# THEORETICAL QUESTIONS

D.C. GENERATOR

1. 1.   What is a basic type of D.C. machine?
2. 2.   Explain the principle on which a generator works.
3. 3.   Explain the construction and working of an elementary generator.
4. 4.   Describe briefly various parts of a D,C. machine.
5. 5.   Why is a commutator and brush arrangement necessary for operation of a D.C. machine?
6. 6.   Name the main parts of a D.C. machine and state the materials of which each part is made.
7. 7.   Enumerate all the parts of a D.C. machine and indicate their functions.
8. 8.   Give the materials and functions of the following parts of a D.C. machine:

(i)                                    Field poles

(ii)                                 Yoke

(iii)                               Commutator

(iv)                               Commutating poles

(v)                                  Armature.

1. 9.   Give the constructional features and working principle of a D.C. generator. Draw a cross-sectional view of a 4 pole D.C. generator and label there on all parts. Also sketch the shapes of:

(i)                                    Commutator segment with riser, and

(ii)                                 Armature stamping.

1. 10.                Give the advantages and uses of lap and wave windings.
2. 11.                Explain the following terms as applied to a D.C. armature winding.

(i)                                    Front pitch

(ii)                                 Back pitch

(iii)                               Pole pitch

(iv)                               Commutator pitch.

1. 12.                Draw up the winding table for a 4 pole, wave connected armature having 30 coil sides and give a developed diagram of the winding showing the polarity and position of the brushes, the main poles and the direction of motion of the armature for a D.C. motor.
2. 13.                Draw the developed winding diagram of lap winding for 6 poles, 18 slots with two coil sides/slot, double layer showing therein position of poles, direction of motion, direction of generated e.m.f and position of brushes.
3. 14.                Derive the e.m.f. equation of a D.C. generator.
4. 15.                Deduce an expression for the voltage induced in a D.C. generator.
5. 16.                Write a short note on equiliser rings.
6. 17.                How are ratings of electrical machines expressed?
7. 18.                Draw the magnetic circuit of a 4 pole D.C. machine.
8. 19.                Explain different methods of excitation of D.C. generators with suitable diagrams.
9. 20.                How are D.C. generators classified?
10. 21.                What is the difference between a separately excited and a self-excited generator?
11. 22.                Sketch the following types of D.C. generators:

(i)                                    Shunt

(ii)                                 Series

(iii)                               Compound.

State with reason(s) where each is used?

1. 23.                What is the difference between the short-shunt and long shunt compound generators?
2. 24.                With the help of a neat diagram show power division in a D.C. generator.
3. 25.                Answer the following questions briefly:

(i)                                    State the principle on which generators operate.

(ii)                                 Name the materials of which the following parts of a D.C. machine are made and why?

1. Frame
2. Armature
3. Bushes.

(iii)                               Why are field coils provided in a D.C. generator?

(iv)                               What is the function of an armature in a D.C. generator?

(v)                                  Of what material are the laminations of an armature made up of?

(vi)                               What is the function of a commutator?

(vii)                             What purpose is served by brushes in a D.C. machine?