Why are transformers needed in the power system?

 

1 . Electrical energy is generated at places where it is easier to get water head, oil or coal for hydroelectric, diesel or thermal power stations respectively.

2. Then energy is to be transmitted at considerable distances for use in villages, towns, and cities located at distant places.

3. As already shown transmission of electrical energy at high voltages is economical, therefore. 

4. Some means are required for stepping up the voltage at generating stations and stepping down the same at the places where it is to be used.

5. Electrical machine used for this purpose is a transformer.

6. In our country the electrical energy is usually generated at 6.6 or 11 or 33 KV, stepped up to 132, 220, 400 & 765 KV with the help of a step-up transformer for transmission and then stepped down to 66kv or 33kV at grid substations for feeding various substations, which further stepped down the voltage to 11KV for feeding distributing transformers stepping down the voltage further to 400I230 volts for the consumer uses.

7. Transformers are extensively used like, instrument transformers for metering purposes. 

8. One to One ration transformer( The transformers having equal primary and secondary voltages) are used to electrically isolate the two parts of an electrical circuit.

9. In high voltage laboratories the transformers are used to provide very high voltages for testing purposes, termed as testing transformers.

10. In electrical communication circuits transformers are employed for a variety of purposes.

11. In radio and television circuits input transformers, interstage transformers, and output transformers are widely employed.

12. Transformer is also employed in telephonic circuits, instrumentation circuits, and control circuits.

13. Indeed the transformer is a device that plays a vital and essential role in many facets of electrical engineering.

14. Transformer in AC machines that

• Does so without change of frequency 
• Does so by the principle of electro magnetic induction 

15. The Energy transfer usually takes place with a change of voltage, although this is not always necessary.

16. Since its basic construction requires no moving parts so it is often called the static transformer and it is a very rugged machine requiring the minimum amount of repair and maintenance.

17. Owing to the lack of rotating parts there are no friction or winding losses.

18. Further the other losses are relatively low.

19. So that the efficiency of a transformer is high. typical transformer efficiencies at full load lie between 96 % and 97 % and with extremely large capacity transformers the efficiencies are as high as 99 % .

20. The cost per kva output of transformers is quite low as compared with other electrical machines.

21. As there are no teeth slots or rotating parts, and the winding can be immersed in oil, it is not difficult to insulate transformers for very high voltage.

Facts: Why we do not give DC to the Electrical Transformer?

Ans: 

1. A transformer can not operate on DC supply and never be connected to a dc source.

2. If a rated DC voltage is applied to the primary of a transformer, the flux produced in the transformer core will not vary but remain constant in magnitude and, therefore, no flux will be produced in the secondary coil except at the moment of starting the supply to the primary winding.

3. Thus the transformer is not capable of raising or lowering the DC voltage.

4. Also there will be no self-induced emf in the primary winding, which is only possible with varying flux linkage, to oppose the applied voltage and since the resistance of primary winding is very less, therefore, a large current will flow into the primary winding which may cause the burning out of the primary winding coil.

5. This is the reason that  DC is never applied to a transformer.