There is a misconception around ‘No-load Current’ drawn and the ‘Power consumed’ by a 3 Phase AC Induction Motor when it is not coupled to the driven equipment.
The No-load Current, which produces the magnetic field in the motor, can be categorized into the following components:
- Magnetizing component
- Loss component (Hysteresis & Eddy current loss)
The No-load Current is not a direct addition of Magnetizing component & Loss component current. This current, for a given KW, varies for different manufacturers. There are no standards or thumb rules to specify the limit of No-load Current. No-load current can be as high as 65 % of full-load current. However, the magnetizing component is very high on no-load, which doesn’t result in actual power consumption as it is a wattless component.
- Power consumption is proportional to the product of the Current & Power factor (PF)
- The power factor at no-load is as low as 0.1 and can go even higher than 0.88 at higher loads.
Consider the below illustration,
|At no-load||At full-load|
|Current drawn||10 A||20 A|
|Power factor (PF)||0.10||0.88|
Basis the above example, we can understand that there is no harm if the no-load current is high as long as the PF is low. Hence, No-load Current value should not be taken as a parameter for the performance of the motor.