Message Board Thread - "34.5 kv bus connection .."

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34.5 kv bus connection .. manuel-thermoimagen 5/26/2008
Please i would appreciate any coments about this image.

This is a 34.5kv bus, i found hot spot almost in the bottom of the insulator.

according your experience, can you tell me what is producing this hot spot?..

what we did in order to eliminate any disturbing noise was:
- Taken images from several angles in order to avoid reflections.
- clean superficially with alcohol any dust or contaminant, using high voltage equipment to do so.
- ground wire doesnt finished that high, so it is posible that high voltage wire inside be broken??

thanks for your advice

roberto.cruz@thermoimagen.com

 
Re:34.5 kv bus connection .. Carl M 5/26/2008
How old is this termination? You say that the ground sheild doesn't go that far, but the semiconductor in the cable does. It may be that the cable stresscone has contamination, or a nick in the insulation and/or semiconductor.
 
Re:34.5 kv bus connection .. TDLIR 5/26/2008
Roberto,

I would check with airborne ultrasonic to confirm corona discharge or tracking. Visually inspect the insulator for a white dust residue.

Hope this helps.

Sonny James
www.learnndt.com
www.tdlir.com
 
Re:34.5 kv bus connection .. kfs 5/27/2008
I've seen this on a number of 33kV cable terminations (temperature rise up to 17°C). The manufacturer stated that it is 'dry-banding' which can not be stopped. The material is designed to withstand this activity and the white chemical deposit can be cleaned off but will return. I've not had any termination subsequently fail.
 
Re:34.5 kv bus connection .. TDLIR 5/27/2008
Dry banding AKA Tracking.

Unfortunately, I would have to disagree with kfs on this in that dry banding (tracking) can be a very serious problem. I have seen insulators blow because of this problem. You can repair this problem by cleaning or replacing the insulator and reducing contamination and moisture.

In right conditions, you can visually see the discharge (static tree/dendrite sparks).

Best Regards,

Sonny James
 
Re:34.5 kv bus connection .. kfs 5/27/2008
Sonny,

I was quoting the manufacturer's response to the temperature rise seen on the surface of 33kV heatshrink insulation. Inirtially we were quite concerned and several years ago removed a full termination for examination but found no evidence of a defect/deterioration apart from surface discoloration. In the manufacturer's opinion there is 'no harm to the termination' and 'and the measured temperature rise is no reason to be worried....'. As I said we've not had a 33kV heatshrink type termination identifed with with dry banding during an IR survey (2 yearly) that has subsequently failed.

That might not apply to other types of termination or other manufacturers.
 
Re:34.5 kv bus connection .. manuel-thermoimagen 5/27/2008
final customer call:

customer will de-energize this bus in order to remove this insulator, then will make new one.

i will try to get pictures of inside of the hot spot area once insulator be at the shop.

regards!!

roberto.cruz@thermoimagen.com
 
Re:34.5 kv bus connection .. TDLIR 5/27/2008
kfs,

I apologize if I misunderstood your post. Please note for future reference that determining the severity of Tacking with temperature is not recommended. Airborne ultrasonic seems to be the preferred method of detecting and monitoring tracking.

I just remembered about a paper that was presented at the 2006 IRINFO conference by James Brady on this exact topic.

It is a good paper with good information on identifying tracking and corrective actions. You can read the paper here:

http://irinfo.org/Articles/article_8_1_2006_brady.html

Roberto, let us know how things go on this matter. Try to get close up pictures of the insulated area where you noticed the hot spot.

Best Regards,

Sonny James
 
Re:34.5 kv bus connection .. emado 6/1/2008
Carl M wrote:
is this termination? You say that the ground sheild doesn't go that far, but the semiconductor in the cable does. It may be that the cable stresscone has contamination, or a nick in the insulation and/or semiconductor.
this refare to bad simeconductor and that is meaning there is some leakag,all termination failour caused by this reasone
 


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