Troubleshooting a Faulty 3 Phase Motor

AI Thread Summary
A user experienced overheating issues with a 3-phase motor, even under no load, and found that resistance readings and short circuit tests were normal. A local rewind shop identified a fault in one of the rotor bars. The discussion explains that a 3-phase induction motor operates similarly to a transformer, where current is induced in the rotor (squirrel cage) by the stator windings. A short in the rotor can lead to overheating, akin to a transformer with a shorted turn. The rotor's secondary windings are simple, often resembling a hamster's wheel. To test for faults, one can check for continuity between the rotor cage and the iron core; there should be no current path.
wolram
Gold Member
Dearly Missed
Messages
4,410
Reaction score
555
i had a problem with a 3 phase motor last week that
had me stumped, it would rapidly overheat even under
no load, resistance readings of the windings cheked
out ok as did short circuit tests, a report from
the local rewind shop said that one of the BARS on
the rotor was found to be the fault, can someone
please explain what they mean, and how to test for
this fault?
 
Physics news on Phys.org
An 3-phase induction motor works a bit like a transformer. Current is induced (hence the name of the motor) in the secondary (the squirrel cage on the rotor) by the primary (stator) windings.

If there is a short on the rotor, you get the same problem as a transformer with a shorted turn in the secondary - bug induced currents and overheating.

The secondary (rotor) windings are very simple - often just a single turn of copper per winding, and if you could remove the secondary winding from the rotor intact, it would look (in some motors) like a hamster's wheel, or 'squirrel cage'.

The short was (I guess) between the cage and the magnetic (iron) path through the rotor. You can check for that by just belling between the cage and the iron stampings - there should be no current path.
 
many thanks CEPTIMUS, its obvious isn't it, thick old me.
 

Thread '1:1 versus 2:1 Mechanical Advantage debate'

The rope is tied into the person (the load of 200 pounds) and the rope goes up from the person to a fixed pulley and back down to his hands. He hauls the rope to suspend himself in the air. What is the mechanical advantage of the system? The person will indeed only have to lift half of his body weight (roughly 100 pounds) because he now lessened the load by that same amount. This APPEARS to be a 2:1 because he can hold himself with half the force, but my question is: is that mechanical...
View full post »

Thread 'Newton's first law?'

Some physics textbook writer told me that Newton's first law applies only on bodies that feel no interactions at all. He said that if a body is on rest or moves in constant velocity, there is no external force acting on it. But I have heard another form of the law that says the net force acting on a body must be zero. This means there is interactions involved after all. So which one is correct?
View full post »
Thread 'Beam on an inclined plane'

Thread 'Beam on an inclined plane'

Hello! I have a question regarding a beam on an inclined plane. I was considering a beam resting on two supports attached to an inclined plane. I was almost sure that the lower support must be more loaded. My imagination about this problem is shown in the picture below. Here is how I wrote the condition of equilibrium forces: $$ \begin{cases} F_{g\parallel}=F_{t1}+F_{t2}, \\ F_{g\perp}=F_{r1}+F_{r2} \end{cases}. $$ On the other hand...
View full post »

Similar threads

Induction motor rotor design features
Replies
4
Views
2K
Engineering How to calculate rotor flux of the three phase squirrel cage induction motor?
Replies
4
Views
2K
3-phase delta supply to a 3-phase synchronous motor?
Replies
1
Views
1K
Where can I find a controller for a 3 Phase AC motor?
Replies
4
Views
2K
What is causing the strange ground current loop in this motor circuit?
Replies
6
Views
2K
Electrical Rewinding old 3-phase stator: Non-symmetrical layout
Replies
43
Views
10K
Understanding Synchronous Rotation in 3-Phase Induction Motors
Replies
7
Views
2K
Understanding Rotor RMF in Squirrel Cage & Slip Ring Induction Motors
Replies
1
Views
2K
Determining inductive reactance from a 3-phase AC circuit
Replies
17
Views
3K
3-phase Induction Motor:Supply given to Rotor & Stator winding shorted
Replies
1
Views
7K

Hot Threads

Recent Insights

Back
Top