5KV Distribution

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Ricmcd

Member
Location
Lompoc, Ca. USA
I'm considering all options to feed (3) 200 Amp services (Separate Houses) on an 80 acre parcel in the mountains of Idaho. The incoming utilities enter the property in one corner and are currently stepped down to 240/120 single phase. I'm considering stepping the voltage up to 4160 and running a main underground line approximately 2000'. I would be stepping voltage back down at each location. Does anybody have experience with this type of distribution? My questions are as follows;
1. We get 3' of snow a year here, will this be a major concern for a ground mount transformer?
2. Is this the most cost effective to distribute power to 3 separate homes when they are this far from the source?
3. Can the 240-4160 transformers be reverse connected and are they relatively maintenance free and dependable?
4. What is the correct wire type (5KV) for and underground (in conduit) installation? (Shielded or unshielded)
5. I was planning on grounding each transformer so is there some reason to pull a ground with the MV Cable?

I'm open to all ideas, this is not typically the kind of work stuff we do, I'm looking mostly for design ideas that could save $$$ yet be dependable. Thanks for your responses in advance!
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Locally with similar situations (other than the snow :)) POCO would simply install their HV to a pad located closer to the houses once they had easements, etc. Most of our POCOs rely on the E/C to install the UG conduit and then install the wire charging by the ft.
Have you perused that option (POCO lines).
You may well find the initial cost is less plus they are responsible for maintenance, failures, etc.
 

Ricmcd

Member
Location
Lompoc, Ca. USA
Locally with similar situations (other than the snow :)) POCO would simply install their HV to a pad located closer to the houses once they had easements, etc. Most of our POCOs rely on the E/C to install the UG conduit and then install the wire charging by the ft.
Have you perused that option (POCO lines).
You may well find the initial cost is less plus they are responsible for maintenance, failures, etc.


The utility company wants well over 100K to continue their primary to all three locations. This is absurd so I would like to eliminate them from the equation
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Wow! Bit pricey are they not :)
Do you have a calculated load ? Unless these are big power users I think you will find a possible answer in stepping up to 600v and the back down a viable option. You might well keep a reasonable voltage drop with a 500 kcmil or 750 kcmil AL and avoid a whole realm of expense and pitfalls that accompany voltages over 600.
It might also be worth addressing power use billing. If the usage is going to be re-billed to the individual homes you could stumble into a area where ordinances prohibit re-billing bu non-utilities. Often surmountable but worth taking into consideration.
 

JRW 70

Senior Member
Location
Eastern Central Missouri
Occupation
Testing and Engineer
Cost Comparison

Cost Comparison

Two thousand feet sounds like a long distance until the
price of MV (4160Y2400V) equipment comes into the picture.
For a privately installed system, shielded cable may be
the requirement. (if it were mine I would want shielded to
be speced. even if unshielded were permitted)
Even with the large wire size needed for a LV installation,
it is still probably cheaper and easier to have someone work
on it than the MV. (I'm going on pricing that small of a system
out. If the distance were miles and ten or more loads then the
cost/benefit ratio would become more favorable.) If by chance
you can get a really good deal on the transformers, MV cable,
some kind of cable protection (like a recloser, fusible cutout or
a CB) the snow issue shouldn't cause the pad mount transformers
too much trouble, after all if they are loaded that much they will
melt the snow/ice and start being convection cooled normally.

In summary, investigate the costs of operation, maintenance and
installation. Either way will work, just which is more practical and
hopefully easiest on whoever has to work on it in the future if
maintenance needs come up.

JR
 

JRW 70

Senior Member
Location
Eastern Central Missouri
Occupation
Testing and Engineer
2014 NEC

2014 NEC

I just had an afterthought to the above. In the 2014 NEC
haven't they raised LV to 1kV (1000V)? If you could get the
right equipment, this could be done in a way to stay out of the
MV regs. And for this small of a system it may be the best
compromise. I don't know what areas/locations have moved
up to the 2014, but it might get you a little higher voltage
without all of the MV considerations. Your inspecting athourity
may allow the use of the 2014 if it would help (by getting special
permission). Hope your project goes well and is a success.

Jimmy
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
LV is now up to 1000V, but residential installations are still limited to 600V, yes?
Not sure if this affects distribution voltage in this situation.
 

