# Model Paper DEEE III SEM ||DC Machines EE- 302||

## BOARD DIPLOMA EXAMINATIONS, (C-14)

### DEEE-THIRD SEMISTER EXAMINATIONSMODEL PAPEREE-302  D.C. MACHINESTime: 3Hours Total marks: 80

###### PART-A

NOTE: Answer all questions. 3X 10=30

Each question carries three marks.

1. Write about dynamically induced EMF?

2. Compare Lap and wave winding in different aspects?

3. Draw the separately excited D.C generator and name the parts?

4. List the effect of armature reaction in D.C machines?

5. Draw the external characteristic curve of a D.C shunt generator?

6. State the Fleming’s left hand rule?

7. Why series motor is having high starting torque?

8. State the necessity of speed control of d.c. motor

9. State the necessity of starter in d.c motor?

10. What is meant by Regenerative Test.

PART-B                                                5 X 10=50
Instructions: 1) Answer any five questions.
2) Each answer carries ten marks.

Each question carries ten marks.

1. Explain the working of simple loop D.C Generator?

2. A shunt generator delivers 195A, at terminal p.d of 250V. The armature resistance and
shunt field resistance are 0.02ohm and 50ohm respectively. The iron and friction losses
equal 950 W .

Find (i) Emf generated (ii) Copper losses (iii) o/p of prime mover (iv) Electrical efficiency?

1. Derive the formula for De-magnetising AT/Pole & Cross magnetising A T/Pole for a d.c
generator?

2. A 4pole lap wound dc generator with 450armature conductors supplies a current of
150amps. The brushes have been displaced through 3 angular degrees from the
geometrical neutral axis. Calculate (i) Demagnetising AT/pole (ii) Cross magnetising
AT/pole (iii) The additional field current for neutralising the demagnetisation is the field
winding has 1000 turns/pole?

3. (i) explain the principle operation of D.C Motor with neat sketches?

(ii) Explain the significance of back EMF in dc motors and its formula?

1. Explain the different losses & power stages in d.c motor?

2. A 200V shunt motor has armature resistance of 0.04ohm and runs at 1000 rpm, when
the armature current is 60A.If the torque is unchanged; find the speed and armature
current when the field strength is reduced by 20%?

3. Explain how break test is conducted on d.c shunt motor with a neat sketch, also write
the merits and de-merits of the test?