As per IEC 60076 Part-1, Booster Transformer is defined as a Transformer of which one winding is intended to be connected in series with a circuit in order to alter its voltage and/or shift its phase. The other winding is an energising winding.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.Booster transformers are single-phase transformers with the ratio 1:1. They have low impedance values, but despite that, they must tolerate the stresses of short-circuit currents. Primary voltages are typically 15 kV or 25 kV, which are the usual nominal AC voltages of catenary feeders in railways around the whole world. The nominal current is usually between 200A and 800 A. Frequencies in electric railways are 50 Hz, and the power ratings of booster transformers are 100-800 kVA.