The transformer is a static device (i.e. the one which does not contain any rotating or moving parts) which is used to transfer electrical energy from one ac circuit to another ac circuit, with an increase or decrease in voltage/current but with none change in frequency. This is shown in fig.1
it is important to remember that input to a transformer and output from a transformer both are alternating (AC) quantities.
The function of a transformer:
The electrical energy is generated and transmitted at extremely high voltages. The voltage is to be. then reduced to a lower value for its domestic and industrial use. This is done by using a transformer.
Thus it is possible to reduce the voltage level using a transformer (then the transformer is called a step-down transformer). On the other hand, we can also use the transformer to increase the voltage level (step-up transformer).
The power transmission system using transformers is shown in Fig.2 When the transformer changes the voltage level, it changes the current level also.
Types of Transformer:
Transformers are designed for either single-phase or three-phase Supply. Accordingly, they’re called as single-phase transformers or three-phase transformers. However, the principle of operation for both kinds is the same.
Principle of Operation:
The construction of a single-phase transformer is as shown in Fig.3. It consists of two highly inductive coils (Windings) wound on an iron or steel core. The winding (coil) connected to the ac supply is named as the primary coil whereas the opposite one is named because of the secondary coil.
The ac supply is connected to the primary winding whereas the load is connected to the secondary winding.
The primary and secondary windings are isolated from each other as well as from the iron core. Thus there’s absolutely no physical connection between the first and secondary windings. The symbolic representation of the transformer is shown in Fig.3.
The principle of operation of a transformer has been explained in Table 1.1.
Thus thanks to primary current, there’s an induced voltage within the secondary coil thanks to mutual induction. Hence the emf induced within the secondary is named because of the mutually induced emf.
Can the transformer operate on DC?
The answer is no. The transformer action doesn’t happen with an immediate current of constant magnitude. Because With a DC primary current, the flux produced in the core is not alternating but it is of constant value. As there is no change in the flux linkage with the secondary winding, the induced emf within the secondary coil is zero.
lf dc applied to the primary then there is a possibility of transformer core saturation. If core saturates the primary will draw excessively large current. Therefore the applicant of DC should be avoided.
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