计及不可测分支负荷电源助增效应的有源配网幅值差动保护新判据

A New Criterion of Amplitude Differential Protection for Active Distribution Network Considering Load Power Effect of Unmeasurable Branches

电流相量差动保护是性能最为优良的保护判据。但是,在配网中应用时,由于条件所限,一般很难保证线路两侧电流测量的同步性。幅值差动保护通过挖掘传统差动保护中幅值蕴含的故障信息,在配网中可最大化地提升保护性能。然而,当不可测分支为以感应电机为主的大容量负荷时,现有的幅值差动保护判据难以同时满足保护的安全性和灵敏性。为解决以上难题,分析了感应电机的故障电源效应,从机理上揭示了含感应电机型不可测分支的线路故障前后两侧电流幅值的变化规律。在此基础上,提出一种新型幅值差动保护判据:利用故障前后线路两侧电流幅值之差,分别构成制动量和动作量,并且制定了自适应动作特性曲线,解决了由于感应电机反充电流造成的区内高阻故障和区外严重故障的辨识困难问题。仿真结果表明,该判据可有效规避感应电机接入线路导致保护误动的风险,并且在此前提下,具有保护区内全线100Ω的耐受过渡电阻能力。

Current vector differential protection is the most excellent protection criterion,but it is difficult to ensure the synchronization of current measurements on both sides of the line due to limited conditions when it is applied in distribution network.Amplitude differential protection can maximize the protection performance in distribution network by mining the fault information contained in the amplitude of traditional differential protection.However,when the unmeasurable branch is a large capacity load mainly consisting of induction motors,the existing criteria of amplitude differential protection can not meet the security and sensitivity of protection at the same time.In order to solve the above problems,the characteristics of fault power effect of induction motor were analyzed;the variation law of current amplitude on both sides of the line with induction motor type unmeasurable branch before and after fault was revealed from the mechanism.On this basis,a new criterion of amplitude differential protection was proposed.The difference between the amplitude of the two sides of the line before and after the fault constitutes the amount of braking and action,and an adaptive motion characteristic curve was developed.The difficulty of identifying high resistance faults in the area and serious faults outside the area caused by the back charging current of induction motor was solved.The simulation results show that the criterion can effectively avoid the risk of protection misoperation caused by the induction motor connecting to the line,and has the ability to withstand the transition resistance of 100Ωof the whole line in the protection area.