What type of motor has a rotor with coils

What type of motor has a rotor with coils

A motor with a rotor winding typically refers to a wound-rotor asynchronous motor (also known as a slip-ring motor), where the rotor's winding consists of copper wire coils rather than the conductor bars of a squirrel-cage rotor. Below are key details about this type of motor:

1. Basic Structure and Characteristics
Rotor Structure: The iron core slots of the wound rotor are embedded with three-phase symmetrically distributed copper windings. The ends of the windings are connected to external resistors or control devices via slip rings and brushes. This design allows the rotor resistance to be adjusted through external circuits, thereby controlling the starting current and torque.
Difference from squirrel cage rotors: Squirrel cage rotors use aluminum or copper bars directly cast into a closed loop, featuring a simple structure but no external circuit connection; whereas wound rotors achieve adjustable rotor circuits through slip rings, making them suitable for applications requiring high starting torque or speed regulation.

2. Working Principle
The working principle of a wound-rotor asynchronous motor is based on electromagnetic induction:
Rotating magnetic field: When three-phase stator windings are energized with alternating current, a rotating magnetic field is generated, which cuts the rotor coils and induces current.
Torque Generation: The interaction between the rotor current and the rotating magnetic field generates electromagnetic torque, driving the rotor to rotate. By adjusting the external resistance of the rotor, the slip rate can be modified, enabling smooth speed regulation or improved starting performance.

3. Application Scenarios
High starting torque requirement: For heavy-duty equipment such as cranes, steel rolling mills, and mining machinery, external resistors are used to limit starting current and enhance starting torque.
Speed regulation control: Achieve speed adjustment by rotor resistance or frequency converter, suitable for production lines or fan systems requiring precise control.

4. Advantages and Disadvantages
Advantages: Low starting current, high starting torque, and superior speed regulation performance compared to squirrel-cage motors.
Disadvantages: Complex structure, higher maintenance costs (requiring periodic replacement of brushes and slip rings), and slightly lower efficiency compared to squirrel-cage motors.

5. Other motor types with rotor-mounted coils
Synchronous motor: Some synchronous motors also have excitation windings (coils) on the rotor, which require DC excitation to establish a fixed magnetic field and operate synchronously with the rotating magnetic field of the stator.
DC motor: The armature (rotor) winding achieves current commutation through the commutator and brushes, but it belongs to a brushed structure, differing in principle from asynchronous motors.

In summary, motors with rotor-wound coils are primarily wound-rotor induction motors, whose core advantages lie in controllable starting and speed regulation performance, making them widely used in industrial heavy-duty equipment. For higher efficiency or maintenance-free designs, permanent magnet synchronous motors or brushless DC motors may serve as alternatives.