|Electric Motor Working|
The relation between the speed of the motor and its frequency is given by the expression
N = 120f/P.
From this expression, it is evident that the speed of the motor is directly proportional to the supply frequency. Thus any decrease or increase in frequency will affect the speed of the motor.
When a 50 Hz motor is made to run on 60 Hz supply:
It is general practice in several countries to have all house-hold items and equipments rated for 50 Hz supply. So when such small domestic devices are connected to a 60 Hz supply, they cause a severe problem. For better understanding, let us visualize this small calculation:
[(60Hz – 50 Hz)/ 50 Hz] * 100 = 20 %.
Also this 50 Hz motor will operate perfectly on a 60 Hz supply provided its supply voltage is stepped-up.
60 Hz/ 50 Hz = 6/5 * 100 = 120 %.
60 Hz motor connected to 50 Hz supply:
It is same as the above, but instead of stepping-up the supply voltage, it is necessary to step-down the supply voltage.
50Hz/ 60 Hz = 5/6 * 100 = 80 %.