Extreme distance voltage drops

[teh_engineer]

Good morning,

I'm working on a roadway project, which is new territory for me (I only have experience with projects with runs no greater than maybe 1000') , and have a question regarding voltage drops, specifically over extremely long distances.

This project has one power distribution cabinet for license plate readers &c well over 6500' away from the source distribution point (highway administration building), which is 3P, 277/480V (I was told that there was no MV 4160V available, and there aren't any usable utility poles nearby). I'm calculating about (6) 600kcmil to just barely achieve 3% drop for a 200A panel 6500' away, which seems like a ludicrous amount of material and unfeasible from a practical standpoint.

My question is: are there any special modifications to the voltage drop formula for long distances?
If not, is there any equipment that is typical for these sorts of installations that will help mitigate or correct the voltage drop, e.g. voltage regulators or buck boost transformers every x feet? I'm thinking that there are practical limitations as well, e.g. the length of cable spools and maximum reasonable pull distance

Thanks in advance

 

[ptonsparky]

Figure the voltage drop for the expected load, not the size of the panel. You could
bump it up to 600 then drop it down but again figure for the expected load.

 

[infinity]

Sounds like you need a MV transformer on each end.

 

[masterinbama]

Sounds like you need a MV transformer on each end.

I concur

Sent from my LML211BL using Tapatalk

 

[electrofelon]

Figure the voltage drop for the expected load, not the size of the panel.

Yes very important. Not panel size, not breaker size, not article 220 load, preferably not even nameplate load - ACTUAL load.

I am guessing the actual load for something like this is quite small, but being a roadway project, there are probably many people willing to waste lots of money.

 

[kwired]

Probably a small enough load one should consider a battery and solar panel.

 

[Hv&Lv]

Aren’t these readers 12VDC anyway?

 

[synchro]

Probably a small enough load one should consider a battery and solar panel.

Or if the peak loads are significantly higher than the long-term average load, a much smaller gauge run could charge a battery which handles the peak load currents.

 

[kwired]

Or if the peak loads are significantly higher than the long-term average load, a much smaller gauge run could charge a battery which handles the peak load currents.

yes

 

[ramsy]

I'm calculating about (6) 600kcmil to just barely achieve 3% drop for a 200A panel 6500' away..

If the load is not inductive, try a Power Factor near 1.00
Moving 0.7 to 1.00 drops several points

 

[LarryFine]

For this distance, I'd propose a battery-powered system with a solar charger.

 

[kwired]

Good morning,

I'm working on a roadway project, which is new territory for me (I only have experience with projects with runs no greater than maybe 1000') , and have a question regarding voltage drops, specifically over extremely long distances.

This project has one power distribution cabinet for license plate readers &c well over 6500' away from the source distribution point (highway administration building), which is 3P, 277/480V (I was told that there was no MV 4160V available, and there aren't any usable utility poles nearby). I'm calculating about (6) 600kcmil to just barely achieve 3% drop for a 200A panel 6500' away, which seems like a ludicrous amount of material and unfeasible from a practical standpoint.

My question is: are there any special modifications to the voltage drop formula for long distances?
If not, is there any equipment that is typical for these sorts of installations that will help mitigate or correct the voltage drop, e.g. voltage regulators or buck boost transformers every x feet? I'm thinking that there are practical limitations as well, e.g. the length of cable spools and maximum reasonable pull distance

Thanks in advance

Can you clarify exactly what your load is? I read license plate readers and thought some sort of optical reading device that probably is only 25 maybe 50 VA max. Don't know what "&c well" means. But sounding like actual load is way under 200 amps and if you are calculating VD off of 200 amps you will get very large conductors for this. Without calculating I can see you having something close to a 200 amp conductor being used for voltage drop reasons when all you really have is a single 15 or 20 amp circuit at the load end of this.

 

[drcampbell]

"&c": et cetera
(but I think he meant to say "et alia")

 

[kwired]

"&c": et cetera
(but I think he meant to say "et alia")

If so still sounding like very light loads. I'd still be pushing for battery and solar charging unit.

 

[ptonsparky]

I get about 5.3% VD for a single phase 480v load of 10KVA. (21 amps.) Used 4/0 AL. No PF figured in.

Solar is probably best but you want wire.

 

[kwired]

I get about 5.3% VD for a single phase 480v load of 10KVA. (21 amps.) Used 4/0 AL. No PF figured in.

Solar is probably best but you want wire.

sounds to me like this might be well under 10 kVA though, maybe only 50 or 100 VA max.

 

[ptonsparky]

sounds to me like this might be well under 10 kVA though, maybe only 50 or 100 VA max.

Exactly. He doesn’t need anywhere close to 21 amps, let alone 200.

 

[zbang]

There's a whole lot we don't know, it could be a single reader, could be a bank of reader with some datacom to connect and a freeze-protect heater. Might even have lights. Even adding all that up, a WAG says under 2kva. Send it out at 480 and drop it down "out there" (it worked out to 1 or 2g copper).

It's probably also worth pricing out an MV run

 

[broadgage]

If the load is modest, it will probably be specified for 120 volts, thereby requiring a transformer at the load.
Therefore start at the supply end with 480 volts not 277.
Consider ascertaining what voltages the load will accept, you may find that more than 3% voltage drop is acceptable.

As an example, consider the following

480 volts actual at supply end.
456 volts actual at load end (5% voltage drop)
Select the 460 volts tap on the step down transformer, this should produce about 119 volts on the secondary.

If the loading is more substantial, then it might worth asking the utility if MV service could be obtained nearer the point of use.

 

[ggunn]

Sounds like you need a MV transformer on each end.

That would work, but two things to consider are the losses in the transformers and the quiescent load that the transformers will present even if there is no load on the other end of the feeder.