What is the difference between three phase synchronous and three phase asynchronous?

AC asynchronous motors! Let's talk about why it is called an asynchronous motor! The frequency of power frequency alternating current in China is 50 cycles per second (50nz s)!

The three sets of windings of the three-phase motor are all distributed in a 360-degree circumferential magnet core (magnetic field) according to a difference of 120 degrees! With the fewest phases, each phase needs two sets of windings! That is, there is a pair of magnetic poles!

With a frequency of 50 cycles and 60 seconds per minute, the rotation speed of the three-phase alternating magnetic field is up to 3000 revolutions! The general asynchronous AC motor has a rotor magnetic armature that is staggered and closed! In the rotating magnetic field of the stator core, it must form a staggered angle with the magnetic field in order to obtain the rotation distance!

In other words, its rotational speed is always behind the speed of the stator's rotating magnetic field! That's where async comes in! (The synchronous motor has its own unique structure), of course, the motor will have 2-pole, 4-pole, 8-pole designs according to needs!

The more poles, the slower the rotational speed! But the turning distance has increased! So drag the motor at low speed and more!

Most of the commonly used motors are 4 poles!

In fact, the working principle of AC asynchronous motor is roughly clear!

A three-phase alternating current of 50 cycles per second generates a rotating alternating magnetic field in a three-phase winding divided by 120 degrees of difference! (The rotational speed depends on the number of three-phase poles distributed in the stator during a week!) The rotor with a closed squirrel cage conductor embedded in the core generates a strong induced current in a strong rotating magnetic field!

This alternating current at the same frequency and stator current also generates a strong alternating rotating magnetic field! As long as it is at a different angle (asynchronous rotation) to the rotating magnetic field of the stator, it will keep spinning!

The key to synchronous three-phase AC motor synchronization is that its rotor does not need to be in step with the stator magnetic field! Because it has its own independent magnetic field, the magnetic pole! It can be a permanent magnet! It can also be excited! This way it can be synchronized with the rotating magnetic field of the stator!

The prerequisite for a three-phase asynchronous motor to rotate is to have a rotating magnetic field, and the stator winding of the three-phase asynchronous motor is used to generate a rotating magnetic field. We know that the voltage between the phases of the three-phase power supply is 120 degrees different in phase, and the three windings in the stator of the three-phase asynchronous motor are also 120 degrees different from each other in the spatial orientation, so that when the three-phase power supply is introduced in the stator winding, the stator winding will produce a rotating magnetic field, after the stator winding produces a rotating magnetic field, the rotor conductor (squirrel cage bar) will cut the magnetic field lines of the rotating magnetic field and generate an induced current, and the current in the rotor guide bar interacts with the rotating magnetic field to produce electromagnetic force. The electromagnetic torque generated by the electromagnetic force drives the rotor to rotate in the direction of the rotating magnetic field. In general, the actual speed of the motor is lower than the speed of the rotating magnetic field.

For this reason, we call the three-phase motor an asynchronous motor.

Three-phase synchronous motors are different working states of three-phase generators.

The rotor of the three-phase synchronous motor has n pairs of magnetic poles, these magnetic poles are arranged in the order of n-s-n-s ---, there are coils on the magnetic poles, all the coils are connected in series, and the last two ends are connected to two copper slip rings on the rotor shaft, and the copper slip rings are insulated from the shaft. The excitation power supply is in contact with the copper slip ring through the carbon brush, so that the excitation current passes through the excitation coil on the magnetic pole, so that the magnetic pole generates magnetic force.

For electric motors, there are three-phase AC windings on the stator that generate a rotating magnetic field that pulls the rotor (the poles) to rotate.

In the case of generators, the rotating poles of the rotor induce the three-phase AC windings on the stator to make it generate electricity.

When three-phase alternating current passes through a winding of a certain structure, a rotating magnetic field is generated. Under the action of a rotating magnetic field, the rotor rotates with the rotating magnetic field. If the speed of the rotor is exactly the same as the speed of the rotating magnetic field, it is a synchronous motor; If the speed of the rotor is less than the speed of the magnetic field, that is, the two are not synchronized, it is an asynchronous motor.

The asynchronous motor has a simple structure and a wide range of applications. Synchronous motors require the rotor to have fixed magnetic poles (permanent magnet or electromagnetic), such as alternators and synchronous AC motors!

1. Rotational speed. The asynchronous motor is the stator that feeds alternating current to generate a rotating magnetic field, and the rotor is induced to produce a magnetic field, so that the two magnetic fields act so that the rotor rotates with the rotating magnetic field of the stator. Among them, the rotor is slower than the stator rotating magnetic field, there is a slip, and it is not synchronized, so it is called an asynchronous machine.

The rotor of the synchronous motor is artificially added with direct current to form a constant magnetic field, so that the rotor will be synchronized with the rotating magnetic field of the stator, which is called a synchronous motor.

