Aboutcleggsan Expertise All technical areas of Electronics Engineering.
Experience BSEE, MBA, Design, R&D, University Research.
Senior Life Member of IEEE. Life Fellow of AES.
Organizations IEEE, Consumer Electronics Society, Audio Engineering Society.
Broad teaching experience; work experience mostly in consumer electronics and conversion from analog to digital technologies. Pioneer in digital audio at all levels.
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The text above is a follow-up to ...
-----Question-----
Dear all
Just now I meggered a compressor winding for 15 HP AC.Two compressores actually.For compressor 1, R-Y(0.2 ohm),Y-B(50 ohm),R-B(60 ohm) and for compressor 2 all phases are 0.82 ohm,which I concluded balance fpor each phase where as for compressor 1 not balance.Now I have a doubt since from theory the one with low ohm could be shorted but when I tested and replace the timer,top up the gas,this compressor can run(comp 2).Seems the 'shorted' compressor is OK.For compressor 1, we didnt test but it could be faulty since the phases ohms are not balance,or might be 1 phase is faulty.
1.Which one is consider faulty?
-----Answer-----
I am confused. Meggering is usually for testing insulation qualities from windings to case or winding one to winding two. In normal conditions the resistance is very high - in the megohms or millions of ohms. That is why they call it meggering. If there is an insulation short or leakage the resistance will drop down to something much less - or to a short which is near zero ohms.
dURING THE TEST WE USE 500v AND WE DISCONNECTED THE PAHSES FROM THE TERMINAL.wE CLIPPED THE METER AT TWO PHASES AT A TIME AND STAR EASURING.YES IT IS WINDING.WE ARE MEASURING THE INSULATION OF THE WINDINGS AND THE RESUKT ARE AS PER PREVIOUS EMAIL.ITS A COMPRESSOR.IM NOT SO SURE WHETHER FOR GOOD WINDING INSULATION THE READING SHOULD BE AT MEGAOHM.BUT FOR CABLE ,YES.
The resistances you are reporting are more like the winding resistance. And, you did not say if the unit was removed from external connections. And, did you rotate the shaft to different positions and take more measurements?
So, I think you need to do more checking and make the test conditions more clear for better understanding of exactly what you were measuring.
Cleggsan
Answer Thanks, that helps.
I suggest you, also, using a plain and simple vom, check for shorts to the case, shorts across windings and see if these readings are congruous with the megger readings (under stress). That will raise the confidence level in making the right conclusions.
I am hesitating to draw a definite conclusion only because strange things can happen with windings in motors and generators. For example, the slight difference in readings of two supposedly identical windings can mean there is a shorted turn buried down in the coil. It will still run, but over time become hot from IR losses and eventually burnout more turns of the windings.
