A pilot protection for HVDC transmission line based on polarity characteristics of control signal deviation

In order to solve the problem that the long-time delay of traditional differential protection which has reduced the reliability of high voltage direct current line backup protection, consider the control strategies and response characteristics of the converter controller, a pilot protection for HVDC transmission line based on polarity characteristics of control signal deviation is proposed. By analyzing the fault characteristics of the converter control signal during the fault, drawn the conclusion that when the DC system occurs fault, from the converter dynamic regulation stage to the fault steady-state, the deviation of rectifier constant current control signal and the deviation of inverter constant current control signal will meet the positive polarity and the deviation of inverter constant extinction angle control signal will meet the negative polarity, but these polarity characteristics are not satisfied when the AC system occurs fault, therefore, the protection criterion is constructed. The simulation results show that the proposed backup protection principle has strong anti-transition-resistance ability and high reliability. Compared with the traditional differential protection, the proposed principle can reliably identify the internal fault from the converter dynamic regulation stage to the fault steady stage, which improves the reliability of the traditional HVDC line backup protection.