DR.
BABASAHEB AMBEDKAR TECHNOLOGICAL UNIVERSITY, LONERE
Regular/Supplementary Winter Examination – 2024
Course: B. Tech Branch : Electrical Engineering/Electrical and Electronics Engineering/Electrical
and Power/Electronics and Power
Subject Code & Name: BTEEC302 Electrical Machines-I Semester : III
Max Marks: 60
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Date:07/02/2025
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Duration: 3 Hr.
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Instructions to the Students:
1. Each question carries 12 marks.
2. Question No. 1 will be compulsory and include objective-type questions.
3. Candidates are required to attempt any four questions from Question No. 2 to Question No. 6.
4. The level of question/expected answer as per OBE or the Course Outcome (CO) on which the
question is based is mentioned in ( ) in front of the question.
5. Use of non-programmable scientific calculators is allowed.
6. Assume suitable data wherever necessary and mention it clearly.
(Level/CO) Marks
Q. 1 Select the correct alternative (Compulsory Question) 12
1 The constant losses in transformer is/are ---- Remember 1
a. Copper loss b. Eddy current c. hysteresis d. both b & c
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loss loss
2 In a three phase star-delta transformer what is the angle difference Remember 1
between primary and secondary phase voltage?
a. Delta side b. star side lags c. star side d. delta side
lags by -300 by -300 leads 300 leads 300
3 In dc generator if field winding attains the critical resistance____ Understand 1
a. machine will b. machine will c. field winding d. the voltage
generate generate will burn generated will
maximum maximum be zero
voltage power
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4 Inter pole winding is connected in -------- Remember 1
a. series with b. series with c. parallel with d. parallel with
armature main pole armature main pole
5 Cross magnetization effect of armature reaction affects which of the Understand 1
following?
a. b. reduction of c. reduces the d. both 2 & 3
commutation main field flux terminal
voltage
6 For starting a dc motor a starter is required to --- Remember 1
Page 1
a. limits the b. starts the c. limits the d. none of the
starting current motor speed of the above
motor
7 In a 6 pole dc machine, wave winding is used. The number of parallel Apply 1
paths are -----
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a.6 b. 4 c. 2 d. 1
8 Maximum power will be developed when back emf is equal to -- Remember 1
a. supply b. half of the c. double the d. all of the
voltage supply voltage supply voltage above
9 If the field connection of a dc shunt motor is changed then ---- Understand 1
a. it will run in b. motor will c. it will run in d. it will run in
the same not run opposite same direction
direction by direction
slowly
10 Transformer core is laminated to reduce ------- Remember 1
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a. eddy current b. hysteresis c. both A & B d. none of
loss loss above
11 Scott connections are used for ---- Apply 1
a. Single phase b. Three phase c. three phase d. any of above
to three phase to single to two phases
connection phases
connection
12 If a hybrid stepper motor has a rotor pitch of 360 and a step angle of Evaluate 1
90 the number of its phases must be ---
a.4 b. 2 c. 3 d. 6
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Q. 2 Solve the following. 12
A) Justify “Transformer is a constant flux device.” Remember 6
B) A 40 KVA transformer has iron loss of 450 Watt and full load copper Evaluate 6
loss of 850 watt. If the power factor of the load is 0.8 lagging, Find:-
i) Full load efficiency
ii) The load at which maximum efficiency occurs
iii) The maximum efficiency
Q.3 Solve the following. 12
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A) Explain the construction of three phase core type transformer. Understand 6
B) A 3-phase delta – star step down transformer delivers power to a Evaluate 6
balanced 3-phase load of 120 KVA at 0.8 power factor. The input line
voltage is 11kV and the transformation ratio of the transformer is
0.10. Determine the line voltages, line currents, phase voltages and
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phase currents on both sides of a transformer.
Q. 4 Solve Any Two of the following. 12
A) Derive the emf equation of Generator. How it will be implemented to Apply 6
lap and wave connected armature winding?
B) A DC generator has an armature emf of 100 Volts when the useful Evaluate 6
flux per pole is 20 mWb and speed is 800 rpm. Calculate the
generated emf.
i) With the same flux and a speed of 1000 rpm. &
ii) With the flux per pole 24 mWb and speed of 900rpm
C) Explain armature reaction? What are its effects? Understand 6
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Q.5 Solve Any Two of the following. 12
A) Derive the relation between armature current and armature torque Understand 6
for dc motor. Hence obtain this equation for dc series and shunt
motor.
B) A 250 volt dc shunt motor on no load runs at 1000 rpm and takes 5 Evaluate 6
amp. from supply. Its armature and shunt field resistances are 0.2Ω
and 250 Ω respectively. Calculate the speed when loaded taking a
current of 50 amp. The armature reaction weakens the field by 3%.
C) Illustrate the principle of DC motor. What is the significance of back Apply 6
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emf?
Q. 6 Solve Any Two of the following. 12
A) Explain the construction and working principle of BLDC motor with its Understand 6
applications.
B) Write a short note on Stepper Motor. Understand 6
C) Explain the different types of magnetic system Understand 6
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