{A transformer is a device used in the power transmission of electric energy. The transmission current is AC. It is commonly used to increase or decrease the supply voltage without a change in the frequency of AC between circuits. The transformer works on the basic principles of electromagnetic induction and mutual induction.
The transformer, in a simple way, can be described as a device that steps up or steps down voltage. In a step-up transformer, the output voltage is increased, and in a step-down transformer, the output voltage is decreased. The step-up transformer will decrease the output current, and the step-down transformer will increase the output current to keep the input and output power of the system equal.
The transformer works on the principle of Faraday’s law of electromagnetic induction and mutual induction.
There are usually two coils – primary coil and secondary coil – on the transformer core. The core laminations are joined in the form of strips. The two coils have high mutual inductance. When an alternating current passes through the primary coil, it creates a varying magnetic flux. As per Faraday’s law of electromagnetic induction, this change in magnetic flux induces an EMF (electromotive force) in the secondary coil, which is linked to the core having a primary coil. This is mutual induction.
Overall, a transformer carries out the following operations:
1. Transfer of electrical energy from one circuit to another
2. Transfer of electrical power through electromagnetic induction
3. Electric power transfer without any change in frequency
4. Two circuits are linked with mutual induction
The transformer is basically a voltage control device that is used widely in the distribution and transmission of alternating current power.
The general purpose of using transformers was to maintain a balance between the electricity that was generated at very high voltages and consumption which was done at very low voltages.}
 

A village with demand of 800kW electric power at 220V is located 30km from an electric plant generating power at 440V. The resistance of each wire of the two wire line carrying power is $0.25\Omega /km$ . The village gets power from the line through a 4000V-220V step down transformer at a substation in the village. Assume negligible power loss in the transformers.