AC power has become popular and advantageous because of easy generation, transmission with fewer losses to long distances due to stepping up voltage and stepping down the voltage to the desired level. In Industries 70% of the motors and drives used are Induction motors, hence ac motors in general means induction motors. Induction motors were preferred in industries due to the advantages of its rugged construction, less maintenance and can be operated in explosive atmospheres also. Therefore Induction motors ruled out all the motors in industries in every application. But DC motors were still used in certain applications where induction motors cannot fulfill the need. so, dc motors have its own significance in industries. This is because some special characteristics they possess.
Advantages of DC motors
1. Speed control over a wide range both above and below the rated speed: The attractive feature of the dc motor is that it offers the wide range of speed control both above and below the rated speeds. This can be achieved in dc shunt motors by methods such as armature control method and field control method. This is one of the main applications in which dc motors are widely used in fine speed applications such as in rolling mills and in paper mills.
2. High starting torque: dc series motors are termed as best suited drives for electrical traction applications used for driving heavy loads in starting conditions. DC series motors will have a starting torque as high as 500% compared to normal operating torque. Therefore dc series motors are used in the applications such as in electric trains and cranes.
3. Accurate steep less speed with constant torque: Constant torque drives are one such the drives will have motor shaft torque constant over a given speed range. In such drives, shaft power varies with speed.
4. Quick starting, stopping, reversing and acceleration.
5. Free from harmonics, reactive power consumption and many factors which makes dc motors more advantageous compared to ac induction motors.
Disadvantages of DC motors
- High initial cost
- Increased operation and maintenance cost due to the presence of commutator and brush gear.
- Cannot operate in explosive and hazard conditions due to sparking occur at brush (risk in commutation failure)
Applications of DC motors
Some of the applications of dc motors are Steel mills, paper mills, cranes and elevators, electric trains and much more etc.