Troubleshooting a Faulty 3 Phase Motor

In summary, the conversation discusses a problem with a 3-phase motor that was rapidly overheating even under no load. The resistance readings and short circuit tests showed no issues, but a report from a local rewind shop revealed that one of the rotor's bars was the cause of the problem. The conversation then delves into how a 3-phase induction motor works and explains that a short on the rotor can cause similar issues as a transformer with a shorted turn. The short was most likely between the rotor's squirrel cage and the magnetic path. To check for this, one can test for a current path between the cage and iron stampings.
  • #1
wolram
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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?
 
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  • #2
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.
 
  • #3
many thanks CEPTIMUS, its obvious isn't it, thick old me.
 

1. What are the common signs of a faulty 3 phase motor?

Some common signs of a faulty 3 phase motor include overheating, excessive noise, vibrations, and sudden loss of power.

2. How can I determine if my 3 phase motor is the cause of an electrical problem?

You can use a multimeter to test the motor's voltage, current, and resistance. If the readings are significantly different from the motor's specifications, it is likely the cause of the electrical problem.

3. What are the main components of a 3 phase motor?

The main components of a 3 phase motor include the stator (stationary part), rotor (rotating part), bearings, and windings.

4. How can I troubleshoot a faulty 3 phase motor?

You can troubleshoot a faulty 3 phase motor by checking for loose connections, testing the voltage and current, inspecting the windings for damage, and checking the motor's bearings for wear and tear.

5. What are some common causes of 3 phase motor failure?

Some common causes of 3 phase motor failure include overloading, overheating, voltage fluctuations, and lack of maintenance.

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