A Method To Suppress Transformer Inrush Current And Its Controller Design

Transformer is the hub connecting the grid and the user,it is indispensable in the power system.Its operating status also affects the stable operation of the power system.When the transformer is switched on with no load,due to the randomness of the closing time,the magnetic flux of the transformer core is often saturated,and due to the non－linearity of the iron core material,magnetizing inrush current will be generated.The magnetizing inrush current of transformer will cause wrong action of differential protection of transformer,and make the transformer operate abnormally and cannot be normally closed.The large magnetizing inrush current will also damage the circuit breaker and the windings of transformer,it will cause pollution to the power grid.Therefore,it is particularly important to suppress the magnetizing inrush current of the transformer.This article reviews the related literatures,expounds the research significance of the transformer magnetizing inrush current,introduces the current research status of magnetizing inrush current at home and abroad,summarizes the existing inrush current suppression technology,and analyzes the shortcomings of these methods.Then the mechanism and damage of magnetizing inrush current are introduced.The characteristics of magnetizing inrush current of single-phase transformer and three-phase transformer are analyzed.For single-phase transformers and three-phase transformers,the simulation models of transformer no-load closing were established in MATLAB to simulate the phenomenon of magnetizing inrush current.Through the simulation results,we can further observe the characteristics of magnetizing inrush current and prepare for the next step.In this paper,the method of suppressing the magnetizing inrush current of the transformer by the improved phase control technology is studied in detail,and the suppression principle of the method is analyzed.This method controls the opening and closing angles of transformers to suppress the magnetizing inrush current of transformer no-load closing.According to this principle,the suppression of excitation inrush current of single-phase transformer and three-phase transformer is analyzed respectively,then using MATLAB simulation tools to further analyze the inhibition effect of the method for single-phase transformers and three-phase transformers.In addition,the situation of adding DC bias to the transformer when it is switched on with no load is studied,the mechanism of DC bias is elaborated,and its influence on the magnetizing inrush current when the transformer is switched on with no load is analyzed.Based on this,a strategy of controlling the circuit breaker to close at the peak point of each phase voltage to suppress the transformer magnetizing inrush current is proposed for adding DC bias conditions,and the effect of the control strategy is analyzed through simulation.Based on the principle of improved phase control technology,this paper designs a magnetizing inrush current controller using this principle.The magnetizing inrush current controller is based on DSP control.Its design is divided into hardware design and software design.The hardware circuit realizes signal acquisition and execution,including main control communication modules,signal acquisition modules,and digital input and output modules.The software program implements data memory and processing,including external interrupt subfunctions and timer interrupt subfunctions.After the design is completed,Field Test and Analysis the inhibitory effect of Magnetizing Inrush Current Controller.