Squirrel cage induction motors and wound rotor induction motors are two common types of AC (alternating current) induction motors, both widely used in various industrial and commercial applications. They differ in their rotor construction and the way they control starting and speed characteristics.
Rotor Construction:
Squirrel Cage Induction Motor: In a squirrel cage motor, the rotor is made up of a cylindrical core with evenly spaced conductive bars (usually made of aluminum or copper) embedded in the slots of the core. The bars are short-circuited at both ends by two end rings, resembling a squirrel cage.
Wound Rotor Induction Motor: In a wound rotor motor, the rotor winding consists of insulated coils of wire wound around the rotor core's slots. The rotor winding is brought out to slip rings, which can be externally connected to various external resistors or other devices.
Starting and Speed Control:
Squirrel Cage Motor: Squirrel cage motors are known for their simplicity and ruggedness. They have high starting torque and are often used in applications where frequent starting and stopping is required. However, their speed control is limited, and they typically operate at a relatively constant speed (synchronous speed minus slip).
Wound Rotor Motor: Wound rotor motors offer more flexibility in terms of speed control. By varying the external resistance connected to the slip rings, the rotor current and hence torque characteristics can be adjusted. This allows for better control of starting torque, speed, and even the ability to achieve higher efficiency in some cases.
Maintenance and Reliability:
Squirrel Cage Motor: Squirrel cage motors have fewer moving parts (no slip rings and brushes), making them more reliable and requiring less maintenance. They are often preferred in applications where maintenance access is limited.
Wound Rotor Motor: Wound rotor motors have slip rings and brushes, which can wear out over time and require maintenance. However, their speed control capabilities often make them suitable for applications where precise control over speed and torque is essential.
Applications:
Squirrel Cage Motor: Squirrel cage motors are commonly used in applications where constant speed is acceptable, such as industrial pumps, fans, blowers, and conveyors.
Wound Rotor Motor: Wound rotor motors find applications in situations requiring adjustable speed and torque, such as crane drives, hoists, winding machines, and high-inertia loads.
In summary, squirrel cage induction motors are simpler, more rugged, and require less maintenance, but offer limited speed control. Wound rotor induction motors provide greater speed control and starting torque adjustment capabilities, but come with the added complexity of slip rings and require more maintenance. The choice between the two types depends on the specific requirements of the application.