Understanding Synchronous vs Asynchronous Generators and Supply from the Rotor

Electrical generators come in various types, with synchronous and asynchronous generators being two of the most widely used. Both types serve the same basic function of converting mechanical energy into electrical energy, but they differ significantly in their design, operation, and supply mechanisms. This article will explore the differences between synchronous and asynchronous generators and explain how to take supply from the rotor.

Synchronous Generators

Definition: Synchronous generators operate at a constant speed that is synchronized with the frequency of the electrical grid. The rotor spins at a speed that maintains a fixed relationship with the magnetic field produced by the stator.

Construction: They can use either a permanent magnet or an electromagnet for the rotor. The stator has windings that generate electricity as the rotor's magnetic field rotates past them.

Operation: Synchronous generators need an external source to energize the rotor, such as a DC supply. They can operate at leading, lagging, or unity power factor, making them flexible for a wide range of applications.

Output: The output frequency of a synchronous generator is determined by its rotor speed and the number of poles.

Asynchronous Generators

Definition: Also known as induction generators, asynchronous generators do not operate at a constant speed. They generate power when the rotor spins faster than the synchronous speed of the magnetic field in the stator.

Construction: These generators typically use a squirrel cage or wound rotor. The rotor is not magnetically locked to the stators magnetic field.

Operation: Asynchronous generators can produce power when mechanically driven above synchronous speed. They rely on the difference (slip) between synchronous speed and rotor speed to induce current in the stator windings. They usually do not require an external DC supply for excitation.

Output: The output frequency varies with rotor speed, making them less suitable for applications requiring a constant frequency.

Supply from the Rotor

In Synchronous Generators: The supply is typically taken from the stator windings. However, the rotor can be connected to an external DC source to create the necessary magnetic field for operation. If the rotor is an electromagnet, its winding is powered by a separate excitation system.

In Asynchronous Generators: The supply is mainly taken from the stator windings. The rotor slip creates the necessary electromagnetic induction, and the rotor itself does not directly provide electrical supply. Instead, it generates a magnetic field that induces current in the stator.

Summary

Synchronous generators maintain a constant speed and require an external power source for excitation, whereas asynchronous generators can operate at varying speeds and do not require external excitation.

Both types of generators take supply from the stator, with the role of the rotor differing based on the generator type. Understanding these differences is crucial for selecting the appropriate generator for specific applications.

Keywords: synchronous generators, asynchronous generators, rotor supply