Guru Tegh Bahadur Institute of Technology
Department of Electrical and Electronics Engineering
Semester - 4
ElectroMechanical Energy conversion -II (ETEE – 202)
ASSIGNMENTS
Assignment – 1
1. (a) Obtain the speed-frequency relationship of synchronous generator.
(b) Derive the expression of coil span factor and distribution factor
(c) How is armature reaction compensated in synchronous generators?
2. (a) What are the conditions for parallel operation of 3-phase synchronous generators.
(b) A 1000 KVA, 6.6 KV, 3-phase, 50 Hz star connected synchronous generator
has a synchronous reactance of 25Ω per phase. It supplies full load
current at 0.8 lagging p.f. and rated terminal voltage. Compute the terminal
voltage for the same excitation when the generator supplies full load current at 0.8
leading p.f.
(c) Explain the dark lamp method of synchronization of synchronous generators.
3. (a) What are the effects of change of prime mover input on the synchronous 7
generator?
(b) Draw and explain the curves between power developed and the power angle for
salient-pole and non-salient pole synchronous generators.
(c) A 2500 V, 3-phase star connected motor has a synchronous reactance of 5Ω per
phase. The motor input is 1000 KW at rated voltage and an excitation emf of
3600 V (line). Calculate the line current and power factor.
Assignment – 2
1 (a) Explain the working principle of induction motors.
(b) Explain the use of synchronous motors for power factor compensation.
(c) A 600 V, 6-pole, 3-phase, 50 Hz, star connected induction motor has a
resistance and reactance of 0.4Ω and 7 Ω respectively. It takes a
current of 15A at unity power factor when operating with a certain field current.
With the field current remaining constant, the load torque is increased until the
motor draws a current of 50A. Find (he torque (gross) developed and the new
power factor.
2. (a) Explain the terms "Synchronous watts" and "Slip" of induction motor.
(b) Explain the production of rotating magnetic field in air-gap of 3-phase induction
motors.
(c) A 6-pole, 50 Hz, 3-phase induction motor running at full load develops a useful
torque of 160 Nm and the rotor emf is observed to make 120 cycle/min. Calculate
the net mech. Power developed. If the torque loss in friction and windings is 12
Nm. Find the copper-loss in rotor windings, the input to the motor efficiency. 800
W are the stator losses.
3. (a) Draw and explain the speed-torque characteristics of single-phase induction motor.
(b) Describe the split phase and shaded pole induction motors.
(c) A 220 V, 50 Hz, 6-pole single phase induction motor has the following circuit
model parameters.
Assignment 3
1. (a) Explain the working principle of synchronous motors.
(b) Explain the use of synchronous motors for power factor compensation.
(c) A 600 V, 6-pole, 3-phase, 50 Hz, star connected synchronous motor has a
resistance and synchronous reactance of 0.4Ω and 7 Ω respectively. It takes a
current of 15A at unity power factor when operating with a certain field current.
With the field current remaining constant, the load torque is increased until the
motor draws a current of 50A. Find (he torque (gross) developed and the new
power factor.
2. (a) Explain the terms "Synchronous Speed" and "Slip" of induction motor.
(b) Explain the double field revolving theory of 1-phase induction
motors.
(c) A 4-pole, 50 Hz, 3-phase induction motor running at full load develops a useful
torque of 250 Nm and the rotor emf is observed to make 220 cycle/min. Calculate
the net mech. Power developed. If the torque loss in friction and windings is 15
Nm. Find the copper-loss in rotor windings, the input to the motor efficiency.
1800W are the stator losses
Assignment 4
Synchronous Machines II
1 Explain the Two reaction theory, Synchronous Machines
2 Derive the Power Expressions for cylindrical and salient pole machines?,
3 Give the Performance characteristics of Synchronous Machines II
4 Give the principl e of operation of Synchronous Motor
5Explain the starting methods of Synchronous Motor6 Give the Torque-angle characteristics of Synchronous Motor7 Explain the V-curves of Synchronous Motor8 Write short notes
Hunting and damping,
Synchronous condenser,
Reluctance motor.
Assingment-5
1. (a) Obtain the speed-frequency relationship of synchronous generator.
(b) Derive the expression of coil spanfactor and distribution factor
(c) How is armature reaction compensated in synchronous generators?
2. (a) What are the conditions for parallel operation of 3-phase synchronous generators.
(b) A 1000 KVA, 6.6 KV, 3-phase, 50 Hz star connected synchronous generator
has a synchronous reactance of 25Ω per phase. It supplies full load
current at 0.8 lagging p.f. and rated terminal voltage. Compute the terminal
voltage for the same excitation when the generator supplies full load current at 0.8
leading p.f.
(c) Explain the dark lamp method of synchronization of synchronous generators.
3. (a) What are the effects of change of prime mover input on the synchronous 7
generator?
