Het zelfstartvermogen van een driefasen inductiemotor

Have you ever thought about what makes the big machines in factories and workshops run? Many of them use a special type of motor. This motor is called a three-phase induction motor. The coolest thing about it is that it can start all by itself. You just give it power, and it begins to turn. This is very important, and it is the reason these motors are used so often.

In this article, you will find out the simple reason behind this self-starting magic. We will explain step-by-step how a 3-phase power source makes a special force. This force gets the motor spinning with no outside help. You do not need to be an engineer to get it. We will use easy words and simple examples to explain how this strong induction motor works.

So, What Is a Three-Phase Induction Motor?

A three-phase induction motor is a kind of electric motor. You can think of it as the main engine for big jobs in the world. It is strong, simple, and you can count on it. The name of the motor tells you a lot. “Three-phase” means it uses a special type of electricity. This power has three separate flows of current. “Induction” means it uses the power of magnets to make its moving part spin without any wires touching it.

This motor has two main parts. The first part is the stator. The stator is the outside part of the motor that stays still. It does not move. The second part is the rotor. The rotor is the part on the inside of the motor that can spin around. The magic of the induction motor happens because of how these two parts work with each other. They use electricity and magnets to create strong movement and to turn heavy things.

Why Is Being “Self-Starting” Such a Big Deal?

The self-starting capability of a three-phase induction motor is its best-known trick. But why is that so important? Think about having to push a huge fan every time you wanted it to start. Or think about having to spin a heavy water pump with your hands to get it moving. That would be very hard and not very useful. A self-starting motor fixes this problem.

When we say a motor is self-starting, it means you just have to give it power. It will then start to spin and make its own turning force. It does not need an outside push. It also does not need a fancy starter tool from the outside to get it moving. This self-starting feature makes the induction motor very, very easy to use. You just flip a switch, and it starts working. This easiness is a big reason why this type of motor is used in so many machines.

What Is the Stator and What Is Its Job in an Induction Motor?

The stator is the base of the induction motor’s strength. It is the big, round, and heavy outside shell of the motor. It stays perfectly still when the motor is on. Inside the stator, there are small grooves that hold coils of wire. We call these the stator windings. There are three different sets of windings. There is one set for each phase of the 3-phase power supply.

When you hook up the 3-phase electric supply to the motor, current goes through these stator windings. The stator’s job is to change this electricity into a strong, magnet-like field. But it is not just a normal magnetic field. Because of the 3-phase power, the stator can produce a very special kind of field. This field is a rotating magnetic field. This field is the secret that gives the motor the power to start and rotate. The stator is the part that makes the “push” without ever touching the rotor.

How Does a 3-Phase Power Source Make a Spinning Magnetic Field?

This is where the real fun starts. A 3-phase power supply is not just one flow of electricity. It is three separate flows, or phases, of current. These three flows of current are timed just right. They get stronger and weaker one after the other. This happens in a smooth pattern that repeats. It is like three friends pushing a merry-go-round. The first friend pushes. Then the second friend pushes. Then the third friend pushes, and it starts all over again. Their pushes are spread out just right. This makes the merry-go-round spin smoothly all the time.

The stator windings are placed in a circle. Each set of windings is hooked up to one of the three phases.

• When Phase 1 has the most power, it makes a magnetic field in one direction.
• A little bit later, Phase 2 has the most power. It makes a field in a new direction.
• A little bit after that, Phase 3 has the most power. It makes a field in another new direction.

Because these power peaks happen in the right order, the total magnetic field does not just show up and go away. Instead, it looks like it is spinning around the inside of the stator at a steady speed. This is the rotating magnetic field. The stator uses the 3-phase supply to produce this spinning force field, and no parts of the stator have to move. The speed of this field has a special name: synchronous speed.

(This is a simple chart to show how the field moves)

What Part Does the Rotor Play in an Induction Motor?

Now, let’s talk about the second main part: the rotor. The rotor is the part of the induction motor that is the part that really spins and gets the job done. The most common kind of rotor is called a “squirrel cage” rotor. It looks a little like a cage for a pet hamster. It has solid bars on the sides that are joined by rings on each end. These bars are often made from aluminum or copper.

