Research On Fault Phase Selector Of Protective Relay For Double Circuit Line Of The Same Tower Based On Six-Sequence Component Theory

As a important electric power transmission model,double circuit lines on the same tower have been increased, because it may enhance the transmission capacity of each way, reduce used ground and save cost. There are120 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.There is mutual-induction between the phases also between the lines in double circuit lines, thus the protective relay used in single circuit lines will act incorrectly.One of our aspirations is correctly analyze those problems, so the six-sequence component theory is presented,eliminating the mutual-induction is its virtuality.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.Except for segregated current differential pilot principle,the fault phase selection is a key factor whether the protective relay will act correctly or not. The research on the behavior of the sequence current elements under various cross line faults in double circuit lines is presented. The result of the research indicated that error phase may be selected by above the element under such faults conditions. Then the phasor condition between the phase currents under cross line faults in double circuit lines are analyzed. A new fault phase identification method is proposed,which is based on comparing the difference of the fault voltage judging the phasor.condition between the fault currents .The fault phase selector is integrated by three components including the negative-sequence and zero-sequnce current element and the fault voltage judging element..