1. How Electricity enters in our houses Electricity supplied to us at our home is 220 volt and A.C.. This main line power and the wires carrying it are called the mains. The mains may often bring two different supplies 5A and 15A. The two rating are important since we use a variety of application such As Bulbs and Tubes, Heaters, Radios, TV sets, Refrigerators and so on. Some of these need 5A power while others need 15A power.

3. Transformer A transformer is a static piece of apparatus by means of which electric power in one circuit is transformed into electric power of the same frequency in another circuit. It can raise or lower the voltage in a circuit but with a corresponding decrease or increase in current. The output voltage and current depends upon the number and turns of wires used in the primary and secondary winding of the transformer.

4. According to it the voltage may be step up and step down. If the secondary winding of transformer has more turns than the primary winding it is called step up T/R. this is used whenever it is necessary to increase the voltage. In step down transformers the secondary winding has less turns than primary winding of the transformer.

6. A transformer is a device that transfers electric power from one circuit to another. It does so without a change of frequency. It accomplishes this by electromagnetic induction and where the two circuit are in mutual inductive influence of each other.

7. Working principle In it's simplest form it consist of, two inductive coils which are electrically separated but magnetically linked through a path of low reluctance. If one coil (primary) is connected to source of alternating voltage, an alternating flux is set up in the laminated core, most of which is linked with the other coil in which it produces mutually-induced e.m.f. (according to Faraday's Laws of Electromagnetic Induction. If the second coil (secondary) circuit is closed, a current flows in it and so electric energy is transferred (entirely magnetically) from the first coil to the second coil.

8. Types of transformer 1. According to construction:- a. Core type b. Shell type transformer c. Berry type transformer 2. According to the system of winding used in the transformer:- a. single phase b. Three phase c. Auto transformer

9. 3. According to system of cooling of the transformer:- a. Natural air blast cooled b. Oil immersed self cooled c. Oil immersed water cooled 4. According to use:- a. Power transformer:- i. For low tension transmission lines i.e. From 2000 to 15000 KVA. ii. For high tension transmission lines i.e. from 15000 KVA and above

10. B. Distribution transformer:- i. Small and medium type from 5 to 500 KVA ii. Large type from 500 to 2000 KVA C. Instrument Transformer:- used with measuring instrument. D. Auto transformer:- used for low voltage circuits

11. Advantages of Transformer 1.It is one of the economical devices to transmit the electrical power at high voltage and voltage can also be reduced at the desired voltage when required. 2. Its efficiency is very high in comparison to other electrical to other electrical machines. 3. since there is no rotating part in it, so it has very less noise. These can be designed for very high as there is much space to insulate the winding.

12. 5. It can be operated very easily with little attention. 6. It is very useful and cheap device for the distribution and transmission of electrical energy from place to place. 7. Its maintenance cost is less in comparison to other electrical machineries. 8. it can be taken from place to place very easily and is even used in house and in industries.