The most important thing to know about the rotor in an induction motor is that it is not hooked up to any outside power. There are no wires that go to it. It just sits inside the stator, able to spin freely. Its job is to respond to the magnetic field that the stator makes. The rotor is the part that gets “fooled” into spinning by the rotating magnetic field. The simple design of the rotor, with no parts that rub or need direct wire connections, is what makes the induction motor so strong and able to last a long time.

How Does the Spinning Magnetic Field Make the Rotor Move?

Here is how the stator and rotor work with each other. The stator produces a strong rotating magnetic field. This field spins around inside the motor and goes through the rotor. As the magnetic field moves across the metal bars of the rotor, a rule of science called “electromagnetic induction” starts to work. The moving magnetic field creates a voltage. This voltage makes a strong electric current flow inside the rotor’s bars.

Now, the rotor has its own current flowing in it. When current flows through a wire or a bar, it makes its own magnetic field. This means we now have two magnetic fields. One is the big, spinning field from the stator. The other is a new field around the rotor, made by the new current. These two magnetic fields then work on each other. The stator’s field pushes and pulls on the rotor’s field. This pushing and pulling is what makes the rotor begin to spin.

What Is Torque and How Does It Help the Induction Motor Start?

Torque is just a turning or a twisting force. When you use a tool to tighten a screw, you are using torque. In an induction motor, the way the stator’s field and the rotor’s field work together makes a strong turning force, or torque, on the rotor. The rotating magnetic field from the stator is always moving. It pulls the rotor along with it. This is like holding a carrot on a stick to make a donkey walk.

This torque is what gives the induction motor its self-starting capability. The moment you turn on the 3-phase power, the rotating magnetic field appears. This field right away creates a current in the rotor. This current makes a second magnetic field, and the two fields working together produce torque. This torque is strong enough to get the rotor moving, even though it wants to stay still. The torque produced makes the rotor start to spin. It tries to catch up with the spinning field from the stator. This is why the motor is self-starting.

Why Can’t a Single-Phase Induction Motor Start by Itself?

It is easier to understand why a three-phase induction motor is self-starting when you look at a motor that is not. This is the single-phase induction motor. You can find these motors in things around your house, like fans and fridges. A single-phase power source has only one flow of current that moves back and forth.

When you give single-phase power to a motor’s stator, it does not produce a rotating magnetic field. Instead, it makes a field that just gets stronger and weaker in one spot. It does not spin. This shaky field cannot decide which way to push the rotor. So, the rotor just sits still and makes a humming sound. It has no starting torque. To make a single-phase induction motor start, it needs an extra part, like a capacitor. This part helps make a second magnetic field that is a little off-beat. This gives the rotor the first push it needs to start spinning in one direction.

Does the Self-Starting Capability Mean Zero Help Is Needed?

When we say a three-phase induction motor has a self-starting capability, we mean it does not need any outside push or pull to start. You do not have to spin it with your hand. You also do not need fancy extra electric parts just to create the starting movement. The motor is self-starting because its simple design, when used with a 3-phase supply, makes its own starting force all by itself.

All the motor needs is the correct kind of power. The 3-phase supply is the secret. The induction motor does not require any other outside tools to get moving. The way the three phases of current arrive in the right order lets the stator produce a rotating magnetic field. This field is all the “help” the rotor needs to begin to spin. The whole system works right away.

What Makes This Self-Starting Motor So Tough and Trustworthy?

The three-phase induction motor is a top choice for big jobs because its self-starting design is also very simple and tough. The rotor has no special wires that need their own power. It also has no brushes that can wear out over time. The main parts are the stator, which does not move, and a simple, solid rotor. There are very few parts that can break.

This simple design, along with its strong self-starting capability, makes the three-phase induction motor a great choice for hard jobs. It can start even when it has to move heavy things. It runs at a speed that is almost always the same. And it can work for many years and does not need much care. The power to just connect it to electricity and have it start every single time is what has made this wonderful induction motor the most used motor in the world.

Belangrijke punten

• A driefasen inductiemotor can start all by itself because its power source helps it make a turning force.
• De stator is the part that doesn’t move. It has wires that connect to the 3-phase power supply.
• A 3-phase supply makes a special rotating magnetic field inside the stator.
• De rotor is the part that spins. It has no wires connected to it directly.
• The rotating magnetic field from the stator creates a current inside the rotor.
• This current in the rotor makes its own magnetic field, which works with the stator’s field to make a turning force (torque).
• This starting koppel is strong enough to make the rotor rotate without any outside push.