News from Japan

It is well known that a high inrush current will be induced if a voltage is input to a transformer at random phase angle. Such current could lead to a reduction in power quality experienced as voltage fluctuations and would be particularly harmful to a small grid or a weakly interconnected power network. To reduce the inrush current, the voltage phase at which the transformer is energized must be controlled. Phase-controlled switching methods were originally developed in the mid-1980s and have been applied to transformers, transmission lines, reactor coils, and shunt capacitor banks.