Transformer Inrush Current Reduction by Power Frequency Low Voltage Signal Injection to the Tertiary Winding

When transformers are energized under no-load or lightly loaded condition, inrush currents may flow in the primary circuit. These currents are high-magnitude, harmonic-rich currents generated when transformer cores are driven into saturation. Inrush currents have an adverse effect on the security and stability of power systems. In this paper, a new simple and efficient technique for inrush current reduction is proposed. It is based on injecting a low voltage power frequency signal into the tertiary winding, thus arresting the core flux entering into deep saturation. The effectiveness of the proposed solution is established both through computer simulations and laboratory experiments. The investigations indicate that the method reduces magnetizing inrush currents significantly.