Subject Code: 131701
GUJARAT TECHNOLOGICAL UNIVERSITY
--- Content provided by FirstRanker.com ---
BE - SEMESTER-III (OLD) EXAMINATION — WINTER 2018
Date: 05/12/2018
Subject Name: Electrical Machines
Time: 10:30 AM TO 01:00 PM
Instructions:
--- Content provided by FirstRanker.com ---
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
Q.1 (a) Explain working principle of transformer in detail and also derive E.M.F. Equation of transformer. [07]
(b) Develop equivalent circuit of a 1-phase transformer. Draw the phasor diagrams for no-load and load conditions. [07]
--- Content provided by FirstRanker.com ---
Q.2 (a) Why 1-phase induction is not self-start? Explain starting methods of 1-phase induction motor. [07]
(b) Explain 3-point starter use to start DC motor. [07]
Q.3 (a) Obtain the equivalent circuit of a 200/400 —V, 50 Hz, 1 Phase Transformer from the following test data: [07]
O.C.Test: 200 V, 0.7 A, 70 W - on L.V. side
S.C. Test: 15V, 10 A, 85 W - on H.V. side.
--- Content provided by FirstRanker.com ---
Calculate the secondary voltage when delivering 5 KW at 0.8 p.f. lagging, the primary voltage being 200V.OR
Q.3 (b) What is armature reaction? What are the methods to improve armature reaction? [07]
Q.4 (a) Explain Equivalent circuit of three phase induction motor. [07]
OR
--- Content provided by FirstRanker.com ---
Q.4 (b) Draw and explain the internal -and- external characteristics of d.c. shunt generators. [07]
Q.5 (a) Explain different speed control methods for 3 phase induction motor. [07]
(b) Explain Parallel operation-of two three phase transformers with necessary conditions. [07]
Q.5 (a) A 4-pole, lap-wound, d.c. shunt generator has a useful flux per pole of 0.07 Wb. The armature winding consists of 220 turns each of 0.004 Q resistance. Calculate the terminal voltage when running at 900 r.p.m. if the armature current is 50 A. [07]
OR
--- Content provided by FirstRanker.com ---
Q.5 (b) What is voltage regulation? Explain synchronous impedance method for finding voltage regulation of alternator. [07]
Q.5 (a) What is hunting? Why damper winding use to reduce hunting? What are the applications of synchronous motor? [07]
(b) State and explain condition of synchronizing alternator with infinite bus bar. [07]
Q.5 (a) Explain the Swinburne’s test of a d.c. machine for finding losses with necessary Diagram. [07]
--- Content provided by FirstRanker.com ---
Total Marks: 70
OR
Q.5 (a) Derive the condition for Maximum torque for induction motor and explain Torque - Slip characteristics. [07]
(b) An 18.65-kW, 4-pole, 50-Hz, 3-phase induction motor has friction and windage Losses of 2.5 per cent of the output. The full-load slip is 4%. Compute for full load (a) the rotor Cu loss (b) the rotor input (c) the shaft torque (d) the gross electromagnetic torque. [07]
--- Content provided by FirstRanker.com ---
This download link is referred from the post: GTU BE/B.Tech 2018 Winter Question Papers || Gujarat Technological University