Analysis of the influence of asymmetry of non-transposition lines with same tower on zero sequence differential protection

The characteristic of non-transposition lines on the same tower (NTLST) is that the line parameters are asymmetric. When a short circuit occurs on the line, the impedance matrix is a full matrix and cannot be subjected to symmetry analysis. However, the asymmetry influences the operation performance of the zero-sequence differential protection (ZSDP). The impedance matrix characteristics of (NTLST) is studied in the paper. The impedance matrix is symmetrized partially to form a single line symmetry matrix with mutual inductance between double circuit lines. A detailed study on the sequence network diagrams, calculation methods for differential zero sequence current was conducted when fault occurs on the NTLST. The asymmetric factors affecting ZSDP can be studied from the expression of zero sequence current, including the asymmetry of parameters such as line installation structure, different spacing between different phase lines and fault type, including crossing line fault between same-name phases and different-name phases. The factors that affect the correct operation of ZSDP was proved by large number of simulation experiments by PSCAD. When cross line faults with different-name phases occurs, the ZSDP will malfunction.