Synchronous motors is different from asynchronous motors_Wolong Nanyang Explosion-proof Motor, China Motor Manufacturer

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Synchronous motors is different from asynchronous motors

source：未知 time：2024-07-01 10:49nbsp; click：

Different principles

For synchronous motors, the speed is synchronized with the rotating magnetic potential, while the speed of asynchronous motors is lower than the electromagnetic speed; regardless of the load size, the speed of synchronous motors will not change as long as they do not lose step, while the speed of asynchronous motors changes with the load size at all times. Structurally, asynchronous motors have no permanent magnets and rely on the rotating magnetic field generated by the stator to cut the rotor cage structure, as shown in the figure below:

Quote from someone else's answer:

For synchronous motors, both the stator and the rotor generate magnetic fields, that is, the stator winding generates a rotating magnetic field after passing three-phase alternating current, and the rotor magnetic field can be generated by a DC excitation coil or a permanent magnet. The stator magnetic field and the rotor magnetic field are like two magnets, attracting each other with the same polarity; since the stator magnetic field rotates at the power supply frequency, it drives the rotor to rotate together, and the two have the same speed. Because the rotor angular velocity is equal to the synchronous speed (consistent with the power supply frequency), it is called a synchronous motor. For asynchronous motors, taking the cage type as an example, only the stator winding generates a rotating magnetic field when three-phase alternating current is passed, and the rotor "cage" can be understood as a set of closed wires, which have no current or magnetic field. When the rotating magnetic field of the stator cuts the conductor of the rotor "cage" (conversely, the conductor cuts the magnetic lines of force, Faraday's law of electromagnetic induction), an induced current is generated on the rotor; at this time, according to Ampere's law, the current-carrying wire will be subjected to a force in the magnetic field, driving the rotor to move. However, the rotor speed can never reach the speed of the stator's rotating magnetic field, because once they are equal, it is equivalent to the rotor and the magnetic lines of force being relatively stationary, the conductor will not cut the magnetic lines of force, and no induced current can be generated. Without current, there is no Ampere force. Without Ampere force, the rotor will decelerate under the action of the load torque. After deceleration, the rotor speed is lower than the synchronous speed, and the conductor begins to cut the magnetic lines of force again... Therefore, the rotor speed can never reach the synchronous speed (that is, the speed of the stator rotating magnetic field determined by the power supply frequency), which is also the origin of the "asynchronous" of the asynchronous motor. This is the essential difference between the two.

Advantages and Disadvantages

1. Synchronous Motor

Advantages: The power factor of the synchronous motor can be adjusted. In situations where speed regulation is not required, the application of large synchronous motors can improve operating efficiency.

Disadvantages: The cost is higher than that of asynchronous motors.

There are three main applications, namely as a generator, motor and compensator. Running as a generator is the main operating mode of synchronous motors. Small synchronous motors are beginning to be widely used in variable frequency speed regulation systems. Synchronous motors can also be connected to the power grid as synchronous compensators. At this time, the motor does not carry any mechanical load, and it sends the required inductive or capacitive reactive power to the power grid by adjusting the excitation current in the rotor to achieve the purpose of improving the power factor of the power grid or regulating the power grid voltage.

2. Asynchronous motor

Advantages: Asynchronous motor is an AC motor, and the ratio of its speed under load to the frequency of the connected power grid is not a constant relationship. Therefore, it has the advantages of simple structure, easy manufacturing, use and maintenance, reliable operation, small mass and low cost. Asynchronous motors have higher operating efficiency and better working characteristics. They run at a constant speed from no-load to full-load, and can meet the transmission requirements of most industrial and agricultural production machinery.

Disadvantages: Since the speed of the asynchronous motor has a certain slip relationship with the speed of its rotating magnetic field, its speed regulation performance is poor (except for AC commutator motors). For transportation machinery, rolling mills, large machine tools, printing and dyeing and papermaking machinery that require a wide and smooth speed regulation range, it is more economical and convenient to use DC motors.

Application: As a motor, its power range ranges from a few watts to tens of thousands of kilowatts. It is the most widely used motor in various industries of the national economy and people's daily life, providing power for a variety of mechanical equipment and household appliances. For example, machine tools, small and medium-sized steel rolling equipment, fans, water pumps, light industrial machinery, metallurgy and mining machinery, etc., are mostly driven by three-phase asynchronous motors (Asynchronous Motor); single-phase asynchronous motors are widely used in household appliances such as electric fans, washing machines, refrigerators, air conditioners, etc. Asynchronous motors can also be used as generators in wind power plants and small hydropower stations.

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