送出直流对工频变化量元件的影响机理分析

Mechanism analysis of the impact of DC system on power-frequency variation protections

为了从理论上分析送端交流系统工频变化量保护的动作特性,建立了送端交流系统故障下的整流侧直流系统的等值工频变化量阻抗模型。基于所建立的数学模型,并结合直流控制系统的故障响应特性,对不同故障情况下直流系统的等值工频变化量阻抗特性进行了分析,进而分析了送出直流对工频变化量元件的影响。研究表明:在送端交流系统故障情况下,直流等值工频变化量阻抗在大部分条件下呈容性,可造成工频变化量距离元件保护范围的缩小和工频变化量方向元件的误判。最后通过PSCAD/EMTDC仿真软件对理论研究进行了仿真验证。

In order to analyze the operating characteristics of power-frequency variation protections of the sending-end AC system theoretically,the mathematical model of DC system at the rectifier side which is represented by a power-frequency variation impedance in fault superimposed network is deduced in the case that fault occurs in the sending-end AC system.Based on the mathematical model and the response characteristics of HVDC control system,the characteristics of the equivalent power-frequency variation impedance of DC system are analyzed under different fault conditions.Then the impact of DC system on power-frequency variation protections is analyzed based on the fault characteristics of DC system.According to the analysis,when fault occurs in the sending-end AC system,the equivalent power-frequency variation impedance of DC system is capacitive under most fault conditions,which reduces the zone of distance protection based on power-frequency variation and results in misjudgment of directional protection based on power-frequency variation.In the end,the result is verified by simulations on PSCAD/EMTDC.