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DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
QUESTION BANK – EE 2302 ELECTRICAL MACHINES II
UNIT I
SYNCHRONOUS GENERATOR
PART A
1. Name the various types of alternators.
i. Turbo alternator ii. Salient pole alternator
2. Write the EMF equation of a three-phase alternator.
The emf equation of alternator is
E = 4.44 K
c
K
d
Ф f T volts
Where
E = Induced emf per phase
K
c =
Pitch factor
K
d
= Distribution factor
T = No of turns connected in series in each phase
3. Why do cylindrical Alternators operate with steam turbines?
Steam turbines are found to operate at fairly good efficiency only at high speeds. The
high speed operation of rotors tends to increase mechanical losses and so the rotors should
have a 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.
4. Which type of Synchronous generators are used in Hydro-electric plants and why?
As the speed of operation is low for hydro turbines used in Hydro-electric plants,
salient pole type Synchronous generators are used. These allow better ventilation and also
have other advantages over smooth cylindrical type rotor.
5. What are the advantages of salient pole type construction used for Synchronous machines?
Advantages of salient-pole type construction are :
➢ They allow better ventilation
➢ The pole faces are so shaped that the radial air gap length increases from the pole
center to the pole tips so that the flux distribution in the air-gap is
sinusoidal in shape which will help the machine to generate sinusoidal emf
➢ Due to the variable reluctance the machine develops additional reluctance
power which is independent of excitation
6. How does electrical degree differ from mechanical degree?
Mechanical degree is the unit for accounting the angle between two points based on their
mechanical or physical placement. Electrical degree is used to account the angle between two
points in rotating electrical machines. Since all electrical machines operate with the help of
