The three-phase asynchronous motor is composed of two b […]
The three-phase asynchronous motor is composed of two basic parts: a fixed stator and a rotating rotor. The rotor is installed in the inner cavity of the stator and supported on two end covers with the aid of bearings. In order to ensure that the rotor can rotate freely in the stator, there must be a gap between the stator and the rotor, which is called an air gap. The air gap of the motor is a very important parameter, and its size and symmetry have a great influence on the performance of the motor. Figure 2 shows the components of a three-phase cage asynchronous motor.
The stator consists of a stator three-phase winding, a stator core and a frame.
The stator three-phase winding is the circuit part of the asynchronous motor. It plays a very important role in the operation of the asynchronous motor and is a key component for converting electrical energy into mechanical energy. The structure of the stator three-phase winding is symmetrical. Generally, there are six outlet terminals U1, U2, V1, V2, W1, W2, which are placed in the junction box outside the base and connected into a star (Y) or delta ( △), the stator core is a part of the magnetic circuit of the asynchronous motor. Since the main magnetic field rotates relative to the stator at a synchronous speed, in order to reduce the loss caused in the core, the core is made of 0.5mm thick high-permeability silicon steel sheets, with silicon steel sheets on both sides It is coated with insulating varnish to reduce the eddy current loss of the iron core.
The frame is also called the case. Its main function is to support the stator core and to withstand the reaction force generated by the entire motor load during operation. The heat generated due to internal losses during operation is also dissipated through the frame. The frame of medium and small motors is generally made of cast iron. Large-scale motors are often formed by welding with steel plates due to the inconvenient pouring of their large fuselage.
The rotor of an asynchronous motor is composed of a rotor core, a rotor winding and a rotating shaft.
The rotor core is also a part of the magnetic circuit of the motor, which is also laminated with silicon steel sheets. Different from the stator core punching sheet, the rotor core punching sheet is slotted on the outer circle of the punching sheet. After the laminated rotor core, many slots of the same shape are uniformly formed on the outer cylindrical surface of the rotor core for placing the rotor windings.
The rotor winding is another part of the asynchronous motor circuit. Its function is to cut the stator magnetic field, generate induced electric potential and current, and force the rotor to rotate under the action of the magnetic field. Its structure can be divided into two types: cage winding and winding winding. The main features of these two types of rotors are: the cage rotor has a simple structure, is convenient to manufacture, economical and durable; the wound rotor has a complex structure and is expensive, but the rotor circuit can introduce an external resistor to improve the starting and speed regulation performance.
The cage-shaped rotor winding is composed of a guide bar placed in the rotor slot and end rings at both ends. In order to save steel and improve productivity, the guide bars and end rings of low-power asynchronous motors are generally cast from molten aluminum at one time; for high-power motors, because the quality of cast aluminum is not easy to guarantee, copper bars are often inserted into the rotor core slot In the middle, then the end rings are welded on both ends. The winding of the cage rotor is closed by itself and does not need to be powered by an external power source. Its appearance is like a cage, so it is called a cage rotor.