Running power 4000 feet

[petersonra]

You must not come out to God's country very much. What you said is fairly true around where I live, but you don't have to go too much further west to find places that are several miles away from the nearest electric utility. Even those places I mention are easy to get power to compared to many places in the Rocky Mountain range.

Might even be a different POCO.

20 kW is not a lot of power but if someone is building something needs that much power one would expect that there is some kind of access to it.

If it is that rural, it seems unlikely it would need engineered drawings.

 

[kwired]

Might even be a different POCO.

20 kW is not a lot of power but if someone is building something needs that much power one would expect that there is some kind of access to it.

If it is that rural, it seems unlikely it would need engineered drawings.

The thing is when using say 7200 volts like many POCO would for the application, the cost of the trench/conduit/cable is the same for a 20 kw load as it is for 1000 kw load, the transformer is going to be different, but that will be that way no matter how long cable run is. POCO's also do sometimes cut you a deal depending on how much energy is expected to be sold, so the more energy to be sold the better deal you may get from having them install infrastructure to supply it.

 

[Tony S]

Our SWA (Single Wire Armoured) cable is rated 600/1000V, what is the voltage rating of a cable of similar construction?

With the voltage rating of SWA I’d be looking at 900V centre tapped. The cable size rises dramatically for 600V. I wouldn’t want to be paying for it, any of it for that matter.

 

[Tony S]

For 600V to scrape in at just under 3% volt drop would need a 95mm² SWA.
900V gets in at 50mm² with just over 2% volt drop.

These values are based on BS7671 but it doesn’t mater which code/regulation is used the end result it the same, double the cable size.

 

[winnie]

Can you do that? Use a transformer above its listed applied voltage? Legally??

Most 'low voltage' transformers have _insulation_ rated for 600V. So the question about properly applying the transformer is to make sure that the coils are seeing the correct 'terminal to terminal' voltage, not necessarily the expected 'terminal to ground' voltage.

The common situation where this is encountered is a 'buck-boost' transformer. For example, a transformer nominally rated 120/240V primary and 16/32V secondary is commonly used to boost 208V up to 236V. This means that the '32V' coil is actually being used at about 120V relative to ground; but you only have 28V across that coil.

In this case, three single phase 5kVA 208V:120V transformers could be banked together in a wye autotransformer configuration, to give a 21.5kVA bank. You would put the 120V coils in wye on the 208/120V supply, so these coils would see their correct voltages. The 208V coils would develop 208V by transformer action. These would be placed in series with the 120V coils, giving a wye output with a 338V L-N voltage, or 568V L-L.

The output of this transformer is _not_ a separately derived system, so grounding requirements would be different.

What I don't know is the _legality_ of this installation in terms of OCPD and grounding requirements.

-Jon

 

[kwired]

Can you do that? Use a transformer above its listed applied voltage? Legally??

450.4(B):

A transformer field-connected as an autotransformer shall be identified for use at elevated voltage.

 

[Fulthrotl]

Thank you! Those numbers are a life saver! :happyyes:

Then I will go with 3 phase.

Im however tempted to pick a 208 delta 600Y transformer just so I can have a mid point ground.


If I did choose 1000 volts, I would need cable other then typical THHN/THWN?

i'm guessing that if you start pricing stuff, the pain of cost will move you back into the
middle of the road... there's been a number of suggestions here, but when you start
pricing it out..... what does bumping it to 1000 do for you, and what's it do to you?

there's been a lot of different suggestions, but we are only talking about a 20kw load.
if you use a delta, you'll be limited on balancing your loads. you've not mentioned
what you actually want to hook up to this, so we are all guessing here. as it's a small
load, i'm guessing you might want to have it balanced as much as possible.

 

[Barbqranch]

If I was the one actually paying the piper, I would want to know how much time 20 kva was really needed, and could I get by w/ a lot less, and something else to handle the power if the heavy demand was there. Maybe a gas driven air compressor, or such. Or, could it be cut using load shedding (water heater perhaps)?

 

[texie]

Currently 20kva of power needs to be run to an outbuilding about 4000 feet away. To keep wiring practical the voltage will be stepped up at the main building, run via underground conduit, and then stepped back down. My question is it is possible to use 1000 volts between the two buildings instead of 600 volts and if so how would one go about doing it? I want to keep VD no more then 3% across this run.

You could consider this as a possible economical solution:

 

[mbrooke]

You could consider this as a possible economical solution:

That would work, but isnt this forbidden in the 2014 code? Or do I reclassify that as an MGN?

 

[mbrooke]

i'm guessing that if you start pricing stuff, the pain of cost will move you back into the
middle of the road... there's been a number of suggestions here, but when you start
pricing it out..... what does bumping it to 1000 do for you, and what's it do to you?

there's been a lot of different suggestions, but we are only talking about a 20kw load.
if you use a delta, you'll be limited on balancing your loads. you've not mentioned
what you actually want to hook up to this, so we are all guessing here. as it's a small
load, i'm guessing you might want to have it balanced as much as possible.

