Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2019 Summer 6th Sem New 2160912 Design Of Dc Machines And Transformer Previous Question Paper
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI(NEW) ? EXAMINATION ? SUMMER 2019
Subject Code:2160912 Date:10/05/2019
Subject Name:Design of DC Machines and Transformer
Time:10:30 AM TO 01:30 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) Describe importance of mitered joints in transformer. 03
(b) Discuss the factors affecting the selection of specific magnetic loading in
transformer.
04
(c) For a transformer show that e.m.f. per turn Et = k?Q where Q = kVA
rating. Explain how service condition of transformer affect the value of K.
07
Q.2 (a) What is window space factor? On wat factors does it depend? 03
(b) Show the complete magnetic path in a sketch of 4 pole d.c. machine. 04
(c) How will the output and losses in a transformer vary with the linear
dimensions?
07
OR
(c) Design a 250KVA, 2000/400 Volt, 50 HZ, 1 phase, core type oil immersed
self cooled power transformer with following data:
Induced emf per turn = 15 Volt
Max flux density Bm= 1.2 wb/m
2
Current density= 2.75 A/mm
2
Window space factor = 0.3
Height of the window Hw/ width of window Ww = 3
Assume 3 stepped core and Ai=0.6d
2
, a= 0.9d
Determine the main dimensions of the core and yoke
07
Q.3 (a) Why circular coils are always preferred over rectangular coils for winding a
transformer?
03
(b) Define specific magnetic loading and specific electrical loading in d.c.
machine.
04
(c) Give the important guidelines in selecting no. of poles in d.c. machine
design.
07
OR
Q.3 (a) State the relation between Wight of copper and iron for minimum volume
of transformer.
03
(b) Explain the differences between Power and Distribution transformer. 04
(c) Give reasons for following:
1)Why are tapping provided on HV winding ?
2) Why cores of transformers are stepped?
07
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Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI(NEW) ? EXAMINATION ? SUMMER 2019
Subject Code:2160912 Date:10/05/2019
Subject Name:Design of DC Machines and Transformer
Time:10:30 AM TO 01:30 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) Describe importance of mitered joints in transformer. 03
(b) Discuss the factors affecting the selection of specific magnetic loading in
transformer.
04
(c) For a transformer show that e.m.f. per turn Et = k?Q where Q = kVA
rating. Explain how service condition of transformer affect the value of K.
07
Q.2 (a) What is window space factor? On wat factors does it depend? 03
(b) Show the complete magnetic path in a sketch of 4 pole d.c. machine. 04
(c) How will the output and losses in a transformer vary with the linear
dimensions?
07
OR
(c) Design a 250KVA, 2000/400 Volt, 50 HZ, 1 phase, core type oil immersed
self cooled power transformer with following data:
Induced emf per turn = 15 Volt
Max flux density Bm= 1.2 wb/m
2
Current density= 2.75 A/mm
2
Window space factor = 0.3
Height of the window Hw/ width of window Ww = 3
Assume 3 stepped core and Ai=0.6d
2
, a= 0.9d
Determine the main dimensions of the core and yoke
07
Q.3 (a) Why circular coils are always preferred over rectangular coils for winding a
transformer?
03
(b) Define specific magnetic loading and specific electrical loading in d.c.
machine.
04
(c) Give the important guidelines in selecting no. of poles in d.c. machine
design.
07
OR
Q.3 (a) State the relation between Wight of copper and iron for minimum volume
of transformer.
03
(b) Explain the differences between Power and Distribution transformer. 04
(c) Give reasons for following:
1)Why are tapping provided on HV winding ?
2) Why cores of transformers are stepped?
07
2
Q.4 (a) Describe any one method to improve commutation in d.c. machine. 03
(b) Explain different methods of cooling of transformer 04
(c) What are the types of windings commonly used in transformer and on what
basis they are selected?
07
OR
Q.4 (a) Explain design of brushes in d.c. machine 03
(b) Explain No load current calculations for 3 phase transformers. 04
(c) A 600 kVA , 6600 / 400 V , 50 hz delta-star 3 ph. Core type transformer has
the following data: width of h.v. and l.v. winding are 3 cm for both .; Height
of H.V.winding and L.V. winding = 40 cm. ; Length of mean turn =1.5 m
; h.v. winding turns =220 ; width of duct between hv and lv winding = 2 cm.
Calculate the leakage reactance of the transformer referred h.v. side.
07
Q.5 (a) The length of air gap is not uniform under the entire pole face, why it is done
in d.c. machine?
03
(b) Explain the factors affecting for the choice of armature diameter and
armature core length in d.c. machine.
04
(c) Find the suitable no of poles and the diameter of the core of a 400 KW 550
volt , 180 RPM, d.c. generator having 92% efficiency. Assume an average
flux density in the air gap of about 0.6 wb/m
2
and ampere conductor per
meter to be 35000 and ratio of pole arc/pole pitch =0.7.
07
OR
Q.5 (a) Discuss how the size of the core of a d.c. machine depends upon its(i) rating
(ii) speed
03
(b) Write note on selection of number of armature slots in D.C.machine. 04
(c) Find main dimensions of a 5 kW , 250 V , 4 pole, 1500 rpm D.C. shunt
generator if the required data is : full load efficiency = 87%, pole arc/pole
pitch = 0.66 ; avg. flux density = 0.42 Wb/m
2
.; Ampere conductors / m
=15000. Machine is designed with pole arc to pole pitch ratio equal to 0.66.
07
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This post was last modified on 20 February 2020