Motor Load-Torque

[broc028]

Hi guys,

I have a 3 phase induction motor and have calculated the load (calculated to be 75%) and the full load torque by using the following:
(HP x 5252)/Full load RPM

Would it be fair to say that the actual torque required by the load can be calculated as follows:
Actual Torque=Full Load Torque/0.75.

Thanks.

 

[waross]

No.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

I assume you estimated the fraction of full load based on speed (slip) or based on the current (accounting for efficiency and power factor as needed).

An induction motor speed does not change by a large fraction from no-load to full load and so can be considered roughly constant speed. So the output torque is roughly proportional to the output power. Assuming no speed changing device (belt, gearbox etc), the load input torque is roughly the same (neglecting tranmsission losses) and so would be proportional to your estimated load (not inversely proportional as your /0.75 suggests)

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[waross]

Change

Actual Torque=Full Load Torque/0.75.

to

Actual Torque=Full Load Torque * 0.75.

Bill
--------------------
"Why not the best?"
Jimmy Carter