Overload on three phase induction motor
Overload on three phase induction motor
(OP)
Can you answer how many percent a three phase induction motor can be overloaded considering safety??
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Overload on three phase induction motor
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RE: Overload on three phase induction motor
RE: Overload on three phase induction motor
If the ambient temperature is less than the temperature that the motor is rated for, some overload may be possible. It is difficult to put a percentage on it.
A motor with a service factor greater than 1.0 may be overloaded to th limit of the service factor.
Bill
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"Why not the best?"
Jimmy Carter
RE: Overload on three phase induction motor
*Since this s an international forum, "Service Factor" is a term from NEMA MG-1 motor design specifications for North America that denotes an overload capacity in a motor, but is intended to be "temporary", or rather non-continuous, with "continuous" being defined in different specs as typically meaning 3hours or more. But the actual time references in the definition of Service Factor were all removed some years ago, likely under lobbying pressure from OEMs who did not want to have to use the next size up for a +15% need. So now all the spec says is something weakly stated to the effect of "you can expect shorter life and torque or current specs may be different..."
The closest analog in IEC motor design specs is the "Duty Cycle" rating system, S1 - S8, but as far as I can tell, it is to allow for different ratings with LESS continuous load, never with more. In other words the highest rating is a continuous load at the nameplate rating.
"Will work for (the memory of) salami"
RE: Overload on three phase induction motor
In machine tool world the motors are often rated with the S1-S8 rating system. Most common is the S6-30 for higher than continuous rating for 30 minute duty cycle.
Example attached: 20hp continuous, 25hp for 30 minutes, 30hp for 1 minute....
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RE: Overload on three phase induction motor
http://www.baldor.com/pdf/manuals/PR2525.pdf
.pdf page 49, paper page 43.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Overload on three phase induction motor
Thus, you would be programming a relay to lie below the thermal curve, so that in the event the overload exceeds the relay curve, the relay will trip out.
Now, if you want occasional o/l on the motor, exercising the service factor may be the only option. As long as the thermal content does not exceed the prescribed limits by the manufacturer, you are ok.
RE: Overload on three phase induction motor
If you are thinking for S1 duty cycle (continuous work), then I agree with Waross: "zero percent."
Also, I agree with the jraef's explanation regarding the "service factor". I think it is rather a commercial then a technical term.
http://winding.wix.com/design
RE: Overload on three phase induction motor
However I agree service factor is still an ambiguous concept from a user's standpoint... what is he to do with this info. Not clear and open to interpretation.
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(2B)+(2B)' ?
RE: Overload on three phase induction motor
Assuming the motor is rated for an ambient temp of 40 deg C, the motor winding temp will rise by 100 deg C above the 40 deg C ambient when it is running at rated current.
The winding temperature of 140 deg C is 15 deg C below the winding insulation rated withstand temperature. RTDs would be typically set to trip the motor at 150 deg C. This allows for short time overloads without exceeding the motor winding temperature rating.