PPT: Synchronous Machines | Electrical Machines - Electrical Engineering (EE) PDF Download

 Page 1


Introduction to 
Synchronous 
Machines
Page 2


Introduction to 
Synchronous 
Machines
Fundamentals of Synchronous Machines
A synchronous machine is an AC rotating machine whose speed under steady state condition is 
proportional to the frequency of the current in its armature. The magnetic fields created by both stator 
currents and rotor field current rotate at synchronous speed, resulting in steady torque production.
These machines are primarily used as generators, especially for large power systems like turbine and 
hydroelectric generators in grid power supply. They can also function as motors in applications requiring 
constant speed, and as synchronous condensers for power factor correction.
Power Generation
The bulk of electric power 
is produced by polyphase 
synchronous generators 
with ratings of several 
hundred MVA.
Motor Applications
Used in constant-speed 
drives or with frequency 
changers for variable-
speed applications.
Power Factor Correction
Unloaded synchronous 
machines can adjust 
reactive power by 
controlling rotor field 
current.
Page 3


Introduction to 
Synchronous 
Machines
Fundamentals of Synchronous Machines
A synchronous machine is an AC rotating machine whose speed under steady state condition is 
proportional to the frequency of the current in its armature. The magnetic fields created by both stator 
currents and rotor field current rotate at synchronous speed, resulting in steady torque production.
These machines are primarily used as generators, especially for large power systems like turbine and 
hydroelectric generators in grid power supply. They can also function as motors in applications requiring 
constant speed, and as synchronous condensers for power factor correction.
Power Generation
The bulk of electric power 
is produced by polyphase 
synchronous generators 
with ratings of several 
hundred MVA.
Motor Applications
Used in constant-speed 
drives or with frequency 
changers for variable-
speed applications.
Power Factor Correction
Unloaded synchronous 
machines can adjust 
reactive power by 
controlling rotor field 
current.
Stator Construction
The stator is the stationary part of the synchronous machine and forms a critical component of its overall structure. It is 
built up of sheet-steel laminations with slots carefully designed on its inner periphery to house the windings.
A three-phase winding is placed in these slots, creating the armature of the machine. This winding is always connected in 
star configuration, with the neutral point connected to ground for safety and proper operation.
Laminated Core
Sheet-steel laminations reduce eddy 
current losses while providing 
magnetic path for flux.
Three-Phase Winding
Carefully designed windings placed in 
stator slots to create rotating 
magnetic field.
Star Connection
Windings connected in star 
configuration with grounded neutral 
for safety and proper operation.
Page 4


Introduction to 
Synchronous 
Machines
Fundamentals of Synchronous Machines
A synchronous machine is an AC rotating machine whose speed under steady state condition is 
proportional to the frequency of the current in its armature. The magnetic fields created by both stator 
currents and rotor field current rotate at synchronous speed, resulting in steady torque production.
These machines are primarily used as generators, especially for large power systems like turbine and 
hydroelectric generators in grid power supply. They can also function as motors in applications requiring 
constant speed, and as synchronous condensers for power factor correction.
Power Generation
The bulk of electric power 
is produced by polyphase 
synchronous generators 
with ratings of several 
hundred MVA.
Motor Applications
Used in constant-speed 
drives or with frequency 
changers for variable-
speed applications.
Power Factor Correction
Unloaded synchronous 
machines can adjust 
reactive power by 
controlling rotor field 
current.
Stator Construction
The stator is the stationary part of the synchronous machine and forms a critical component of its overall structure. It is 
built up of sheet-steel laminations with slots carefully designed on its inner periphery to house the windings.
A three-phase winding is placed in these slots, creating the armature of the machine. This winding is always connected in 
star configuration, with the neutral point connected to ground for safety and proper operation.
Laminated Core
Sheet-steel laminations reduce eddy 
current losses while providing 
magnetic path for flux.
Three-Phase Winding
Carefully designed windings placed in 
stator slots to create rotating 
magnetic field.
Star Connection
Windings connected in star 
configuration with grounded neutral 
for safety and proper operation.
Rotor Types: Salient Pole Design
The rotor carries a field winding supplied with direct current through slip rings by a separate DC source. Salient pole rotors feature projecting poles 
mounted on a large circular steel frame fixed to the alternator shaft.
These rotors are used in low-speed alternators (120-400 RPM) typically driven by water turbines. The individual field pole windings are connected in 
series, creating alternate north and south poles when energized.
Low Speed Application
Used in 120-400 RPM 
applications like hydroelectric 
generators
Physical Characteristics
Large diameter with short axial 
length to accommodate many 
poles
Speed Limitations
Not suitable for high speeds 
due to excessive windage loss 
and mechanical stress
Pole Requirements
Requires many poles to 
achieve 50 Hz frequency at 
low rotational speeds
Page 5