1000 volts knocks down on conductor size both from reduced current and voltage drop. There is some gain in doing so.


Im still on the transformer idea, running 500mcm isnt what I want to do.

 

[GoldDigger]

That would work, but isnt this forbidden in the 2014 code? Or do I reclassify that as an MGN?

You have two separate SDS in the chain in addition to the service, so I do not see any problem with multiple ground/neutral bonds. Having an EGC join two ground electrodes for the same building together instead of a bonding jumper may be an issue. But mostly an issue of what you call it and how you size the wire, not on the electrical connectivity.

 

[mbrooke]

You have two separate SDS in the chain in addition to the service, so I do not see any problem with multiple ground/neutral bonds. Having an EGC join two ground electrodes for the same building together instead of a bonding jumper may be an issue. But mostly an issue of what you call it and how you size the wire, not on the electrical connectivity.

So this skips as an outbuilding? I remember older codes allowed this, but I am sure new additions of the NEC do not...?

 

[curt swartz]

1000 volts knocks down on conductor size both from reduced current and voltage drop. There is some gain in doing so.


Im still on the transformer idea, running 500mcm isn't what I want to do.

The difference between 600 volts and 1000 volts is going to minimal as far as wire size. Going with 600 volts will allow you to use off the shelf equipment (transformers, panels, disconnects) and standard THWN or XHHW wire. Going with 1000 volts will require custom special order equipment and more expensive medium voltage wire. You will also have additional cost for terminating the medium voltage.

I would guess the bump from 600 to 1000 will add a substantial cost to the project.

Another thing to consider is future repair. If the transformers fail or get damaged the customer is going to be without power for an extended time while new equipment is built. 600 volts transformers and distribution equipment are stock items.

 

[victor.cherkashi]

Maybe your equipment can handle high voltage drop and you can avoid install transformers

Sent from my Nexus 5 using Tapatalk

 

[mbrooke]

The difference between 600 volts and 1000 volts is going to minimal as far as wire size. Going with 600 volts will allow you to use off the shelf equipment (transformers, panels, disconnects) and standard THWN or XHHW wire. Going with 1000 volts will require custom special order equipment and more expensive medium voltage wire. You will also have additional cost for terminating the medium voltage.

How is 1000 volt wire terminated differently?

I would guess the bump from 600 to 1000 will add a substantial cost to the project.

I probably will if equipment is special ordered. .

Another thing to consider is future repair. If the transformers fail or get damaged the customer is going to be without power for an extended time while new equipment is built. 600 volts transformers and distribution equipment are stock items.

Good point, that I will consider as well.

 

[mbrooke]

Maybe your equipment can handle high voltage drop and you can avoid install transformers

Sent from my Nexus 5 using Tapatalk

I did the math, assuming 120/240, unity power factor and 50 amps of balanced load (little to no neutral current), I would need 600 kcmil copper to have 3% voltage drop or 750 kcmil for a 3.5% voltage drop. Pulling this 4,000 feet will be a new one.

At a full 80 amps the voltage drop is 4.7%, but I would call this exceptable since a full 80amps of load is will not be common or continuous.

One the other hand going 600 volts I can use 1/0 copper or 3/0 AL assuming 20amps of current (50 on the 120/240 secondary)

1000 volts will let me use #4 cu at a 2.6% voltage drop, #6 for a 4% drop and #2AL for a 2.7% drop.

There is a difference between 1000 and 600 volt when it comes to cable savings.

 

[GoldDigger]

Continued....
Not sure where or if it is in [2011] or earlier. but the use of the grounded conductor only in the feeder to the outbuilding is, as called out on the diagram, allowed by 250.30(A)(1) in the [2014] code specifically when an SDS is used.

 

[mbrooke]

Continued....
Not sure where or if it is in [2011] or earlier. but the use of the grounded conductor only in the feeder to the outbuilding is, as called out on the diagram, allowed by 250.30(A)(1) in the [2014] code specifically when an SDS is used.

Let me read that...

EDIT, is this it?

Exception No. 2: If a building or structure is supplied by a
feeder from an outdoor transformer, a system bonding
jumper at both the source and the first disconnecting means
shall be permitted if doing so does not establish a parallel
path for the grounded conductor. If a grounded conductor
is used in this manner, it shall not be smaller than the size
specified for the system bonding jumper but shall not be
required to be larger than the ungrounded conductor(s).
For the purposes of this exception, connection through the
earth shall not be considered as providing a parallel path.
Exception No. 3: The size of the system bonding jumper
for a system that supplies a Class 1, Class 2, or Class 3circuit,
and is derived from a transformer rated not more
than 1000 volt-amperes, shall not be smaller than the derived
ungrounded conductors and shall not be smaller than
14 AWG copper or 12 AWG aluminum.

 

[Tony S]

You’ll be OK when this appears on the driveway