Download unit-2: dc motor

DC Machines & Synchronous Machines
10EE54
Assignment Questions:
UNIT-2: DC MOTOR:
1. Explain the significance of back emf in dc motor.
2. Derive the torque equation of a dc motor. And discuss T v/s Ia and N v/s Ia
Characteristics
of dc motor.
3. Explain i) Characteristics of DC Shunt Generator
ii) Characteristics
of
DC Shunt Motors
4. Derive the expression for electromagnetic torque developed in a DC motor.
Unit 3 and 4: Losses, Efficiency& Testing of Dc Machines
1. Explain Swinburne’s test for finding the efficiency of a D.C. machine. Can this method
Applicable to d.c. series motors.
2. Describe Hopkinson’s test in detail with its advantages disadvantages.
3. How the efficiency of each machine on full load is obtained from the regenerative test ?
DC Machines & Synchronous Machines
10EE54
4. Describe the retardation test as applied to the d.c. shunt machines.
5. How can stray losses of machine be determined with the help of a retardation test with and
Without the knowledge of moment of inertia.
6. What is the method available for testing d.c. series motor? Explain it in detail.
7. Explain how you will obtain efficiency of d.c. machine by field’s test.
Unit-5: SYNCHRONOUS MACHINES
1. Explain in detail the constructional features of a three phase alternator.
2. Discuss the advantages of rotating field type of alternators.
3. List the difference between salient type and non-salient type of rotor construction.
4. 4. Establish the relationship between the
speed for a three phase alternator.
number of poles, frequency and the synchronous
DC Machines & Synchronous Machines
10EE54
5. Establish the working principle of a three phase alternator.
6. What is difference between degrees mechanical and degrees electrical? Explain.
7. With the help of neat sketches, explain the various types of windings used in alternators.
8. Derive the generalized expression for an induced e.m.f. per phase in three phase alternator,
when coils are not full pitch and concentrated in one slot.
9. Define and state the expressions for,1) Pitch factor
2) Distribution factor
10. Derive the expressions for the pi tch factor and Distribution factor.
11. Briefly explain the significance of chording and distribution factors. Develop the emf
12. Equation for a synchronous generator having fractional pitch and distributed windings.
13. Explain the methods adopted to eliminate harmonics in the voltage in an alternator
14. A 3Φ, 50 Hz, star connected salient pole alternator has 216 slots with 5 conductors per slot. All
the conductors of each phase are connected in series; the winding is distributed and full pitched.
The flux per pole is 30 mwb and the alternator runs at 250 rpm. Determine the phase and line
voltages of emf induced.
15. A 3Φ, 16 pole, star connected salient pole alternator has 144 slots with 10 conductors per slot.
The alternator is run at 375 rpm. The terminal voltage of the generator found to be 2.657 kV.
Dteremine the frequency of the induced emf and the flux per pole.
16. A 4 pole, 3 phase, 50 Hz, star connected alternator has 60 slots with 4 conductors per slot. The
coils are short pitched by 3 slots. If the phase spread is 600, find the line voltage induced for a
flux per pole of 0.943 wb.
Unit 6 : Voltage Regulation
1. Which are the various parameters of an armature winding of a synchronous generator? Draw its
equivalent circuit.
2. Explain the effect of armature reaction on the performance of an alternator. How it depends on
the load p.f.? Explain with suitable diagrams.
3. What is armature reaction reactance? Explain.
DC Machines & Synchronous Machines
10EE54
4. Explain the concept of synchronous reactance and impedance.
5. State the voltage equation of an alternator and explain each term in it.
6. Derive an expression for the induced e.m.f. in an alternator in terms of terminal voltage, p.f.
and armature, from the phasor diagram.
7. What is voltage regulation? How it is defined for an alternator.
8. Explain the direct loading method determining the regulation of an alternator.
9. What is potier reactance? Now it is determined by potier triangle? How it is used to determine
regulation?
10. Write a note on armature reaction in alternators.
11. Write a note on MMF method of predetermining the regulation.
Unit 7: Synchronization of Alternators
1.
Derive an expression for power developed in a salient pole synchronous generator.
2.
What are the conditions to be satisfied before a 3 phase alternator is synchronized to
Infinite Bus bars?
3.
Describe a method of synchronizing the 3 phase alternator to the infinite bus giving the
relevant circuit diagram.
DC Machines & Synchronous Machines
4.
10EE54
Describe a method of synchronizing a 3 phase synchronizing machine to the infinite bus bars
two bright one dark lamp method with relevant circuit diagram.
5.
Discuss the effect of speed-load characteristics of the prime movers on the load sharing of
two alternators connected in parallel.
6.
Derive an expression for power developed in a non-salient pole alternator.
7.
Write a note on synchronizing power on no load and on load.
8.
Discuss the factor on which the division of load between two alternators take place when they
are working in parallel.
9.
Describe Slip test and explain how the reactance are calculated using it.
10. Draw and explain the phasor diagram for a salient pole alternator based on two reaction
Unit 8: Synchronous Motors
1. Explain the construction features of the synchronous motor.
2. Why synchronous motors are not self-starting ? Explain.
3. What are the various methods of making synchronous motors self-starting.
DC Machines & Synchronous Machines
10EE54
4. When loaded, does the speed of the synchronous motor changes? if not, explain how the
Synchronous motor reacts for the changes in the load condition .
5. Explain the effect of variable excitation on the behavior of the synchronous motor under
constant condition.
6. What is synchronous condenser? Explain with the phasor diagram.
7. State the various application areas of the synchronous motor.
8. Write a note on damping windings in synchronous machine.
9. Explain the methods of starting the synchronous motor.
10. Write a note on hunting in synchronous motor.
11. Derive an expression for the power developed per phase of a synchronous motor.
12. Derive an expression for the maximum torque developed by the synchronous motor.