Fault Simulation And Phase Selection Study For Double-Circuit Transmission Lines On The Same Tower

Multi-Circuit transmission lines on the same tower,including the same voltage level or different voltage levels,have lots of advantages such as large transmission capacity and saving land resources for transmission.Because of that,they are now widely used in modern power system.Double-circuit transmission lines,for example,they also bring the complexity and diversity of the line fault,such as more than 120 kinds of total fault,and crossing-line types of fault which reach near 100.According to the requirement of line protection,it is necessary to select the fault phase quickly and accurately to remove the fault.Because the mathematical model of double-circuit lines on the same tower is very complex,it is difficult to calculate the fault voltage and current with the general circuit equations.Based on the six-sequence components mathematical model and the boundary conditions under various fault conditions,the analytical formula of the six-sequence voltage and the six-sequence current of the double-circuit lines on the same tower are derived.The amplitude relation and the phase relation of each sequence electric quantity under the fault condition of the double-circuit lines on the same tower are analyzed by the analytical formula of the voltage and current of each sequence.At the same time,because of the complexity of the variation characteristics of the electrical quantity and the difficulty of theoretical analysis of the same pole and frame line fault,the fault model of the double-circuit lines on the same pole are simulated by the ATP-EMTP program and the typical faults are been simulated as well.The simulation results show that ATP-EMTP can accurately simulate all kinds of faults of double-circuit lines on the same tower,and provide a good analysis method for solving the fault protection of double circuit-lines on the same tower.On the basis of this,the phase selection strategy based on the six-sequence components method is summarized,and a new scheme for fault phase selection is proposed.The method combines the advantages of six-sequence components selection,zero-sequence and negative-sequence phase selection and low voltage phase selection.Based on the comprehensive analysis of the fault state of double-circuit lines on the same tower,the fault phase can be selected accurately by using different characteristic criteria under different fault conditions.The advanced nature of the new scheme is verified by the example of 220 k V double-circuit transmission lines on the same tower in Qingyuan Power Grid area.