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In the field of electric motors, asynchronous motors and synchronous motors are two common types, and they have significant differences in their working principles and performance characteristics. Understanding the principles and differences between these two types of motors helps us better understand how electric motors work and how they can be used in different application scenarios. So, are you wondering what exactly is the difference between an asynchronous motor and a synchronous motor? Next, let's unravel this mystery together.
Classification of three-phase motors
Three-phase motors are the backbone of automation and industrial processes. These motors are capable of providing efficient power for a wide range of machines and automation applications. However, not all three-phase motors are created equal and can be classified according to their structure and the process by which the electric potential is utilized.
Three-phase motors are divided into two categories: synchronous motors and asynchronous motors, and asynchronous motors are also known as induction motors. Asynchronous motors can be further divided into two different types according to their structure: squirrel cage induction motors and wound rotor induction motors.
What is a synchronous motor?
The three-phase synchronous motor runs at a synchronous speed, and the rotor poles are aligned with the rotating stator poles. When the magnetic poles are aligned, the motor is said to be running at a synchronous speed. This type of motor always runs at synchronous speed, which means that synchronous motors cannot achieve variable speeds.
Synchronous motors require a secondary DC power supply to feed and magnetize the rotor, and DC current is fed to the motor through the use of open rings. Permanent magnets can also be used for rotors. Since the motor needs to run at synchronous speed to work, it is usually necessary for the starting mechanism to rotate the motor at or near the operating speed before the motor can function properly.
The rotor's DC power supply is typically powered by the main AC power supply, rectified into the DC circuit supplied to the rotor, so while two different supply voltages are required, they both use the input three-phase AC power supply.
What is an asynchronous motor?
Asynchronous motors work differently than synchronous motors. The induction of an asynchronous motor is the process of generating an electric current in a conductor by placing it near or inside a changing magnetic field. Induction is only possible in AC current circuits because a change in the magnetic field causes a current to be induced when the current switches between states.
Asynchronous motors use this principle to generate mechanical torque through a constant magnetic change in the alternating current in the windings. Since the stator is fed with three-phase electricity, a rotating magnetic field that is constantly changing with respect to the rotor is generated.
Since the rotation of the magnetic field is relative to the rotor, the rotor will be in a constant state of trying to "catch" the rotating magnetic field. This means that the rotation speed of the induction motor is always slower than the speed of the rotating magnetic field.
The difference between the two
Let's take a closer look at synchronous motors. Since synchronous motors are not induction motors, a power supply needs to be installed on the rotor. The power supplied to the rotor must be DC in order to properly energize the rotor windings.
In addition to the DC power supply, synchronous motors require a starting mechanism to bring the motor to synchronous speed before the motor is operating under operating conditions.
Synchronous motors can adjust the power factor lag to 1 or lead by changing the excitation within the rotor. The induction motor is always in a hysteresis state.
Since synchronous motors are typically more complex, they typically require more parts and are therefore more expensive. Although they may initially cost more, they tend to be more efficient than induction motors, allowing for a recoup of cost differences over time.
When choosing a three-phase motor, it is important to consider how the motor will be used, the environment in which it will be used, the energy efficiency of the motor, and of course, the cost. Three-phase motors can be used in many automation and manufacturing processes, although they don't operate in the same way. Through an in-depth understanding of asynchronous motors and synchronous motors, we can better apply and exert the functions of electric motors to promote the progress and development of technology.
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