Cooperation research between electrode line transversal differential protection and bridge differential protection in HVDC project

Abstract

On July 14, 2017, the electrode line occurred ground fault near the ZhaoQing converter station of GaoZhao HVDC, the Delta Bridge Differential Protection(87CBD) of the valve area protection acted before the Electrode Line Transversal Differential Protection (60EL) of electrode area protection, which leads to the pole blocking. In view of the exposed problem between the 87CBD and the 60EL about the cooperation of the protection delays, the paper studies the feasibility of the delays adjustment. Overall considering from the aspects from the 87CBD delay, the 60EL export time, the 60EL measurement error, the cooperation of the 60EL and the restart blocking time, and so on, the optimization is proposed which improves the 60EL delay for 400ms, and improves the restart blocking time for 400ms. Simulation show that the proposed measures are feasible and effective, to ensure that when the electrode line fault occurred near the converter station, the pole blocking can avoid by the DC restart sequence of the 60EL.