Ricmcd

Member
Location
Lompoc, Ca. USA
I just had an afterthought to the above. In the 2014 NEC
haven't they raised LV to 1kV (1000V)? If you could get the
right equipment, this could be done in a way to stay out of the
MV regs. And for this small of a system it may be the best
compromise. I don't know what areas/locations have moved
up to the 2014, but it might get you a little higher voltage
without all of the MV considerations. Your inspecting athourity
may allow the use of the 2014 if it would help (by getting special
permission). Hope your project goes well and is a success.

Jimmy

I'm not too worried about the installation costs as I will install all the components my self. I'm thinking I will run a separate conduit from each of the meters located just inside the property line to avoid having to try to sub meter the power. I will set a step up transformer at that point and either go overhead or underground depending on cost and trench ability. Some of the areas are very rocky so I may be forced to go overhead. Once the home locations are selected that will be determined. My biggest concern is wire cost at this distance. We install 240 to 480 step up/down transformers all the time. I have never installed a(single phase) 240 to 4160 step up or step down ground mount transformer. If I am forced to go overhead it's a no brainer, pole mounted transformers to step down are very common. The initial step up transformer is something I have not seen. Not sure the material cost of doing it this way but it would save dramatically in wire costs. I was hoping to find someone that has done this type of installation to see if they have run into maintenance or availability issues. Never the less I will run all the numbers when load and distance are known. Just hoping to narrow down the options when it comes to feasibility
 
If you're going to consider MV distribution, why not take that from the PoCo and avoid the step-up part? OTOH, if you've never MV underground wiring, you'll want to hire a MV contractor to do the terminations, so figure that into the cost calcs. (And figure in the additional safety equipment if you do part of the MV work yourself.)
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
2000' is far, but doable. On one particular project a year ago, I needed about 100 amps of 240v single phase. I had the power company set a 480/277v 3 phase service and then simply stepped it down at the load. This was much simpler then step up/down transformers but it may bump your customer up to commercial service rates. May still work out to be less than the losses from one more idle transformer though...

Don't forget to take into account, although the power company's price is expensive, it is THEIR primary wire they have to take care of. So you may save money now doing it yourself, but if it ever fails, now it's the customers money paying to fix it.
 
Last edited:

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
... the snow issue shouldn't cause the pad mount transformers too much trouble, after all if they are loaded that much they will melt the snow/ice and start being convection cooled normally.

Actually if the transformers become completely buried in snow, they could overheat and fail. The heat they produce will only melt the nearby snow creating an insulating snow cave.
Luckily becoming completely buried in snow is an extremely uncommon occurrence, even 'up north' from here where the snow exceeds 200" on a fairly regular basis.
Since 1975 I have, personally, experienced only one such failure.
 

John120/240

Senior Member
Location
Olathe, Kansas
This is really outta my league. POCO stops at say the road. You are going to run 2,000 feet with 4160V or some such. Then step down to 120/240V. Then separate meters at each residence if I understand. So is POCO OK with some body else doing the middle part of the run ?
 

JRW 70

Senior Member
Location
Eastern Central Missouri
Occupation
Testing and Engineer
Initial Step-Up

Initial Step-Up

If your supplying company won't give you 4.16kV, then
the step up(s) are in the same ballpark price range as the
step downs. If exact ratio is needed, then a specific step
up with taps would be the way to go. If tolerances are not
needed to be that precise, just use a step down in reverse
(unless prohibited on the nameplate or accompanying docs.)

And Mr. Dungar is right about the "igloo" effect, but that would
be a pretty extreme case, as stated by him ( only knowing of
one in his career )

And since this is privately owned, try to use SC/Overload
that will really actually protect your lines. In the utility
industry, the "blow clear" philosophy is used where here
tight protection to more closely protect may be a wise
design decision.

JR
 

Ricmcd

Member
Location
Lompoc, Ca. USA
If your supplying company won't give you 4.16kV, then
the step up(s) are in the same ballpark price range as the
step downs. If exact ratio is needed, then a specific step
up with taps would be the way to go. If tolerances are not
needed to be that precise, just use a step down in reverse
(unless prohibited on the nameplate or accompanying docs.)

And Mr. Dungar is right about the "igloo" effect, but that would
be a pretty extreme case, as stated by him ( only knowing of
one in his career )

And since this is privately owned, try to use SC/Overload
that will really actually protect your lines. In the utility
industry, the "blow clear" philosophy is used where here
tight protection to more closely protect may be a wise
design decision.

