Study On Technology Of Inrush Current Identifying And Restraining For Transformer

The power transformer is the capacity exchange hub and the key interconnectionpoint of the power system. Therefore, whether it can operate correctly and stably hasdirect influence on the power supply reliability of the whole power system. Afteryears of development, the overall performance of the power transformer’s protectionin China has made great progress. However, its correct operation rate is still relativelylow, compared with other protections. Once the power transformer goes wrong, it willnot only have serious influence on the whole power system, but also bring greateconomic losses. Fail to distinguish or restrain magnetizing inrush current correctlyand quickly is one of the most important reasons for the transformer’s misoperation inthe differential protection. As a result, going thoroughly into the protection of thepower transformer, putting forward more accurate method to discern the magnetizinginrush current and taking more efficient measures to restrain the magnetizing inrushcurrent are of great importance for improving the correct operation rate oftransformer’s protection.Based on the collection and consultation of materials at home and abroad, thispaper thoroughly analyzes the reasons why the magnetizing inrush current generatesand discusses the magnetizing inrush current’s influence on the differential protection.And then it expounds the present methods that can distinguish and restrainmagnetizing inrush current, and analyzes their merits and demerits respectively.This paper use the methods that based on parameter variation of the transformerto distinguish magnetizing inrush current and internal fault current, on the basis ofdeep analysis of the transformer’s internal structure and the circuit model. Since thelow input of the current leads to the identification model cannot be identified and theproblem of criteria for convergence among the present methods, this paper putsforward to a new algorithmic model and a criteria for convergence on the basis ofmathematical statistics. The simulation experiment demonstrates that the methodbased on parameter variation can precisely distinguish the magnetizing inrush currentand internal fault current and that the improved programme can identify the internalparameters on the condition that the transformer operates well.The greatest shortcoming of the present methods that distinguish the magnetizinginrush current is the permission of the existence of transformer’s magnetizing inrush current. The existing of magnetizing inrush current can not only have an influence onthe correct operation of the transformer, but also can, to some extent, cause electricalpollution to the electric system. Based on this fact, this paper proposes a method thatadopts the technique of selection angle and simultaneously parallels a capacitor on thelow-pressure side to restrain the magnetizing inrush current. By simulationexperiment, it has been proved that this programme can effectively restrain thetransformer’s magnetizing inrush current.