Message Board Thread - "MV Stress Cones"

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MV Stress Cones zmiller 6/29/2009
I have been looking at some 15KV Stress Cones. Thermal contrast is very difficult due to the high voltage low current. I have performed some baseline imaging finding some uniformly heated cones. I have also found a few with some very small abnormally heated areas below the bells. I know that the corona will cause added heating of the material with a failing cone but how much and primary area I am unsure of without added experience. Does anyone have any experience or guidelines to follow with stress cones? I have attached an image that we were visually able to see tracking on two of the three cones that are clearly failing. A and B phase were failing, this image is from the back so we are facing C-B-A. These cones were clearly failing however temperature variance across the material was very small (less than a degree) Any help for future imaging on MV cones would be great.

Thanks
 
Re:MV Stress Cones Mr. G 7/6/2009
I believe that the issue is tracking due to contamination (dirt & humidity) This type of stress cone is and has been an issue. The tracking would be visible in low light conditions or with a day light corona camera. There is little to no temperature produced by corona, but the failure of the cone will still give you a possible flashover condition. I am aware of inexpensive on-line PD detection systems that can be installed and will monitor 24/7 in the MCSG compartments and cable termination compartments. Otherwise you will find that a run-to-failure event is possible. Just using ultrasound or IR is not enough.
 
Re:MV Stress Cones Laland 7/6/2009
Am sorry but I my not have gotten the terminology.. What is a stress cone?
 
Re:MV Stress Cones zmiller 7/7/2009
Mr. G wrote:
ve that the issue is tracking due to contamination (dirt & humidity) This type of stress cone is and has been an issue. The tracking would be visible in low light conditions or with a day light corona camera. There is little to no temperature produced by corona, but the failure of the cone will still give you a possible flashover condition. I am aware of inexpensive on-line PD detection systems that can be installed and will monitor 24/7 in the MCSG compartments and cable termination compartments. Otherwise you will find that a run-to-failure event is possible. Just using ultrasound or IR is not enough.
Hey Thanks for the response MR G. We have found that the cones had some possible issues during installation that did not show up on the original commissioning tests. It seems that a small air gap under the cone is the problem area. My theory is that although the heat generated is very small it is able to compound under the cone material, due to the thermal conductivity of the materials of the stress cone we see an increase in temperature at the copper band and small temp deltas at the problem location of the rubber insulating material. I have found that once the cone fails and the rubber splits open all the delta's disappear and the material appears uniform. Obviously the corona increases at this time and produces very little heat. I am doing some additional investigation of some good "just tested" cones to compare this theory. FYI we did use a corona camera and it seems unless the issue is on the outside of the cone it does not show us problems inside the cone itself. Let me know what you think of my theory on this I appreciate any feedback.
 
Re:MV Stress Cones Dnicejr1 7/8/2009
You can also use night vision devises to see the corona verse buying a $50K camera.
 


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