Damaged transmission wire caused by arc incident or contributing cause of arc incident?

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nuckythompson

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As I mentioned in another post, we had an incident where a 69kv line arced to a boom truck crane. After the fact, we noticed the transmission wire was frayed at the location of the arc. The root cause is the crane was within limits of approach, but I am wondering, if that wire was frayed to begin with, could that have contributed to the arc event? Any thoughts?

Other post - https://forums.mikeholt.com/threads...ectrical-contact-with-overhead-lines.2575234/

Thank you all! :)
 

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Nope. The minimum approach distance values are, in fact, not made up. That irregularity would not make much of a difference.
 
The closest permitted approach has a huge safety factor. The dielectric of air is about 3 million volts per meter. The closest permitted approach is 10'.
 
nuckythompson said:
As I mentioned in another post, we had an incident where a 69kv line arced to a boom truck crane. After the fact, we noticed the transmission wire was frayed at the location of the arc. The root cause is the crane was within limits of approach, but I am wondering, if that wire was frayed to begin with, could that have contributed to the arc event?
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Probably not. I don't think that the insulation on those conductors is anywhere near thick enough to contain 69kV. IMO the arc caused the insulation damage, not the other way round.
 
ggunn said:
Probably not. I don't think that the insulation on those conductors is anywhere near thick enough to contain 69kV. IMO the arc caused the insulation damage, not the other way round.
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For uninsulated wire (often see for HV transmission lines?) any covering would be to protect the wire and also to provide a smooth surface to reduce corona discharge. If a bare strand were to be broken rather than just frayed apart from other strands, the potentially resulting sharp point will encourage corona discharge and reduce the arc starting distance slightly. Presumably well within the safety factor of approach distance.

When a lineman is preparing to do uninsulated work on a transmission line he wears a Faraday suit and makes initial contact with the line using a conducting stick which is long compared to the arc distance and has a corona point on the end to make sure that the capacitive current flows through the stick rather than arcing to his suit or his face!
 
GoldDigger said:
For uninsulated wire (often see for HV transmission lines?) any covering would be to protect the wire and also to provide a smooth surface to reduce corona discharge. If a bare strand were to be broken rather than just frayed apart from other strands, the potentially resulting sharp point will encourage corona discharge and reduce the arc starting distance slightly. Presumably well within the safety factor of approach distance.

When a lineman is preparing to do uninsulated work on a transmission line he wears a Faraday suit and makes initial contact with the line using a conducting stick which is long compared to the arc distance and has a corona point on the end to make sure that the capacitive current flows through the stick rather than arcing to his suit or his face!
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I've seen videos of those guys servicing high tension transmission lines from helicopters. I'm sure they make lots of money but it ain't for me.
 
GoldDigger said:
You certainly cannot be afraid of heights. :)
To me the voltage would be completely secondary.
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Extreme heights scare me as well, but I realize that my fear is irrational. Intellectually I know that a fall of 10 feet onto concrete would probably be fatal and more than that wouldn't make any difference, but looking at photos of the high wire artist that walked the wire between the twin towers in NYC in 1974 gives me the willies.


I guess I am more scared of what I would be thinking all the way down than of the impact itself.
 
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