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What is the difference between a squirrel cage rotor and a wound rotor in a three-phase asynchronous motor?

Release time:

2023-05-12 14:16

What is the difference between a squirrel-cage rotor and a wound rotor motor? Three phase asynchronous motor consists of stator and rotor. The stator is a fixed part of the motor, which is used to generate rotating magnetic field. It is mainly composed of stator core, stator winding, base and other components. The rotor is the rotating part of the motor, which is composed of rotor core, rotor winding, shaft and other parts. Its main function is to obtain the rotating torque under the action of rotating magnetic field. Rotors are divided into two types according to their structure: squirrel cage rotors and wound rotors:

1. Squirrel cage rotor

The rotor winding is composed of multiple guide bars inserted into the rotor slot and two circular end rings. If the rotor iron core is removed, the entire winding looks like a squirrel cage, hence it is called a cage winding. Small and medium-sized rotors are generally made of cast aluminum.

For motors above 100KW, copper bars and copper end rings are welded together. The phase number of the squirrel cage asynchronous motor rotor is the number of guide bars on the squirrel cage rotor, and the number of turns per phase is equal to 1/2 turns. The rotor winding does not need to be insulated against the ground. The number of rotor poles is obtained asynchronously by the magnetic electromotive force of the stator winding, so it is always equal to the number of pole pairs of the stator winding and independent of the number of bars in the squirrel cage rotor.

The squirrel cage rotor, as shown in the figure below, is installed with copper bars in the iron core groove of the rotor, and both ends are welded with end rings, resembling a squirrel cage in shape. The commonly used starting methods for squirrel cage asynchronous motors include direct starting, reduced voltage starting, variable frequency starting, or soft starter starting.

2. Wound rotor

The winding of a wound rotor is similar to the stator winding, and medium-sized motors often use double-layer windings. The three-phase windings are connected in a star shape, with three end wires connected to three copper (or steel) slip rings installed on the shaft and connected to the external circuit through brushes. The number of phases and pole pairs of the rotor winding of a wound asynchronous motor is always the same as the stator, with relatively more turns per phase and higher induced electromotive force. The rotor winding needs to be insulated against ground.

The commonly used starting methods for wound asynchronous motors are direct starting, rotor series resistance starting, or frequency sensitive rheostat starting. There is no need to resort to frequency conversion or soft starter startup.

Squirrel cage type, control motor operation is relatively simple. The winding motor has a complex structure, high price, and relatively complex control of motor operation, resulting in relatively few applications. However, wire wound motors are mainly used in heavy-duty loads due to their high starting and operating torque.

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