Farm Power And Machinery (1+1)

Selection of Electric Motors

The starting requirements of equipment and the maximum current that may be drawn from the single phase power service are the two most important requirements for selecting an appropriate motor. However, choosing a motor that will meet load requirements without exceeding temperature and torque limits are also equally important considerations. Hence, the first step in motor selection is to determine the load characteristic such as power or torque requirements, speed and duty cycle.

• To select the right type of motor for any particular job, the following factors should be considered:
• The characteristic of the power supply whether A.C or D.C. ; single or three phase, 50 or 60 cycles supply is available.
• Horse Power requirement - to avoid over loading, slightly higher size should be preferred.
• Duty requirement - continuous or intermittent duty.
• Speed of operation - should be selected with the consideration of the machine to be driven.
• Starting current requirement should be known before selecting the motor for a particular use.
• Atmospheric and environmental conditions-humidity, splashing of liquids, excess dust etc. should be kept in view.
• Over load protection device-this always desirable if the motor is equipped with such a device.
• Price-it is quite logical to select the lowest price motor that will do the job satisfactorily.
• However, the price should not be the first consideration.
• By measuring the mechanical output of a motor and the electrical input to the motor under different load conditions with the help of ‘Prony Brake’ dynamometer, the torque-speed characteristic curves can be developed