Research On The Elimination Technology Of Transformer Inrush Current

With the rapid development of power system in China,the use of power transformers is becoming more and more extensive.When the transformer is no-load closed or put into operation again after cutting out from power grid,inrush current which is similar to the short-circuit current will occur in the primary winding.It has a tremendous impact on the protection actuating,safety of equipment and system operation.These papers carry out the research of inrush current which are based on this serious problem.Firstly,this paper introduces the basic phenomenon of inrush current happening in the windings of transformer,and explains its causes.Then this paper analyses the amplitude,dead angle,harmonics and other basic features of inrush current.Based on the structure and working principle of single-phase transformers,the author focuses on the fundamental electromagnetic relationship when no-load closing.On this basis,a mathematical model of single-phase transformer no-load switching is proposed,and the formulas of core flux and inrush current are deduced and several major factors affecting inrush current are discussed.Moreover,a simulation model of single-phase transformer no-load switching is established with Matlab/Simulink.Finally,the author analyses the strategies of selecting phase and finishes the experiments on the phase-control closing and residual-flux measurement.The main work of this paper is completed as follows:?According to the domestic and overseas advance of the current transformer inrush current newest case,the author studied on the transformer no-load closing transient flow processes and suppress a variety of programs conducted theoretical-analysis in this paper.?Using Matlab to establish a no-load closing model of single-phase transformer to analyze the two main factors that affect the amplitude of inrush current:closing angle of source voltage and residual flux of core.If the residual flux of core is known,the inrush current could be completely suppressed by controlling the closing angle of source voltage.?Focusing on the most popular strategies of selecting phase,three different selecting-phase strategies are proposed,and their principles are explained.?Based on the best tactics of phase-closing,the author proposes an improvement method and uses anti-parallel thyristor and triggering circuit to build a simple experiment device to achieve closing of any phase of single-phase transformers.Then the relationship between inrush current and voltage closing-phase tested,and relationship between residual flux and voltage opening-phase is measured.