Electrical Engineering - QB

QUESTION BANK

Subject: TT 2201 – Electrical Engineering

UNIT I

Part A

1. State Ohm’s law.
2. Define resistance and specific resistance.
3. Define temperature co efficient resistance.
4. Define electrical power and energy.
5. State Kirchhoff’s law.
6. Three resisters 5Ω, 10Ω, 15Ωare connected in series across 120v supply. Find total current, total resistance, voltage across each element.
7. Define magnetic flux and magnetic flux density
8. Define magnetic field strength and magneto motive force.
9. Define reluctance, permeability.
10. State faradays law of electromagnetism.
11. State Flemings left and right hand rule.
12. Define self and mutual inductance.
13. Two 50 ohms resistors are connected in series with unknown resistor R connected across one of them. When the total circuit resistance R is 60 ohms, calculate the value of unknown resistor.
14. Define coefficient of coupling.
15. The two resistors R1 < R2 are in parallel. When R2 is varied between R1 and infinity R1 < R2 < infinity. What is the minimum and maximum value of the equivalent R?
16. Write the expression for force experienced by a current carrying conductor placed in a magnetic field.

Part B

17. State and explain the following
1. Ohm’s Law
2. Kirchhoff’s Law

18. a) Derive an expression for the effective resistance of

                                             i.            Two resistors connected in series

                                            ii.            Two resistors connected in parallel

        b) Compare series and parallel circuits.

19. a) Derive an expression for Ohm’s law of magnetism.

b) What are the similarities and differences between electric and magnetic circuits?

20. Explain a) Hysteresis loss b) Eddy Current loss
21. Derive an expression for energy stored in a magnetic field.
22. State and explain Kirchhoff’s voltage and current laws.            
23. (i)  State and explain Faraday’s law of electromagnetic induction.  

(ii)  Derive the expression for force experienced by a current carrying conductor 

        placed in a magnetic field.

UNIT II

Part- A

       

1. Define Average value and RMS value.
2. What is meant by balanced and unbalanced load?
3. Define form factor and peak factor.
4. Define resonance.
5. Define line voltage and line current in star and delta connection.
6. Define R-curve in single phase circuits.
7. Define time period and frequency.
8. Define selectivity.
9. Define quality factor.
10. What is an alternating quantity?
11. Write down the expression for total power in a three phase system.
12. What is meant by power factor and its significance in an AC circuit?

Part B

       

13. Explain the behavior of alternating current through R, L, C, RL, RC and RLC.                                                                                                                                                                      
14. Explain bandwidth, selectivity in series resonance.
15. Explain the relation between line and phase values of voltage and current in
16. Star connection
17. Delta connection                                               
18. Explain briefly how 3 phase power can be measured using two wattmeter and single wattmeter methods.
19. A coil of inductance 2 mH and resistance 4 Ω is connected      in series with 0.3 µF capacitor. The circuit is connected to 5 V variable frequency supply. Calculate the resonance frequency and the voltage across the coil and capacitor at resonance.
20. Three identical coils connected in delta across 400V, 50HZ, three phase supply take a line current of 15A at a power factor 0.8 lagging. Calculate the phase current.
21. Derive Form factor & Peak factor. And obtain these factors for a sinusoidal wave.
22. Explain the merits and demerits of using poly phase systems over single phase systems.
23. Prove that in a series RLC circuit:

Resonant Frequency= Bandwidth * Quality factor.

UNIT III

Part- A

1. What is the significance of back emf?
2. What is the necessity of a starter?
3. What are the applications of DC generators?
4. What are the different methods of speed control of DC motor?
5. In every DC motor, generator action occurs and in every DC generator, motor action occurs- Justify.
6. What are the different types of motors?
7. What is the function of commutator?
8. What is the purpose of armature?
9. What are the characteristics of DC generator?
10. What are the losses in a generator?
11. What is critical resistance?
12. Write the two methods of winding the armature coil?
13. What are the parts of a DC machine?
14. What are the characteristic of DC motor?
15. Write the application of a DC shunt motor.
16. Write the application of a DC series motor.
17. What are the applications of a DC compound motor?
18. Draw the torque-speed characteristics of the DC series motor.
19. Draw the torque-speed characteristics of the DC shunt motor.
20. Why series motor should not be started with no load?
21. What are the various causes for the failure of a generator to build up?
22. What is the need for the generation of back emf in a DC motor?

