A compound motor is an electric motor that combines the features of both series and shunt motors. It is also known as a cumulative compound motor. This type of motor has both a series of field winding and a shunt field winding, which are connected in series with each other.
Types of Compound Motors:
- Long Shunt Compound Motor
- Short Shunt Compound Motor
Construction of Compound Motor:
The construction of a compound motor is similar to that of a DC shunt motor with an additional series winding. The main components of a compound motor are:
- Armature: The armature is the rotating part of the motor and consists of a core, windings, and commutator.
- Field windings: A compound motor has two field windings, a shunt winding and a series winding.
- Commutator: The commutator is a set of copper segments that are mounted on the armature shaft. It is used to switch the direction of current flow in the armature windings as the rotor rotates.
- Brushes: The brushes are carbon blocks that make contact with the commutator and transfer the current to the armature windings.
- Frame: The frame is the outer casing of the motor and provides support for the components.
The series winding of the compound motor is made of a few turns of thick wire with low resistance and is connected in series with the armature winding. This winding produces a strong magnetic field when current flows through it. The shunt winding is made of many turns of thin wire with high resistance and is connected in parallel with the armature winding. This winding produces a weaker magnetic field but is more stable.
The construction of a compound motor is more complex than that of a DC shunt motor, but it provides better performance in certain applications where a variable load is required. The series winding provides a high starting torque, while the shunt winding provides a constant speed.
Working of Compound Motor:
The compound motor combines the properties of a shunt and a series motor to produce a motor that is efficient, has high starting torque, and is capable of working at variable speeds. The shunt field winding provides a constant magnetic field, while the series field winding produces a magnetic field that varies with the load. The result is a motor that can handle high loads and maintain a relatively constant speed.
Advantages of Compound Motor:
- High starting torque
- Good speed regulation
- Better efficiency compared to series motors
- Can be operated at variable speeds
Disadvantages:
- Complex construction
- High cost compared to other types of motors
- Difficult to control and maintain the speed at low loads
Applications
- Elevators and hoists: Compound motors are used in elevators and hoists because they require high starting torque to lift heavy loads, as well as constant speed to ensure a smooth ride.
- Machine tools: Compound motors are used in machine tools like lathes, milling machines, and grinders because they require high starting torque to overcome the initial resistance of the material being worked on, and a constant speed to ensure accuracy and precision.
- Traction applications: Compound motors are used in traction applications like electric trains, trams, and trolleybuses because they require high starting torque to get the vehicle moving, as well as constant speed to ensure a smooth ride.
- Cranes and winches: Compound motors are used in cranes and winches because they require high starting torque to lift heavy loads, as well as constant speed to ensure a smooth operation.
- Conveyors: Compound motors are used in conveyor systems because they require high starting torque to move heavy loads, as well as constant speed to ensure a steady flow of material.