饱和铁芯型故障限流器通过增大电感值抑制短路电流上升速率,然而电感变化将改变输电线路故障特征,进而影响继电保护对直流输电系统双极短路故障的检测.针对上述问题,提出一种考虑饱和铁芯型故障限流器的双极短路故障检测方法,该方法具有检测速度快、灵敏性与可靠性高的优点,能够准确判别区内、区外故障.首先,分析故障情况下换流站的等效电路,对故障限流器铁芯磁化曲线进行线性拟合,建立双极短路故障等效电路,建立微分方程并求解,得到故障电流与限流器两端电压的解析表达式,据此提出基于限流器两端电压变化情况的双极短路故障检测方法;其次,搭建双端口±100 kV柔性高压直流输电系统(voltage source converter based high voltage direct current,VSC-HVDC)仿真模型,验证该方法的有效性,并与传统方法进行对比,验证该方法具有更快的检测速度;最后,分析短路电阻对该方法的影响,搭建多端口 VSC-HVDC仿真模型,结果表明,对于475 Ω及以下的短路电阻,该方法均能够准确识别故障,且能够准确识别区内、区外故障.
A bipolar short-circuit fault detection method for flexible DC transmission system with saturated iron-core type fault current limiter
Saturated iron-core fault current limiter suppresses the rise rate of short-circuit current by increasing the inductance value.However,the change of inductance will change the fault characteristics of transmission lines,and then affect the detection of bipolar short-circuit faults in direct current(DC)transmission systems by relay protection.In view of the above problems,a bipolar short-circuit fault detection method considering saturated iron-core fault current limiter is proposed.The method has the advantages of fast detection speed,high sensitivity and high reliability,and can accurately identify faults in and out of the area.Firstly,the equivalent circuit of the converter station under fault conditions is analyzed,the magnetization curve of the core of the fault current limiter is linearly fitted,and the bipolar short-circuit fault equivalent circuit is established.The differential equation is established and solved,the analytical expressions of the fault current and the voltage at both ends of the current limiter are obtained,and a bipolar short-circuit fault detection method based on the voltage change at both ends of the current limiter is proposed.Secondly,a two-port±100 kV flexible voltage source converter based high voltage direct current(VSC-HVDC)simulation model is built to verify the effectiveness of this method.Compared with traditional methods,it is proved that this method has faster detection speed.Finally,the influence of short-circuit resistors on the proposed method is analyzed,and a multi-port VSC-HVDC simulation model is built.The results show that for short-circuit resistors of 475 Ω and below,this method can accurately identify faults,and can accurately identify faults in and out of the region.
flexible DCfault current limiterbipolar short circuitfault detectionvoltage change rate
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