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No load current and Full load current of an Induction motor

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Posted 15 January 2004 - 06:37 PM

I would like to know what is the difference between the current drawn by the 3 phase induction motor at no load and at full load? Does it follows any general convention ??
Thanks in Advance.

#2 marke


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Posted 15 January 2004 - 07:11 PM

At full load, the current drawn is a combination of the"work current" loss currents and the magnetising current.
The work current is the current required to produce shaft torque and is directly proportional to the shaft loading in KW.

At no load, there is no work current, but the magnetising current remains, and a reduced loss current also remains.

Typically, the no load current is between 60% rated current on very small machines and 20% rated current on large two pole machines.
On medium sized three pahse motors as found in industrial applications, it is common for the no load current to be in the range of 25 - 35% rated current.

Trends: As the motor size increases, the no load current (%) reduces.
As the motor speed is reduced (increasing poles) the no load current (%) increases.

Best regards,

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