Application Research Of Inrush Current Suppression Method Of Transformer No-Load Closing Excitation

As an indispensable equipment in power system,transformer plays an important role in power transmission,and its stable operation directly affects the safety and stability of the system.Under the background of large-scale construction of uhv power grid,large-capacity transformers are put into use one after another.While meeting the requirements of energy conversion and transmission,the inrush current problem of large-capacity transformers becomes increasingly obvious,and the resulting harmonic,voltage distortion,voltage sag and other problems affect the stable operation of the system.In this context,this paper makes an in-depth study of the generation mechanism,operation characteristics and influencing factors of transformer inrush current.On this basis,it puts forward a variety of inrush current suppression methods,and analyzes the advantages and disadvantages of different methods and engineering applications.The main research work of this paper is as follows:(1)The fundamental causes of inrush current in no-load switching of transformer are analyzed,and the related factors affecting the magnitude of inrush current are pointed out.Due to the presentiment of the closing moment that the magnetic flux and core remanence do not match,the core is rapidly saturated and generates inrush current,which is mainly related to rated magnetic density of transformer,winding structure,core remanence,closing phase Angle and closing resistance of circuit breaker.(2)Analyze the harm and influence of inrush current of transformer excitation,and illustrate the case.The non-periodic component and the second harmonic of the larger excitation inrush current will cause the bus voltage of ac system to be distorted obviously.In dc dense area,ac voltage distortion will cause the inverter phase transition Angle to change constantly.If the triggering Angle is adjusted continuously,the power of dc transmission will fluctuate greatly.At the same time,the inrush current has certain influence on winding mechanical strength and transformer differential protection.(3)The inrush current of excitation is inhibited by optimizing the rated magnetic density of transformer not exceeding 1.7t,limiting the test current of dc resistance to 5A,demagnetizing the core before closing,increasing the closing resistance of circuit breaker,installing phase selective closing device and other measures;By comparing the cost,operation complexity and excitation inrush current suppression effect,the method of adding phase selective closing device to suppress excitation inrush current was determined,and the effectiveness of the method was verified by no-load closing test of transformer with phase selective closing device carried out in laboratory and 220 kV substation respectively.