It has long been established that PD (partial discharge) activity generally increases with humidity. In dry conditions PD can reduce to levels below detection, whereas, in humid conditions the same equipment will clearly show PD.

Is the apparent change in PD due to a change in the propagation path (PD source to sensor) or a genuine reduction in the actual PD?

Or, to put it another way, does the PD remain constant but become easier to detect in higher humidity conditions?

Thanks Alan, I'm concerned mainly with PD on switchgear."PD source to sensor" refers to the path between the site of the PD (internal or external to the insulation) and the sensor being used. Acoustic for airborne energy, capacitive coupled for transient earth voltages or HFCTs.

Mo, Thanks for the clarification. Now it sounds more like a sensor calibration question, and you want to correlate the outputs of both sensors. I'm not sure what type of acoustic transducer you're using, but maybe the manufacturer can provide a calibration curve of response vs ambient humidity. Interesting concept; why not through RF and video processing into the mix to really refine what's going on.

Alan

Hello Mo, I believe that PD changes with the environment. Alan comment is also true as contaminants are affected by moisture. Another factor is pressure. Dry weather typically has a different pressure relative to a humid or wet environment. A good paper to look for:" A Guide to Electrical Insulation Design in Aerospace Vehicles"... that has some interesting charts and citing additional resources to use digging deeper.
I hope this helps.
Norm

Mo. Are you sure you are detecting PD and not corona?

Hi Ian, I am looking for PD. This could be internal to the insulation (due to gas filled voids) or external tracking across the insulation surface (due primarily to surface contamination). External PD is generally phase to earth, corona is the ionisation of the air adjacent to the conductor. That's my understanding anyway, welcome any comments.

Mo. That is how I understand PD and corona too. I think of PD internal to an insulating material to be a problem. PD on the surface, I hypothesize is a nuisance as it is not doing any damage to the insulating material, just moving through contamination, and as the contamination is destroyed, the PD will diminish.
I imagine that as the humidity increases, PD will reduce and tracking in the contamination will increase, if it is really dirty
With corona however, the intensity should be the same.
The Ultrasound signal for each is different and can help to determine what is present.
What is the objective of your study?