A Fault Phase Selection Scheme of Currents With Assistant Voltages for Common-tower Double-circuit Transmission Lines Using One-terminal Electrical Quantities

For common-tower double-transmission lines,the algorithms of phase selection schemes based on currents for back-up relay protection’s first section are complicated or the selection results are not accurate enough.Furthermore,the saturation of current transformers(CTs) caused by near-terminal faults may result in inaccurate phase selection or missing some fault phases.To solve these problems,a fault phase selection scheme based on currents,in which the voltages are assistant electrical quantities,was proposed for common-tower double-transmission line using one-terminal electrical quantities.At the beginning stage of faults,the power-frequency fault components of 3 one-terminal voltages and the 3 one-terminal same-name-phases’ sum-currents were applied respectively for selecting the fault phases and the results were integrated to discriminate the fault phases.This way can avoid the negative effects of CT saturation when the fault is at lines’ near terminal and the disadvantages of phase selection only using voltages when the fault is at the middle of the lines or far terminal.Then,by comparing the fault component values and phases of same-name-phase currents,the fault phase-lines can be identified.And if CT saturation occurs,the steady state fault currents will be used for selecting the fault phase-line.The proposed scheme is simple,reliable,and can deal with all kinds of short circuit faults on same-tower double circuit lines.The result of ATP-EMTP simulation shows that the proposed scheme can reliably select fault phase-lines when the fault occurs at the near side of parallel lines with a length range of 80%,which means it can serve for the relay protection’s first section.