25kV Underbuild

[ahearn10]

Hi all,

I am wondering if someone out there can help me out with a question about phase spacing. Currently our system has two 12kV circuits on a pole line. The top is energized and the bottom is spare.

The need for a 25kV line has arouse and I was wondering if I could use the spare bottom circuit to deliver it. Of course I would have to reinsulate the line with 25kV rated insulators.

My question is about the phase spacing on the crossarms. The existing crossarms are only 7ft long with 2ft phase spacing on one side of it. The other side is fine I think as I have 4ft of space between the pole and the conductor.

What phase spacing do I have to maintain between conductors at 25kV and between my pole in the middle of the arm? Also to make things more complicated I would have to deal with 12kV drop leads going through the 25kV circuit to get to my distribution transformers. Any help would be greatly appreciated.

Thanks!

 

[davidbeach]

First off, higher voltages should always be higher up the pole. Secondly, there is probably a code that answers the rest of your questions. In the US that would be the NESC. Elsewhere it will likely be something else.

 

[magoo2]

12 and 25 kV sound like North American voltages. I agree with David. The NESC requires the higher voltage to be on top.

 

[cuky2000]

Search in the net Engineering Standard such as JEA (Jacksonville Electric Authority) or RUS for rural & cooperative utilities. There are information available that could help.

Compact design without shield wire but with surge arrester appear to be a good option to consider for the higher voltage on top and transfer the energized 12 kV to the lowest underbuilt. That may require some planing and logistics to implements this changes.

 

[ahearn10]

Thanks for the help guys, I agree with moving the 25kV circuit to the top. I was trying to save some time as this is only supposed to be a temporary feed.

 

[bacon4life]

This thread had a similar discussion.

http://www.eng-tips.com/viewthread.cfm?qid=144865&page=362

 

[jghrist]

http://www.usda.gov/rus/electric/bulletins.htm

has US Rural Utility Service 25 kV specifications and drawings that might be useful.

 

[linehand]

My experience is never try to save time by shortcutting on powerline construction. It may be a good time to have a good look at your equipment and change out questionable insulators, crossarms, conductors, etc. Build it right the first time.