Research On Controlled Switching Technology Of Non-load Transformer

In the process of power generation,transmission and distribution,intelligent substation and other intelligent systems have developed rapidly,which put forward more stringent requirements for the intellectualization of electrical equipment.In the conversion process of different voltage levels,power transformer plays a very important role as the main substation equipment.The inrush current of power transformer is a kind of electromagnetic transient phenomenon,which is essentially the process of electromagnetic relationship changing from transient to steady state.The controlled switching technology is an effective way to suppress the inrush current of non-load transformer,and it is also an important embodiment of equipment intellectualization.With the help of transformer magnetization curve and formula deduction,this paper expounds the generating principle of inrush current,establishes the statistical simulation model of three-phase non-load transformer in ATP-EMTP simulation software,and carries out statistical simulation analysis on the influence of the dispersion of closing time of circuit breaker,residual flux of transformer core and pre-breakdown characteristics of circuit breaker on inrush current.This paper expounds the suppression measures of inrush current,deduces and analyses the mechanism of inrush current suppression by circuit breaker closing resistance method through mathematical formula,determines the selection of closing resistance value and working time by simulation,simulates different controlled strategies,puts forward the controlled closing method with installing circuit breaker closing resistance,and compares the inrush current suppression effects of various measures.This paper analyses and simulates affecting factors of residual flux,such as opening time,the transient process after opening and the voltage sharing capacitor of circuit breaker.On the basis of studying the influencing factors of residual flux,a method of residual flux measurement based on least square method is proposed.This method is an improvement of voltage integration method,which is most commonly used in engineering.The accuracy of residual flux measurement is improved by accurately obtaining the upper limit of voltage integration.In order to improve the interactivity of residual flux measurement,an interactive platform for residual flux measurement is designed in MATLAB,and the accuracy of the proposed method is verified by simulation.In this paper,the hardware system of controller uses FPGA as the core,and uses Verilog HDL language to complete software programming.The program is simulated synthetically,and the correctness of the logic and sequence of program is verified.The trigger test of the controller is carried out,and the trigger reliability of the controller is verified.The test platform of non-load transformer is built.First,the closing and opening test of circuit breaker is carried out,and the inherent closing and opening time and mechanical dispersion are tested.Then,the closing test of non-load transformer is carried out.The inrush current waveform of closing is collected by oscilloscope,and the inrush current of random closing and controlled closing considering residual flux is compared.The test results show that the inrush current can be effectively suppressed when using the method of controlled closing.