Types of DC Motors
There are three main types of DC motors:
The shunt and series type of DC motor have only one field winding on the pole of the stator, while the compound type has two separate field windings wound on the stator of each pole.
Motor Characteristics
The performance of a motor can be judged by its characteristic curves known as motor characteristics. There are basically three important characteristics:
- Torque and Armature Current Characteristic (Ta/Ia)
- Speed and Armature Current Characteristic (N/Ia)
- Speed and Torque Characteristic (N/Ta)
Note:
- Torque v/s Armature Current and Speed v/s Armature Current are known as
Starting Characteristics.
- Speed v/s Torque is known as the Running Characteristic.
Applications of D.C. Motors
1. Shunt Motors
The shunt motor is an approximately constant speed motor. Its characteristics make it highly suitable for applications where steady speed is required.
- Applications:
- Where speed should remain almost constant from no-load to full-load.
- Where the load has to be driven at different speeds, each of which needs to remain nearly constant.
- Industrial Uses: Lathes, drills, boring mills, shapers, spinning and weaving machines, etc.
2. Series Motors
The series motor is a variable speed motor i.e., its speed is high at low torque and low at high torque. It develops very high starting torque but runs at dangerously high speed under light or no-load conditions.
- Applications:
- Where large starting torque is required, e.g., elevators and electric traction.
- Where the load experiences heavy fluctuations and the speed must automatically reduce at high torque and increase at low torque.
- Industrial Uses: Electric traction, cranes, elevators, air compressors, vacuum cleaners, hair dryers, sewing machines, etc.
3. Compound Motors
Compound motors are of two types: Differential-compound and Cumulative-compound. Differential-compound motors are rarely used due to poor torque characteristics. However, cumulative-compound motors are widely used where a fairly constant speed is required despite irregular or suddenly applied heavy loads.
- Industrial Uses: Presses, shears, reciprocating machines, etc.