Solid-state on-load transformer tap changer

Switching logic is defined for a single-phase transformer tap changer using thyristor switching. A laboratory model validates the theory and shows that tap changing is possible in less than one cycle over the whole power-factor spectrum. Waveform sampling and the use of a microprocessor based control system provides improved control and additional features such as data logging etc. Two schemes are considered for the application of thyristor tap changing to three-phase transformers. Economic viability is strongly dependent on the associated power system and its abnormal operating features, namely system fault currents and especially the degree of exposure of the transformer to lightning surges.