NIE

2. Principle Of Operation

3. • Operate on principle of electromagnetic
induction
• Stationary armature and rotating field
• Rotor is rotated using a prime mover
• When the rotor rotates, the stationary
conductors are cut by the magnetic flux
• Hence emf is induced
• In three phase alternators, the rotor flux will
induce 3 voltages displaced in time by 120
degree
• Emf induced is AC in nature
• AC voltage will give rise to AC current when a
load is connected to stator

4. Advantages of stationary armature
• Current can be delivered directly from fixed
terminals on the stator. This reduces voltage
drop due to brushes
• Easy to insulate stationary armature windings
• Bracing of armature windings is easier.
Deformation of windings can be avoided.

5. Construction of Alternators
• Stator frame
• Armature core

6. Cylindrical rotor

7. Salient pole rotor

8. Damper windings
•Also called as amortissuer windings
• Copper bars located in slots in pole shoe
•Bars are SC at both ends by heavy copper rings
•Alternators are not self starters so they provide
starting torque

9. Ratings of an Alternator
• Line to line voltage
• Full load KVA
• Power factor
• Field voltage
• Maximum field current
• Resistance of stator winding

10. Regulation of an Alternator
The voltage regulation is the change in terminal
voltage of the secondary from no load to full load
voltage.
• When the alternator is loaded, the terminal voltage
drops. This depends on the load and load power
factor