Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 3rd Sem New 2130904 Dc Machines And Transformer Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?III (New) EXAMINATION ? WINTER 2018
Subject Code:2130904 Date:12/12/2018
Subject Name:DC Machines and Transformer
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
MARKS
Q.1 (a) Define pitch factor, coil span and distribution factor. 03
(b) Derive the condition for maximum efficiency of single phase
transformer.
04
(c) Explain O.C. and S.C test of single phase transformer. 07
Q.2 (a) Give classification of dc generators with neat connection diagram. 03
(b) Explain any four part of dc machine. 04
(c) Draw and explain internal and external characteristics of dc series
generator.
07
OR
(c) Draw and explain performance characteristics of dc shunt motor. 07
Q.3 (a) Describe function of compensating winding. 03
(b) Define armature reaction. Explain cross magnetizing and
demagnetizing effects of armature reaction in brief.
04
(c) A long shunt compound generator delivers a load current of 50A at
500V and has armature, series field and shut field resistances of
0.05?, 0.03 ? and 250 ? respectively. Calculate the generated
voltage and the armature current. Allow 1 V per brush for contact
drop
07
OR
Q.3 (a) State advantages and disadvantages of Swinburne?s test. 03
(b) Explain field control method for controlling speed of dc shunt motor. 04
(c) The Hopkinson?s test on two shunt machines gave the following
results for full load:
Line voltage: 250V, Current taken from supply excluding field
currents: 50A, Motor armature current: 380A, field currents: 5A and
4.2A.Calculate the efficiency of the machine working as a generator.
Armature resistance of each machine is 0.2 ?
07
Q.4 (a) Justify following statements:
i. Transformer core is laminated.
ii. CT secondary should never be kept open.
iii. Transformer rating is in KVA.
03
(b) Explain polarity test of single phase transformer. 04
(c) A 25KVAtransformerhas 500 turns on the primary and 50 turns on
secondary winding. The primary is connected to 3000V, 50Hz
Supply. Find the full load primary and secondary currents. The
secondary emf and the maximum flux in the core Neglect leakage
drops and no load primary currents.
07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?III (New) EXAMINATION ? WINTER 2018
Subject Code:2130904 Date:12/12/2018
Subject Name:DC Machines and Transformer
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
MARKS
Q.1 (a) Define pitch factor, coil span and distribution factor. 03
(b) Derive the condition for maximum efficiency of single phase
transformer.
04
(c) Explain O.C. and S.C test of single phase transformer. 07
Q.2 (a) Give classification of dc generators with neat connection diagram. 03
(b) Explain any four part of dc machine. 04
(c) Draw and explain internal and external characteristics of dc series
generator.
07
OR
(c) Draw and explain performance characteristics of dc shunt motor. 07
Q.3 (a) Describe function of compensating winding. 03
(b) Define armature reaction. Explain cross magnetizing and
demagnetizing effects of armature reaction in brief.
04
(c) A long shunt compound generator delivers a load current of 50A at
500V and has armature, series field and shut field resistances of
0.05?, 0.03 ? and 250 ? respectively. Calculate the generated
voltage and the armature current. Allow 1 V per brush for contact
drop
07
OR
Q.3 (a) State advantages and disadvantages of Swinburne?s test. 03
(b) Explain field control method for controlling speed of dc shunt motor. 04
(c) The Hopkinson?s test on two shunt machines gave the following
results for full load:
Line voltage: 250V, Current taken from supply excluding field
currents: 50A, Motor armature current: 380A, field currents: 5A and
4.2A.Calculate the efficiency of the machine working as a generator.
Armature resistance of each machine is 0.2 ?
07
Q.4 (a) Justify following statements:
i. Transformer core is laminated.
ii. CT secondary should never be kept open.
iii. Transformer rating is in KVA.
03
(b) Explain polarity test of single phase transformer. 04
(c) A 25KVAtransformerhas 500 turns on the primary and 50 turns on
secondary winding. The primary is connected to 3000V, 50Hz
Supply. Find the full load primary and secondary currents. The
secondary emf and the maximum flux in the core Neglect leakage
drops and no load primary currents.
07
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2
OR
Q.4 (a) Differentiate between core type and shell type transformer. 03
(b) State cooling methods of cooling transformer. Explain any one
method in brief.
04
(c) A 230/230V,3KVA transformer gave the following results:
O.C.Test:230V,2amp,100W
S.C Test:15V,13amp,120W
Determine the regulation and efficiency at full load 0.8 p.f.lagging.
07
Q.5 (a) Define following Terms:
All day efficiency, Regulation and pole pitch
03
(b) Write a short note on Auto transformer. 04
(c) State the necessity of starter .Explain 4 point starter with neat sketch. 07
OR
Q.5 (a) Draw connection diagrams and winding diagrams for Dd0, Yd1, and
Dy11.
03
(b) Write a short note on Off load tap changer. 04
(c) Explain V-V connection of 3 phase transformer. 07
*************
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This post was last modified on 20 February 2020