Do you have any or know of any photos or mpeg images of corona inside any high voltage cabinets (4160kv or higher)?
Please contact me:
Jim Hall Co-ed: Uptime Magazine
Ultra-Sound Technologies
Vendor-Neutral
jhall1616@comcast.net

This image was taken two weeks before catastrofic failure on a 34.5 KV transformer. The cause, bad terminal installation.

Hey Don: Nice picture. How come no one believed you. This image would suggest a severe problem requiring immediate response. My feeling is whenever infrared confirms a tracking problem on high voltage gear, it is best to leave the room immediately, since current is already flowing to ground. From the look of that image, I have no doubt that you have an insulation fault. Did you check it with ultrasound?

Dan - Thanks for sharing that. I agree it sounds like an interesting case and I would love to understand it better.

I assume this is a cable landing on an oil-filled bushing?
Is this supposed to be an example of corona or bad connection?
If corona, is the cable shielded?
If the cable is shielded, where it the stress cone located in the picture? (there should be one near termination of shielded cable... if not then I think that would be a big problem right there!!).
Is there a temperature scale available?
Is there a visual photo available accompanything the thermal image? Any photo of failed component or description of the failure?

From these images it looks as if the cable shields are not grounded. The attached photograph shows what I expect to see here.

bushing_picture.doc (160 KB, 37 downloads)

Excellent pics to see practical corona example. but Is this inside switchgear? How you are able to get clear visual image ? You are not using any windows to take IR for kind of MV switchgear panels?

I also would like to share some info/ pics with you guys. This is not for HV but for LV transformer at 6 KV terminations. You will find both pictures before and after repair.

Thanks & regards

pdf-FORUM_DISCUSSION.pdf (98 KB, 46 downloads)

Corona shows up in UV part of the spectrum and is not nomally visible with Infrared cameras. See the attached site fo corona pics.

http://www.specialcamera.com/uvcam/corimage.html

JV-You are correct. However, corona will cause an insulator to turn into a high resistance conductor. As this happens, current, at low levels, will flow to ground. At this state, infrared can pick up heat produced by flow across the high resistance. This, at least, is my interpretation of what occurs. Using infrared and ultrasound together, I have confirmed the presence of both heat and ultrasound emissions from tracking on high voltage equipment on many occasions. I suggest that this condition is a precursor to catastrophic failure. However, in most cases of switch gear corona, no heat is present and I rely on ultrasound to identify the problem.