Different DC motors are used in industry for various applications. Which type of motor will suit a particular load depends on the requirements of the load and characteristics exhibited by the motor. Applications of different motors are as under:
DC Shunt Motor Applications
Fig. 1: DC Shunt Motor Torque speed characteristics.
Characteristics of shunt motor described in Fig. 1 indicate that it is a nearly constant speed motor having its starting torque (torque at N = 0) 30% to 40% more than its rated torque and the speed of shunt motor can be adjusted over a wide range. Therefore, such a motor can be used for the following applications:
- Various machine tools such as lathe machines. drilling machines, milling machines etc.
- Printing machinery
- Paper machines
- Centrifugal and reciprocating pumps
- Blowers and fans etc.
However a three-phase squirrel cage induction motor which has almost similar characteristics (except availability of speed control over a wide range) is used for most of the applications stated above. This is because, induction motor is cheaper in cost, mechanically robust and as it works on a.c. supply, no additional arrangement is required to generate d.c. supply.
DC Series Motor Applications
Fig. 2: DC Series Motor Torque speed characteristics.
Series motor characteristics shown in Fig 2 indicate that it develops very high starting torque and it has adjustable varying speed. Therefore, for any load which needs high starting torque, series motor is the only suitable dc motor. Series motors are very widely used for the following applications:
- Electric trains,
- Diesel-eclectic locomotives,
- Cranes,
- Hoists,
- Trolley cars and trolley buses,
- Rapid-transit systems,
- Conveyers etc.
DC Cumulative Compound Motor Applications
These motors have high starting torque. They can be operated even at no loads as they run at a moderately high speed at no load. Hence cumulative compound motors are used for the following applications :
- Elevators
- Rolling mills
- Punches
- Shears
- Planers
DC Differential Compound Motors Applications
The speed of these motors will increase with increase in the load, which leads to an unstable operation. Therefore we cannot use this motor for any practical applications.
Selection of DC Motors for a Particular Application
D.C. shunt motor
D.C. shunt motor is used to drive pumps, lathes machine tools, prime mover for generators due to constant speed characteristic.
D.C. series motor
This has a very high starting torque. Hence it is used in applications like traction, cranes, hoists etc. which require high starting torque.
D.C. compound motor
This has higher starting torque but has finite speed at no load. It is used to driving rolling mills, cutting and shearing tools, presses etc.