High-Voltage Three-Phase Asynchronous Motors: A Comparison Of Squirrel-Cage And Wound RotorsHigh-Voltage Three-Phase Asynchronous Motors: A Comparison Of Squirrel-Cage And Wound Rotors

High-voltage three-phase asynchronous motors consist of two main components: the stator and the rotor. The stator is the stationary part, responsible for generating a rotating magnetic field, and is primarily composed of the stator core, stator windings, and frame. The rotor is the rotating part, consisting of the rotor core, rotor windings, and shaft, whose main function is to generate rotational torque under the influence of the rotating magnetic field. Based on structural differences, rotors are classified into two types: squirrel-cage rotors and wound rotors.

1. Squirrel-Cage Rotor

The rotor winding is made up 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 "cage winding." For small and medium-sized motors, cast aluminum is commonly used for the rotor.

For motors above 100 kW, copper bars and copper end rings are welded together. The number of phases in a squirrel-cage asynchronous motor is equal to the number of conductor bars on the rotor, with each phase having 1/2 turn. The rotor winding does not require insulation to ground. The number of pole pairs in the rotor is induced asynchronously by the stator winding magnetomotive force, so it always matches the number of pole pairs in the stator winding and is independent of the number of conductor bars in the squirrel-cage rotor.

Common starting methods for squirrel-cage asynchronous motors include direct-on-line 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. Medium-sized motors often use double-layer windings, with the three-phase windings connected in a star configuration. Three terminals are connected to three copper (or steel) slip rings mounted on the shaft, which are connected to an external circuit via carbon brushes. In a wound-rotor asynchronous motor, the number of phases and pole pairs of the rotor winding are always the same as those of the stator. Each phase has a relatively large number of turns, resulting in a higher induced electromotive force, and the rotor winding requires insulation to ground.

Common starting methods for wound-rotor asynchronous motors include direct-on-line starting, rotor series resistance starting, or frequency-sensitive rheostat starting. Variable-frequency starting or soft starter starting is unnecessary and redundant.

Squirrel-cage motors are relatively simple to control and operate. In contrast, wound-rotor motors have a more complex structure, higher cost, and more complex control, leading to fewer applications. However, due to their larger starting and running torque, wound-rotor motors are mainly used in heavy-load applications.

In summary, high-voltage three-phase asynchronous motors with squirrel-cage and wound rotors each have their own technical advantages and application adaptability, and the core of their selection lies in matching the actual working conditions and operational requirements of industrial scenarios. High-Voltage Three-Phase Asynchronous Motors serve as the core equipment for high-power industrial drives, and the differences in rotor structures directly determine their starting performance, speed regulation capabilities, and operation and maintenance costs. Only by scientifically selecting models based on the load characteristics, energy-saving requirements and service environment of production scenarios can the equipment efficiency be maximized, providing reliable power support for the efficient and stable operation of industrial production.