Research On Algorithm Of The Distance Protection Measured Impedance And The Online Check Of The Transmission Line With STATCOM

As the representative of the second generation of the Flexible AC transmission systems(FACTS) devices, Static synchronous compensator(STATCOM) has the outstanding performance to provide voltage support, compensate the reactive power and improve system transient stability, etc. Because of the simple principle and the advantage of less affected by the system operating mode distance protection are widely used in the main protection and backup protection of transmission line.As the transmission lines connected to the STATCOM, the compensation current will change the feature of fault phase selection method. At the same time, it changes the measured impedance traditional of distance protection, affecting the action of distance protection.The STATCOM circuit simulation model is established by the PSCAD, and a new suitable method of phase selection is put forward to solve the problem of phase selection method using the mutation of the phases current. The simulation results verify the correctness of this method. For STATCOM compensation current has an impact on distance protection measured impedance, the paper put forward an improved algorithm of measuring impedance and the simulation results show that this method can effectively eliminate the additional impedance caused by the compensating current and the transition resistance. Because the STATCOM can make protection easy to appear the phenomena of refusing action and error action, in order to achieve the orderly online check to improve the efficiency of the online checking, a comprehensive evaluation method of the protection importance is put forward. This method considers the importance topology structure, the importance of the line in terms of power transmission, and the influence of the STATCOM, and the simulation results verify the rationality and validity of the method.