Introduction to 
Synchronous 
Machines
Fundamentals of Synchronous Machines
A synchronous machine is an AC rotating machine whose speed under steady state condition is 
proportional to the frequency of the current in its armature. The magnetic fields created by both stator 
currents and rotor field current rotate at synchronous speed, resulting in steady torque production.
These machines are primarily used as generators, especially for large power systems like turbine and 
hydroelectric generators in grid power supply. They can also function as motors in applications requiring 
constant speed, and as synchronous condensers for power factor correction.
Power Generation
The bulk of electric power 
is produced by polyphase 
synchronous generators 
with ratings of several 
hundred MVA.
Motor Applications
Used in constant-speed 
drives or with frequency 
changers for variable-
speed applications.
Power Factor Correction
Unloaded synchronous 
machines can adjust 
reactive power by 
controlling rotor field 
current.
Stator Construction
The stator is the stationary part of the synchronous machine and forms a critical component of its overall structure. It is 
built up of sheet-steel laminations with slots carefully designed on its inner periphery to house the windings.
A three-phase winding is placed in these slots, creating the armature of the machine. This winding is always connected in 
star configuration, with the neutral point connected to ground for safety and proper operation.
Laminated Core
Sheet-steel laminations reduce eddy 
current losses while providing 
magnetic path for flux.
Three-Phase Winding
Carefully designed windings placed in 
stator slots to create rotating 
magnetic field.
Star Connection
Windings connected in star 
configuration with grounded neutral 
for safety and proper operation.
Rotor Types: Salient Pole Design
The rotor carries a field winding supplied with direct current through slip rings by a separate DC source. Salient pole rotors feature projecting poles 
mounted on a large circular steel frame fixed to the alternator shaft.
These rotors are used in low-speed alternators (120-400 RPM) typically driven by water turbines. The individual field pole windings are connected in 
series, creating alternate north and south poles when energized.
Low Speed Application
Used in 120-400 RPM 
applications like hydroelectric 
generators
Physical Characteristics
Large diameter with short axial 
length to accommodate many 
poles
Speed Limitations
Not suitable for high speeds 
due to excessive windage loss 
and mechanical stress
Pole Requirements
Requires many poles to 
achieve 50 Hz frequency at 
low rotational speeds
Rotor Types: Non-Salient Pole Design
Non-salient pole rotors feature a smooth solid forged-steel radial cylinder with slots along the outer periphery. Field windings are 
embedded in these slots and connected in series to slip rings for DC excitation, with unslotted regions forming the poles.
This design is used in high-speed alternators (1500 or 3000 RPM) driven by steam turbines. For 50 Hz frequency, these turboalternators 
typically have 2 poles (3000 RPM) or 4 poles (1500 RPM), resulting in small diameters but very long axial lengths.
Mechanical Advantages
The cylindrical construction provides 
exceptional mechanical robustness 
necessary for high-speed operation. This 
design minimizes windage losses and 
ensures noiseless operation even at 
speeds of 3000 RPM.
The solid forged-steel construction can 
withstand the tremendous centrifugal 
forces generated during high-speed 
rotation.
Electrical Advantages
The smooth cylindrical surface creates a 
more sinusoidal flux distribution around 
the periphery, resulting in superior EMF 
waveform compared to salient-pole 
designs.
This improved waveform quality is 
particularly important for power 
generation applications where harmonic 
content must be minimized.
Cylindrical rotors have small diameters but 
very long axial lengths to accommodate 
the necessary field windings while 
maintaining structural integrity at high 
speeds.