Subject Code: 160804
GUJARAT TECHNOLOGICAL UNIVERSITY
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BE SEMESTER-VI (OLD) EXAMINATION - WINTER 2017
Subject Name: Electrical Machine Design
Time: 02:30 pm to 5:00 pm
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) Deduce an expression for the M.M.F required for the air gap of an armature with slots and ducts. [07]
(b) What are the factors that limit the design of an electrical machine? [07]
Q.2 (a) Show that for minimum total material cost of a 3-phase transformer the ratio (Weight of iron/Weight of copper) should be equal to the ratio (specific cost of Copper (Rs. /kg) / specific cost of iron ((Rs. /kg)). [07]
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(b) State the advantages of hydrogen cooling in alternators. Explain radial and axial ventilation with the help of sketches. [07]
OR
(b) Deduce an expression for the design of core for Square and cruciform sections also state the reason why circular coils are always preferred in comparison to rectangular coils. [07]
Q.3 (a) What are the types of windings commonly used in transformer and on what basis are they selected? [07]
(b) Explain: [07]
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- Significance of cruciform core in transformer.
- Design difference between power & distribution transformer.
OR
Q.3 (a) Explain various factors affecting selection of Numbers of armature slots for D.C. machine. [07]
(b) Explain how eddy current loss occurs and derive an expression for eddy current loss in a magnetic material. [07]
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Q.4 (a) Define specific magnetic loading (Bav) and specific electric loading (ac) and obtain an expression for the “output co-efficient for a d.c. machine. [07]
(b) Explain the design procedure in the design of field windings for a D.C. shunt machine. [07]
OR
Q.4 (a) Explain the Real and Apparent flux densities. [07]
(b) Explain radial and axial ventilation with the help of sketches. Give the advantages of hydrogen cooling in alternators. [07]
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Q.5 (a) Discuss the factors that determine the choice of air-gap in induction motor. [07]
(b) List and explain briefly the limitations being imposed in the design of electrical machines also discuss the modern trends in the design. [07]
OR
Q.5 (a) What are the types of windings commonly used in transformer and on what basis are they selected? [07]
(b) Derive the condition for the optimum design of transformer for the minimum cost and minimum losses. [07]
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Date: 13-11-2017
Total Marks: 70
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