Untuk mempercepat proyek Anda, Anda dapat melabeli Tumpukan Laminasi dengan detail seperti toleransi, bahan, permukaan akhir, apakah isolasi teroksidasi diperlukan atau tidak, kuantitasdan banyak lagi.
The three phase induction motor is a very important tool in today’s factories. You can find this strong induction motor in many places, like workshops and on farms. But these motors usually run at only one speed, which is a constant speed. What if you need to make a fan go slower or a conveyor belt go faster? This is why speed control is so useful. This guide will teach you some simple ways to manage the control of three phase induction motors. When you read this, you will learn how to make your machines run better. You will also learn to save power and make your work go more smoothly. We will explain tricky ideas in easy steps. This will make them simple for you to understand and put into practice.
Many tasks do not require a motor to run at its top speed all the time. For example, think about a water pump. Sometimes you need to move a lot of water. Other times, you only need to move a little. You waste a lot of power if your induction motor is always running at full speed. Speed control lets you match the motor speed to the work you need to do. This is very important for controlling the speed.
Using good speed control of three phase motors gives you many good things. It helps you save electricity, and that saves you money. It makes your machines get less damage over time. This helps them last for a longer time. It also helps you have more control over your work. For instance, you can start a conveyor belt slowly so that items do not fall off. Good speed control makes a great induction motor even better. It becomes more helpful and wastes less power.
Before we talk about speed control, let’s look at how a 3-phase induction motor works. It has two main parts. These are the stator and the rotor. The stator is the part on the outside that stays still. Inside of it are coils of wire which are called the stator winding. The rotor is the part on the inside that spins around.
When you send a three-phase supply of voltage to the stator winding, something interesting takes place. It makes a rotating magnetic field. You can picture it as a magnet that is spinning around inside the stator. This magnetic field moves past the bars on the rotor. This creates, or induces, a voltage and a current inside of them. This induced rotor current makes its own magnetic field. The two magnetic fields push and pull on each other. The stator field then drags the rotor with it, which causes it to spin. The motor is called an induction motor because the voltage is made in the rotor without any wires touching it.
The speed of the rotating magnetic field inside the stator is known as the synchronous speed. This is the fastest possible speed the induction motor can reach. The math rule for synchronous speed (Ns) is:
Ns = (120 x f) / P
The real rotor speed is always a little bit slower than the synchronous speed. The tiny difference in speed between the synchronous speed and the rotor speed is called “slip.” This slip is what lets the induction motor create turning force, or torque, and do work. If there was no slip, the induction motor would have zero torque. So, to change the speed of an induction motor, we must either change the synchronous speed or change the slip. The synchronous speed of the motor is the most important part.
Yes, you certainly can! Controlling the induction motor from the stator side is a very normal thing to do. This means we make a change to the power that is going into the stator. This is how we adjust the speed. These methods like changing the voltage or frequency are well-liked. This is because you do not need to make changes to the induction motor itself.
There are three main ways to do this:
Each method of speed control has its good points and its bad points. We will look at each one. This will help us see how it works for the induction motor. This kind of speed control from the stator circuit is used in many places.
One way to control the speed of an induction motor is to change the supply voltage. You can use a device like a transformer to make the voltage going to the motor also lower. When the voltage applied to the stator goes down, the torque produced by the induction motor goes down by a lot. The torque is connected to the voltage multiplied by itself. This means that a small drop in voltage will lead to a very big drop in torque.
This method of speed control is easy to do, but it is not the best choice for many tasks. When the torque decreases, the induction motor will slow down. But, the slip increases, which means that more energy is lost as heat inside the rotor. This makes the induction motor waste more power, and it might get too hot. This speed control technique is sometimes used for small motors that run fans or pumps. In those cases, the load torque gets smaller when the speed goes down. The power factor also gets worse at a low voltage.
Do you remember the math rule for synchronous speed? It showed that the speed depends on the number of poles. The pole changing method of speed control is based on this idea. Some special kinds of induction motor are made with a stator winding that can be wired in a new way. This is done to make a different number of poles. For instance, you could change a motor from having 4 stator poles to having 8 stator poles.
