An electric motor is a device that converts electrical energy into mechanical energy. It uses the energized coil (that is, the stator winding) to generate a rotating magnetic field and acts on the rotor squirrel-cage closed aluminum frame to form a magneto-electric power rotating torque. Motors are divided into DC motors and AC motors according to different power sources. Most of the motors in the power system are AC motors, which can be synchronous motors or asynchronous motors (the stator magnetic field speed of the motor and the rotor rotation speed do not maintain a synchronous speed).

The motor is mainly composed of a stator and a rotor, and the direction of the energized wire in the magnetic field is related to the direction of the current and the direction of the magnetic field line (magnetic field direction). The working principle of the motor is that the force of the magnetic field on the current causes the motor to rotate.

Three-phase asynchronous motor

The structure of a three-phase asynchronous motor consists of a stator, rotor, and other accessories.

(1) Stator (static part)

1. Stator core

(1) Function: A part of the magnetic circuit of the motor, and the stator winding is placed on it.

(2) Structure: The stator core is generally punched and laminated by 0.35-0.5 mm thick silicon steel sheets with an insulating layer on the surface, and evenly distributed slots are punched in the inner circle of the core to embed the stator windings.

(3) There are the following types of stator core slots:

a. 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.

b. Half-open slot: can be embedded with formed windings, generally used for large and medium-sized low-voltage motors. The so-called formed winding means that the winding can be insulated in advance and then put into the slot.

c. Open slot: It is used for inserting and placing forming windings, and the insulation method is convenient. It is mainly used in high-voltage motors.

2. Stator winding

(1) Function: It is the circuit part of the motor, which is connected to a three-phase alternating current to generate a rotating magnetic field.

(2) Structure: It consists of three windings with the same structure that are separated by a 120° electrical angle from each other in space and arranged in teams. Each coil of these windings is embedded in each slot of the stator according to a certain rule.

(3) The main insulation items of the stator winding are as follows: (guarantee the reliable insulation between the conductive parts of the winding and the iron core and the reliable insulation between the winding itself).

a. Insulation to the ground: the insulation between the entire stator winding and the stator core.

b. Phase-to-phase insulation: the insulation between the stator windings of each phase.

c. Surge: insulation between turns of each phase stator winding.

(4) Wiring in the motor junction box:

There is a wiring board in the junction box of the motor. The six wires of the three-phase winding are arranged in two rows, up and down. (W1), the number of the three wiring piles in the lower row from left to right is 6 (W2), 4 (U2), and 5 (V2). Connect the three-phase windings in a star connection or a delta connection. All manufacturing and maintenance should be arranged according to this serial number.

3. Machine base

(1) Function: Fix the stator core and the front and rear covers to support the rotor, and play the role of protection and heat dissipation.

(2) Structure: The frame is usually cast iron, the frame of a large asynchronous motor is generally welded with steel plates, and the frame of a 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 and protect the

There are ventilation holes in the end caps at both ends of the base of the type motor so that the air inside and outside the motor can be directly convection to facilitate heat dissipation.

(2) Rotor (rotating part)

Rotor core of three-phase asynchronous motor:

(1) Function: As part of the magnetic circuit of the motor and placing the rotor winding in the core slot.

(2) Structure: The material used is the same as the stator, which is punched and laminated from 0.5 mm thick silicon steel sheets. The outer circle of the silicon steel sheet is punched with evenly distributed holes for placing the rotor windings. Usually, the inner circle of the silicon steel sheet after the stator core is punched is used to punch the rotor core. Generally, the rotor core of small asynchronous motors is directly press-fitted on the rotating shaft, and the rotor cores of large and medium-sized asynchronous motors (with a rotor diameter of 300-400 mm or more) are pressed on the rotating shaft with the help of the rotor bracket.

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