Analysis of Inrush Current of Transformer on EMTDC

Using EMTDC software,we establish the simulation models including source,transformer and current-transformer and simulate the inrush current and its second wave transferred from the current-tansformer when transformer is switched on under no load at different phase angles of source in order to analyze whether or not the differential protection will act incorrectly,caused by the inrush current and the inner fault.By analyzing the results of simulation,the second harmonic value and dead angle of inrush current are obtained under different switched-on phase angles.We find the characteristics of inrush current unchanged when the inrush current flows across the current-transformer,so we do not think the protection will act inrcorrectly.Furthermore,the inrush current will not make the differential protevtion act incorrectly under any switched-on phase angle even if transformer has surplus magnetism.The blocking conditions of differential protection can be re-adjusted by using the simulation results.