Regulating Transformers

Booster transformer is one which is often used towards the end of a power line to raise the voltage to the desired value. It is used for controlling the voltage of a feeder at a point far away from the main transformer. The secondary of the booster transformer is connected in series with the line, and its primary is supplied from the secondary of the regulating transformer. The output winding of the regulating transformer is so connected to the primary of the booster transformer that the voltage injected in the line VB is in phase with the supply VS.