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Foudrette (Electrical) (OP)
26 Feb 06 12:16
Hello,
I have to study a very complex cable route, related to a bridge crossing.
138kV XLPE cables are intended to be pulled :
- first in a steel riser along the pier of the bridge
- and in fiberglass tubes along the bridge
- Finally, the cable goes down from the bridge in another steel riser.
The overlength of the cable route is equal to roughly 3500 ft and many bends are observed on the different transition areas (underground/pier - pier/bridge - bridge pier - pier/underground)

Main cable dimensions are as follows :
- outer diameter : 2.94 inches
- weight : 12.6 lbs/ft
- Inner diameter of the pipes :10"
The 3 phases are expected to be pulled together after being assembled using straps.
Has someone any experience in laying HV cables in such an unusual configuration ?
Is there any software you could recommend for pulling strength and SWP calculations in this configuration (we usually use Pull Planner but it seems non appropriate in our case) ?
Which are your main recommendations for such a cable installation on bridge ?

Thank you for your help,
Foudrette



 
wareagle (Electrical)
26 Feb 06 14:30
American Polywater has software that can ssist you.
www.polywater.com
waross (Electrical)
26 Feb 06 14:37
Hello Foudrette
It sounds like you have an interesting challenge.
Expect the three cables to twist as they go around each bend. I have seen a lot of time wasted trying to prevent this twist on cables from 1000V to 25000V. This is why experienced pullers connect the pulling line to the cable with a swivel. A cable will usually twist when it is pulled around a bend. With a single cable, it's usually of no consequence, but with more than one cable pulled together, as the individual cables twist, they end up twisting together. Anyone who has seen electricians trying to save time by pulling more than one cable together in tray will know that the time spent trying unsuccesfully to prevent the twisting and then to unwind the cables wastes much more time than is ever saved. If the cables are pulled into pipes and are not visible this is probably not important, as long as you can accept the twisting and don't try to stop it. Be aware that your pulling sheaves must be large enough to pass the cable in the twisted configuration.
I would advise that any helper lines that are connected part way in the pull be soft fibre rope rather than steel cable. Some spans will pull without twisting and some will twist. You may have to stop from time to time to unwind the helper lines from the cables. Better to have a soft rope winding around your conductors than a wire rope. I expect that your primary pulling line will be a wire rope attached to the cable ends with a swivel.
I would also suggest determining the maximum force that the cable can withstand without sustaining damage. Select a primary pulling winch that can be arranged to stall before the cable is damaged. Look for a place where the cable is accessible for a great enough distance to attach helper tuggers to assist if nescessary.
yours
BJC (Electrical)
26 Feb 06 17:35
You ask for recommendations and mine are:
1.) add a couple of splice boxes and pull in segiments.  If you are really pulling it in one pull the supply reels will have to be huge.  
2.) Try a sample calc with a .1 FF and a straigh pull, no bends, no ups no downs.  12.6x3x.2x3000= 22,000 Lbs.  It gets worse with a few bends. I am assuming a weight of 12.6 lbs per phase.
Cable that size is usually configured with a "skid wire" o a lessen friction and damage.
I recommend starting with an accurate isometric diagram of the conduit.  Calculate the pull tension manually using Xcel.  USe the EPRI guidline if you can find it in a book.  The major cable manufactures all have examples of tension calculations.  
The skid wire arround a cable or group lessens tension and keeps the lubricate in the pipe more efficiently.  Cable resting on the bottom of a pipe squeezes and rubs the lubricant from between the cable and the pipe wall.
After you have the isometric diagram of the run call the cable vendor and get their input. They will help, they don't want you to fail with their cable.
Include on your diagram all the set up and pull points, include locations where you can install intermediat pull point ( splice boxes).
I think if you research this you'll find that cable this size in pulled in pipe, not conduit but pipe with a smooth interior. Steel pipe back pulled into a directionally drilled hole is pretty common.
Beware of sidewall pressure and minimum bending radii. Get the data from the cable vendor.  
I don't have much faith in the fiberglass raceway.  Yose a non streach rope, lots of soap and hopefully the rope and or the skid wires won't cut a hole in it.
LEt us know what goes on.

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