations, this study proposes a new method for measuring the zero-sequence distribution parameters of partial parallel double-circuit transmission lines based on a distributed parameter model. The method employs phase-mode transformation to represent the voltage and current at both ends of the lines through forward and backward voltage/current modes. Combined with the chain parameter matrix theory, expressions for the line impedance matrix and admittance matrix are derived without parameter simplifications. The proposed method achieves line parameter measurement under both power outage and live line conditions based on synchronous measurement. The measurement accuracy and robustness of the proposed method are validated through PSCAD/EMTDC simulations, and further demonstrated through successful field live line measurement tests on two 500 kV partial parallel double-circuit transmission lines. The measurement results indicate that the proposed method can measure the distribution parameters of the partial parallel double-circuit lines precisely. Furthermore, the proposed method is extended to a universal measurement method for the distribution parameters of n -circuit transmission lines and the phase parameters of asymmetric transmission lines.