Electrical Transformer is a static device that transfers electric power from one circuit to another without change of frequency. Since there is no rotating part in a transformer so it is a static device. Transformer operates on ac supply. In transformer operation two electrical circuits are not connected to each other rather they are interlinked by a common magnetic circuit
Principle
Transformer works on the principle of mutual inductance between two or more inductively coupled coils. Here one of the windings is called primary which is energized by an alternating voltage source and secondary winding is connected to the load. If a voltage source is applied to a primary winding coil it produces alternating current in it. This produces an alternating magnetic flux in the core of the transformer. Alternating magnetic flux links with primary and secondary coil turns and induces in them an emf by self induction and mutual induction respectively. The emf induced in secondary drives a current through the load connected across the secondary winding.
Transformation ratio (K) : It is defined as the ratio of no. of turns in the secondary winding to the no. of turns in the primary winding.
Es/Ep =Ns/No
Ip/Is=Es/Ep=Ns/Np=K
Where, Es=Secondary Voltage ,Ep=Primary Voltage,Ns=Secondary no.of turns,Np=Primary no.of turns
Types Of Transformers
Step up & Step Down Transformer : These types of transformers are used for step up and step down of voltage levels during transmission of power from the generator. In step up transformer low voltage winding (l.v) is primary and in step down transformer high voltage (h.v) winding is primary.
Single Phase & Three Phase Transformer :
Single phase transformer consists only of a single winding in primary which induces flux in the core and is linked to the secondary winding. Hence in single phase only two Windings are present one is input and other is output which delivers power. Single phase transformers are small in size compared to > 3 phase transformers.
In three phase transformers there will be three Windings in the primary and three Windings in the secondary. The connection of primary and secondary is based on the vector group.
Current (C.T ) & Potential Transformer (P.T) :
Electrical instrument transformers (CT & PT) transform high currents and voltages to standardized low and easily measurable values. CT is used for measurement of electric current. The C.T is described by its current ratio from primary to secondary. CT transforms high value current to lower value. PT or voltage transformer is used to step down the system voltage to low value which can be fed to relay for protection purpose.
Autotransformer
In an auto transformer, one single winding is used as primary winding as well as secondary winding. But in two windings transformer two different windings are used for primary and secondary purpose
Distribution & Power Transformer :
Distribution transformers are used in distribution networks to step down the transmission voltage level for demand centres. Power transformer are operated at peak loads .It is used at each end of transmission line in generating stations and substations for stepping up or down the voltage level