Induction Motor Definition

Induction motor, also known as "asynchronous motor", is a device in which the rotor is placed in a rotating magnetic field, and under the action of the rotating magnetic field, a rotational torque is obtained, so that the rotor rotates. The rotor is a rotatable conductor, usually in the shape of a squirrel cage. Invented in 1887 by electrical engineer Nikola Tesla. The concept, inventor, working principle, basic structure, working mode, braking mode, asynchronous characteristics, specifications and fault inspection of induction motor are introduced.

Through the relative movement of the rotating magnetic field generated by the stator (the speed of which is the synchronous speed n1) and the rotor winding, the rotor winding cuts the magnetic field line to generate an induced electromotive force, thereby generating an induced current in the rotor winding. The induced current in the rotor winding acts with the magnetic field to generate electromagnetic torque, which makes the rotor rotate. Because when the rotor speed gradually approaches the synchronous speed, the induced current gradually decreases, and the generated electromagnetic torque also decreases accordingly. When the asynchronous motor works in the motor state, the rotor speed is less than the synchronous speed. In order to describe the difference between the rotor speed n and the synchronous speed n1, a slip is introduced.

Induction motor stator

The stator of the induction motor consists of three parts: the stator core, the stator winding and the frame. The stator core is part of the main magnetic circuit. In order to reduce the eddy current and hysteresis loss caused by the exciting current and the rotating magnetic field in the iron core, the iron core is made of silicon steel sheets with a thickness of 0.5mm. For motors with larger capacity, silicon steel sheets are coated with insulating paint on both sides as insulation between sheets. The small stator core is stacked with silicon steel sheets, compacted into a whole and then fixed in the machine base; the medium and large stator cores are made up of fan-shaped punching pieces. In the inner circle of the stator core, many grooves of the same shape are punched evenly. to embed the stator windings. Small induction motors usually use semi-closed slots and single-layer (scattered) windings wound with high-strength enameled wires, and slot insulation is placed between the coil and the iron core. The semi-closed slot can reduce the reluctance of the main magnetic circuit and reduce the excitation current, but it is inconvenient to insert the wire. Medium-sized induction motors typically use half-open slots. Large high-voltage induction motors use open slots. for easy wiring. In order to obtain better electromagnetic performance, medium and large induction motors use double-layer short-distance windings.

The rotor consists of a rotor core, a rotor winding and a rotating shaft. The rotor core is also a part of the main magnetic circuit, which is generally made of silicon steel sheets with a thickness of 0.5mm. The core is fixed on the rotating shaft or rotor bracket. The appearance of the entire rotor is cylindrical. Rotor windings are divided into two types: squirrel type and wound type.

1. Squirrel rotor

The cage winding is a self-closing winding. It consists of a bar inserted into each rotor slot and annular end rings at both ends. If the iron core is removed, the entire winding is shaped like a "circular cage", so it is called a cage winding. (Figure 5-1). In order to save copper and improve productivity, small cage motors generally use cast aluminum rotors; for medium and large motors. Since the quality of cast aluminum is not easy to guarantee, a structure in which copper bars are inserted into the rotor slots and end rings are welded on both ends is adopted. The cage induction motor is simple in structure and easy to manufacture, and is an economical and durable motor. So it is very widely used.

2. Wound rotor

The slot of the wound rotor is embedded with a three-phase winding composed of insulated wires, and the three outgoing wires of the winding are terminated

To the three collector rings set on the rotating shaft, and then lead out through the brush. As shown in Figure 5-3. The characteristic of this rotor is that an external resistance can be connected to the rotor winding to improve the starting and speed regulation performance of the motor.

Compared with the squirrel-cage rotor, the wound rotor has a slightly more complicated structure and a slightly more expensive price, so it is only used when the starting current is small, the starting torque is large, or the need to be dispatched.

To sum up, the stator part mainly includes stator iron core, stator winding, and base, and the rotor part mainly includes rotating shaft, rotor iron core, and rotor winding (closed conductor). The slot, its role is to embed the winding.

Hangzhou New Hengli Electric Machine MFG. Co., Ltd. (Originally Hangzhou Hengli Electric Machine MFG. Co., Ltd.) was founded in 1954.