Excitation (magnetic) facts for kids
Have you ever wondered how big machines like generators and motors work? A key part of them is something called excitation.
Excitation is a special process that helps create a powerful magnetic field using electric current. Think of it like making a temporary magnet with electricity.
This magnetic field is super important because it makes parts inside these machines, like the rotor, spin. The rotor is the spinning part of a motor or generator.
Sometimes, the magnetic field comes from a permanent magnet. But often, it's made by special wires called "field coils." To make these coils act like a magnet, electricity needs to flow through them. The device that does this job is called an exciter.
Contents
How Excitation Works
Imagine you have a coil of wire. If you send an electric current through this wire, it creates a magnetic field around it. This is the basic idea behind excitation.
In large machines, this magnetic field is needed to make the machine work. For example, in a generator, the spinning part (rotor) needs to move through a strong magnetic field to create electricity.
If the machine uses "field coils" instead of permanent magnets, it needs a constant supply of electricity to keep those coils magnetic. This is where the exciter comes in.
The exciter provides the electric current to these field coils. It's like giving the coils the energy they need to become powerful magnets.
Types of Excitation
There are a few ways to provide this exciting current. The main difference is where the electricity for the exciter comes from.
Self-Excited Machines
Some machines are "self-excited." This means they use a small part of the electricity they produce themselves to power their own exciter.
It's like a generator creating its own magnetic field. Once it starts, it keeps itself going. This is common in many DC generators.
Separately Excited Machines
In other machines, especially very large ones, the exciter gets its power from a completely different source. This is called "separately excited."
This separate power source might be a smaller generator or a battery. This method gives more control over the magnetic field. It is often used in big power plants.
Permanent Magnet Machines
Not all machines need an exciter. Some use strong permanent magnets to create their magnetic field.
These magnets don't need electricity to work. They are always magnetic. This makes the machine simpler, but you can't easily change the strength of the magnetic field.
Why Excitation is Important
Excitation is crucial for many reasons in electric machines.
It allows us to control the strength of the magnetic field. By changing the amount of current going to the field coils, we can make the magnetic field stronger or weaker.
This control is important for managing the power output of a generator. It also helps control the speed and power of an electric motor.
Without proper excitation, many modern generators and motors would not work efficiently. It's a fundamental part of how these amazing machines create and use electricity.
Images for kids
-
A 100 kVA direct-driven power station AC alternator with a separate belt-driven exciter generator, date c. 1917.
-
A self-excited shunt-wound DC generator is shown on the left, and a magneto DC generator with permanent field magnets is shown on the right. The shunt-wound generator output varies with the current draw, while the magneto output is steady regardless of load variations.
-
A separately-excited DC generator with bipolar field magnets. Separately-excited generators like this are commonly used for large-scale power transmission plants. The smaller generator can be either a magneto with permanent field magnets or another self-excited generator.
-
A field coil may be connected in shunt, in series, or in compound with the armature of a DC machine (motor or generator).
-
Alternator of 1930s diesel generating set, with excitation dynamo above
