Characteristic Analysis Of A Locomotive Transformer With Split Types Of Windings By A Field-Circuit Combined Method

The general structure of the split-type transformer is that the high-voltage winding is composed of several branches in parallel,and the low-voltage winding is split into several parts of equal rated capacity,which are coupled tightly with the branches of the high-voltage winding respectively.There is no electrical connection but a weak magnetic connection between the split low-voltage windings and they can operate individually or simultaneously.Owing to the large short-circuit impedance and slight impact on the state of windings with weak magnetic coupling,the split-type transformer has the characteristics of limiting the short-circuit current and improving the reliability of power supply.And it has been widely used in power system,especially for locomotive transformer.Firstly,a three-dimension magnetic field analysis model of four-split transformer is established based on ANSYS software.And on the basis of magnetic field analysis,the inductance matrix between multiple windings with magnetic coupling is calculated.And then,the circuit equations are written to calculate the characteristics of the transformer.This article takes a four-split locomotive transformer produced by China Railway Group as an example to analyze several operating characteristics.They can be listed as followings:the current among high-voltage branches and the voltage upon low-voltage side without load or four low-voltage windings with rated load during normal operation;the current distribution of the high-voltage branches and the short-circuit impedance at the input with single low-voltage winding running;the relevant characteristics of a single low-voltage winding under the inter-turn short circuit condition.To Analyze the characteristics of inter-turn short circuit,the fault winding should be divided into two windings,and there are totally nine windings among the high and low voltage side.According to the analysis of normal operation,solving related features should based on the analysis and magnetic field calculation of the 9 winding inductance matrix and the circuit equation.The analysis of the inter-turn short circuit faults takes into account the number and position of short-circuits between the turns(upper,middle and lower parts of the windings)to investigate the effects of different turns and locations to the results.From the comparison of the unload current and the rated voltage of low-voltage side with the manufacturer's design value,the result of the agreement shows the correctness of the method.Finally,the article also established a simulation model based on MATLAB/Simulink platform to replace the circuit equation solution,and simulation analysis is performed on the above operating conditions.This article analyzes the characteristics of the multi-split locomotive transformer by using the "field-road" method,and the normal operation and fault conditions are examined especially at the same time.The verification and analysis are performed under the simulation model of the MATLAB/Simulink platform,and obviously,it is a relatively new and comprehensive attempt about transformer analysis methods.