采用换流器控制信号变化量极性特征的高压直流线路纵联保护

A pilot protection for high voltage direct current (HVDC) transmission line based on polarity characteristics of control signal deviation is proposed to solve the problem of insufficient performance of traditional HVDC transmission line backup protection. Analyzing the fault characteristics of the converter control signals from the fault transient stage to the fault steady stage, it is concluded that when the fault occurs in DC system, the deviations of constant current control signals at rectifier and inverter are positive and the deviation of constant extinction angle control signal at inverter is negative, while these polarity characteristics are obviously different when the fault occurs in AC system. By observing the polarity differences of control signal after the fault occurs on the AC/DC side, a start criterion based on the change rate of control signal amplitude and a protection main criterion based on the polarity characteristics of control signal deviation are established. Combining the blocking signal of DC bus protection, a novel DC transmission line pilot protection principle is proposed to identify the fault that occurs on it. The simulation results show that the proposed backup protection can identify the DC line fault within 25-100 ms, and it can also effectively identify the 500 Ω high resistance fault. The protection principle only needs the transmission of single-way logic information and lower communication requirement, and works longer during the fault transient stage to the fault steady stage, and its overall performance is better than the traditional current differential protection.