Research On Fault Line Selection For Non-Direct Earth Neutral System Based On Two-Phase-Current Transform

When a single phase-to-earth fault occurs in non-direct earth neutral system, it is necessary to give an alarming and select the fault line quickly. But, wrong signals are usually made as selecting the fault line in the system.During the past decade many principles and methods have been put forward to solve this problem. Almost all of them are based on comparisons of zero sequence current fundamental wave or harmonic transient component among all the lines. According to the previous experts'studies, zero-sequence current of fault line exclude currents of fault line itself. It is a vital defect to those methods.A novel method of identifying fault line for single phase-to-earth fault in non-direct earth neutral system based on two-phase-current transform (TPCT) is presented. TPCT is one algorithm that the currents of phase-a, -b and–c of each line add their leading current of phase-b, -c and–a that is turned 60 degree clockwise, respectively. The criterion of faulted-line identification is that the three-phase currents by TPCT of healthy line are equal while the three-phase currents by TPCT of faulted line are different, which has been proved sufficiently from theory. Computer simulation show that the method of the proposed fault-line identification is not affected by fault resistance and load flow and can identify fault line correctly when a single phase occurs in non-direct earth neutral system.