The inrush current analysis and restraining method of energizing no-load transformer

If a no-load transformer is switch on or switch off, or in the period of voltage recovery when suffered from an external fault, a big excitation inrush current will appear in transformer windings, this may lead to the damage of the device, and bring impact to power grid, sometimes it will make the differential protection of the transformer misoperation. Also, is likely to have a serious impact on the power system of the voltage quality, so to study excitation inrush current of transformer is of great significance. This paper analyzes the characteristics of excitation inrush current of a transformer, and uses MATLAB to establish the inrush current simulation model. Two methods of restrain excitation inrush current are discussed, including delaying switching strategy and interpolate earth resistance strategy. Simulation and analysis show that the combination of two methods can effectively inhibit the excitation inrush current.