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The Importance of Proper Motor Overloads

4K views 28 replies 17 participants last post by  Norcal 
#1 ·
This 2HP motor came into our shop for repair, and when they yanked the end-bell, this is what they found.





That's the remains of a cast aluminum rotor. My expert opinion is I think it got a little warm. :laughing:
 
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#6 ·
I don't know enough about it to say if it's possible for an intra-rotor failure to cause that kind of heat without causing overcurrent in the stator? I'll run it by our motor gurus and see if they have any theories. I handled the hell out of it right before lunch, and now despite washing my hands, I am eating the stinkiest sandwich ever.
 
#3 ·
A little grease and its good to go.

Here its a loosing battle to have out maintenance, pump and service electricians change the o/l's when changing motors.
The answer is always the same, "It worked before" & "Its suppose to run at the service factor, that's why it's labeled".
 
#5 ·
This 2HP motor came into our shop for repair, and when they yanked the end-bell, this is what they found.





That's the remains of a cast aluminum rotor. My expert opinion is I think it got a little warm. :laughing:
The same thing happened in an I-R screw compressor. The 60 HP must've got hot that the rotor melted in the same way. The compressor and the motor bearings didn't seize and the overloads were correct. A special OEM motor, made for IR, by Reliance. The new motor was made by Weg.
 
#9 ·
No.

If a motors windings are OK, but it draws high amps the bearings are bad. Probably dry.

30 bucks in new bearings and about 15 minutes in time and you have a motor that is good to go.

That is of course unless the endbells are wallowed, then its junk.

Even at a high rate of pay, that is way cheaper then a new motor. Especially if its some type of odd frame, or god forbid of German manufacture.

That 2 HP motor could run $4000.00 bucks and be 5 weeks out.
 
#18 ·
I would be willing to bet that the windings in the rotor began shorting out, leading to heat concentrated in the rotor, not so much the stator.

Notice how the stator is burned in only a few places, not the entire winding.

Aluminum melts at about 1200º, there's no way the stator got hot enough to melt the rotor.

BTW, that looks like a 2 pole design; somewhere around 3450 RPM.
 
#23 ·
I worked at a firm, that made high quality, OEM motors.
It was definitely a fault in the injection cast, squirrel cage rotor. One of the bars, might've been a high resistance bar, due to a casting fault. There was many variables in the casting operation.
I was involved in engineering testing and I witnessed rotors, failing in this manner.
 
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