4160 V feeder

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steve66

steve66

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Illinois
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Engineer
Can someone recommend a cable type to use as a feeder for the primary of a 4160V transformer?

I know MV-90 specifies the voltage range and temperature, but what else do I need to specify. I think I saw something about MV cables now requiring a metal sheild? Is that right?

Looking at Southwires web site, it looks like XLP is a standard insulation for MV cable. It also looks like there is a choice between a tape or a wire shield.

Steve
 
Re: 4160 V feeder

Originally posted by steve66:
Can someone recommend a cable type to use as a feeder for the primary of a 4160V transformer?

I know MV-90 specifies the voltage range and temperature, but what else do I need to specify. I think I saw something about MV cables now requiring a metal sheild? Is that right?

Looking at Southwires web site, it looks like XLP is a standard insulation for MV cable. It also looks like there is a choice between a tape or a wire shield.

Steve
Click to expand...
You need to order the conductor material (copper or alum). Wire or tape, not particularly critical. Just order your termination kits for the one you buy. I prefer wire shield, but have used both.
The other insulation, at a premium to xlp, is EPR, tho I think it starts at 15kv insulation.
I rewired (4160) the campus of a small school in 1989. We pulled over 50,000' of 500kcm 5kv cable (xlp) plus a ton of smaller sizes in a new duct bank. Since that time, there has never been any problem with the campus primary system.
Prior to this, the primary was 'messenger hung' in the campus steam tunnels. It blew out regularly due to hot steam and corrosion from leaks in the system, always on the coldest day in the winter.
 
Re: 4160 V feeder

Steve

You definitely need shielded cable, the type will depend on your particular choices, and what is in the rest of the plant. You will want some spare cable just in case.

As far as insulation, I believe that EPR is far superior to XLP. If outages are at all critical, consider EPR, although at 5kv the stresses aren't too bad.

Jim T
 
Re: 4160 V feeder

Thanks. I don't see aluminum conductors for XLP in southwire's catalog. So I'll just specify copper.

I'm also going to specify the triplexed cable. But what size conduit does one need for a cable that is almost 2" in diameter? The area of the cable is pi*1" = 3.1 sq in. If I divide that by the 53% area allowed for one conductor, that means the conduit has to have an area of 6 sq in. So a 3" conduit would be required?

Steve
 
Re: 4160 V feeder

For 4160V. I'd use shielded with copper conductor. Tape shield is the type of shielding that we use. Am a firm believer in EPR insulation based on our experience in outdoor or wet locations. Have had trouble with XLP insulation.
 
Re: 4160 V feeder

I'm not sure that I'd use triplexed cables. Shielded cables have strict tension limits, and depending on the length of pull, you may have trouble. I normally suggest single cables.

Secondly, even with a triplexed cable, I would use 40% not 53% for my conduit fill.

Jim T
 
Re: 4160 V feeder

What size cable are you using? If it is for that 750kva xfmr, I cannot imagine using anything larger than 1/0....#2 might even suffice. It is certainly not 2" in diameter.
1/0 epr is only .789 in diameter. 1/0 xlp is .848. (Southwire table)

Having said that, 3" is likely a good choice for pulling the cable. Add an equipment ground wire (#4 or #6) and you are all set.

I agree with the 'single conductor' cable. Easier to handle, set up and pull. :D
 
Re: 4160 V feeder

Thinfool:

I agree that 1/0 seems plenty large. But I would like to fuse the primary high enough to make sure the fuses can handle the inrush. And with that in mind, the NEC seems to require a 3/0 cable. My earlier post explains my situation more completely.

Steve
 
Re: 4160 V feeder

Originally posted by steve66:
fuse the primary high enough to make sure the fuses can handle the inrush.
Click to expand...
Steve,
Can you spec a fuse with the time/current value such that it will hold on inrush and still protect the 1/0 properly?
 
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