An electric motor (commonly known as a "motor") is an electromagnetic device that converts or transmits electrical energy based on the law of electromagnetic induction.
An electric motor (commonly known as a "motor") is an electromagnetic device that converts or transmits electrical energy based on the law of electromagnetic induction. It is represented by the letter M in a circuit. Its main function is to generate driving torque, serving as a power source for electrical appliances or various machines. A generator is represented by the letter G in a circuit. Its main function is to convert electrical energy into mechanical energy.
An electric motor mainly consists of an electromagnet winding or distributed stator winding to generate a magnetic field, a rotating armature or rotor, and other accessories. Under the action of the rotating magnetic field of the stator winding, current flows through the armature squirrel-cage aluminum frame, and the armature rotates due to the magnetic field.
Motor manufacturing process content
1. Machining processes: including rotor machining and shaft machining.
2. Core manufacturing process: including the manufacturing of laminations for the magnetic pole core and the lamination stacking.
3. Winding manufacturing process: including coil manufacturing, winding installation and insulation treatment (including short-circuit ring welding).
4. Squirrel cage rotor manufacturing process: including the stacking of rotor cores and rotor die casting.
5. Motor assembly process: including riveting of bracket components, riveting and assembly of main and auxiliary stators of the motor, etc.
Basic structure
I. The structure of a three-phase asynchronous motor consists of a stator, a rotor, and other accessories.
(I) Stator (stationary part)
1. Stator core
Function: Part of the motor's magnetic circuit, on which the stator windings are placed.
Construction: The stator core is generally made of silicon steel sheets with an insulating layer on the surface , which are stamped and stacked. The inner circle of the core has evenly distributed slots for embedding the stator winding.
The stator core slot types include the following:
Semi-closed slots: These motors have higher efficiency and power factor, but winding and insulation are more difficult. They are generally used in small, low-voltage motors.
Semi-open slots: These can accommodate pre-formed windings and are generally used in large and medium-sized low-voltage motors. Pre-formed windings are windings that have been pre-insulated before being placed into the slot. Open slots: These are used to accommodate pre-formed windings, offering convenient insulation methods, and are mainly used in high-voltage motors.
2. Stator winding
Function: It is the circuit part of the electric motor. When three-phase alternating current is applied, it generates a rotating magnetic field.
Construction: It consists of three identical windings arranged in a symmetrical manner, spaced 120° apart in space. The coils of these windings are respectively embedded in the slots of the stator according to a certain pattern.
The main insulation items of the stator winding are as follows: (ensuring reliable insulation between each conductive part of the winding and the core, and reliable insulation between the windings themselves).
1) Ground insulation: Insulation between the stator winding as a whole and the stator core.
2) Phase-to-phase insulation: Insulation between stator windings of each phase.
3) Inter-turn insulation: Insulation between turns of each phase stator winding.
Wiring inside the motor junction box:
Every motor junction box contains a terminal block. The six wire ends of the three-phase windings are arranged in two rows, top and bottom. The top three terminals are numbered from left to right as 1 (U1), 2 (V1), and 3 (W1), and the bottom three terminals are numbered from left to right as 6 (W2), 4 (U2), and 5 (V2). The three-phase windings are connected in either a star or delta configuration. This numbering should be followed during manufacturing and maintenance.
3. Base
Function: To fix the stator core and the front and rear end covers to support the rotor, and to provide protection and heat dissipation.
Construction: The frame is usually made of cast iron. The frame of large asynchronous motors is generally welded from steel plates, while the frame of micro motors is made of cast aluminum. The frame of enclosed motors has heat dissipation fins on the outside to increase the heat dissipation area, and the frame of protective motors has ventilation holes at both ends of the end cover to allow direct air convection between the inside and outside of the motor, which is conducive to heat dissipation.
(II) Rotor (Rotating Part)
1. Rotor core of a three-phase asynchronous motor:
Function: As part of the motor's magnetic circuit and to house the rotor windings within the iron core slots.
Construction: The materials used are the same as the stator, made of 0.5 mm thick silicon steel sheets, punched and stacked. The outer circumference of the silicon steel sheets has evenly distributed holes punched to house the rotor windings. The rotor core is usually made by punching the inner circumference of the silicon steel sheets after the stator core has been punched. Generally, the rotor core of small asynchronous motors is directly pressed onto the shaft, while the rotor core of large and medium-sized asynchronous motors (rotor diameter of 300-400 mm or more) is pressed onto the shaft with the help of a rotor support.
2. Rotor windings of a three-phase asynchronous motor
Function: It cuts the rotating magnetic field of the stator to generate induced electromotive force and current, and forms electromagnetic torque to make the motor rotate.
Structure: It is divided into squirrel cage rotor and wound rotor.
1) Squirrel-cage rotor: The rotor winding consists of multiple conductor bars inserted into the rotor slots and two annular end rings. If the rotor core is removed, the entire winding resembles a squirrel cage, hence the name squirrel-cage winding. Small squirrel-cage motors use cast aluminum rotor windings, while motors above 100KW use copper bars and copper end rings welded together.
2) Wound rotor: The winding of the wound rotor is similar to that of the stator winding. It is also a symmetrical three-phase winding, usually connected in a star configuration. The three leads are connected to the three current collectors on the shaft and then connected to the external circuit through brushes.
Features: Due to its more complex structure, wound-rotor motors are not as widely used as squirrel-cage motors. However, by using slip rings and brushes to connect additional resistors and other components in series in the rotor winding circuit, the starting, braking, and speed regulation performance of asynchronous motors can be improved. Therefore, they are used in equipment requiring smooth speed regulation within a certain range, such as cranes, elevators, and air compressors.
(III) Other accessories for three-phase asynchronous motors
1. End cap: provides support.
2. Bearing: Connects the rotating part to the stationary part.
3. Bearing end cap: Protects the bearing.
4. Fan: Cools the electric motor.
II. The DC motor adopts an octagonal fully laminated structure, which not only has high space utilization but also can withstand pulsating current and rapid load current changes when powered by a static rectifier. DC motors generally do not have a series winding, making them suitable for automatic control technologies requiring forward and reverse motor rotation. Series windings can also be manufactured according to user needs. Motors with a center height of 100–280 mm have no compensating winding, but motors with a center height of 250 mm and 280 mm can be manufactured with compensating windings depending on specific circumstances and needs. Motors with a center height of 315–450 mm have compensating windings. The external dimensions and technical requirements of motors with a center height of 500–710 mm conform to IEC international standards, and the mechanical dimensional tolerances of the motors conform to ISO international standards.
