Basics of Generator

Basics of generator 

1. What is a Generator?

                  

 A Generator is a machine which converts Mechanical Energy into Electrical Energy.

2. On which principle a Generator works?

 Generator works on Faradays laws of “Electro Magnetic Induction ”

3. What are Faradays laws of Electro Magnetic Induction?

    1.First Law

 Whenever a conductor cuts magnetic flux an E.M.F is induced in that conductor.

                  

    2. Second Law

             The magnitude of the induced e.m.f. is equal to the rate of change of flux linkage.                 

4. What are the two main parts of an AC Generator?

1.   Stator

2.   Rotor

5. What is the main difference between an AC Generator and DC Generator?

 In an AC Generator the field is rotating and the armature is  stationary whereas in DC Generator the  field is stationary and the armature is rotating.

6. What are the advantages of stationary armature and rotating field in an AC  Generator?

1. It is easy to take output from the stationary armature.

2. It is easier to insulate stationary armature for higher voltage.

3. Low voltage excitation supply can be easily supplied to the rotor through slip rings.

7. What is the  relation between the frequency, pole and speed of a Generator?

                   F = PN/120 Hz

                   Where

                       P is the No.of Poles

                       N is the Speed in RPM.

8. In a Generator with 2 pole, and speed 3000 rpm, what is the frequency          

     of  the induced emf ?

                   F = PN/120

                      = 2 x 3000/120

                      = 50 Hz.

9. What is the connection of winding in a stator?

                   Double star connection.

10. What is the efficiency of a Generator?

                   98.55%

11. What is the coolant used to cool stator winding?

                   Demineralised water.

12. What is the coolant used to cool rotor winding?

                   Hydrogen.

13. What are the advantages of Hydrogen gas as coolant over others?

1.   Density is 1/14 of air.

2.   Windage loss is low.

3.   Low noise.

4.   Heat transfer co efficient is 1.5 times higher than air.

5.   Thermal conductivity is 7 times higher than air.

14. What are the losses in a Generator?

1.   Stator copper

2.   Stator iron

3.   Rotor copper

4.   Windage loss

5.   Stray loss

6.   Friction loss

15. What is Short Circuit Ratio (SCR) of a Generator?

      It is the ratio of the field current required to produce rated voltage

      on open circuit to the field current required to circulate rated current on

      short circuit.

16. What is the value of SCR in a 210 MW Turbo alternator?

                   SCR = 0.49