MISCONCEPTION ON NO-LOAD CURRENT

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:

1. Magnetizing component
2. 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.

Important

• 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,

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.