Remote Site Power - 250W on 24 Volt wire - Options at the Chair Lift

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brycenesbitt

Senior Member
Location
United States
Looking at delivering power to a remote site, 2225 feet from base 3 phase power.
The need is some 250W, for a low voltage communication relay.
Seeing if there are any clever ways.

The options would seem to be:
  1. Trenching through solid rock, mixed volcanic and granite, in an area subject to rockfall.
  2. Using an existing set of active aerial tramway towers.
  3. Going tree to tree, in an area that drifts 10 to 40 feet of snow in winter.
  4. Installing dedicated poles and wires and protecting those poles, installing poles by helicopter.
  5. Solar, set up for stormy weeks of below freezing weather.
  6. Diesel power, with refill once or twice per year in summer when gravel road access is possible. (The area is subject to wildfire as well).
An existing effort to trench apparently did not go deep enough, either way the power cables were damaged.
A prior effort using solar panels was technically challenged and failed repeatedly.


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You might say that the tramway is the obvious choice, eh? Yet the tramway apparently falls under ANSI B77.1-2017:

Code: 
2.2.1.1 Applicable codes:  All electrical systems shall comply with American National Standard, ANSI/NFPA 70 & IEEE C2-2017.

So far so good, but we get a bit deeper:

Code: 
2.2.1.3 Protection
All electrical equipment with operating voltages above 24 volts nominal shall be marked conspicuously with
letters/numbers that are no smaller than ¼ inch (6 mm) in height.... “Danger High
Voltage”
All power equipment shall be protected against overloads by circuit breakers or fuses.

Ok so far, but then:

Code: 
2.2.1.4 Overhead cables
Only signal, communication, control circuit cables and wire rope associated with rescue systems may be
supported between towers that support the aerial tramway.

Voltage shall be limited to low voltage, 24 volts  nominal.
EXCEPTION – Circuits for telephone systems may exceed the low voltage requirements.

Overhead cables shall be positioned in such a way that they do not contact the haul rope, track rope, or carriers
under normal aerial tramway operating conditions. If cable parts and displaces from its normal position, the
aerial tramway shall stop (see 2.2.3(h))

2.2.12.3 lighting
Aerial tramway towers and terminal structures may be used for supporting lights, subject to the following requirements:
(b) The service conductors to each aerial tramway tower or terminal structure shall be underground or in
rigid raceways. No wiring shall be supported between towers and no open wiring shall pass over or under
the aerial tramway;

So they pretty clearly don't want power strung between poles, even with GFCI and supervision and supervisory
circuits that shut the lift down if a wire comes loose.

The telephone exception is probably for the "RING" voltage, assuming anyone remembers how that works.
But we're not doing a "telephone".

So that's either trying to deliver 250W at 24 Volts and claiming it's a telephone.... or.... something else....
 
zbang said:
What's the outage tolerance? Is 24/7 needed or can it go without for weeks at a time?
Click to expand...
Communications equipment, needed 24/7. Peak usage in the evenings, but more or less constant.
The previous battery system lost ground during periods of cloudy daytime weather. Snow on the solar
did melt, but sometimes that area gets inches of rim ice and 100 mph plus winds, followed by cycles of above and below freezing weather. 40 foot drifts not uncommon. Overall temperatures are mild though, just deep snow.
 
I wouldn't even try to send 10+ amps at that low of a voltage over that distance by normal means.

So, creative. Hmmm. :unsure: Is there a limit to the current and/or quantity of 24v circuits you can run?

Or, how about sending 24v AC hexaphase over sets of seven wires and rectifying it at the load end?
 
LarryFine said:
Or, how about sending 24v AC hexaphase over sets of seven wires and rectifying it at the load end?
Click to expand...
Oooh, now 'yer thinking.

And if the seven wires were single phase not hexaphase, and at the same potential, no need to insulate them, so just can use a seven conductor stranded cable..... justification galore !

Or the standard has that "phone line" exception for "telephone circuits".
Ah, but wait, they just said 24V. Thus -24V should be fine, right? So +24V to -24V at 60 Hertz "DC" ?
Or just a phone line that's constantly ringing at 20 Hz AC 105 volts nominal over the 52.1V DC baseline ....
en.wikipedia.org

Tip and ring - Wikipedia

en.wikipedia.org en.wikipedia.org

--
That or a diamond blade ditch witch. So hard to decide.

--
Or try to get the ANSI standard modernized.
 
