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IR to avoid Flashover?
10-29-2012, 03:50 PM (This post was last modified: 10-29-2012 03:52 PM by p_emmel5.)
Post: #1
IR to avoid Flashover?
Question: Can IR be used to avoid possible Flashover of high voltage insulators?
Background: We had one of our 500KV lines flashover to ground via the insulator. Now the "powers that be" want me to perform IR on a weekly basis to avoid this situation in the future. I performed an IR survey in conjunction with a Corona survey. Anywhere the tech saw Corona activity, I saw nothing even with the camera tuned to a very tight window.

I can see dry-band on the skirts and some areas of a slight Delta T. (approximately 1-2 degf) but, that just may be the difference between the Emissivity of the insulator (Polymer) and dirt/salt deposits. Plus we see those anomalies on a regular basis being the fact that we are 100 yards from the Pacific Ocean.

Personal Opinion: Performing IR on a weekly basis as a precursor to avoiding Flashover is a waste of time. Corona surveying seems to be the technology for this situation. Corona sees on the UV specturm and Thermography in the IR spectrum. According to the tech, even Corona surveying isn't an exact science when it comes to Flashover.

Thanks,
Pete
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10-30-2012, 05:38 PM (This post was last modified: 10-30-2012 05:46 PM by acardoso.)
Post: #2
RE: IR to avoid Flashover?
First, let's start to divide the UV light in three bands, C, B, and A, and after talk about Corona. The UVC band is “ozone” one, the UVB is the “tanned” one and the UVA the cancer one. The presence of UVC light in the sun light provides us the “blue sky” and we can say UVC band is the start of the ionizing radiation zone. When the molecule of O2 is beamed with UVC, the 2 electron bonds are “cracked” and, at those moments, we have the conditions for the formation of O3 molecules, Ozone. Ozone can “do” 2 things, decay to regular Oxygen, or act as a strong oxidizer.

When the first’s tiny surge paths start to form on the surface of the insulators, it doesn’t matter why, the Corona effect is already present, but we cannot see it. Those tiny Coronas are short-circuits, no Joule effect, and emit UVC light. Collaterally, they produce Ozone. This localized production, in the end, rots the insulator.

When the damage can be "seen" with thermography, is already too late.

http://www.youtube.com/watch?v=Muxjyvwox...creen&NR=1
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10-12-2013, 09:30 PM
Post: #3
RE: IR to avoid Flashover?
I would agree. We survey T&D equipment on a daily basis and very rarely do we see dirt buildup on the insulators manifest itself as a hotspot. As acardoso said, by the time you see it with the IR camera you are probably too late. Corona or UE Gun would probably work better in that situation.

-mike
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11-07-2013, 11:13 AM
Post: #4
RE: IR to avoid Flashover?
With IR you will only see the heat generated during arcing conditions. The corona camera (UV camera) will detect any UV activity generated in the high electical field. In your case near coastal conditions your problem is highly likely due to contamination on the insulators. In order to find these possible flash-overs you need the contaminate to be wet (high humidity conditions) so that it tracks leakage current. You will then be able to detect the dry-band arcing that occurs as the current path begins to dry up from the current flow. Although possible to see with the IR camera - it would be very difficult. Only a couple of degrees as the arc is so small. However an arc produces tons of UV light and the corona camera will pick it up very easily. The problem with this situtation is that it is very time sensitive. If the insulator is dry, you see nothing. If it is very wet you will see nothing as the leakage current is flowing. You will only be able to detect the contamination as the insulator dries up. Good luck! Now, if you were looking for insulator problems such as cracking, lack of corona ring or other failures, then you want to use the corona camera during dry conditions. IR and UV tools work well together, but they do not see the same problems.
Cheers!
-Curtis
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