A Sequential Phase Energization Technique for Transformer Inrush Current Reduction—Part I: Simulation and Experimental Results

This paper presents a new, simple and low cost method to reduce inrush currents caused by transformer energization. The method uses a grounding resistor connected at a transformer neutral point. By energizing each phase of the transformer in sequence, the neutral resistor behaves as a series-inserted resistor and thereby significantly reduces the energization inrush currents. The proposed method has been tested by computer simulation and laboratory experiments. Both results show that the method has a performance similar to that of the resistor pre-insertion scheme. The proposed method is much less expensive, however, since there is only one resistor involved and the resistor carries only a small neutral current in steady-state.