Malfunction Mechanism Analysis due to Nonlinearity of Transformer Core

The differential protection is prone to mal-operate under certain conditions, that is, in the presence of the magnetizing inrush and the CT(current transformer) transient saturation. To interpret the phenomenon reasonably, mathematic models for studying the transient course are proposed considering nonlinearity of transformer core. Based on these models, the characteristics of the differential currents during the above conditions are analysed. A variety of simulation tests are carried out to validate the proposed models.