Fault Phase Selection For Six-phase Transmission Lines Based On Six-sequence Transformation

As the technical support of intelligent electric grid, UHV grid has being built a good platform for it. Six-phase transmission system which occupys a narrow line corridor and has little impact of the environment can not only evidently improve power transmission density, but also easily operate with three-phase system coordinately and compatibly. It can lower phase to phase voltage, and has little to do with the breaking capacity of contacts of the high voltage breaker. Six-phase transmission system is the important developmental direction of UHV transmission technology. Therefore, it will be an ideal transmission scheme to use six-phase transmission technology in UHV grid in our country. It is an advanced theory research to analyse faults of the UHV six-phase transmission system, and to do research on fault location and fault selection as well as new protection principle based on fault feature.More transmission phases of six-phase transmission line, more complex faults are. As phase selection theory used in traditional three-phase transmission line can not use in six-phase transmission line, research on fault phase selection for six-phase transmission line is of great important theoretical and practical value.This article introduces the method which bases on six-sequence component to analysis120kinds of fault of six-phase transmission system that are divided into13types. This method can effectively eliminate mutual inductance, and get the current characteristics between six sequence components. It is probably to use the amplitude characteristic and the phase feature of current sequence components at the protection to select the fault phase. The article also introduces the method of fault phase selection which bases on correlation analysis. And this method is used to identify phase relationship between six sequence components quickly and accurately to recognize fault types and determine fault phases. Theory analysis and simulation tests confirm that the method of fault phase selection can overcome the disadvantages of the distributed capacitance and transition resistances, and it can correctly select phase at any kind of operation mode and fault condition. This method has the effective phase selection logic for six-phase transmission line.