Low confiability of transmision line

[cpinedai]

I work at a government's power utility company that is in charge of three areas: Generation, Transmision and Distribution, however, my area of work is distribution. The area of Transmision has been presenting a serious of apertures in the transmision line due to atmospheric discharges. The transmision line that brings electricity to the north coast of this country is a radial transmision line and we do not have another power line to back up in case the power line opens up (aperture). I need help as to how I may suggest ideas to my fellow transmision engineers to reduce the number of black outs that occurs everytime a power line is struck by lightning. Sometimes the substation relay is successful in doing the reclose but sometimes is not. Two years ago they grounded every tower and has helped a lot but not enough.

 

[wbd]

What is the voltage of the line? Is there a shield wire? Is there lightning arresters on this line? If so, what is the spacing, every other tower,? What is the outage caused by, flashing over the insultors to the tower?

 

[cpinedai]

Sorry, I guess I forgot to give more details. I just spoke to a friend that works at the Transmision departament and told me that they do not have lightning arresters on the line just in the substations. Also the mayor cause of outages is the flashing over the insulators. The type of tower is the kind of that has one tip with a single shield wire and trying to change it to a two tip tower it would be very expensive due to the economical problems that the utility has. So, if there is some economical solutions I would be glad to hear them and pass them over.

 

[jghrist]

Improving tower grounding will increase the effectiveness of the shield wire. Lightning that strikes the shield wire will cause a high voltage on the tower when it flows into a high resistance ground. There may be a "backflash" from the tower to the conductor, resulting in an outage.

 

[stevenal]

Are some towers more prone than others? Add arresters and ground rods at these locations. You may want to adjust your reclosing open interval to allows enough time for the arc gases to dissipate. Unless the insulators are damaged, the fault should be temporary allowing successful reclosure.

 

[wbd]

If it's confined to certain towers and is backflash, you could change out the insulators to a higher voltage class to give more spacing. Another method is to add lightning arresters along the line periodically and double check that your grounding is solid.

 

[waross]

Has anyone had experience with lightning rods on the towers to try to avoid strikes?
respectfully

 

[wfowfo]

Could contamination of the insulators be a problem? We have a serious buzzard problem where the roosting birds on the crossarm defecate all over the bells. We've mounted bird quards and have lessened the problem considerably.

 

[jghrist]

waross,

Conventional lightning rods do not avoid strikes, they just intercept them to safely carry the surge current to ground. The shield wire serves the same purpose.

There are "early streamer emission" (ESE) terminals that are claimed by their manufacturers to prevent strikes, but I believe the general consensus is that they do not work. Google "lightning ESE".

 

[waross]

Thanks for the info, jghrist
respectfully