Study On Faulted Phase Selection Principle For Double-circuit Lines On The Same Pole Based On Nine-Current

As a important electric power transmission model, the double circuit lines on the same tower have been increased, because the transmission on ability is strong, it may reduce used ground and save cost. There are 120 kinds of faults occurred in double circuit lines, for the existence of the cross country faults. It is very complex when we calculate and analyze the faults occurred in double circuit lines, so it is very significant to study the character of cross country faults in double circuit lines and bring forth a fault phase selection scheme used in double circuit lines.The six phase current on the same terminal of double lines can be contacted by fibre channel, or based on information sharing condition on smart grid, and then constitute a set of virtual current using by the current of the same phase. A new fault phase identification method is proposed, which is based on comparing the difference of the nine current. The fiber channel and the smart grid only transmit electric parameters without electrical connection, so every phase can get the electric parameters of the other phases and won't be affected by their electric parameters.We can get the sequence current and sequence voltage of double circuit lines when its mathematics model was associated with the boundary condition of the faults. Then we analyzed the special problems in double circuit lines using the theory above. The results of analysis will support the fault phase selection scheme used in double circuit lines later. the fault phase selection is a key factor whether the protective relay will act correctly or not. Then the relations of the nine currents under cross line faults in double circuit lines are analyzed. A new fault phase identification method is proposed, which is based on nine current. This principle can do accurate actions when judging the fault between two same lines on double-circuit transmission line, and making the fibre channel and microprocessor protection apply jointly can identify whether some lines is in condition-based maintenance automatically. Phase segregated current differential protection based on fiber-optical must be used as the main protection, but differential protection will quit when channel is in fault, this paper studies phase selection of components of the new protection principle based on nine current can be used as back up protection of the differential protection,and it can be adopted as the main protection when the differential protection is resected.