Part B

23. (i) Explain the principle on which a generator works

(ii) Derive the emf equation of a dc generator              

24. Using Swinburne’s test, explain how to predetermine the efficiency of a DC machine

                                 i.            as a generator

                                ii.            as a motor

25. Explain the working of 3 point started with a neat diagram
26. Derive an expression for

                                 i.            Torque developed in the armature

                                ii.            Speed equation for a DC motor

27. Write short notes on the speed control methods for

                                 i.            DC Shunt motor

                                ii.            DC series motor

28. The output of a shunt generator is 500 A at a terminal voltage of 250 volts. If armature resistance is 0.04 Ω and shunt field resistance is 50 Ω. What is the generated emf?
29. (i) Derive the emf equation of DC generator.

(ii) Draw Open circuit and load characteristics of DC shunt and DC series generators.

30. (i) Define torque equation of a DC motor.

(ii) Explain different methods of speed control of DC Shunt motor.   

UNIT IV

                                                   Part- A

1. What are the losses in a transformer and how do they vary with load?
2. Write the principle of operation of 3φ alternators?
3. What is the principle the transformer?
4. Give the expression for emf  induced in the primary of the transformer
5. What is the regulation of a transformer?
6. What is the test to be conducted for finding is on & copper loss in a transformer?
7. What are the two types of motors employed in a 3 phase induction motor?
8. What is meant by slip?
9. Give the expression for torque equation of 3 phase induction motor
10. What is synchronous impedance?
11. What are the types of transformer core?
12. List the different types of induction motor.
13. The transformer rating is in KVA & not in KW, why?
14. Why does the reactance of three phase induction motor greatly vary between starting & running condition?

Part B

15. (i) Derive the condition for maximum efficiency of a single phase transformer.

(ii) A 40 KVA transformer has an iron loss of 450 W and full load cu loss of   

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

16. Explain construction and working principle of three phase Induction motor with neat sketch.
17. Explain briefly on any two of the following

                                                         i.            Open circuit and short circuit of transformer

                                                        ii.            Core loss and eddy loss in transformer

18. (i)Explain the construction and operation of a single phase transformer.

(ii)Derive the emf equation of a transformer.

19. (i)Draw and discuss the Torque-slip characteristics of a three phase induction 

     motor.

(ii) In induction motor having six poles operates on 50 Hz supply. If it works on  

      full load at 960 rpm.Find %of slip.

20. (i)  Explain OC&SC tests of a single phase transformer.

(ii)  Also explain how the efficiency of a single phase transformer can be predetermined from OC& SC tests.

21. Explain with the help of vector diagram, the synchronous impedance method of determining voltage regulation of an alternator.

                                 

UNIT V

Part- A

1.       What is meant by creeping in energy meter?

2.       Define nominal ratio of instrument transformer.

3.       List two instruments for measurement of frequency.

4.       Write the function of instrument transformer.

5.       Write any two advantages of digital voltage.

6.       Explain the purpose of Schmitt trigger in digital frequency meter.

7.       Give the importance of iron loss measurement.

8.       What is ampere-hour and watt-hour?

9.       What are resistors and diodes checked using digital millimeters?

10.    What is the need to evaluate phase- angle error in instrument transformers?

11.    State the reason for non-uniform scale of moving iron instruments and uniform scale of a PMMC instruments.

12.    What is the power factor when two wattmeter readings are equal in a two wattmeter method of power measurement?

Part B

13.    Explain the construction details of induction type energy meter and explain its principle of operation.

14.     Explain the principle and construction of the following

               1. Attraction type MI instrument

               2. Permanent magnet type MC instrument

15.    Write briefly (i) Torque in indicating instrument

                (ii) Measurement of power using two Wattmeter methods

                (iii) Induction type energy meter.

16. What are the different types of torques necessary for the successful operation of any        

        indicating instrument?

17. Explain briefly how are these torques produced in various instruments.

18.  (i) Describe the construction & working of an Electrodynamometer type 

             instrument.

19. Derive the torque equation of an Electrodynamometer type instrument.