Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2019 Summer 3rd Sem New 2130904 Dc Machines And Transformer Previous Question Paper
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?III (NEW) EXAMINATION ? SUMMER 2019
Subject Code: 2130904 Date: 18/06/2019
Subject Name: DC Machines and Transformer
Time: 02:30 PM TO 05:00 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) What are different parts of a DC machine? Explain the use of
commutator.
03
(b) Explain construction and working principle of auto-transformer. 04
(c) Define armature reaction. Explain armature reaction effect in DC
machine. How it can be minimized?
07
Q.2 (a) Mention the conditions for satisfactory parallel operation of three
phase transformers.
03
(b) Explain the internal and external characteristics of D.C. Shunt
Generator.
04
(c) The armature of a 230?volt shunt motor has a resistance of
0.18 ohm. If the armature current is not to exceed 76 amp,
calculate: (a) the resistance that must be inserted in series
with the armature at the instant of starting; (b) the value to
which this resistance can be reduced when the armature
accelerates until Ec is 168 volts; (c) the armature current at
the instant of starting if no resistance is inserted in the
armature circuit. (Assume a 2-volt drop at the brushes.).
07
OR
(c) Explain voltage build up process of D.C. Generator. Also derive
E.M.F. equation of D.C. Generator.
07
Q.3 (a) Why transformer rating is in KVA? 03
(b) Write a short note on current transformer and its applications. 04
(c) Terminal voltage of a long-shunt compound generator is 230 V when
it delivers 150 A. Determine
(i)Induced emf (ii) total power generated by armature.
Consider: Shunt field resistance = 92 ?, Series field = 0.015 ?,
Series field diverter resistance = 0.03 ? and armature resistance =
0.032 ?.
07
OR
Q.3 (a) Explain Scott connection of 3-phase transformer. 03
(b) Explain: compensating winding and interpoles in dc machine. 04
(c) Discuss essential and desirable conditions to be satisfied for parallel
operation of two single phase transformers.
07
Q.4 (a) Draw and differentiate between long shunt & short shunt compound
generator.
03
(b) Explain the load characteristics of DC shunt generator. 04
(c) What is the necessity of starter in DC motor? Explain three point
starter with neat sketch.
07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?III (NEW) EXAMINATION ? SUMMER 2019
Subject Code: 2130904 Date: 18/06/2019
Subject Name: DC Machines and Transformer
Time: 02:30 PM TO 05:00 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) What are different parts of a DC machine? Explain the use of
commutator.
03
(b) Explain construction and working principle of auto-transformer. 04
(c) Define armature reaction. Explain armature reaction effect in DC
machine. How it can be minimized?
07
Q.2 (a) Mention the conditions for satisfactory parallel operation of three
phase transformers.
03
(b) Explain the internal and external characteristics of D.C. Shunt
Generator.
04
(c) The armature of a 230?volt shunt motor has a resistance of
0.18 ohm. If the armature current is not to exceed 76 amp,
calculate: (a) the resistance that must be inserted in series
with the armature at the instant of starting; (b) the value to
which this resistance can be reduced when the armature
accelerates until Ec is 168 volts; (c) the armature current at
the instant of starting if no resistance is inserted in the
armature circuit. (Assume a 2-volt drop at the brushes.).
07
OR
(c) Explain voltage build up process of D.C. Generator. Also derive
E.M.F. equation of D.C. Generator.
07
Q.3 (a) Why transformer rating is in KVA? 03
(b) Write a short note on current transformer and its applications. 04
(c) Terminal voltage of a long-shunt compound generator is 230 V when
it delivers 150 A. Determine
(i)Induced emf (ii) total power generated by armature.
Consider: Shunt field resistance = 92 ?, Series field = 0.015 ?,
Series field diverter resistance = 0.03 ? and armature resistance =
0.032 ?.
07
OR
Q.3 (a) Explain Scott connection of 3-phase transformer. 03
(b) Explain: compensating winding and interpoles in dc machine. 04
(c) Discuss essential and desirable conditions to be satisfied for parallel
operation of two single phase transformers.
07
Q.4 (a) Draw and differentiate between long shunt & short shunt compound
generator.
03
(b) Explain the load characteristics of DC shunt generator. 04
(c) What is the necessity of starter in DC motor? Explain three point
starter with neat sketch.
07
2
OR
Q.4 (a) Explain ?All day efficiency? of the transformer. 03
(b) Explain critical field resistance of d.c. shunt generator with its
significance
04
(c) A 20 kVA, 2200/220 V, 50 Hz, 1- phase transformer gave the
following readings.
O.C test : 220 V, 4.2 A, 148 Watt (L.V. side open)
S.C test : 86 V, 10.5 A, 360 Watt (H.V. side shorted)
Determine: (i) Regulation at full load and 0.8 lagging p.f.
(ii) Power factor on Short circuit.
07
Q.5 (a) A 6600/400 V single phase transformer has primary resistance of 2.5
? and secondary resistance of 0.01 ? Calculate total equivalent
resistance referred to primary and secondary.
03
(b) Draw a no load phasor diagram of a 1- phase transformer and
explain.
04
(c) Explain the direct load test for determination of voltage regulation
and efficiency of transformer with necessary diagram.
07
OR
Q.5 (a) Write a note on ? grounding transformer. 03
(b) Draw connection diagram and vector diagram for following
connections of 3-Phase transformer.
(i) Dd6
(ii) Dy1
04
(c) Explain on load tap changing of transformer. 07
.
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This post was last modified on 20 February 2020