Investigation Of Fault Analysis Method And Protection For Quadruple-circuit Transmission Lines With Asymmetric Parameter

With the development of urbanization and economic development,the electricity consumption of the cities is increasing.However,the line corridor is too scarce to meet the demand of transmission capacity.The quadruple-circuit transmission lines on the same tower are widely used to solve this problem.These quadruple-circuit lines can effectively save transmission corridors,increase transmission capacities,reduce construction costs,and so forth.In some areas,in order to meet the needs of the power supply,double-circuit lines have been re-constructed into quadruple-circuit lines.Besides,quadruple-circuit lines with different voltage levels have been built to save the transmission corridor.Since the number of conductors in quadruple-circuit transmission lines is larger than that in traditional transmission lines,the coupling relationship between the conductors is more complex in quadruple-circuit transmission lines.Considering the differences between conductor types,conductor positions,and space structure of the conductors arrangement in the re-constructed transmission lines and quadruple-circuit transmission lines with different voltage levels,the self-impedances are no more identical in these transmission lines.These transmission lines are called as quadruple-circuit transmission lines with asymmetric parameters,due to the inconsistency of self-impedances of each line.It is more difficult to analyze the coupling relationship between the conductors.The fault currents of the same fault type in different lines will be different in quadruple-circuit transmission lines with asymmetric parameters,which is not conducive to the protections in the power systems.This will have a significant impact on the stability and reliability of power systems.In order to improve the reliability of power system,a new decoupling method should be studied and new protection schemes should be studied for the quadruple-circuit transmission lines with asymmetric parameters.This paper is a summary of the research work of the author during the period of the study on the fault analysis method and protection of the quadruple-circuit transmission lines with asymmetric parameters:1.According to the structural characteristics of quadruple-circuit transmission lines with asymmetric parameters,a new phase-mode transformation method is put forward to decouple the mutual impedance completely.Considering transformation procedure of the existing decoupling methods and new method,an extended deoupling method is proposed for quadruple-circuit transmission lines.Besides,the simulation model of the quadruple-circuit transmission lines with asymmetric parameters is constructed,which lays solid foundation for fault analysis and protection of quadruple-circuit transmission lines with asymmetric parameters.2.Combined with sequence-component analysis methods that based on traditional phase-mode transformation methods,principles for the sequence-component analysis of quadruple-circuit transmission lines with asymmetric parameters are elaborated.Independent sequence-component networks and system impedance modification methods are proposed based on these principles.Besides,simplification method for compound sequence network is put forward to help calculate fault currents in quadruple-circuit transmission lines with asymmetric parameters.3.A fault line and phase selection method is proposed for quadruple-circuit transmission lines with asymmetric parameters.Combined with characteristics of independent sequence components and the fault boundary conditions in quadruple-circuit transmission lines with asymmetric parameters,the relationship between the sequence components is analyzed.Considering the influence of distribution coefficient at fault location on the measured sequence currents,fault type recognition method is put forward based on amplitude relationship between sequence currents.Fault line selection method and fault phase selection method are proposed based on angle relationship between the sequence currents.4.A transverse differential current protection scheme is proposed for quadruple-circuit transmission lines with asymmetric parameters.Considering the parameter asymmetry in quadruple-circuit transmission lines with asymmetric parameters,the fault sequence currents are analyzed and calculated during a fault.The transverse differential sequence currents calculation method is proposed for setting up the threshold value of the transverse differential relay.Besides,line selection unit and comparing unit are proposed to improve the sensibility and reliability the transverse differential relay.5.The capacitance current compensation methods of longitudinal differential protection are proposed for quadruple-circuit transmission lines with asymmetric parameters.Based on the characteristics of admittance matrix of quadruple-circuit transmission lines with asymmetric parameters,the decoupling relationship of distributed capacitance in the transmission lines is analyzed.According to the equivalent ? model of transmission lines,the capacitance current in the transmission lines are calculated,in order to improve the accuracy of the differential protection in quadruple-circuit transmission lines with asymmetric parameters.Finally,all the achievements are summarized,and the problems to be solved in the research and the further research directions are suggested.