An Adaptive Scheme for Parallel Line Distance Protection

This paper describes an adaptive protective relaying scheme for parallel-line distance protection. The scheme adjusts its operation, based on the availability of input signals, to achieve an optimal distance protection performance on parallel lines influenced by mutual coupling effect. When available, zero sequence current from the parallel line is used to fully compensate the mutual coupling effect. The zero sequence current ratio is used to avoid possible false operations on a healthy line, which may result from such compensation. When the parallel lines´ zero sequence current is not available, the line operating status is used instead to select proper zero sequence current compensation factors in impedance calculation. Default zero sequence current compensation factor is used when both parallel lines´ zero sequence current and line operating status signals are not available. The performance of the scheme has been verified on a simulated network and the results are presented.