Factors Governing Selection of Electric Motors:

Parallel to the growth of machine tools, an equally rapid progress has been made in the field of electric motors. The electric motors of various designs are available to meet the needs of various classes of industry. So the selection of electric motor itself has become an important and tedious process. The conditions under which an electric motor has to operate and the type of load it has to handle, determine its selection. The various factors that are to be considered in the selection of an electric motors for a particular service are :

1. Nature of Electric Supply.

2. Types of Drives.

3. Nature of Load.

4. Electrical Characteristics.

  • Operating or Running Characteristics.
  • Starting Characteristics.
  • Speed Control.
  • Braking Characteristics.

5. Mechanical Considerations

  • Types of Enclosures.
  • Types of Bearings.
  • Types of Transmission For Drive.
  • Noise Level.
  • Heating and Cooling Time Constants of the Motor.

6. Service Capacity and Rating.

  • Requirements For Continuous, Intermittent or Variable Load Cycle.
  • Pull-Out Torque and Overload Capacity.

7. Appearance.

8. Cost Considerations.

  • Capital or Initial Cost.
  • Running or Operating Cost—power factor, losses, maintenance and depreciation etc.

From the above it is seen that a large number of factors are to be considered in making the choice of an electric motor for a given drive. Although in the list of various considerations the cost has been placed at the end, yet the final choice has to be governed by it. The motor selected must fulfil all the necessary load requirements and at the same time it should not be very costly if it has to be a commercial success. In any particular case some of the factors may be definitely fixed by existing circumstances while others will probably be conflicting and, therefore, for making most satisfactory choice understanding of various possibilities is necessary. The basic problem is of matching the mechanical output of the electric motor with the load requirements, i.e., to provide a motor with the correct speed-torque characteristics as demanded by the load.