Study On Relay Protection For Quadruple-circuit Lines With Different Voltage Grades

With the rapid development of China's economy,the power industry as the lifeblood of the national economy,has also been rapid developed.Power network expands throughout the whole country.With the continuous development and construction of power grids,the aerial corridors of transmission lines become more and more tense.Multi-circuit transmission line on the same tower in China has been large-scale applied in the transmission and distribution network.Coupling and mutual inductance among the transmission lines brings new challenges to traditional protection.How the characteristics of protection criterion changes,are the protection scheme still applicable are problems to be solved urgently.Based on the actual application of the four-circuit lines of the double-circuit line,quadruple-circuit lines of different voltage grades,fault analysis and relay protection research status relay protection schemes of quadruple-circuit lines of different voltage grades are proposed.Considering the characteristics of negative sequence current of the quadruple-circuit lines of different voltage grades,a new transverse differential protection and line selection method based on the action signal of the transverse differential protection is proposed.Negative sequence currents of each line are calculated and analyzed,when a fault occurs,negative-component based transverse differential protection approach is proposed.The setting value of the protection and the line selection method is also proposed.A new grounding distance protection scheme is proposed for the quadruple-circuit lines of different voltage grades.Considering the influence of zero-sequence mutual inductance among the transmission lines,when cross line grounding fault occurred in quadruple-circuit lines of different voltage grades,the deviation of measured impedance could lead to malfunction or disoperation of the relay.Based on the traditional approach of the zero-sequence mutual inductance,a new zero sequence current compensation coefficient for quadruple-circuit lines of different voltage grades applied to the ground distance protection of quadruple-circuit lines of different voltage grades considering the zero sequence coupling of different voltage is proposed.When the cross line ground fault occurs,the impedance measurements will be proportional to the distance between the relay location and the fault location.Considering the shortcomings of the quadruple-circuit lines of different voltage grades grounding distance protection scheme and the weak anti-transition resistance capability,the zero-sequence reactance relay is applied to the quadruple-circuit lines of different voltage grades grounding distance protection to enhance its anti-transition resistance performance.At the same time,the direction of the fault is identified by using the negative-sequence abrupt directional element,which is not influenced by the load impedance and has strong directivity.The combination of the directional element and the zero-sequence reactance relay improves the resistance of the transition resistance while the directionality is kept.