A squirrel cage motor is a type of AC induction motor, which is widely used in various applications due to its simple construction, low cost, and reliable operation. The name “squirrel cage” is derived from the shape of the rotor, which resembles a cage-like structure with bars or conductors on the surface.
Types of squirrel cage motor:
- Single-phase squirrel cage motor: It is a type of motor that runs on a single-phase power supply and is commonly used in home appliances and small machines.
- Three-phase squirrel cage motor: It is a type of motor that runs on a three-phase power supply and is widely used in industrial applications such as pumps, fans, and compressors.
- Wound rotor squirrel cage motor: It is a type of motor that has a wound rotor instead of a squirrel cage rotor, and is used in applications requiring precise speed control or high starting torque.
Construction of squirrel cage motor:
A squirrel cage motor consists of two main parts, the stator and the rotor. The stator is a stationary part, which consists of a cylindrical frame made of laminated steel sheets. Inside the stator, there are evenly spaced slots, which are designed to hold the stator windings.
The rotor, on the other hand, is a rotating part that is placed inside the stator. It is made of a cylindrical core, which is also made of laminated steel sheets. On the surface of the rotor, there are conductive bars or “squirrel cage” conductors, which are arranged in a cage-like structure.
Working of squirrel cage motor:
When an AC voltage is applied to the stator windings, it creates a rotating magnetic field that rotates at the synchronous speed. The rotating magnetic field induces an EMF in the rotor conductors, which causes a current to flow in the bars. Due to the interaction between the rotating magnetic field and the current in the bars, a torque is produced, which causes the rotor to rotate in the same direction as the magnetic field.
Advantages:
- Simple construction and low cost.
- High starting torque, which makes it suitable for heavy load applications.
- Low maintenance requirements.
- Wide range of sizes and power ratings.
- High reliability and long service life.
Disadvantages:
- Low efficiency at low loads and partial loads.
- Limited speed control range.
- Cannot be used in applications requiring precise speed control.
- Requires external starting means to overcome initial inertia.
Applications
- Fans and pumps: Squirrel cage motors are commonly used in fans and pumps because they are efficient and have a low starting torque.
- Compressors: Squirrel cage motors are used in air compressors because they can handle high loads and have a long life span.
- Conveyors: Squirrel cage motors are used in conveyor systems because they are rugged, efficient, and have a high starting torque.
- Machine tools: Squirrel cage motors are used in machine tools such as lathes, milling machines, and grinders because they provide precise speed control.
- Agriculture: Squirrel cage motors are used in agricultural equipment such as irrigation pumps and grain augers because they are durable and can handle heavy loads.
- HVAC systems: Squirrel cage motors are used in heating, ventilation, and air conditioning (HVAC) systems because they are reliable, efficient, and have a low starting torque.
- Elevators: Squirrel cage motors are used in elevator systems because they can provide high starting torque and operate at a wide range of speeds.