EE6504 EM2 2marks
Anna University Regulation 2013 EEE EE6504 EM2 2marks & 16marks for all 5 units are provided below. EE6504 EM2 Short answers, Question Bank for Electrical Machines 2 is listed down for students to make perfect utilization and score maximum marks with our study materials.
1. Why a 3-phase synchronous motor will always run at synchronous speed?
Because of the magnetic coupling between the stator poles and rotor poles the motor runs exactly at synchronous speed.
2. What are the two classification synchronous machines?
The classification synchronous machines are:
i. Cylindrical rotor type
ii. Salient pole rotor type
3. What are the essential features of synchronous machine?
i. The rotor speed is synchronous with stator rotating field.
ii. Varying its field current can easily vary the speed.
iii. It is used for constant speed operation.
4. Mention the methods of starting of 3-phase synchronous motor.
a. A D.C motor coupled to the synchronous motor shaft.
b. A small induction motor coupled to its shaft. (Pony method)
c. Using damper windings started as a squirrel cage induction motor.
5. What are the principal advantages of rotating field system type of construction of synchronous machines?
- Form Stationary connection between external circuit and system of conditions enable the machine to handle large amount of volt-ampere as high as 500 MVA.
- The relatively small amount of power required for field system can be easily supplied to the rotating field system via slip rings and brushes.
- More space is available in the stator part of the machine for providing more insulation to the system of conductors.
- Insulation to stationary system of conductors is not subjected to mechanical stresses due to centrifugal action.
6. Write down the equation for frequency of emf induced in an alternator.
F = PN / 120 Hertz
Where P = No. Of poles
N = Speed in rpm.
7. What are the advantages of salient pole type of construction used for synchronous machines?
- They allow better ventilation.
- The pole faces are so shaped radial air gap length increases from the pole center to the pole tips so that flux distribution in the air gap is sinusoidal in shape which will help to generate sinusoidal emf.
- Due the variable reluctance, the machine develops additional reluctance power, which is independent of excitation.
8. Why do cylindrical rotor alternators operate with steam turbines?
Steam turbines are found to operate at fairly good efficiency only at high speeds. The high-speed operation of rotor tends to increase mechanical losses, so the rotors should have smooth external surface. Hence smooth cylindrical type rotors with less diameter and large axial length are used for synchronous generators driven by steam turbines with either 2 or 4 poles.
9. Which type of synchronous generators are used in Hydroelectric plants and why?
As the speed of operation is low, for hydro turbines used in hydroelectric plants, salient pole type synchronous generators are used. These allow better ventilation and also have other advantages over smooth cylindrical type rotor.
10. What is the relation between electrical degree and mechanical degree?
Electrical degree e and mechanical degree are related to one another by the number of poles P, the electrical machine has, as given by the following equation.
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EE6504 EM2 2marks
Anna University 5th SEM EEE EM2 2marks 16 marks
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Anna University EEE EM2 short answers Regulation 2013
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