The squirrel cage rotor and the wound rotor are two types of rotors used in induction motors. These rotors differ in their construction and performance characteristics. Let's explore the differences between them:
Squirrel Cage Rotor:
The squirrel cage rotor is the most common type of rotor used in induction motors due to its simplicity, ruggedness, and low maintenance requirements. It is called a "squirrel cage" because of its appearance, resembling a cage made of conducting bars. The rotor consists of a laminated iron core with conducting bars (usually made of aluminum or copper) embedded in the slots on the periphery. The bars are short-circuited at both ends by end rings.
Operation: When the stator windings are energized, an alternating magnetic field is created, which induces currents in the squirrel cage bars. These induced currents in the rotor bars generate their own magnetic field, which interacts with the stator's magnetic field, producing torque and causing the rotor to rotate.
Advantages:
Simple and robust construction.
Low maintenance as there are no slip rings or brushes.
Suitable for applications with constant or variable speed requirements.
Disadvantages:
Limited control over the motor's starting torque and speed.
Wound Rotor (Slip Ring Rotor):
The wound rotor, also known as a slip ring rotor, is a less common type of rotor used in induction motors. It has a three-phase winding similar to the stator winding, and the winding ends are brought out through slip rings rather than short-circuited end rings. External resistors or variable resistors (rheostats) are connected to the slip rings to control the rotor's resistance.
Operation: During starting, the rotor resistance is set to a maximum value, which reduces the starting current and provides higher starting torque. As the motor accelerates, the resistance is gradually reduced to increase the motor's speed. Once the motor reaches the desired speed, the rotor resistance is usually short-circuited, essentially turning it into a squirrel cage rotor.
Advantages:
Better control over starting torque and speed.
Suitable for applications requiring high starting torque, like heavy loads or high-inertia systems.
Used in wound rotor induction generators, which can provide reactive power support and speed control.
Disadvantages:
Higher maintenance due to the presence of slip rings and brushes.
More complex construction compared to the squirrel cage rotor.
In summary, the squirrel cage rotor is simpler, requires less maintenance, and is more commonly used in most induction motor applications. On the other hand, the wound rotor provides better control over starting characteristics and is suitable for specific applications that demand higher starting torque and speed control.