New Protection Methods Considering Impedance Characteristics Of New Type FCL

With the increasing scale of the power grid,the coupling degree of the network is deepening,the short circuit current increases quickly.Short-Circuit current exceeding standard has become one of the important technical bottlenecks restricting the construction of power grid.Therefore,new type fault current limiter based on power electronic devices and superconducting principles has been developed rapidly.While,with the installation of FCL,a series of problems arise.The time-varying characteristics of impedance make the fault transient process more complicated,and bring nonnegligible influence to quick break protection,especially for the high voltage and ultra high voltage system with high speed requirement.Moreover,the input and the dynamic process of the current limiting impedance also bring new challenges to the traditional relay protection.For thyristor controlled series compensation fault current limiter(TCSC-FCL),the piecewise mathematical model and dynamic process of the cross interval jump between inductive reactance interval and capacitive reactance interval have been researched and analyzed.Then,a mathematical expression of dynamic impedance characteristics of TCSCFCL is proposed.On this basis,a starting criterion based on power frequency variable is proposed and an original distance protection setting strategy based on dynamic offset impedance circle,in order to eliminate the influence of TCSC-FCL dynamic impedance characteristics is put forward,after analyzing the influence of dynamic impedance on distance protection.Finally,a typical grid model including TCSC-FCL is established,and the correctness of dynamic impedance time function and the distance protection setting strategy is verified.For superconducting fault current limiter(SFCL),the mathematical model of resistance type superconducting fault current limiter is established firstly.Then,it indicates that the input of the superconducting current limiter changes the circuit model before and after the fault,so that the power frequency variation impedance relay based on the pre fault memory data does not satisfy the superposition condition.An adaptive current quick break protection considering the impedance characteristics of superconducting current limiter is proposed,after the similarity and difference in principle and performance of the adaptive current quick break protection and power frequency variation impedance relay are discussed.Finally,the feasibility and effectiveness of the new method is verified by simulation in EMTDC/PSCAD.