Mitigating voltage drop on a 2,000' 480 V feeder

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MRKN

Member
Location
California, USA
Looking at installing a panelboard to serve ~150 kW of load, but the only available and convenient voltage source nearby is 480... unfortunately it's about a 2,000' conduit run. The load is pretty variable so I can't look at things like capacitors for voltage support (unless it was automatically switched in/out?). I guess the obvious solution is to oversize the conductors to the point where voltage drop is 3% along the run, but I'm wondering if there's a better option? The only thing that comes to mind is a load tap changer on a 1:1 transformer, but not sure if those exist at the 480V level. Fishing for ideas, something I'm not aware of.
 
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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
MRKN said:
Looking at installing a panelboard to serve ~150 kW of load, but the only available and convenient voltage source nearby is 480... unfortunately it's about a 2,000' conduit run. The load is pretty variable so I can't look at things like capacitors for voltage support (unless it was automatically switched in/out?). I guess the obvious solution is to oversize the conductors to the point where voltage drop is 3% along the run, but I'm wondering if there's a better option? The only thing that comes to mind is a load tap changer on a 1:1 transformer, but not sure if those exist at the 480V level. Fishing for ideas, something I'm not aware of.
Click to expand...
I'm not recommending this, necessarily, but you could theoretically use a pair of transformers to step the voltage up and back down on either end of the run.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
infinity said:
How much of a savings is there in going from 480 up to 600 volts and back down to 480?
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IDK, never tried it myself, it’s just been suggested before.

I would be looking at determining what the actual maximum load is. 3% VD is a good goal but unless required by specs or the AHJ, it’s not necessarily required. OP and customer will need to decide what is acceptable.
 
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zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
(Looks like we're all assuming this is a feeder, not a service.)

infinity said:
How much of a savings is there in going from 480 up to 600 volts and back down to 480?
Click to expand...

I'd expect not much although using a pair of transformers at all makes for one less CCC (no grounded conductor, it's an SDS at the far end), the 20% higher voltage won't buy much in the way of reduced wire size.

For that power, might make sense going into the MV realm (4kv delta, maybe?). Whole different set of problems, of course.

Does this have to be in conduit or could it be overhead? MV overhead could be the way to go. Lots of local factors, of course.
 
C

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Looks like parallel 500 AL would get it done.

We've used Cable-In-Conduit but not at that size, I would contact both of these companies to see what they offer:

https://www.duraline.com/content/600-volt-aluminum

https://www.southwire.com/documents/CIC_sales_flier_web.pdf

If cablecon didn't work out, we'd run parallel 4" pvc and set (3)4x4x4 vaults at the beginning, middle, and end of the runs. 500AL at 1000' between vaults isn't an issue with the right pulling equipment, we've done it.

I never really cared for the transformer idea myself, it's more equipment to fail, and you have 24/7 idle losses from the transformers.
 
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sameguy

Senior Member
Location
New York
Occupation
Master Elec./JW retired
Go green! Set a windmill and some pv! What that won't work hmm.
I too would call the poco and look at the cost.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
ptonsparky said:
Time to call the POCO, if they aren't bankrupt.
Click to expand...

That's what I would try first. Parallel 500 AL with pipe is going to be 35-38k in just materials. Stepping up to 15KV class MV and then back down: Say 10k best case for 2 used/surplus transformers, 15KV primary cable is about 2 bucks a foot so 12k in cable, so thats 22k plus whatever you want to use for conduit (CIC might be the ticket) and transformer pads, and losses forevs.....
 
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MRKN

Member
Location
California, USA
This is not a point of interconnect - it's all owned and operated by the same entity. My thought with staying low voltage is that it keeps things simple, the only other available voltage is 12 kV, same distance away. Perhaps the easiest is to run a 12 kV feeder with some sort of armored cable (no conduit required) and a small dry type ~200 kVA transformer on a small pad?

edit: I realize I have been omitting some information like the presence of an existing 12 kV feeder the same distance away that could be used. Apologies.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
MRKN said:
This is not a point of interconnect - it's all owned and operated by the same entity. My thought with staying low voltage is that it keeps things simple, the only other available voltage is 12 kV, same distance away. Perhaps the easiest is to run a 12 kV feeder with some sort of armored cable (no conduit required) and a small dry type ~200 kVA transformer on a small pad?

edit: I realize I have been omitting some information like the presence of an existing 12 kV feeder the same distance away that could be used. Apologies.
Click to expand...

Yeah that sounds like the way to go since you only need one tranny. One POCO I have worked with gets 15KV primary in conduit, just unroll it and lay it in and done. Others require sand backfill which IMO is more of cost than conduit but if you have the right equipment and guys maybe not.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I think that 3 parallel sets of 400kcmil Al will meet your 3% voltage drop requirements. Higher voltage options are certainly more efficient and use less materials, but staying at 480V simplifies lots of the safety issues.

-Jon
 
Tony S

Tony S

Senior Member
Location
Resting under the Major Oak UK
ggunn said:
I'm not recommending this, necessarily, but you could theoretically use a pair of transformers to step the voltage up and back down on either end of the run.
Click to expand...

zbang said:
(Looks like we're all assuming this is a feeder, not a service.)



I'd expect not much although using a pair of transformers at all makes for one less CCC (no grounded conductor, it's an SDS at the far end), the 20% higher voltage won't buy much in the way of reduced wire size.

For that power, might make sense going into the MV realm (4kv delta, maybe?). Whole different set of problems, of course.

Does this have to be in conduit or could it be overhead? MV overhead could be the way to go. Lots of local factors, of course.
Click to expand...

A system I designed last year is being installed now. 50kVA single phase delivered over a mile needed something drastic. Two transformers .433/3.3kV and 3.3/.25kV means a small 35mm² armoured cable is being used, it still weighs 4 tons. I gave up counting had we gone for a LV cable.

I looked at extending the 11kV supply but the smallest standard cable I could find was 70mm² added to that was the switchgear. The cost of the transformers was less than the alternatives.
 
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