Partial discharge testing

[cornbread]

A bit off topic.. we are installing some equipment to monitor on line partial discharge. The equipment is showing we have some partial discharge, we plan on monitoring to see if it gets worse (can'think its going to get any better ... humidity seems to be a hugh factor). My gut tells me we should shutdown and correct the problem, however there is another camp that is of the mind set that we need to monitor the situation and see if it get worse and at some point in the future decide if action is needed. At what point does partial discharge become a safety issue?

 

[GoldDigger]

I am not familiar with the term "partial discharge". Some context please?

 

[charlie b]

Boy are you taking me back into my past! I first came across the notion of a ?Partial Discharge Test? (PD) in the context of condition monitoring for large motors. A PD test is a determination of the level of activity of high frequency discharges internal to the stator windings. The following is taken from a report of a research project funded by the Electric Power Research Institute (EPRI) over 17 years ago. I think I can risk publishing copyrighted material, in part because of its age, but mostly because I wrote it.

Any two conductors that are separated by a void will act as a capacitor, as will insulated conductors in close contact, and an insulated conductor in close contact with the external ground plane. The capacitors act as though connected in series. Thus, the one with the lowest value of capacitance (i.e., the one with the void in the middle, or the one not in close contact with its neighbor) will carry the largest value of voltage. This makes it the weakest link. A high voltage across a void will occasionally force a ?packet of charge? to cross the gap. This results in severe degradation of the insulation at that point, and makes it easier for the next packet of charge to penetrate the insulation. It is thus a self-accelerating failure mechanism. This test can be performed under load, but the connections must be set up in advance. Sensors are connected directly to the motor?s main power leads. Since the electrical frequency of the partial discharges is much higher than the motor?s 60 Hertz, a well-chosen set of filters allows independent observation of the discharges. As was the case with the current signature analysis (CSA), the operator must be trained in recognition and evaluation of the test results. A PD Test can also be performed off-line. This is the most effective test presently available for detecting voids in the insulation, and is the best available at this writing for evaluation of stator problems.

 

[zog]

A bit off topic.. we are installing some equipment to monitor on line partial discharge. The equipment is showing we have some partial discharge, we plan on monitoring to see if it gets worse (can'think its going to get any better ... humidity seems to be a hugh factor). My gut tells me we should shutdown and correct the problem, however there is another camp that is of the mind set that we need to monitor the situation and see if it get worse and at some point in the future decide if action is needed. At what point does partial discharge become a safety issue?

Which system are you using and what type sensor?

Humidity and surface contamination are a factor for sure and left uncorrected can develop into a more serious condition, corona, then failure....thats the whole reason the monitors are there.

 

[cornbread]

I'm not sure, its a temporary system. The sensors set on the outsdie of the cabinet. I'll try to find out more.