Research On The Method For Supressing The Inrush Current Of Unloaded Transformer Based On The Phase-Controlled Switching Technology

Circuit breaker is an important kind of electric equipment in the power system. The intelligent control of the circuit breaker plays a significant role when improving the stability, reliability and safety of the power system. The theoretical analysis, simulation and experiment of the unloaded three-phase transformer, which has three-limb iron core and Y connection on the primary side with ungrounded neutral point, are conducted. The results of simulation and experiment show that the phase-controlled switching strategies can reduce the inrush current dramatically when the unloaded transformer is switched on.Firstly, the structure and working principle of transformer are introduced, and the reason of the inrush current when the unloaded transformer is switched on is presented. Besides, the phase-controlled switching technology is introduced and the state of the art is reviewed in detail. The current control technology for switching the capacitor bank, reactor bank, unloaded transformer and unloaded power transmission line are researched.Secondly, the theoretical analysis of unloaded transformer has two aspects:the phase-controlled switching strategy without considering the residual flux and the phase-controlled switching strategy with considering the residual flux. The simulation model is established in the alternative transient program/the electromagnetic transients program (ATP/EMTP), and MATLAB is used to processing the data of simulation.Finally, the experiment of the phase-controlled switching strategy for unloaded transformer is carried out based on the test platform. The experiment results show that the two control strategies can reduce the inrush current effectively. Comparatively speaking, the method without considering the residual flux is simple but the control effect is limited; the method with considering the residual flux is more complicated but the control effect is better.