Secondary Arc Current Analysis of an Untransposed EHV/UHV Transmission Line With Controllable Unbalanced Shunt Reactor

A conventional four-legged shunt reactor serving untransposed extra-high voltage or ultra-high voltage transmission lines may cause the secondary arc difficult to extinguish and result in single-phase autoreclosing (SPAR) failure. This paper proposed an unbalanced shunt reactor (USR) scheme and focuses on the secondary current analysis with respect to untransposed extra high-voltage/ultra-high voltage transmission lines. The fundamental theory of secondary arc calculation for the untransposed transmission line with USR was provided first, followed by the formulation of USR controlling principles and strategy. To validate the effectiveness of secondary arc current suppression, untransposed 1000-kV single-circuit and double-circuit UTL with USR were simulated using the Electromagnetic Transients Program. The results show that USR is effective in suppressing secondary arc current and recovery voltage for single-circuit and double-circuit UTL, which helps increase the SPAR success probability. Furthermore, the secondary arc current and recovery voltage are not sensitive to the variation of USR neutral reactance; hence, the value of neutral reactance can be decided in a wide range. Finally, USR's role and effect in reducing the inductive electrostatic voltage in double-circuit UTL was discussed when one line is transferred to maintenance.