When you change the number of poles, you get a large jump in speed. A 4-pole induction motor with a 60 Hz power supply has a synchronous speed of 1800 RPM. If you change it to 8 poles, the synchronous speed will drop to 900 RPM. This method gives you different speeds. But, it does not give you a smooth speed control. You can only pick between two, or maybe three, set speeds. This is helpful for things like two-speed fans or certain machine tools. However, the range of speed control is small. It is a simple and effective way to get a step speed change.
This is the best and most common speed control method for a three phase induction motor used today. It is known as Variable Voltage Variable Frequency (V/VVF) or Voltage-to-Frequency (V/f) control. The idea is easy to understand. If you change the frequency of the supply, you will change the synchronous speed of the induction motor. If the speed increases, it is because the frequency was raised. If the speed decreases, it happened because of a decrease in frequency.
For this to work well, you must also change the voltage at the same time as the frequency. The torque of an induction motor relies on the magnetic field (mmf) in the stator. To keep this field and the torque at the same level, the ratio of voltage and frequency (V/f) needs to stay the same. We use a special tool called a drive or an inverter to do this. The inverter takes the normal AC power and turns it into DC power. Then, it uses a process called modulation to change the DC power back into AC power. This new AC power can be at any voltage and variable frequency we want. This gives us very smooth speed control over a very large range of speeds. This is the method of speed control that wastes the least amount of energy.
| Fitur | Kontrol Tegangan | Pole Changing | V/F Control | Rotor Resistance Control |
|---|---|---|---|---|
| Jenis Motor | Any squirrel cage motor | Special pole changing motor | Any squirrel cage motor | Wound rotor induction motors |
| Rentang Kecepatan | Small | Step-based (2-3 speeds) | Very Large | Large, but wastes power |
| Energy Use | Poor, high power loss | Tinggi | Sangat Tinggi | Poor, high power loss |
| Smoothness | Smooth | Not smooth | Very Smooth | Smooth |
| Complexity | Simple | Simple motor, simple switch | Complex electronics (VFD) | Simple (rheostat) |
Yes, but this only works with a special kind of induction motor. Most induction motor types are squirrel cage motor designs. In these motors, the bars in the rotor are fixed in place. For these motors, speed control is not possible from the rotor side. But there is another kind of motor called a wound rotor or slip-ring induction motor. This main motor has coils of wire in its rotor, just like the stator does.
These coils in the rotor are attached to three slip rings on the motor’s shaft. Brushes make contact with these rings. This lets us add an external resistance to the rotor circuit. By making changes to the rotor circuit, we can change the speed and torque behavior of this induction motor. This gives us a whole new set of speed control techniques.
For a wound rotor induction motor, the simplest way to do speed control on the rotor side is by adding rotor resistance. We attach a rheostat (which is a resistor you can change) to the slip rings on the rotor. When we add external resistance to the rotor circuit, it makes the motor act differently. The added resistance increases the slip of the motor for any given torque.
When the slip increases, the rotor speed goes down. So, by just turning the dial on the rheostat, we can get a wide range of speed control. This method of speed control is good for jobs that need a very high starting torque. Some examples are cranes, hoists, and rolling mills. The bad part is a very large power loss. All the extra resistance in the rotor circuit changes electrical energy into heat. It is like trying to drive your car while pressing the brakes. It will work, but it wastes a lot of energy. The starting current can be managed well with this method.
Cascade control is a more complicated method of speed control that also works from the rotor side. It is a smart way to stop wasting all the slip power as heat, which is what happens with rotor resistance control. In this arrangement, you use two motors that are connected to each other. The main motor is a wound rotor induction motor.
The power that comes from the rotor circuit of the main motor is not sent to a rheostat. Instead, that power is used to run a second motor, called an auxiliary motor. This auxiliary motor helps to turn the main shaft. By changing the setup of the auxiliary motor, we can control the slip frequency and the rotor emf in the main motor. This changes its speed. There are a few ways to connect the motors. This can give you four different constant speed choices. This system wastes less energy than rotor resistance control, but it is also more costly and complicated. Today, V/F drives that use a converter and an inverter are often a better option for induction motor speed.
Here is a fast review of what we have learned about speed control for a three phase induction motor:
Untuk mempercepat proyek Anda, Anda dapat melabeli Tumpukan Laminasi dengan detail seperti toleransi, bahan, permukaan akhir, apakah isolasi teroksidasi diperlukan atau tidak, kuantitasdan banyak lagi.
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