A wound rotor motor is a type of AC induction motor where the rotor windings are made of insulated copper wire that is wound around a laminated iron core. The stator windings are stationary and are located in the motor housing.
Construction of wound rotor motor:
The construction of a wound rotor motor involves the following steps:
- Stator: The stator is made up of a laminated iron core with slots on its surface. Copper wire is wound in the slots to form the stator winding. The stator winding is connected to a power supply, which provides the current necessary to create a magnetic field.
- Rotor: The rotor is made up of a laminated iron core with slots on its surface. Copper wire is wound in the slots to form the rotor winding. The rotor winding is connected to slip rings, which are mounted on the rotor shaft. The slip rings allow external connections to be made to the rotor.
- Brush gear: Brush gear consists of carbon brushes that press against the slip rings to make electrical contact. The brush gear is mounted on a stationary part of the motor, and it provides the necessary electrical connection between the stator and the rotor.
- Control equipment: Control equipment is used to regulate the speed and torque of the motor. This equipment typically includes a variable frequency drive (VFD) or a wound rotor resistor.
When the motor is started, the rotor winding is connected to a set of resistors to limit the starting current. As the motor accelerates, the resistors are gradually disconnected, and the rotor winding is connected directly to the slip rings. The slip rings are then connected to the brush gear, which makes electrical contact with the stator winding.
Working of wound rotor motor:
When an AC voltage is applied to the stator windings, a magnetic field is created that rotates around the stator. This rotating magnetic field induces a current in the rotor windings, which creates a second magnetic field that also rotates. The interaction between the two magnetic fields causes the rotor to rotate, which in turn drives the motor’s output shaft.
Types of wound rotor motor:
- Single-phase wound rotor motor
- Three-phase wound rotor motor
Advantages:
- A wound rotor motor has a high starting torque, making it suitable for applications where a high starting torque is required.
- It has a wide speed range and can be easily controlled by varying the resistance of the rotor windings.
- It has a better power factor than a squirrel cage motor, which results in less power loss in the stator windings.
- It is suitable for applications where a variable speed is required, such as cranes and hoists.
Disadvantages:
- The use of slip rings and brushes makes the wound rotor motor more complicated and requires more maintenance than a squirrel cage motor.
- It has a lower efficiency compared to a squirrel cage motor because of the increased losses due to the slip rings and brushes.
- The cost of a wound rotor motor is generally higher than that of a squirrel cage motor due to the additional components required.
Applications
- Cranes and hoists: Wound rotor motors are commonly used in cranes and hoists, where their high starting torque and adjustable speed control make them ideal for lifting heavy loads.
- Mining equipment: Wound rotor motors are used in a variety of mining equipment, such as conveyor belts, pumps, and crushers. These motors can withstand harsh operating conditions and provide high torque at low speeds.
- Wind turbines: Wound rotor motors are used in wind turbines to drive the blades and generate electricity. The adjustable speed control of these motors allows them to optimize their performance in changing wind conditions.
- Paper mills: Wound rotor motors are commonly used in paper mills for powering large machinery, such as pulp refiners and paper machines. These motors provide high torque at low speeds, which is important for the high-torque applications in paper mills.
- Cement mills: Wound rotor motors are also used in cement mills for grinding raw materials and clinker. The high starting torque and adjustable speed control of these motors make them ideal for this application.
- Marine propulsion: Wound rotor motors are used in marine propulsion systems to provide high torque at low speeds, which is important for large ships that require a lot of power to move through the water.