The structure of three-phase asynchronous motor is composed of stator, rotor and other accessories.
（1） Stator (stationary part)
1. Stator core
Function: It is a part of the magnetic circuit of the motor, on which the stator winding is placed.
Structure: The stator core is generally made of 0.35-0.5mm thick silicon steel sheet with insulating layer on the surface and laminated. There are evenly distributed slots punched in the inner circle of the core to embed the stator winding.
The stator core slot types are as follows:
Semi-closed slot: the efficiency and power factor of the motor are high, but the winding embedding and insulation are difficult. Generally used in small low-voltage motors.
Semi-opening slot: it can embed the formed winding, and is generally used for large and medium-sized low-voltage motors. The so-called formed winding means that the winding can be put into the slot after insulation treatment in advance.
Open-type slot: It is used to embed the formed winding, and the insulation method is convenient. It is mainly used in high-voltage motors.
2. Stator winding
Function: It is the circuit part of the motor, which is fed with three-phase alternating current to generate rotating magnetic field.
Structure: It is connected by three identical windings with symmetrical arrangement and 120 ° electrical angle separated from each other in space. Each coil of these windings is embedded in each slot of the stator according to certain rules.
The main insulation items of the stator winding are as follows: (ensure the reliable insulation between the conductive parts of the winding and the iron core as well as the reliable insulation between the winding itself).
(1) Insulation to ground: insulation between the whole stator winding and the stator core.
(2) Inter-phase insulation: insulation between stator windings of each phase.
(3) Inter-turn insulation: insulation between the turns of each stator winding of each phase.
Wiring in motor junction box:
There is a wiring board in the motor junction box. The six wire ends of the three-phase winding are arranged in two rows, and the upper row of three wiring posts arranged from left to right are numbered 1 (U1), 2 (V1), 3 (W1), and the lower row of three wiring posts arranged from left to right are numbered 6 (W2), 4 (U2), and 5 (V2). The three-phase winding is connected in star connection or triangle connection. All manufacturing and maintenance shall be arranged according to this serial number.
Function: fix the stator core and front and rear end covers to support the rotor and play the role of protection and heat dissipation.
Structure: The frame is usually cast iron, the frame of large asynchronous motor is generally welded with steel plate, and the frame of micro motor is made of cast aluminum. There are cooling ribs on the outside of the frame of the enclosed motor to increase the heat dissipation area. The end covers at both ends of the frame of the protective motor are provided with ventilation holes, so that the air inside and outside the motor can be directly convection to facilitate heat dissipation.