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# Janardan Rai Nagar Rajasthan Vidyapeeth 2006 B.Tech Computer Science and Engineering ELECTRICAL MACHINE - Question Paper

Tuesday, 14 May 2013 08:40Web

JRN Rajasthan Vidyapeeth University

COMPUTER ENGINEERING

SEMESTER 4

ELECTRICAL MACHINE

DR

Model Question Paper

#### Time : 3 hrs Maximum marks : 75

Instruction:

1. Question paper is divided into Group A, Group B and Group C

2. Each Group is 25 Marks

3. Figure to the right in bracket indicates marks.

4. Good Handwriting is expected

5. Assume suitable data if necessary.

Group A (25 Marks)

 (5)

Answer any three questions (Question 1 is compulsory)

 (10)

Q.1 Obtain the expression for emf of a transformer?

Q.2 Derive an EMF equation of alternator ?

 (10)

 (10)

Q.3 Comparison between Synchronous Motor and Induction Motor ?

Q.4 Define coil span factor and distribution factor in an alternator. Derive the emf

equation of an alternator ?

 (10)

Q.5 State and explain thevenins theorem with the circuit diagram?

Group B (25 Marks)

Answer any three questions (Questions 6 is compulsory)

 (5)

Q.6 A 40 KVA transformer has an iron loss of 450 w and a full load copper loss of

850 W. If the power factor of the load is 0.8. Calculate full load efficiency and

maximum efficiency.

 (10)

Q.7 A 250 V DC shunt motor has armature resistance of 0.25 Ω. On load it

takes an armature current of 50 A and runs at 750 RPM. If the flux of the motor is

reduced by 10% without changing the load torque, find the new speed of the motor

 (10)

Q.8 Write short notes on auto transformer. Draw the diagram for the 2 types of auto

 (10)

Q.9 Find the current through terminal MN in the circuit. Use Thevenins theorem (10)

Q.10. A three phase, 16 poles, star connected alternator has 192 stator slots with 8

conductors per slot and conductors of each phase are connected in series. The coil

span is 150 electrical. Determine the phase and line voltages of the machine when

is runs at 375 RPM and flux per pole is 0.064 Wb distribution sinusoid ally over the pole

Group C (25 Marks)

All Questions are Compulsory.

Q.11 Fill in the blanks ( each question carry 2 marks)

1.   The equivalent capacitance of identical capacitor in series is ______________ and in parallel is _______________.

2.   The main thing common between Hopkinsons test and fields test is that both need _____________________.

3.   Compared to the secondary of a loaded step up transformer, the primary has ____________ voltage and ____________ current.

4.   A 50 HZ alternator will run at the greatest possible speed if it is wounded for _______________ poles.

5.   While running, a synchronous motor is compelled to run at synchronous speed because of ______________________.

Q.11 Multiple choice question. (Each question carry 2 marks)

1. Armature reaction is an alternator primarily affects

a. Rotor speed

b. Terminal Voltage per phase

c. Frequency of armature current

d. Generated voltage per phase.

2. In a synchronous motor, damper winding is provided in order to

a. Stabilize rotor motion

b. Suppress rotor oscillations

c. Develop necessary starting torque

d. Both b and c

3. The primary and secondary induced emf s E1 and E2 in a two winding transformer are always

a. Equal in magnitude

b. Antiphase with each other

c. In phase with each other

d. Determined by load on the transformer secondary

4. The basic requirement of a DC armature winding is that it must be

a. A closed one

b. A lap winding

c. A Wake winding

d. Either b and c

5. What is the condition for the current flow in a circuit?

a. More number of electrons and protons

b. Potential difference should occur

c. Greater mechanical strength

d. More number of protons

Q.11 True or false (each question carry 1 marks).

1.   Basic unit of energy is watt hour.

2.   For an ideal transformer the voltage source supplied is equal to the secondary electromotive force.

3.   Smaller sized DC machine have permanent magnet poles.

4.   DC excitation is required in induction motor.

5.   The direction of emf in an alternator is found by Flemings left hand rule.

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