Effects of DC magnetic bias on differential protection of transformer

DC magnetic bias will result in saturation of iron and lead to half-cycle distortion of exciting currents. Then large quantity of harmonics will be produced. It may affect correct operation of relay protection. To study the impact on differential protection of transformer, this paper uses PSCAD/EMTDC to create a specific simulation model. In the presence of DC magnetic bias, taking single-phase transformer as an example, the paper simulates differential protection operation when the transformer is switched to the zero-loaded state, as well as the case of internal fault. And the simulation results are analyzed.