electricpete
Electrical
- May 4, 2001
- 16,774
I'm developing a plan to do a root cause analysis for a 13.8kv 8000hp motor which has failed a dc step hi-pot test at approx 24kv. Before the hi-pot test insulation resistance (IR) was approx 8000megaohms to ground at 10kv. After the test IR is only 100Meg at 1kv and 30Meg at 10kv. It is assumed that the insulation to ground has been damaged somewhere.
Now assume that we can narrow the faulted coil to one specific coil (by breaking coil connections and doing IR test on individual coils). But there is no visible evidence of failure point on that coil.
What options are available to try to precisely identify the failure point and failure mechanism of that coil?
Should we try to raise dc voltage as high as possible and look for smoke? Or should we use ac hi-pot for same purpose? Will either of these likely destroy evidence? Is it reasonable to try to expect extract the coil for further examination without causing significant damage (global vpi)?
Would coronoscope be useful? Use it while coil remains in the slots? TVA probe? Other methods/suggestions?
We plan to test some other representative coils to failure (line-end coils, and coils electrically and physicaaly adjacent to the failed coils). Then possibly section those open for examination (along with the failed coil)... at locations possibly including midpoint of slot, first bend outside slot, knuckle.
Also we've checked entire winding terminal resistance with no anomalies. Will check again on the failed coil and compare to other coils.
Any other suggestions for items we should consider for a complete and thorough root cause analysis?
Now assume that we can narrow the faulted coil to one specific coil (by breaking coil connections and doing IR test on individual coils). But there is no visible evidence of failure point on that coil.
What options are available to try to precisely identify the failure point and failure mechanism of that coil?
Should we try to raise dc voltage as high as possible and look for smoke? Or should we use ac hi-pot for same purpose? Will either of these likely destroy evidence? Is it reasonable to try to expect extract the coil for further examination without causing significant damage (global vpi)?
Would coronoscope be useful? Use it while coil remains in the slots? TVA probe? Other methods/suggestions?
We plan to test some other representative coils to failure (line-end coils, and coils electrically and physicaaly adjacent to the failed coils). Then possibly section those open for examination (along with the failed coil)... at locations possibly including midpoint of slot, first bend outside slot, knuckle.
Also we've checked entire winding terminal resistance with no anomalies. Will check again on the failed coil and compare to other coils.
Any other suggestions for items we should consider for a complete and thorough root cause analysis?