Synchronous Machines Explained – Easy Engineering Hub

A synchronous machine is a type of electric motor or generator that operates in sync (or at the same speed) with the frequency of the electrical power supply. These machines are widely used in power generation and industrial applications.

There are two main types of synchronous machines:

Synchronous Motors(convert electrical energy into mechanical energy)
Synchronous Generators(convert mechanical energy into electrical energy)

The term “synchronous” refers to the fact that these machines operate at a constant speed that is directly linked to the power supply frequency. For instance:

A synchronous motor runs at a fixed speed and doesn’t change speed under varying loads (it’s always in sync with the supply frequency).
A synchronous generator must maintain a constant rotational speed to generate electricity at a consistent frequency.

How Synchronous Machines Work

Synchronous Motor (Converting Electrical Energy into Mechanical Energy)

A synchronous motor is an electric motor that operates at a constant speed, synchronized with the frequency of the power supply.

Parts of a Synchronous Motor:

Stator: This is the stationary part of the motor. It contains coils of wire that are connected to an AC power supply. When the AC power flows through the stator, it creates a rotating magnetic field.
Rotor: This is the rotating part of the motor. It has its own magnetic field (either from permanent magnets or a field winding). The rotor is designed to rotate at the same speed as the rotating magnetic field created by the stator.

working:

Rotating Magnetic Field: When AC current flows through the stator coils, it generates a rotating magnetic field.

Rotor Alignment: The rotor, which has its own magnetic field, tries to align itself with the rotating magnetic field of the stator. It will rotate at the same speed as the stator’s magnetic field.

Constant Speed: The key feature of a synchronous motor is that it always runs at a constant speed, known as the synchronous speed. This speed depends on the frequency of the AC supply and the number of poles in the motor.

For example:

If the frequency of the AC supply is 60 Hz and the motor has 4 poles, the synchronous speed would be: Ns=120×604=1800 RPM

So, the rotor must turn at 1800 RPM to stay in sync with the stator’s magnetic field.

Synchronous Generator (Converting Mechanical Energy into Electrical Energy)

A synchronous generator (also called an alternator) works in the opposite direction of the motor. It converts mechanical energy (from a turbine or other source) into electrical energy.

Parts of a Synchronous Generator:

Rotor: This is driven by mechanical power (from steam, water, or wind). It is usually a magnetic field created by either permanent magnets or an electromagnet.

Stator: The stator consists of windings (coils of wire) where electricity is induced as the rotor spins.

Working:

Mechanical Input: The rotor is turned by an external mechanical source, like a steam turbine or water turbine.
Magnetic Field Interaction: As the rotor turns, it creates a rotating magnetic field inside the stator. This rotating magnetic field induces a current in the stator windings due to electromagnetic induction.
Electricity Generation: The AC electricity generated in the stator can be sent out and used in electrical circuits.

Applications of Synchronous Machines

Synchronous Motors:

Power Factor Correction: Synchronous motors can be used to improve the power factor of a system. If a factory is consuming a lot of reactive power (often due to induction motors), a synchronous motor can help balance it out, improving the efficiency of the power supply.
Precise Speed Control: Since synchronous motors always run at a constant speed, they are used in applications where precise speed control is needed, such as in clocks, robots, or some industrial processes.

Synchronous Generators:

Power Plants: Synchronous generators are used in most power plants (coal, hydroelectric, nuclear) to produce AC electricity. The mechanical energy (usually from a turbine) turns the generator’s rotor, generating electricity.
Renewable Energy: Some wind and hydropower systems also use synchronous generators to produce electricity.

Advantages of Synchronous Machines:

Constant Speed: Synchronous motors always run at the same speed, making them ideal for applications where precise speed is required.
Efficient Power Generation: Synchronous generators are widely used in large power plants because they provide stable and reliable electrical power.
Power Factor Correction: Synchronous motors can be used to correct the power factor in electrical systems, helping reduce energy loss.

Disadvantages of Synchronous Machines:

Starting Difficulty: Synchronous motors need special mechanisms (like a starting motor or external help) to start because they can’t start on their own like induction motors. They need to reach the synchronous speed before they can lock in.
Cost and Complexity: Synchronous machines are generally more complex and expensive than induction machines, especially in terms of design and maintenance.