1. Electrical power system
Synchronous Generator
(Alternators)
By:-Abhishek kumar

2. Introduction:-
• Ac generators are usually called alternators.
They are also called synchronous generators
• Rotating machines that rotate at a speed
fixed by the supply frequency and the number
of poles are called synchronous machines
• A synchronous generator is a machine for
converting mechanical power from a prime
mover to a.c. electric power at specific
voltage and frequency.
• Synchronous machine are used primarily as

3. Construction of Three-phase
Synchronous Generator:-
• An Alternators consists of two main parts
namely , the Stator and Rotor.
• The Stator is a stationary part of the
machines. It carries the armature winding
in which the voltage is generated. The
output of the taken from the stator.
• The Rotor is the rotating part of the
machines. The rotor produces the main
field flux.

4. Diagram of 3-Phase Synchronous
Generator:-

5. Speed And Frequency:-
Frequency:-
P=total number of poles
N=speed of field poles in r.p.m.
n=speed of field poles in r.p.s.
f=frequency of the generated voltage in Hz.
N/60 = n
P/2=p
f=PN/120

6. Synchronous Speed:-
• Synchronous speed
Ns = 120f/p
Where
Ns is the called synchronous machine
f = frequency the generated voltage in Hz
P = total no of field poles

7. Advantage of Synchronous generator:-
• In synchronous motor the speed remains
constant irrespective of the loads.
• Synchronous motors can be constructed
with wider air gaps than induction motors
which makes these motors mechanically
more stable.
• In synchronous motors electro-magnetic
power varies linearly with the voltage.

8. Disadvantage of synchronous
Generator:-
• Synchronous motors requires dc excitation
which must be supplied from external sources.
• The cost per kW output is generally higher than
that of induction motors
• Synchronous motors cannot be started on load.
Its starting torque is zero
• When loading on the synchronous motor
increases beyond its capability, the synchronism
between rotor and stator rotating magnetic field
is lost and motor comes to halt .