Research On Fault Line Selection And Relay Protection Of Multi-circuit Transmission Lines On The Same Tower

The unique transmission method of multi-circuit transmission lines on the same tower can effectively save the land area and reduce the construction costs.It has effectively alleviated the contradiction between the shortage of transmission capacity and the continuous increase of national electricity,which has led to more and more The attention of scholars.However,the complicated line-to-phase and phase-to-phase electromagnetic coupling in a multi-circuit transmission line system on the same tower brings new problems to fault diagnosis and various setting thresholds.This article mainly discusses the decoupling method,line identification,compensation calculation,and pilot protection scheme when the parameters are asymmetric on multiple circuits on the same tower.The main contents include:Based on the traditional six-order component method,a new phase-mode transformation matrix is analyzed and deduced to decouple the loop impedance.Based on the relationship between the decoupled independent moduli,a new parameter K is defined.According to the parameter K,the values of the different circuits are different when the circuit fails,and then a new fault line selection criterion is proposed.Through further mathematical analysis and experimental verification,the decoupling process and fault line discrimination are still applicable to double-circuit lines on the same tower that are generally electrically asymmetric.The decoupling ideas and fault line identification between double-circuit transmission lines on the same tower can be further extended to four-circuit transmission lines on the same tower.Corresponding parameters need to be introduced into the decoupling calculation for the four-circuit line that is generally not completely symmetrical in electrical.According to the inverse matrix of the comprehensive transformation matrix,it can be deduced that the asymmetry parameter has nothing to do with the fault line selection criterion,that is,four-circuit Regardless of whether the lines are electrically symmetrical,the faulty line discrimination method can reliably select the corresponding line.In addition,the feasibility of this decoupling idea was tested by calculating the fault short-circuit current.This paper introduces in detail the effects of the capacitance between the ground and the phase on the operating characteristics of the differential relay during the large-area UHV transmission of a single circuit,and combines two differentdecouplings of the same tower dual circuit in the frequency and time domain The idea is to draw a ?-type circuit with corresponding sequence components and modulus,and derive the calculation idea of compensation based on the independent sequence components and modulus based on the equivalent circuit diagram.Starting with the traditional relay protection,the 12-order component method of the joint expansion proposes a longitudinal differential protection scheme suitable for the four-circuit line on the same tower that is more suitable for the actual project.It can be seen from the extended 12-order component method that after decoupling the line parameters,mutually independent co-vector and loop flow can be obtained.According to the characteristic that the circulating current component only exists in the transmission line system,the differential protection calculation based on the circulating flow network is derived.