Improved digital algorithm for adaptive reclosing for transmission lines with shunt reactors

This study presents an improved algorithm of adaptive single-phase auto-reclosing (ASPAR) for extra high voltage transmission lines with shunt reactors. It shows that the odd and even harmonic factors of the faulted phase voltage have different characteristic in different stages after breaker open. During second arc period, the odd harmonics are dominant, while the even harmonics distortion factor calculated by discrete Fourier transform is found in relatively high level after arc extinction. Hence, the calculation of ratio of even harmonic factor to odd harmonic factor (REO) is expected to determine the secondary arc extinction. The algorithm is easy to implement with small computation and no more than 20 ms delay. Moreover, the REO threshold is taken constant at unity and need not be skilfully assigned. Analysis is provided by EMTP emulation as well as filed data, and the high reliability of ASPAR has been verified.