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brycenesbitt said:
Oooh, now 'yer thinking.
And if the seven wires are at the same potential, no need to insulate them, so just can use a seven conductor stranded cable I suppose....
Click to expand...
Not insulated? Not one conductor. Are you back to thinking a large pair of wires?

brycenesbitt said:
The ANSI standard did not specify AC vs. DC: is there an advantage to AC in this context?
Click to expand...
Greater peak voltage to charge filter caps with the nominal equal to DC.
 
wwhitney said:
Is that constant, or peak, or average? If it's 250W peak, and 25W average, that's a lot different than 250W constant.
Cheers, Wayne
Click to expand...
No, unfortunately that's nominal. It's radio repeater gear.
If it were 25W average over a day, buffer batteries would fix that up right quick.
24/7/365 radio repeater, alpine environment. The odd thing here is the ANSI B77.1 restriction.
Now I know why the local ski areas run portable gas generators at the top of their lifts....

But we could be creative. Can't see a rule against attaching a cog to the bullwheel, and just
generating power during operating hours. Oh, wait. Summer. Bummer. Ok, getting silly
batteries and solar sized for summer, bullwheel power harvesting during winter.
 
I think the two options really are either solar w/ lots of batteries and a genset in the winter, or a nice deep trench and sent 240 or 480 up to the top. And if you're pulling wire anyway, consider running 3-phase, it'll only be an extra wire and might be useful.

If there's a repeater up there anyway, any chance of selling space for someone else's transmitter? That would recoup some of the costs.
 
You're on the right track with batteries/solar/diesel. Very likely to be the most reliable and cost effective option. With 3kW of solar you only need about 20 hours/5 days a month of sunshine to stay topped up. Diesel will kick on very rarely. A quick google search found a 100kWh energy storage system with LiFePo, for $120k, but there's probably something cheaper and 60kWh would probably be plenty to almost never use the diesel.

Otherwise just run a 750kcmil "signal" pair along the tramway towers. This should only cost about $120k in copper, so without knowing your trenching costs it may be more cost effective. I've never had to trench so far in such an annoying place.
 
cryptonenologist said:
Otherwise just run a 750kcmil "signal" pair along the tramway towers.
Click to expand...
Might run into a problem with wind load calculations.

At 480v 3-phase, 20 amps, I get 6awg for under 5% drop. At a little over $1/ft, that's under $10k in wire. Use DB wire in a deep enough trench and save on having pipe. (Trenching must be the big expense; after that there's little reason to try shaving a few hundred dollars off the total.)
 
Probably windy up there?
I'd investigate combination of the bull wheel, solar, and small wind turbine with battery backup and possibly a small genset for the really rare no sun, no wind, summer days or the dead calm overcast early winter days before the lift is in operation.

Can you share what the cost goal is? How many Benjamns?

PS: 25 or so years ago, worked on a Haleakala to Big Island 1500W power transfer development project for Nasa, solar array at observatory on Haleakala with microwave xmitter and the receiver on Mona Loa. Pretty pricey though :geek:
 
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There is a boyscout camp near Mt Rainier that has a 2" sch 40 steel water pipe running more than 2000 ft from a waterfall down to the camp. It is just laying on the ground and has been there for years with no problems. It appears to even have survived a large rockfall. (4 ft dia boulders a few yard deep)
How about just laying RMC thru the trees on the ground, use the RMC for the return current path, use whatever voltage under say 250 V you can get away with (NEC required??) and a one aluminum conductor in the RMC.
I'd suggest investigating the lift cables for return current, but over time that would likely destroy roller or ball bearings in the system.
 
Attaching anything to the lift is usually a no-no unless approved by the mfg, so hooking a generator to the bull wheel is likely to "arise speciation" of an inspector.

Maybe a SWER system? (None of this sounds NEC compliant, but it is fun to speculate.) Running 3.4 furlongs (24 chains) of rigid doesn't sound like fun, but it's probably better than trenching though rock.
 
I was sort of joking in post 10, but:
www.electriciantalk.com

HDPE Conduit 353.10(5) Uses Permitted

Can somebody define the intent behind 353.10(5) for HDPE conduit? It reads as follows Uses Permitted: Above ground, except as prohibited in 353.12, where encased in not less than 50mm (2 in.) of concrete. We have a contract underway at our facility where the contractor has run HDPE conduit on...
www.electriciantalk.com www.electriciantalk.com

Essentially run HDPE conduit on the ground surface, and then use concrete 'bagwork' to 'encase' the conduit.
 
This sounds exactly like a high Sierra ski resort.

I know of one such installation I worked on once upon a time.

First off we used low power equipment and cut power consumption way below 250W. Are you sure this can't be done?

They indeed used a 24V generator off the bull wheel in wintertime, also powered something in the shack for the top side lift operators.

In summer there is plenty of sun.

Windmills are questionable because the 170 mph gusts are hard on them.

There were also 1000 gallon propane tanks up there filled in summer by a truck dragged up by a dozer.

Small Honda generators that somebody could run in an emergency.

There is a place nearby where they ran conduit to a rocky peak under a mound of concrete placed on the conduit on the rock.
 
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