I was wondering if any of you have installed a partial discharge analysis device on any of your motors/generators or switchgear. How well has it worked?
I'm installing an Iris PDTrac on a 14000HP synchronous motor (13.2kV) this week. We have several installed globally and we get decent results at higher voltages (above 6kV).
The data is subject to database comparison though, similar to Dobble testing of transformers, etc. The monitor by itself doesn't help much for spot analysis, but is useful for trending in my experience.
We have 20 13.2kv motors instrumented with partial discharge for the last 3-8 years (Iris equipment).
The data itself is easy to take (and of course is taken with motor running). I think there is a little bit of a learning curve to deal with in interpretting the data, particularly intially when there is not a lot of historical data.
It has proven to be a useful tool, particularly now that our understanding of the variability and normal patterns is better. We have had 3 events I can relate:
1 - In one case upon installation of pd sensors we immediately saw high pd. We went in and did an inspection of end turn area and saw severe cracking damage on the connection end jumpers due to oil soaking. Rewind shop repaired in place - we consider it a good save.
2 - We had one motor that showed increasing pd trend however below the alarm level. We did dc step voltage test and found non-linear curve although once again not blatantly bad. Our recommendation was to remove the motor for repair but the plant could not accommodate. Within 2 months the motor failed. Increasing pd was a valid indicator in this case.
3 - We had one motor failed which never showed any change in it's pd, which remained at low levels on tests performed every 3 months (better than vendor recommended 6 month interval). Apparently pd failed to detect the problem.
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I have had very positive results on motors (about 15 in all) 4160 and 13.2 and up. Also positive results on about 5 utility generators 5 MW up to 1.2 GigaW.
All IRIS equipment.
There is a slight learning curve but if you keed in mind the type of insulation, your analysis will be simpler.
For example a Q +/- of 10,000 on mica asphalt might no be anything to get concerned about because this type of insulation even at best will be very high due to the conponents of construction. But if e.g. Q +/- were >250 on thermoset epoxy I would start to do some investigation.
IRIS Power Systems makes good equipment!
Anybody have experience with the C-H line of products?
(I'm also in the process of installing couplers and getting a baseline report from Iris on two 11KV machines, but Eaton CH is knocking at the door, and I intend to go continuous online in the future)
Suggestion: References:
1. Gabe Paoletti, P.E., Division Application Engineer, Alex Golubev, PhD, Manager, R&D, Predictive Diagnostics, Cutler-Hammer Engineering Servives, "Partial Discharge Theory and Applications to Electrical Systems," 1999 TAPPI Conference in March 1999.
