A static device which is used to transform the electric power from one circuit to the other without a direct electrical connection or without changing the frequency but in different levels of voltage, is the transformer. The basis of voltage transfer Faraday’s Law of electromagnetic induction. When current in the first/primary coil changes, the flux (flow of energy through a medium) associated with the second/secondary coil also changes. Due to this changing energy, force is generated (electromotive force) in the secondary coil.
The two important concepts in the working of a transformer are that an electric current produces a magnetic field and second- that a changing magnetic field inside the coil is capable of producing voltage across a coil. Thus, the current in the primary coil produces a magnetic field, which in turn induces voltage across the secondary coil due their close proximity.
The amount of voltage produced in the second coil depends on the number of turns it possesses. If it has a greater number of turns, the voltage produced would be greater and the transformer will be termed “step-up” transformer. Similarly, a lesser number of turns would result in generation of a lesser amount of voltage and the system called “step-down” receptor. Due to this property of adjusting the voltage produced according to the number of turns, shape of the coils, etc, the transformer is a versatile system having a wide range of applications.
Another reason as to why this system is popular around the world, is that various aspects related to its working can be easily tested using simple devices that consume low power. One example of this is the transformer turns ratio test. It is used to correctly measure tap changer performance, shorted turns, open winding, incorrect winding connections, etc, by measuring ratio of the primary to the secondary turns. Another simple method of testing the proper working of the transformer is the BDV test, or Break-down voltage. Used to test the efficiency of insulation oils in a transformer, BDV test is a common procedure in regular check-ups of the machine. It is also called the Dielectric Strength Value. During the working of the transformer, oils become progressively dirty and loose its property of insulation and cooling, which can damage the system. Periodic testing of the oil, thus becomes essential.
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