Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 3rd Sem Old 131701 Electrical Machines Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?III (OLD) EXAMINATION ? WINTER 2018
Subject Code:131701 Date:05/12/2018
Subject Name:Electrical Machines
Time:10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. 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
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
OR
(b) Obtain the equivalent circuit of a 200/400 ?V, 50 Hz, 1 Phase Transformer from
the following test data,
O.C.Test: 200 V, 0.7 A, 70 W - on L.V. side
S.C. Test: 15 V, 10 A, 85 W - on H.V. side.
Calculate the secondary voltage when delivering 5 KW at 0.8 p.f. lagging, the
primary voltage being 200V.
07
Q.3 (a) What is armature reaction? What are the methods to improve armature reaction? 07
(b) Explain Equivalent circuit of three phase induction motor.
07
OR
Q.3 (a) Draw and explain the internal and external characteristics of d.c. shunt
generators.
07
(b) Explain different speed control methods for 3 phase induction motor. 07
Q.4 (a) Explain Parallel operation of two three phase transformers with necessary
conditions.
07
(b) 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 ? resistance. Calculate
the terminal voltage when running at 900 r.p.m. if the armature current is 50 A.
07
OR
Q.4 (a) What is voltage regulation? Explain synchronous impedance method for finding
voltage regulation of alternator.
07
(b) What is hunting? Why damper winding use to reduce hunting? What are the
applications of synchronous motor?
07
Q.5 (a) State and explain condition of synchronizing alternator with infinite bus bar. 07
(b) Explain the Swinburne?s test of a d.c. machine for finding losses with necessary
Diagram.
07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?III (OLD) EXAMINATION ? WINTER 2018
Subject Code:131701 Date:05/12/2018
Subject Name:Electrical Machines
Time:10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. 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
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
OR
(b) Obtain the equivalent circuit of a 200/400 ?V, 50 Hz, 1 Phase Transformer from
the following test data,
O.C.Test: 200 V, 0.7 A, 70 W - on L.V. side
S.C. Test: 15 V, 10 A, 85 W - on H.V. side.
Calculate the secondary voltage when delivering 5 KW at 0.8 p.f. lagging, the
primary voltage being 200V.
07
Q.3 (a) What is armature reaction? What are the methods to improve armature reaction? 07
(b) Explain Equivalent circuit of three phase induction motor.
07
OR
Q.3 (a) Draw and explain the internal and external characteristics of d.c. shunt
generators.
07
(b) Explain different speed control methods for 3 phase induction motor. 07
Q.4 (a) Explain Parallel operation of two three phase transformers with necessary
conditions.
07
(b) 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 ? resistance. Calculate
the terminal voltage when running at 900 r.p.m. if the armature current is 50 A.
07
OR
Q.4 (a) What is voltage regulation? Explain synchronous impedance method for finding
voltage regulation of alternator.
07
(b) What is hunting? Why damper winding use to reduce hunting? What are the
applications of synchronous motor?
07
Q.5 (a) State and explain condition of synchronizing alternator with infinite bus bar. 07
(b) Explain the Swinburne?s test of a d.c. machine for finding losses with necessary
Diagram.
07
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2
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
*************
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This post was last modified on 20 February 2020