Electric motor insulation drop after cleaning
Electric motor insulation drop after cleaning
(OP)
Dear Team,
I have experienced several problem regarding to the compressor motor. Our client have sent the compressor motors range between 250 HP to 450 HP. We are following standard service step by step. After dissemble the motor, we have done IR test at each phase of coil to check the healthy of the coil. Then we have cleaned the coil with high pressure water to eliminate the contaminants. After that we oven baked the stator. After the stator been taken out from oven, we do again IR Test at 1000 V. We found out that the IR dropped after it cooled down. My question is what is cause of insulation drop after clean the coil? Even after we re-varnish the coil, the IR still remain very low. Please advise how to prevent the IR from drop drastically.
Thank you
I have experienced several problem regarding to the compressor motor. Our client have sent the compressor motors range between 250 HP to 450 HP. We are following standard service step by step. After dissemble the motor, we have done IR test at each phase of coil to check the healthy of the coil. Then we have cleaned the coil with high pressure water to eliminate the contaminants. After that we oven baked the stator. After the stator been taken out from oven, we do again IR Test at 1000 V. We found out that the IR dropped after it cooled down. My question is what is cause of insulation drop after clean the coil? Even after we re-varnish the coil, the IR still remain very low. Please advise how to prevent the IR from drop drastically.
Thank you





RE: Electric motor insulation drop after cleaning
RE: Electric motor insulation drop after cleaning
We used a steam cleaner for such work as it breaks down grease easier.
Make sure the stator has thoroughly dried out including insides of slots.
Let the stator cool right down before testing,as a slightly warm stator gives a false reading.
Sometimes a second wash is needed.
Reasons for low readings,dirty slots,old insulation breaking down,damp still tracking.
Test,wash,stove to dry,varnish while hot,stove to cure,cool down,retest.
RE: Electric motor insulation drop after cleaning
RE: Electric motor insulation drop after cleaning
RE: Electric motor insulation drop after cleaning
Also
1 - what values are you reading?
2 - what is the P.I. before / after?
3 - are you temperature-correcting?
=====================================
(2B)+(2B)' ?
RE: Electric motor insulation drop after cleaning
=====================================
(2B)+(2B)' ?
RE: Electric motor insulation drop after cleaning
RE: Electric motor insulation drop after cleaning
Hi guys,
I would like to share one of the insulation drop cases. For this case we have done hipot test using Baker Digital Winding Tester. The result as attached. The insulation has increased but there is EAR(error area ratio)which is impulse test has reached more than 100%.
http://files.engineering.com/getfile.aspx?folder=3...
http://files.engineering.com/getfile.aspx?folder=6...
RE: Electric motor insulation drop after cleaning
After clean/bake @ 1 minute: 8,381 mega-ohms
So, this is the opposite of your original problem statement.
Your new question is related to the surge test results (completely different topic)???
Assuming that's the case, (no relation to original questioh), the "after" definitely shows a significant deviation among phase-lead-pairs worthy of investigation. Was rotor installed at the time? Check the test connections. Consider repeating test and examining behavior as slowly increase voltage on a given phase (zero crossings should not change)
=====================================
(2B)+(2B)' ?
RE: Electric motor insulation drop after cleaning
(A quality DLRO would allow you to detect if it is a dead short)
Based on the info discussed in this thread, I'd suspect that contamination might have washed into some cracks in already compromised insulation (evidenced by the preliminary low meg ohm readings) and was subsequently detected by the surge test.
This underscores the reason that the surge test is accepted as a quality control test. Meg ohm will not detect turn to turn flaws or phase to phase faults (unless the phases are separated and tested piecemeal) As mentioned by Electricpete, this problem may be voltage dependent, and "disappear" at lower levels. Further cleaning may make it "disappear" as well. Flexing the winding by hand may allow a motor repair tech to determine exactly where the flaw is located...
"When you go looking for problems, you will find them... But they may not be the problems you went looking for!"