The Story of Motor and Generator Excitation System

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We have studied a lot about the motor/generator excitation systems. But have we understood it deeply? Let’s discuss the motor and generator excitation system in an interesting way.

What is Excitation? 

From the word excitation, we can guess that it must be a process for exciting something. Suppose, you have a friend who is not so much into studying. He is busy with mobile and video games.

Inattentive Student
Inattentive Student

But when the exam comes he starts to study. Here exam is an excitation system. It is exciting him for study.

For supplying the electromagnetic field of rotor winding, another source is used for the current supply. This system is called the excitation system. You can think of external sources as exam and rotor winding as your friend. 

Objectives of This System

The main objectives of the excitation system are:

  • Dependable 
  • Easy controlling 
  • Easy maintenance 
  • Durability and temporary fast reaction

On which factor excitation amount depends? The necessary excitation amount depends on load current, load power factor, and the speed of the machine. When there is more load current, less speed, and when the system power factor reduces, the system needs more excitation.

An excitation system is a single unit where each alternator has an exciter with a generator shape. The central excitation system has two or more which feed the busbar. The central system is cheap but the system fault affects the alternator of the power plant negatively.

Types of Excitation System / Motor and Generator Excitation System

  • DC Excitation System 
  • AC Excitation System 
  • Static Excitation System 

AC excitation system is of two types.

  • Rotor Excitation System 
  • Brushless Excitation System 

DC Excitation System 

There are two exciters in the DC excitation system. 

  • Main Exciter
  • Pilot Exciter

To control output terminal voltage of exciter, main or pilot exciter maybe work by the main shaft or separately by the motor. Generally, a direct exciter is better because it protects the unit system of operation and is not affected by external factors. The voltage rate of the main exciter is almost 400 volt and the power of the power alternator is almost 0.5%. Exciters of turbo-alternators can cause problems frequently because of their fast speed.

AC Excitation System 

AC excitation system has one alternator and thyristor bridge which is directly connected to the shaft of the alternator. The main exciter can be self-excited or separately excited.

Static Excitation System 

Power grid excitation is done by this process. In this excitation system, the supply is provided by a step-down transformer connected with 3 phase delta connection from the alternator. The primary side of the transformer is connected with the alternator bus and the secondary side supplies power to the rectifier, grid control circuit, and other electrical parts.

Motor and Generator excitation system
Power Grid Excitation

That’s all for today’s topic motor and generator excitation system.

Hope it was helpful for you to understand the motor and generator excitation system.

If you have any queries please do ask in the comment section.

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