(b) Draw and explain the curves between power developed and the power angle for
salient-pole and non-salient pole synchronous generators.
(c) A 2500 V, 3-phase star connected motor has a synchronous reactance of 5Ω per
phase. The motor input is 1000 KW at rated voltage and an excitation emf of
3600 V (line). Calculate the line current and power factor.
Assingment -6
1.Write brief answers
a) why are rotor slots made skewed by small angle to the shaft axis?
b) what is a deepbar 3-phase Induction motor and what are its advantages?
c) what is magnetic locking (cogging) in 3-phase induction motor?
d) what will happen if single phasing occurs of a non working induction motor ?
e) what do you under stand by Synchronous watts . Give formulae?
Q2 a) Discuss in brief ,different methods of starting of 3-phase Induction Motor , with a
particular reference to Star/ delta starting -its advantages & disadvantages.
b) A 3-phase sq. cage Induction motor takes a starting current of 6 times . The full load current
. find the starting torque as a percentage of full load torque if the motor is started a) Direct on
line
b) star /delta starter, the full load slip of the motor being 4% .
Q3 a) Describe the principle of operation of single phase induction motor with helb of Double
field revolving theory.
b) Draw the Equivalent circuit of single phase induction motor . also write expression for
forward and backward current.
Q 4 a) The rotor of 4-pole ,50 Hz , slip ring Induction motor has a resistance of
0,25ohms/phase and runs at 1440rpm at full load . calculate the external resistance per phase
which must be added to lower the speed to 1200rpm, the torque being the same as before.
b) Explain induction generator also list its applications
Assingment -7
Q1
a) why are hydro generators kept low speed?
b) what are the advantages of rotating field system?
c) what is meant by power angle of alternator?
d) what are the causes of harmonics in voltage waveform of an alternator? How this can be
minimized?
e) what do you under stand by infinite busbar ?
Q2 a) Discuss in brief , advantages & disadvantages of hydrogen cooling ? how turbo
alternators cooling is different than hydro generator cooling ?
b) what are the causes of hunting in synchronous machines ? how it can be minimized
Derive the equation for active power output of a cylindrical rotor synchronous generators
connected to infinite bus bar?
b) Draw the curve between field current and armature current of synchronous motor? What is the
shape of the curves?.
Q 4 a) Explain synchronous impedance method for obtaining voltage regulation?
b) Describe Synchronous condensers? Write their applications
Assingment -8
1. What is an alternator?
2. On what principle does it works?
3. What are the different types of alternators? Which is in common use?
4. What the main parts of an alternator?
5. What do you mean by the salient-pole type rotor?
6. Which type of type of alternator is suitable for coupling with steel turbines and why?
7. Which type of alternator is suitable for hydro-electronic plants and why?
8. In which alternator is the salient type rotor used?
9. What type of alternator is used for high voltage generator?
10.Why are the stator cores is laminated?
11. What types of slots provided in stator cores of alternators?
12. What are the types of windings used in three-phase alternators?
13. What is meant by breadth factor?
14. What is the equation of induced emf in an alternator?
15. What will be an effect on increasing the field excitation of an alternator?
16. What is relation between speed and frequency of an alternator?
17. Does changing the number of conductors have any effect on the frequency?
18. How will you adjust the frequency of an alternator?
19. What do you mean by hunting alternators?
20. What will be the effect of increasing the load on alternator?
21. When an alternator supplying a load alone and its excitation is increased, its driving
. 22. On what factor the does the power of an alternator depend?
23. What will be the direction of armature reaction flux when a three phase alternator
supplies?
24. What is called the armature reaction of an alternator?
25. What is synchronous reactance and how does it vary?
26. What do you mean by synchronous independence and impedance drop?
27. What is the formula for calculating the generated emf on load condition?
28. Why is (+-) sign used for synchronous reactance drop?
29. What is alternator voltage regulation? Give the equation of percentage regulation of
an alternator?
30. What are the losses in alternators?
Assingment -9
1. A 1000 kVA, 66 kV, star connected alternator has a resistance of 1 ohm and a
Synchronous reactance of 10 ohm/phase. The machine delivers a load of 600 kW at
0.6 power factor lagging. What is the emf generated in armature?
(Ans. 38180 V)
2. A 3-0, star –connected alternator works at 1600 kVA, 13500 V. The armature
Effective resistance and synchronous reactance are 1.5Ω and 30 Ω/ phase respectively.
Calculate the percentage regulation for a load of 1280 kV at power factors of (i) 0.8
lead (ii) unity and (iii) 0.8 lag.
(Ans. (i) -11.98%, (ii) 3.22% (iii) 18.59%)
3. A 3- 0, star-connected, 600 kVA alternator has rated terminal voltage of 3300 V (line)
having stator resistance and reactance per phase of 0.37 Ω and 4.3 Ω respectively.
Determine the regulation