Operating principle of a transformer

A piece of equipment that is used to regulate the amount of voltage supplied from any source of power is called a transformer. It is used to either lower or raise the amount of voltage supplied depending on the amount of power required in alternating current. A transformer is mostly referred to as an electric power transformer because it is majorly used in regulating alternating currents.  It has three important parts that makes it achieve its intended function: magnetic core which a medium for transfer of flux; primary winding produces magnetic upon connection to electric source; and secondary which produces the desired voltage output.

Electromagnetic induction that was developed by Michael Faraday is the theory behind operation of a transformer. The primary and secondary winding o a magnetic core experience mutual conduction when alternating current is passed through them. The law suggests that the flux linkage in an electrical circuit is directly proportional to the electromotive force induced by the coil.

In the case of a transformer, power is supplied through the primary winding in form of alternating current.  As the current moves, it creates a magnetic flux that experienced a continuous change which is ready to transfer to a nearby winding. Since there is a seconding winding on the magnetic core, this alternating flux will transfer to it to create a new current flow. The second winding experience a change in flux as the alternating flux continues to experience a change in both its direction and amplitude. However for this process to take place continuously there are factors that have to be provided. First of all, there must be a constant flow of alternating current through the both primary and secondary windings. Next, the circuit of the second winding must be closed. Finally, the frequency of the current should not change in both primary and the secondary windings. When these conditions are met then electric power transformer is created in the process. It is important to note that the amount of voltage produced by the second winding is solely dependent on the number of turns in both primary and secondary windings.

This operating principle leads to creation of two types of transformers; a step-up transformer and a step-down transformer. A step up transformer raises the voltage of alternating current while a step-down transformer lowers the voltage of alternating current. A step-up transformer is produced when the number of turns in the secondary windings is more than that of the primary windings causing increase amount of electromotive force, hence increased voltage. Step-down transformer is produced when the number of turns in the primary windings exceeds that of the secondary windings causing reduced electromotive forces, hence reduced voltage produced.

The primary windings and the secondary windings should not be electrically connected during operation but the currents should be allowed to transfer through the magnetic flux. This operation principle allows for current loses in the transformer in both the magnetic core and the copper windings. However the losses are negligible and do not affect the efficiency of a given electric power transformer.








Hayano, S., Nakajima, Y., Saotome, H. and Saito, Y., 1991. A new type high frequency transformer. Magnetics, IEEE Transactions on, 27(6), pp.5205-5207.


Theraja, B.L., Theraja, A.K., Patel, U.A., Uppal, S.L., Panchal, J.C., Oza, B., Thakar, V., Patel, M.R. and Patel, R.M., 2005. A Textbook of Electrical Technology Vol II. Chand & Co., New Delhi.