Bipolar Block Analysis and Inhibition of Higher Voltage at Restarting in Reduced Voltage Mode for Longquan-Zhengping DC Transmission System

Through the analysis of bipolar block of Longquan-Zhengping direct current(DC) transmission system at July 30,2011,the block resulting from the restart failure of pole Ⅰ in reduced voltage mode after faults is studied.According to the logic of the actual control protection system,the root cause of this problem is that the ideal no-load DC voltage can not change rapidly.A modification method based on the real-time calculating of the firing angle limit at the rectifier and inverter station with measured data is proposed to optimize the output of voltage and current regulator,and to solve the matter of higher voltage at restarting in reduced voltage mode.Series tests of this new method have been made based on the simulation model which is the same as the actual DC system and prove its feasibility and effectiveness.