GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-III (Old) EXAMINATION - WINTER 2019
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Subject Code: 131701 Date: 03/12/2019
Subject Name: Electrical Machines
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) Derive an equation for induced EMF of transformer and explain significance of transformation ratio (07)
(b) Explain open-circuit and short circuit test on single phase transformer. (07)
Q.2 (a) Explain condition for parallel operation of two three-phase transformers. (07)
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(b) Explain three-phase to two phase conversion using transformer. (07)
OR
(b) Explain V-V connection of three phase transformer. (07)
Q.3 (a) Explain torque-speed characteristics of three phase induction motor. (07)
(b) Derive an equation for starting torque and running torque of three phase induction motor (07)
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OR
Q.3 (a) Write different starter used for three phase induction motor and explain any one. (07)
(b) Explain chording factor and distribution factor for alternator. (07)
Q.4 (a) Draw vector diagram of loaded alternator with different power factor. (07)
(b) Explain power stages and losses of three phase induction motor. (07)
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OR
Q.4 (a) On what bases DC generators are classified? Classify and explain DC generators. (07)
(b) Write short note on Armature Reaction in DC generators. (07)
Q.5 (a) Explain different characteristics of Dc shunt generator. (07)
(b) Explain different methods of starting single phase induction motor. (07)
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OR
Q.5 (a) Explain ward-Leonard method of speed control of DC shunt motor (07)
(b) Write short note on autotransformer. (07)
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