Reliable coefficient analysis and exploration of phase-to-phase distance protection for short line

Aiming at the situation that distance protection is applied to short lines, impedance measurement errors caused by factors that influence the phase-to-phase distance protection are analyzed based on the worst conditions. On this basis, the relationship between reliable coefficient of zone 1 phase-to-phase distance protection and length of transmission line is explored. A method of setting reliable coefficient is proposed, which makes the setting of zone 1 distance protection more reliable. It effectively avoids the over-reaching problem. Simulation results with PSCAD show the theoretical analysis is correct.