## Tuesday, March 7, 2017

### Engineering Machine Questions

1. With the help of sketches, describe the main construction and working principle of a dc
generator.

2. Explain what do you understand by (i) lap and wave windings (ii) duplex windings

3. Explain why a commutator and brush arrangement is necessary for the operation of a dc
machine.

4. What are the similarities and dissimilarities between lap and wave windings in a dc machine?

5. A 6-pole, lap wound armature has 840 conductors and flux per pole of 0.018 Wb. The
generator is run at 1200 rpm. Calculate the emf generated.

6. Calculate the emf generated by a 4-pole wave wound armature with 45 slots, with 18
conductors per slot when driven at 1000 rpm. The flux per pole is 0.02 Wb.

7. A 4-pole dc generator has 51 slots and each slot contains 20 conductors. The machine has a
useful flux of 0.007 Wb and runs at 1500 rpm. Find the induced emf, if the machine is (i) lap
connected (ii) wave connected.

8. A 4-pole, d.c. generator has a wave-wound armature with 792 conductors. The flux per pole
is 0.0121 Wb. Determine the speed at which it should be run to generate 240 V on no-load.

9. Calculate the flux in a 4-pole dynamo with 722 armature conductors generating 500 V when
running at 1000 rpm when the armature is (i) lap connected (ii) wave connected.

10. An 8-pole d.c. shunt generator with 778 wave-connected armature conductors and running at
500 rpm supplies a load of 12.5 Ω resistance at terminal voltage of 50 V. The armature
resistance is 0.24 Ω and the field resitance is 250 Ω. Find the armature current, the induced
emf and the flux per pole.

11. An 8-pole lap wound dc generator rotated at 350 rpm is required to generate 0.26 kV. The
useful flux per pole is 5 mWb. If the armature has 120 slots, calculate the numbers of
conductors per slot.

12. A short shunt compound generator supplies a current of 110A at 220V. The resistance of
shunt field is 50Ω and the series winding resistance and armature resistance are 0.025Ω and
0.05Ω respectively. Calculate the generated emf?

13. A long shunt compound generator delivers a load current of 50A at 500V and has armature,
series field and shunt field resistances of 0.05Ω, 0.03Ω and 250Ω respectively. Calculate the
generated voltage and the armature current allowing 1V per brush for contact drop.

14. A short shunt compound generator delivers a load current of 30A at 220V and has armature,
series field and shunt field resistances of 0.05Ω, 0.3Ω and 200Ω respectively. Calculate the
induced emf and the armature current allowing the brush drop as 1V per brush.

15. A 6 pole lap wound dc generator has 600 conductors on its armature. The flux per pole is
0.02Wb. Calculate speed at which the generator must run to generate 300V and what would
be the speed if the generator is wave wound?

16. Calculate the generated emf by a 4-pole wave wound generator having 65 slots with 12
conductors per slots when driven at 1200 r.p.m. the flux per pole is 0.02Wb. Calculate emf
generated if the generator is lap wound.

17. A 100kW, 240 V shunt generator has a field resistance of 55Ω and armature resistance of
0.067Ω. Find the full load generated voltage.

18. A 4 pole long shunt lap wound generator supplies 25kW at a terminal voltage of 500V. The
armature and series field resistances are 0.03Ω and 0.04 Ω respectively and shunt field
resistance is 200Ω. Calculate the generated emf considering the brush contact drop as 1V.
Also calculate the number of conductors if the speed is 1200 rpm and flux per pole is
0.02Wb.

### Earthing

Types of Earthing 1). Plate Earthing: 2). Pipe Earthing: 3). Rod Earthing 4). Earthing through the Waterman 5). Strip or Wire Earthing ... 