柔性直流系统输电线路的纵联能量差动保护
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Pilot energy differential protection for transmission lines in flexible DC systems
ZHANG Yanxia， NI Lang， ZHOU Sirui， WEI Le（KeyLaboratory of Smart Grid of Ministry of Education，Tianjin University，Tianjin 3OoO72，China）
Abstract：In order to study the new protection principle of flexible DC lines，the propagation process of electromagnetic wave on a single microelement of transmisson line was analyzed，and the negative exponential decay characteristic of energy was obtained when voltage and current as electromagnetic waves propagating on transmision lines. On this basis，the electromagnetic wave energy relationship between the two ends of the flexible DC system when fault occurs on the line was analyzed，and a pilot energy differential protection method was proposed to distinguish internal and external faults based on the electromagnetic energy difference between both ends of the line.Relying on the short-time calculated electromagnetic wave energy，this protection method can quickly cut offthe fault from the line outlet to the midpoint during the capacitor discharge stage after the fault，and has a strong ability to withstand transition resistor. Besides，the flowchart of protection method was given，the performance of the pilot energy differential protection method was analyzed inthe case of grounding through the transition resistor，and summarizes its advantages and disadvantages.Finally，efectiveness of the protection and the ability to withstand the transition resistor were verified by the simulation model of the flexible DC system.The simulation results show that the protection has clear selectivity and reliable operation when grounded by transition resistor.
Keywords ：flexible DC system; transmission line； propagation characteristics of electromagnetic wave en-ergy；internal fault and external fault； pilot energy diferential protection； transition resistor
0引言
基于电压源换流器的高压直流输电系统（volt-age source converter based high voltage direct currentsystem，VSC-HVDC）被称为柔性直流输电系统，换流器主要包括三相两电平VSC和模块化多电平两种。（剩余11784字）