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 w hole power-factor spectrum. Waveform sampling and the use of a micropr ocessor 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. Eco nomic viability is strongly dependent on the associated power system a nd its abnormal operating features, namely system fault currents and e specially the degree of exposure of the transformer to lightning surge s.