Advantages and Applications of Slip Ring Induction Motors

A slip-ring induction motor is called an asynchronous motor because it does not run at a speed equal to the synchronous speed of the rotor. The rotor of this motor is wire-wound. It consists of a cylindrical laminated steel core and a semi-enclosed recess at the outer boundary to accommodate a three-phase insulated winding circuit.

Slip ring induction motors are a type of wound rotor motor widely used in industrial applications that require high starting torque and variable speed control. Unlike standard squirrel cage induction motors, slip ring induction motors have a series of rings attached to the rotor windings, which enables external resistance to be added to the circuit. This unique design offers several advantages and opens up specific application possibilities, making slip ring induction motors popular in sectors where robust starting capabilities and adjustable speed are crucial.

Why use slip rings?

Slip difference is defined as the difference between the flux speed and the rotor speed. For a torque-producing induction motor, there should be at least some difference between the stator field speed and the rotor speed. This difference is called "slip". A "slip ring" is an electromechanical device that helps transfer power and electrical signals from a stationary to a rotating part.

Slip rings are also known as rotary electrical interfaces, electric rotary joints, rotary rings, or collector rings. Sometimes, depending on the application, slip rings require a higher bandwidth to transmit data. Slip rings improve motor efficiency and performance by improving system operation and eliminating wires hanging from motor connectors.

Slip Ring Induction Motor

Benefits of Slip Ring Induction Motors

High starting torque and low starting current.

In the case of slip-ring (wound rotor) induction motors, the speed can be adjusted by inserting a resistor.

High overload capacity of the slip-ring motor, smooth acceleration under heavy load and no abnormal heating at startup.

Slip-ring induction motors have the advantages of high efficiency, energy saving, low noise, low vibration, safe and reliable operation, easy installation and maintenance, etc. It can be used for various motors of general purpose, such as ball mill, fan, compressor, pump, crusher, cutting machine, transportation machinery and other original motors. In addition, it can also be used to drive large torque inertia fans, coal mills, rolling mills, winches, electric shovels and other machinery, especially suitable for machinery and equipment under special working conditions with high requirements for motor protection.

Slip Ring Induction Motors Disadvantages 

Higher initial and maintenance costs compared to squirrel cage motors due to the presence of slip rings, brushes, short circuit devices, etc.

Poor speed regulation when running with external resistors in the rotor circuit

Lower efficiency and power factor of slip-ring motors compared to squirrel-cage induction motors

Lower power factor at light loads

Sensitivity to supply voltage fluctuations

Heavy Duty High Voltage Slip Ring Motor

Slip Ring Induction Motors Applications

Induction motors typically have a lower starting torque than DC series motors Slip-ring induction motors have the huge advantage of high starting torque compared to squirrel-cage motors. Therefore, slip-ring induction motors are typically used where loads require high starting torque or good speed control. They are used in cranes, hoists, compressors, printing presses, large ventilation fans, and loads requiring speed control, such as for driving lifts and pumps.

(1) Greater starting torque than squirrel cage rotor motors is required.

(2) Insufficient feeder capacity to start squirrel cage rotor motors.

(3) Need for a small range of speed regulation.

(4) "Electric shaft" synchronous drive. Such as compressors, sugar mills, textile machines, winches, wire drawing machines, conveyors and other machinery.

Conclusion

Slip-ring induction motors offer significant advantages in applications where high starting torque, speed control, and durability are essential. Their unique design enables them to meet the demands of various heavy-duty applications, from cranes and conveyors to elevators and industrial mixers. By providing a combination of strength, control, and reliability, slip-ring induction motors remain a crucial component in numerous industrial environments, ensuring efficient and stable operation.

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