Low Voltage Motor Rewinding/Testing

[mpparent]

Hi All,

I'd like to get some feedback on what others have done in regards to the rebuilding/rewinding of motors, sizes 25HP and above. In my opinion, meggering is not that great a test. Are there any other tests you all do? Do you even bother rebuilding motors of this size? In my former life, we wouldn't think of rebuilding motors of this size, but times change.

Mike

 

[petronila]

Hello mpparent,

For testing winding´s motors the megger test is not enought, this test only provides you a Ground Insulation resistance value but don´t provide information about turn to turn winding insulation, Resistance,capacitance and inductance winding readings. the IR too not strees the winding in order to find a weak insulation or problems in earlier stages.If you are looking for shorted windings use a DC surge tester this instrument will show you the winding patterns and you can identify open and shorted coils, turn to turn or phase phase shorts, earthings, and stress the insulatuion in order to find problems in all winding´s components.Another test could be done ussing the MCEMAX manufactured by PDMA this instrument provide static and dynamic information about 6 motor´s fault zones: Insulation,power circuit,power quality,air gap and stator. Also you can use another tester like All test pro IV.

The alternative to replace or rewind motors depends of the motor type and the down time impact in factory. Normally we perform an economic analysis, if the repair cost is above the 50% of new cost the motor is replaced, this works fine for standard type motor below 10 HP.Take account one special small motor could give you many problems if you can´t find the spare at marked, then the only option is repair at any cost.Also is important evaluate the repair time vs New one motor Delivery time and use certified repair shops in order to conserve the motor´s efficiency.

Regards

Petronila

 

[Chiefkocak]

I have a dozen or so motors up to a couple hundred HP each time my ship is in the shipyard. Disassemble, clean, measure bearing fits- repair if needed, bake the windings, reinsulate, meg-if below 100M rewind. Cost is a few hundred instead of a few grand for a rebuild and down time.

As far as PM testing, megger the windings, vibration analysis for the bearings, listen to it with a listening rod, put your hand on it-is it hot, there may be a problem, look inside at the windings.

Been doing motor maintenance for 25 years plus.

Hope this helps.

 

[mpparent]

Thanks...

Mike

Mike

 

[ACY]

In a 'practical' sense, megger the motor to earth and b/n windings, is 'practically' a great test. A 'prefix' tester would help you find shorts between windings.
All other test would be mechanically based. Run the motor and check AMps. If you have access, provide yourself with the tests that have been previously discussed. But 'practically', megger is great, and also simple, sensible tests indicated by Chief are good enough.
As for rewinding 25 HP motor. I assume it is an Imperial motor. In Australia we would rewinf it, if imperial. If Metric frame standard frame, we would replace it.