Travelling Wave Fault Location for Three-Terminal Transmission Line Based on Static Wavelet Transform

In view of the defect in existing travelling wave fault location algorithm that this algorithm is easily affected by wave velocity,a new method for travelling wave fault location of three-terminal transmission line is proposed.Using Clarke's transform the phase currents are turned into independent mode currents,then static wavelet transform(SWT) is applied to mode currents to determine the moments at which travelling wave surges arrive the bus terminals.Firstly the memberships are defined by three initial moments at which the first wave front arrives T-connected buses,and based on the memberships the criterion for distinguishing faulty branch is given.To implement fault location of three-terminal transmission line,based on existing fault location formula for two-terminal transmission line the fault location formula for three-terminal transmission line is derived.Three possible fault conditions near the T-connected node are researched,and a three-time fault location method is put forward to resolve the fault location for the faults occurred near the T-connected node.Comparing with existing fault location methods,due to time-invariance of SWT,making full use of the data measured at three terminals of the three-terminal transmission line and that the wave velocity does not appear in the derived fault location formula,the proposed method can provide more accurate fault location results.Results of simulation using ATP/EMTP show that the proposed fault location method for three-terminal transmission line is simple,reliable and not affected by such factors as transition resistance and fault types and so on.