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Break Down And Full Load Torque Of Ac Motors.


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Dear Friends,


There is confusion in my mind about AC motor’s torque especially “Break down torque” and “Full load torque”. When we look at the torque curve (see the attached picture), it shows that an AC motor can develop max 150% starting torque which is called “Locked rotor torque”. For me, this is the maximum torque limit (150%) which can produce an AC motor whether motor is stationary or during running for just a moment during abrupt load change; but what is the “Breakdown torque” which is 200% within 70-80% of base speed?

Some people call it “No load torque” but I say that torque will be expressed with loading the motor, not without load. If staring or running torque (for a short moment) demand is greater than 200%, a DC motor is used. Am I correct?


"Don't assume any thing, always check/ask and clear yourself".

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I think this illogicity - more torque required at overcoming the inertia not at the start but at a later point - is characteristic of any "engine". It may turn irrelevant and icorrect: all weight-lifters in a competition are able to tear the heaviest barbell from the ground but only the winner will bring it through the more higher from the ground "point of breakdown".

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