2. Structural principle.

The stator windings of synchronous and asynchronous motors are the same, with the main difference being the structure of the rotor.

There is a DC excitation winding on the rotor of the synchronous motor, so an external excitation power supply is required to introduce current through the slip ring;

The rotor of an asynchronous motor is a short-circuited winding that generates an electric current by electromagnetic induction.

The asynchronous motor is simple and low-cost. Easy to install, use and maintain. So it is widely used. Disadvantages: Low efficiency, low power factor, bad for the power grid. Synchronous motors, on the other hand, are capacitive loads with high efficiency, which can improve the power factor of the grid. Many mines are large-scale and unprepared.

1. The structure is different. The rotor of a synchronous motor has windings and there are brushes to supply power to the rotor, whereas the rotor of an asynchronous motor has no windings and no brushes.

2. The principle is different. Both synchronous and asynchronous refer to the relationship between the speed of the motor and the frequency of the power supply. The speed of the synchronous motor is synchronized with the frequency of the power supply AC. The speed of the asynchronous motor is not synchronized with the frequency of the alternating current of the power supply.

3. The application is different. In terms of application, synchronous motors are used in occasions with strict speed requirements, and they are also expensive. Asynchronous motors are commonly used in general occasions and are inexpensive.

1. The rotational speed is different from the rotational speed of the magnetic field. If the rotation speed of the rotor is the same as that of the stator, it is called a synchronous motor, and if it is inconsistent, it is called an asynchronous motor.

2. The rotor speed is different. When the number of pole pairs is constant, there is a strict relationship between the speed and frequency of the motor, and the rotor speed of the asynchronous motor is always less than that of the synchronous motor when it is working.

3. Different use scenarios. In terms of usage scenarios, synchronous motors are used in occasions with strict speed requirements, and they are also expensive. Asynchronous motors are commonly used in general occasions and are inexpensive.

What is the difference between synchronous and asynchronous three-phase motors

Synchronous motor principle.

If the permanent magnet is made into a motor rotor, and the magnetic field of the rotor and the stator are attracted to each other, the permanent magnet of the rotor will rotate together with the magnetic field of the stator windings. If the magnetic field of the stator core rotates faster, the rotor (motor) will also be faster. Because the speed of the motor is the same as the speed of the magnetic field, it is called a synchronous motor, because the magnetic field strength of the permanent magnet is weak and the load is light, many synchronous motor rotors use electromagnets instead of permanent magnets, that is, the rotor is made into an electromagnet.

The coil of the electromagnet is called the excitation winding.

Asynchronous motor principle.

According to the rotor structure, asynchronous motors can be divided into two forms, namely squirrel cage asynchronous motors and wound asynchronous motors. Here we take a squirrel cage asynchronous motor as an example. The rotor of a squirrel cage asynchronous motor is generally a cast aluminum rotor, and its windings are made of copper or aluminum, and the two ends of the windings are welded together, like a squirrel cage.

When the stator is applied with a three-phase alternating current, the rotating magnetic field of the stator cuts the rotor windings, inducing a current on the windings (aluminum strips). windings (aluminum strips). After the current is passed, it is accelerated by electromagnetic force in the magnetic field.

As the motor (rotor) rotates faster and faster, both remain relatively stationary when the rotor speed = stator magnetic field velocity. At this point, there is no relative motion between the rotating magnetic field and the rotor windings (i.e., the rotor windings are not cut), and the rotor loses electromagnetic force and slows down. When the motor decelerates, the rotating magnetic field moves relative to the rotor windings again, and the rotor is accelerated by electromagnetic force.

In simple terms, AC asynchronous motors rely on the rotating magnetic field and the relative motion between the rotor to obtain the rotational force. When the speed of the motor reaches the speed of the magnetic field, the rotational force is lost and the speed becomes slower; After deceleration, there will be relative motion, so it will accelerate again. Therefore, the motor is always in a state of acceleration and deceleration.

Because the motor speed and magnetic field speed are different, it is called an asynchronous motor. Advantages and disadvantages of both and their applications: The speed of the synchronous motor is synchronized with the speed of the stator magnetic field, and the motor speed will not change as long as the motor does not lose its pace, regardless of the motor load.

As long as the power frequency is adjusted, the motor speed can be accurately adjusted, which is suitable for precise speed regulation occasions. Due to its high precision, complex process, high cost and difficult maintenance, synchronous motors are not as widely used as asynchronous motors and are mostly used in large generators.

The rotational speed of the asynchronous motor is lower than that of the stator magnetic field and is load-dependent. The speed of the motor will change with the load. Asynchronous motors are widely used because of their simple structure, low cost, easy installation, and durability.

Asynchronous motors account for at least 80% of China's motors.