Research On Three-Phase Adaptive Reclosing In Distribution Network Based On Harmonic Impedance Measurement Technique

At present, the traditional automatic reclosing would reclose without a detection of fault types in distribution system in China. It would make the working conditions of the breaker worse, and cause serve short-circuit current rush. Especially, with the upgrading of the distribution system, more and more cables lines are applied in distribution system in recent years. The emergence of the mixture of overhead lines and cable lines decreases the automatic reclosing success rate, which hinders the advantages of automatic reclosing. Therefore, it is significant to detect whether the fault still exists before reclosing.In this paper, a novel method is proposed to solve the three-phase adaptive reclosing problems based on harmonic impedance measurement with a consideration of the structures of distribution system. The current and voltage signals are quite weak when the breaker trips out in distribution lines. Therefore, the fault detection can be completed by injecting a signal and analyzing the response. The main idea of the method is injecting a voltage pulse signal controlled by a thyristor into the faulted lines after breakers trip out and a time delay for arc extinguishing, judging whether a fault still exists in the distribution lines by calculating the harmonic impedance of the present system. The fault detection is completed by calculating the ratio between the imaginary and real components of the harmonic impedance. Finally, based on the detection result, breakers would receive a signal of reclosing or not by communication. By controlling the firing angle, the method can change the voltage amplitude flexibly, which not only avoids causing a great current rush to distribution system, but also can find out hidden fault.In this paper, the harmonic impedance expressions under transient faults and permanent faults are given by theoretical analysis, and two theoretical criterions are proposed. By comparison, the criterion using the ratio between the imaginary and real components of the harmonic impedance is selected finally. Simulation and lab tests are important practical means of testing the validity of the theory. The criterion is verified under different firing angles and different fault resistances.Motors connected with the lines may affect the measurement results. The theoretical analysis and simulation experiment are proceed with consideration of the speed drop and residual voltage after AC dump of de-energized motors. The method proposed is proved to be effective in the distribution system containing motor load.With clear theoretical principle and clear physical concept, the proposed method provides a novel feasible way to solve adaptive reclosing problems.