Intermittent motor

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Help went on service call where motor was stalled. Hummed and tripped overloads. There were several issues with the setup that needed repaired so he did. From starter all the way to the motor. All other motors in the group work fine as does this, one most of the time, until the armature stops in a certain position. He can rotate the shaft a few degrees, hit the start button and all is good unless it stops in ’that’ position. Motor shop said there may be a ‘broken bar’ in the armature. I’ve never heard of that before. Can someone explain.
Frame 143TC. 1 HP
 
ptonsparky said:
Motor shop said there may be a ‘broken bar’ in the armature. I’ve never heard of that before. Can someone explain.
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He's likely referring to a broken bar in the "squirrel cage" of the rotor in an induction motor. The squirrel cage is made of bars on the periphery of the rotor which are connected together on their ends by rings to form shorted turns. The bars and rings are typically made of aluminum. Current is induced in these shorted turns by the magnetic field from the stator, hence the name induction motor. This current then produces magnetic fields in the rotor which interact with the magnetic field of the stator to produce torque.

The motor shown is designed for VFDs, so the 6000 RPM is the maximum rating due to mechanical and possibly electrical limitations.

Motor experts like winnie, Jraef, paulengr, etc. could provide more details.
 
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