Potential Transformer

• Potential transformer is the step-down transformer with voltmeter in secondary side. It is same as the power transformer but rating is small. 

• The potential transformer are employed for voltage above 400 V to feed the potential coil of indicating and metering device and relay. 

• These transformer make ordinary low voltage instrument suitable for measurement of high voltage and insulated them from high voltage. 

• The primary winding of the potential transformer is connected directly to the power circuit between two phase or between a phase and ground depending on the rating of transformer and its application. 

• In the secondary winding various indicating and metering device and relay are connected. The primary winding has large number of turns and the secondary winding which has a much smaller number of turns is  coupled magnetically through magnetic circuit to the primary winding. The ratio of primary to secondary voltage is known as Turn ratio. 

• The theory of operation of Potential transformer is essentially same as that of power transformer. The main difference between a potential transformer and power transformer is due to fact that the land current.