Anna
University
B.E./B.Tech.
DEGREE EXAMINATION
NOVEMBER/DECEMBER
2016.
Sixth
Semester
Electrical
and Electronics Engineering
EE 2355
— DESIGN OF ELECTRICAL MACHINES
(Regulation
2008)
Time : Three hours
Maximum : 100 marks
Answer ALL questions.
PART A — (10 ×
2 = 20 marks)
1. What are the major considerations
in Electrical Machine Design?
2. Write down the classification of
magnetic materials.
3. Show how the specific magnetic and
electric loadings are interdependent.
4. Mention any two guiding factors
for the choice of number of poles.
5. Define the term: 'Voltage
Regulation'.
6. What are the methods by which
heat dissipation occurs in a transformer?
7. Write down the equation for
output coefficient in an Induction Motor.
8. Define : Stator Slot Pitch.
9. What are the factors that
influence the choice of specific magnetic loading in a synchronous machine?
10. Define Short Circuit Ratio of a
synchronous machine.
PART B — (5 ×
16 = 80 marks)
11. (a) What are the main groups of
Electrical conducting materials?
Describe the properties and
applications of those materials. (16)
Or
(b) Describe any two methods used for
determination of motor rating for variable load drives with suitable diagrams.
(16)
12. (a) Explain the various steps
involved in the design of Armature winding of D.C. machine. (16)
Or
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(b)
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A design is required for a 50 kW,
4 pole, 600 rpm, d.c. shunt generator, the full load terminal voltage being
220 V. If the maximum gap density is 0.83 Wb/m2 and the armature ampere
conductors per meter are 30,000, calculate suitable dimensions of armature
core to give a square pole face.
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Assume that the full load armature
voltage drop is 3 percent of the rated terminal voltage and that the field
current is 1 percent of rated full load current. Ratio of pole arc to pole
pitch is 0.67. (16)
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13.
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(a)
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Discuss about temperature rise and
methods of cooling in transformers.
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Or
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(b)
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A 6600 V, 60 Hz single phase
transformer has a core of sheet steel. The net iron cross-sectional area is
22.6 × 10–3 m2, the mean length
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is 2.23 m, and there are four lap joints.
Each lap joints takes ¼ times as much reactive mmf as is required per meter
of core. If Bm = 1.1 Wb/m2, determine
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(i) The number of turns on the
6600 V winding and
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(ii) The no load current. Assume an
amplitude factor of 1.52 and that for given flux density, mmf per meter = 232
A/m; specific loss = 1.76 W/kg. Specific gravity of plates = 7.5. (16)
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14.
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(a)
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Describe the steps involved in the
design of magnetizing current for an induction motor from design data.
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(16)
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Or
(b) Estimate the stator core
dimensions and the total number of stator conductors for a 3 Φ , 100 kW, 3300 V,
50 Hz, 12 pole star connected slip ring Induction motor. Assume : average gap
density = 0.4 Wb/m2, conductors per metre = 25,000 A/m, efficiency = 0.9, power
factor = 0.9 and winding factor =0.96.
Choose main dimension to give best
power factor. (16)
15. (a) Explain the step by step
procedure for the design of field winding of Synchronous machine. (16)
Or
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(b)
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A 1000 KVA, 3300 V, 50 Hz, 300
rpm, 3-phase alternator has 180 slots with 5 conductors per slot. Single
layer winding with full pitch
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coils is used. The winding is star
connected with one circuit per phase. Determine the specific electric and
specific magnetic loading's, if the stator bore is 2.0 m and the core length
is 0.4 m. The machine
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has 60° phase spread.
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(16)
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