A novel double-side average equivalent instantaneous inductance in nonsaturation zone based transformer protection

Against the harassment of magnetizing inrush on the differential protection of transformer, in this study by analyzing the variation of the equivalent instantaneous inductance (EII), a novel principle of transformer protection is proposed based on the double-side average equivalent instantaneous inductance in the nonsaturation zone (AEII-in-NZ). During the internal fault occurring, both of the average equivalent instantaneous inductances in the nonsaturation zone (AEIIs-in-NZ) at the primary and secondary winding of the fault phase are very small. However, for the normal running, magnetizing inrush and external fault occurring, at least one side of the AEII-in-NZ keeps a high value. The operating situation of transformer can be correctly diagnosed by calculating and comparing the double sides of AEII-in-NZ. Lots of experimental results verify that the novel transformer protection can get rid of the effect of inrush current, remove the transformer in short time while the internal fault occurring and displays a good immunity to the saturation of current transformer caused by the external fault.