JR


Thank you, the problem I have is Idaho Power will not give us anything but 120/240 single phase and we are having to pay 25K just to get 2 meters set at the property line. for an extra 122k they will take the primary all the way to each residence including the transformers and secondary to the individual meters. I know I can run the secondary a lot cheaper and both meters would be in one location eliminating Idaho Power from having to travel back to the meters. I have spliced and worked on quite a few projects with 2400V, (Oil transfer station facility) and it may be that by going to 2400V will save us enough to make it worth it. I currently live on the central coast of Ca. and don't have to deal with the snow. The utility power had to come in via U/G because that is the only easement we could get across the neighboring property. I would rather not convert back to overhead all though that would be much cheaper. I was looking for a 200A service at each house because I will have to feed a well and shop at each location. Depending on distance only stepping up to 480 will still require large wire (expensive). My thought is if I am going to need to install transformers anyway I should step up to as high of voltage as possible to use the minimum size MV cable available to save costs. I believe all 2.5KV rated wire is minimum #6, maybe #8 (not sure) this would be much cheaper than 250 MCM or 500...
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
If find it hard to believe the utility will put two of their meters at the end of your DIY circuit.
In this area you will have to have one service (meter) ahead of your step-up transformer.
 

Ricmcd

Member
Location
Lompoc, Ca. USA
If find it hard to believe the utility will put two of their meters at the end of your DIY circuit.
In this area you will have to have one service (meter) ahead of your step-up transformer.

They said I could have up to 4 meters for this 80 acres without rezoning the parcel. They also said they could careless what I do with the power after the meter. They're responsibility would only be to the meter.

Because it's unrestricted property the only 2 permits we will need to build is sewer and electricity within a structure. Crazy compared to here in Cali. we need a permit to wipe our butt...LOL
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
They said I could have up to 4 meters for this 80 acres without rezoning the parcel. They also said they could careless what I do with the power after the meter. They're responsibility would only be to the meter.

Because it's unrestricted property the only 2 permits we will need to build is sewer and electricity within a structure. Crazy compared to here in Cali. we need a permit to wipe our butt...LOL

So you will have one meter feeding your step up transformer. The three residences can figure out how to divide up the one bill.
 

Ricmcd

Member
Location
Lompoc, Ca. USA
So you will have one meter feeding your step up transformer. The three residences can figure out how to divide up the one bill.
No I will need two meters, two step up transformers and 2 step down transformers. I will have to run 2 separate conduits and 2 separate MV circuits between transformers. The residences are not close to each other so this will be required whether by the PUC or by me...
 
I'm considering all options to feed (3) 200 Amp services (Separate Houses) on an 80 acre parcel in the mountains of Idaho. The incoming utilities enter the property in one corner and are currently stepped down to 240/120 single phase. I'm considering stepping the voltage up to 4160 and running a main underground line approximately 2000'. I would be stepping voltage back down at each location. Does anybody have experience with this type of distribution? My questions are as follows;
1. We get 3' of snow a year here, will this be a major concern for a ground mount transformer?
2. Is this the most cost effective to distribute power to 3 separate homes when they are this far from the source?
3. Can the 240-4160 transformers be reverse connected and are they relatively maintenance free and dependable?
4. What is the correct wire type (5KV) for and underground (in conduit) installation? (Shielded or unshielded)
5. I was planning on grounding each transformer so is there some reason to pull a ground with the MV Cable?

I'm open to all ideas, this is not typically the kind of work stuff we do, I'm looking mostly for design ideas that could save $$$ yet be dependable. Thanks for your responses in advance!

How about this: go with 600 volts. 240 to 600 transformer after the meters and 600 to 120-240 on the load end. That will keep you in "cheap" gear and conductors. Its pretty tough if not impossible to get 95% of dwellings to draw over 70 amps, so that is 28 amps at 600V so you would only need #2 Al for 5% VD at peak power. Without the transformers you would need 750 for the same VD which is 2.11/foot last I checked, and of course you would need a neutral then too and big pipe. Not sure how much a 20 KVA 120/240->600 transformer or #2 Al is off the top of my head. but sounds like it would be worth the transformer route
 
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