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Types of Synchronous Machine
Comparison between cylindrical rotor
type generator and Salient pole rotor
A synchronous machine is an AC machine whose
speed is proportional to the frequency of
A machine which rotates at a speed fixed by the
supply frequency and the number of rotor poles
is called synchronous machine
It always runs at synchronous or constant speed
and has no slip
Synchronous machine includes synchronous
generators and synchronous motors
2-Pole Salient Pole M/C 4-Pole Salient Pole M/C 4-Pole Cylindrical M/C
Cylindrical Rotor type
Salient Pole Rotor type
A Synch. Generator consists of two main
1) Stator and
The stator is the stationary parts part of the
It works as a armature in synchronous
The armature winding is housed in it
Rotor is the rotating part of the synchronous
It work as a field of the synchronous machine
Field system is rotating in the synchronous
Field winding is housed on it
Field winding is excited by DC supply through
brushes and slip ring
It works on the principle of Electromagnetic
In the synchronous generator field system is
rotating and armature winding is steady.
Its works on principle opposite to the DC
High voltage AC output coming from the
Hydro-generators (Salient Pole Type):
The Synchronous generators driven by water
turbines are known as hydro generators or
Water wheel generators
They have rating upto 750 MW and are driven
at speeds ranging from 100 to 1000 RPM
Turbo-alternators (Cylidrical Rotor
Type or Wound Rotor Type):
They are driven by steam turbines
The efficiency of steam turbine is high at large
speeds, the turbo-alternators are designed for
speed upto 3000 RPM. Turbo-alternators have
ratings upto 1000MW
Engine Driven Generators:
These generators are driven by different forms of
combustion engines at speed upto 1500 RPM and
rating upto 20 MW
These generators are driven by gas turbines have
higher speeds and also higher power ratings
Synchronous motors may be either plain synchronous
machines or synchronous induction machines
The plain Synchronous machine with salient pole is
Synchronous motors have some define advantages
over induction motors and these include constant
speed operation, Power factor control and high
- Also Synchronous motors prove to be cheaper
than induction motors for high power low
- The applications of Synchronous machines
include constant speed drives for
compressors, blowers, low head pumps
- Synchronous compensators are used for
control of reactive power in power supply
- They are designed for ratings upto 100 MVAr
and speed upto 3000 RPM
Synchronous generators are classified in two
category according to its rotor construction:
1) Cylindrical Rotor Type
2) Salient pole Rotor Type
Cylindrical Rotor Type:-
This type machines are High speed machines
(1000 to 3000 RPM)
This type machine has Small diameter and is
large axial length
This type of machines are used in Thermal
power plant and gas turbine power plant
Where speed requires high
Cylindrical rotor does not have poles that are projecting out.
The air gap between the stator and rotor is uniform.
The smooth cylindrical rotor has small no of poles.
Cylindrical rotors are mechanically strong.
They have small diameters and large axial length.
The prime movers used are steam turbines and electric motors.
They are preferred for high speed alternators which range from
1000 to 3000 RPM
Salient Pole rotor:-
Salient pole rotor does have poles that are projecting out from
The air gap between the stator and rotor is non-uniform.
The salient pole rotor has large no of poles.
Saline Pole rotors are mechanically weak.
They have large diameters and small axial length.
The prime movers used are IC engines and law speed turbine.
They are preferred for law speed alternators which range from
100 RPM to 500 RPM