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Reg. No___________ Name:_________________________

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY FIRST SEMESTER B.TECH DEGREE EXAMINATION, JANUARY 2017

EE100: BASICS OF ELECTRICAL ENGINEERING

Max. Marks: 100 Duration: 3 Hours

PART A Answer all questions, each question carries 4 marks

1. State and explain Kirchhoff’s laws.

2. Three resistors R1= 30 �, R2 = 60 �, and R3 =10 � are connected in star. Obtain the

equivalent delta circuit. 3. Explain Faraday’s laws of electromagnetic induction and Lenz’s laws.

4. A10 � resistor and 300 mH inductor are connected in series to a 230V sinusoidal supply. The circuit current is 4A. Calculate the supply frequency and phase angle between current and voltage.

5. Deduce the relationship between line and phase voltage in a star connected system. 6. Draw and explain a typical electrical power transmission scheme. 7. Explain the working principle of a DC motor. 8. What are the losses occurring in a transformer. Explain 9. Explain the working principle of a 3 phase induction motor. 10. Why a single phase induction motor is not self-starting. Explain.

PART B MODULE (1-4)

Answer any four questions, each question carries 10 marks

11. Calculate the current in each branch of the following circuit using mesh analysis. (10)

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12. Asteel ring of circular cross section of 1 cm in radius and having a mean circumference of 94.3 cm has an airgap of 1 mm long. It is uniformly wound with an exciting coil consisting of 600 turns and excited with a current of 2.5 A. Neglecting magnetic leakage calculate (i) m.m.f. (ii) Reluctance (iii) Magnetic flux (iv) Flux density (v) Relative permeability of steel. Assume that steel part takes about 40% of total ATs. (10)

13. a) Define peak factor and form factor of an alternating quantity. (4) b) Derive the rms and average value of a sinusoidal waveform. (6)

14. Three inductive coils, each with a resistance of 22 � and an inductance of .05 H are connected in (i) in star and (ii) in delta, to a three phase 415 V, 50 Hz supply. Calculate for each of the above case (i) phase current and line current and (ii) total power absorbed. (10)

15. With a neat schematic diagram, explain the working of a nuclear power plant. List any three advantages and any three disadvantages of a nuclear power plant. (10)

16. Explain about any two types of non - conventional energy sources available. (10)

MODULE 5 Answer any one full question

17. a) Derive an expression for back emf of a d.c. motor. (6) b) A single phase transformer is to have a voltage rating of 3300/240V. Find the number

of turns in the primary and the secondary if the frequency of operation is 50Hz. The maximum flux in the core may be taken as 0.04 Wb. (4)

OR

18. a) Explain different types of dc motors with respect to excitation and winding connection. (6) b) A 220V dc series motor draws a current of 20A. The armature resistance is 0.1Ω and series winding resistance is 1.2Ω. Find the back emf. (4)

MODULE 6 Answer any one full question

19. a) Compare squirrel cage induction motor with slip ring induction motor. (4) b) Explain any two starting methods used to start a single phase induction motor. (6)

OR

20. a) A four pole, three phase induction motor runs at 1440 rpm at rated load. Calculate the

percentage slip. Supply frequency is 50 Hz. (4)

b) Explain the constructional details and working principle of a single phase induction motor. (6)

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Department of Mechanical Engineering, SCMS School of Engineering and Technology.

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Reg. No._____________ Name:_____________________

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY

SECOND SEMESTER B.TECH DEGREE EXAMINATION, JUNE 2017

Course Code: EE100

Course Name: BASICS OF ELECTRICAL ENGINEERING

Max. Marks: 100 Duration: 3 Hours

PART A

Answer all questions, each question carries 4 marks.

1. A resistor of 5 Ω is connected in parallel with a resistor of R1 Ω. This combination is

connected in series with an unknown resistor of R2 Ω and the complete circuit is then

connected to 50 V dc supply. Calculate the values of R1 and R2, if the power

dissipated by the unknown resistor R1 is 150 W with 5A passing through it.

2. Derive an expression for energy stored in a magnetic circuit.

3. What are the advantages of three phase systems?

4. Derive an expression for three phase power in a star connected system.

5. What are the advantages of renewable sources?

6. What are the advantages of high voltage transmission?

7. What are the losses in a transformer? How these losses can be reduced?

8. With the help of diagrams, explain how dc motors are classified.

9. Define synchronous speed and slip of a three phase induction motor.

10. Explain the constructional details of a single phase induction motor.

PART B

MODULE (1-4)

Answer any four questions, each question carries 10 marks

11. a. Determine the power dissipated in all the three resistors in the following figure

using mesh current analysis. (5)

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b. Determine the current drawn from the supply using start delta conversion. (5)

12. a. A steel ring of 20 cm2 cross-section having a mean diameter of 50 cm is wound

uniformly with 500 turns. Flux density of 1.0 Wb/ m2 is produced by 4000 ampere

turns per metre. Calculate (i) the inductance (ii) the exciting current and (iii) the

inductance when a gap of 1 mm long is cut in the ring, the flux density being 1.0 Wb/

m2. Neglect leakage and fringing. (7)

b. A conductor of length 0.5 m moves in a uniform magnetic field of density 1.1 T at

a velocity of 30 m/s. Calculate the induced voltage in the conductor when the

direction of motion is inclined at 600 to the direction of the field. (3)

13. a. Derive the form factor of a pure sinusoidal wave form. (5)

b. An alternating voltage of (80 + j60) V is applied to a circuit and the current flowing

is (-4 + j10) A. Find (i) the impedance of the circuit, (b) the power consumed and (c)

the phase angle. (5)

14. a. Each phase of a delta connected load has a resistance of 25 Ω and an inductance of

0.15 H. The load is connected across a 400 V, 50 Hz, three phase supply. Determine

the line current, power factor and power consumed. (5)

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b. A balanced three phase star connected load is connected across a 400 V three phase

ac supply. Power consumed by the load is measured using two wattmeter method. The

readings of the two wattmeters are -500 W and 1500 W. Find the current drawn from

the supply and the power factor of the load. (5)

15. With the help of a neat diagram, explain the working of a thermal power plant.

(10)

16. a. With the help of a diagram, explain a power transmission scheme. (5)

b. What are the equipments in a substation? Explain the function of each equipment.

(5)

MODULE 5

Answer any one full question

17. a. What are the parts of a dc generator? Explain each part. (5)

b. A 150 kVA transformer has an iron loss of 700 W and a full load copper loss of

1800 W. Calculate the efficiency at full load, 0.8 power factor lagging. (5)

OR

18. a. A 120 V dc shunt motor draws a current of 200 A. The armature resistance is 0.02 Ω

and shunt field resistance 30 Ω. Find the back emf. (5)

b. A 30 kVA, single phase transformer has 500 primary turns and 30 secondary turns.

The primary is connected to a 3300V, 50 Hz supply. Calculate (i) the maximum flux

in the core, (ii) the secondary emf , (iii) the primary and secondary currents. (5)

MODULE 6

Answer any one full question

19. a. How does a three phase induction motor start? (5)

b. What are the different types of three phase induction motors? What are their

advantages and disadvantages? (5)

OR

20. a. The frequency of the emf in the stator of a 4 pole induction motor is 50 Hz, and that

in the rotor is 1.5 Hz. What is the slip and at what speed is the motor running? (5)

b. Why a single phase induction motor is not self starting? How it can be made self

starting? (5)

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Department of Mechanical Engineering, SCMS School of Engineering and Technology.