A fault phase selection scheme based on ratio of opposite-direction-current to same-direction-current for parallel lines

摘要

On common-tower double-transmission line, there are interline faults possible besides faults on single-circuit line. In order to ensure protection is with right action, the fault phase lines should be picked out correctly. Therefore, the phase selection scheme for relay protection's first section should be reliable. Moreover, for parallel lines, most phase selection algorithms using one-terminal currents are complicate or the selection results are not accurate enough. To solve these problems, a fault phase selection scheme using one-terminal currents, based on ratio of opposite-direction-current to same-direction-current, has been proposed. Research shows that the opposite-direction-current/ same-direction-current ratio values of phases with single phase line faulted are obviously bigger than those of phases with both phase lines faulted. This characteristic can be used for phase selection for double-circuit line. According to the new scheme, the double circuit lines are treated as a whole. And if fault occurs, the power-frequency fault components of the 3 one-terminal same-name phases' sum currents will be applied for discriminating the fault phases firstly. Then, using phase components of fault phases' currents and via comparing the ratio values of opposite-direction-current to same-direction-current, the fault phase lines can be identified synthetically. This proposed scheme is simple and easy to carry out with no need for long data channels. It can fit complicate working environment well and has remarkable ability for phase selection, without influence of mutual inductance between lines. Moreover, it can deal with all kind of short faults on parallel lines, especially has better performance for interline fault. It is better than other phase selection methods applied to double-circuit line, which can't deal with complex interline fault even lead to select wrong phases. ATP-EMTP simulation verified the effectiveness of the new scheme, showing that the propose- scheme can be used to reliably pick the fault phase lines out when the fault takes place 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.