As we know that most electrical power plants are located far away from the load centers. Because the electrical energy generated by thermal and hydro or any other power plants are located at a distance from the consumers. To transmit the generated energy, we cannot directly send the same amount of energy generated to load centers, cause there exist losses in the transmission lines.
Hence to cover these losses, we have to send more than generated voltage i.e., by stepping up the voltage to the required levels and bringing it back to the same voltage levels at the consumer's end i.e., by stepping down the voltage. This stepping up and stepping down the voltage can be done using an electric machine known as a 'Transformer'.
Definition of Transformer :
A transformer is a static (stationary) ac machine, which transfers the electric power (energy) from one electric circuit to another electric circuit with the same frequency. It works on the principle of mutual induction (electromagnetic induction).
Working Principle of Transformer :
It mainly consists of two inductive coils that are electrically separated but magnetically linked through a path of low reluctance as shown in the figure. When one coil of the transformer is connected to an ac supply mains, an alternating flux is set up in the laminated core, most of this flux links with the other coil and produces mutually induced emf (according to Faraday's Laws of Electromagnetic Induction).
The primary winding is connected to the supply mains and the secondary winding is connected to the load circuit.
When the transformer raises the voltage i.e. when the output voltage of a transformer is higher than its input voltage, it is called the step-up transformer, and when it lowers the voltage i.e. when its output voltage is less than the input voltage it is called a step-down transformer.
Note :
The transformer must not be connected to a dc source. If the primary winding of a transformer is connected to a dc supply, then the flux produced will remain constant in magnitude and therefore no emf will be induced in the secondary winding. The primary winding gets short-circuited due to low resistance winding and draws a high current which may damage the winding.
