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2023

AC asynchronous motor

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1.1 AC asynchronous motor structure

AC asynchronous motors, also known as induction motors, mainly include stators, rotors, motor shafts, front and rear bearings, end covers, position sensors, temperature sensors, low-voltage wiring harnesses and high-voltage power wiring harnesses. The stator is composed of a stator core and a three-phase winding; the rotor is usually a cage rotor, including a rotor core and a cage winding. Depending on the power of the motor will choose water cooling or air cooling. (Figure 1)

The working principle of 1.2 AC asynchronous motor

1.2.1 Driving principle of AC asynchronous motor

1.2.1.1 The stator provides a rotating magnetic field

To drive the AC asynchronous motor to provide torque, three-phase alternating current needs to be passed into the stator coil to generate a continuously rotating magnetic field (magnetic field speed is ns). AC asynchronous motor requires that the stator three-phase windings must be symmetrical, and the stator core is spatially different by 120 degrees of electrical angle. The current flowing into the three-phase symmetrical winding must also be symmetrical, with the same size, frequency and phase difference of 120 degrees. Rotation speed of rotating magnetic field, see formula (1).

NS = 60F/P (1)

In the formula, ns is the rotating speed of the rotating magnetic field (also called synchronous speed),r/min; F is the frequency of three-phase alternating current, Hz; P is the number of pairs of magnetic poles. For the drive motor that has been designed and finalized for production, the logarithm of the magnetic stage has been determined, so the factor that determines the rotation speed of the magnetic field is the frequency of the three-phase alternating current. Since the frequency of the power grid in our country is f = 50Hz, the speed of the motor and the number of magnetic poles have a linear relationship. (Figure 2)