Investigation of various affecting factors and reduction technique of transformer magnetizing inrush current

Abstract

Power transformer is one of the most vital and costlier equipment in power system. When the transformer is energized from a standard power source it draws a very high transient current which is called the inrush current. This transient current causes mechanical stress to the transformer, causes protection system mal-function, affects the power system quality and disrupts the operation of sensitive electrical loads like computers, medical equipment etc. so in the present study inrush current is analyzed completely. The study is mainly divided into three parts. In the first part the inrush current phenomena and the type of inrush current in single phase, three phase and multi-transformer operation is explained. In the second part, various factors affecting the inrush current like transformer rating, winding resistance, voltage energization angle, residual flux are analyzed. In the third part, the controlled switching method is analyzed and optimal switching angle is found out by taking both the residual flux and voltage energization angle into account for the reduction of inrush current (25 MVA D-Y three phase transformer is analyzed here). All the simulation works are done in the Matlab Sim-Power system.