Sample design to send 120 VAC 20 amps 700 feet using 110/440 and 440/110 transformers

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Believe it or not I passed the Electrical PE Exam but I haven't used it on my job for seven years so I have forgotten everything.
I'm trying to send 20 amps 120 VAC 700 feet without too much voltage drop and without using huge conductors. So I would like to use For most of you this easy, but I just can't get started.
Is their an example on line?

Thank you in advance.
 
For a given load (power), the higher the voltage, the lower the current and resultant voltage drop. Use a pair of transformers, say 120v (or even 240v) to 600v at the source end, and 600v to 120v at the load end.

You should derive a new grounded conductor at the load end, and earth and bond it as you would an incoming 120v service. I believe that grounding either 600v conductor is optional, but wouldn't hurt to do.

Added I just noticed that your thread title mentions transformers, and you apparently accidentally deleted part of your post.
 
At five times the voltage (600/120), there would be one fifth the voltage drop at 600v vis a vis 120v for a given conductor size. You'd have to come up with an acceptable destination voltage, and then compare the cost of using a large-enough conductor size to the cost of using two 2.5kva transformers.
 
What I meant to say

What I meant to say

I'm sorry, this what I meant to say:

Believe it or not I passed the Electrical PE Exam but I haven't used it on my job for seven years so I have forgotten everything.
I've actually taken it off my business card and email signature out of embarassment
I'm trying to send 20 amps 120 VAC 700 feet without too much voltage drop and without using huge conductors. So I would like to use 120/480 and 480/120 transformers or 120/600 and 600/120 transformers.
For most of you this easy, but I just can't get started.

Is their an example one line diagram on line? For instance what size wire between the transformers? Also how do I connect the H, N and G conductors between the step down and step up transformers.

Thank you in advance.
 
Installer said:
I'm sorry, this what I meant to say:

Believe it or not I passed the Electrical PE Exam but I haven't used it on my job for seven years so I have forgotten everything.
I've actually taken it off my business card and email signature out of embarassment
I'm trying to send 20 amps 120 VAC 700 feet without too much voltage drop and without using huge conductors. So I would like to use 120/480 and 480/120 transformers or 120/600 and 600/120 transformers.
For most of you this easy, but I just can't get started.

Is their an example one line diagram on line? For instance what size wire between the transformers? Also how do I connect the H, N and G conductors between the step down and step up transformers.

Thank you in advance.
Click to expand...

So, full bore at 20A. Okay...3% drop acceptable?
 
Personally, after I calculated the load, if 240V was available I would a pair of trannies with this setup. One for step and one one for step down.

transformer-wiring-diagram-luxury-120-240v-1-phase-wiring-diagram-at-480v-transformer-wiring-diagram.jpg
 
Installer said:
I'm sorry, this what I meant to say:

Believe it or not I passed the Electrical PE Exam but I haven't used it on my job for seven years so I have forgotten everything.
I've actually taken it off my business card and email signature out of embarassment
I'm trying to send 20 amps 120 VAC 700 feet without too much voltage drop and without using huge conductors. So I would like to use 120/480 and 480/120 transformers or 120/600 and 600/120 transformers.
For most of you this easy, but I just can't get started.

Is their an example one line diagram on line? For instance what size wire between the transformers? Also how do I connect the H, N and G conductors between the step down and step up transformers.

Thank you in advance.
Click to expand...

I think you will find using transformers in this situation to be more expensive than just using the appropriate aluminum wire. A "compromise" option perhaps worth investigating is to send 240 to the load (assuming you have 240 available at the source end) and just use one transformer at the load end.
 
electrofelon said:
I think you will find using transformers in this situation to be more expensive than just using the appropriate aluminum wire. A "compromise" option perhaps worth investigating is to send 240 to the load (assuming you have 240 available at the source end) and just use one transformer at the load end.
Click to expand...

Yeah, alternatives, if OP would give details..
 
Installer said:
I've actually taken it off my business card and email signature out of embarrassment.
Click to expand...
Let me encourage you to rethink that decision. You have earned the privilege of describing yourself as a Professional Engineer. There is no place for embarrassment in that description. It does not matter whether your present (or future) job-related duties require you to seal and sign any documents.

 
It would in my view probably be preferable to use thicker wire and eliminate the transformers.

The transformers not only add capital costs and introduce a new point of failure, but also add losses. Someone will be paying forever for the iron losses in the transformers. That could amount to $100 a year or more. Over the life of the installation that could pay for thicker wire.

What is the nature of the load ? Could it be specified for 240 volt operation instead. If a large number of small 120 volt loads are involved, could a 3 wire supply at 120/240 volts be used instead.
 
broadgage said:
It would in my view probably be preferable to use thicker wire and eliminate the transformers.

The transformers not only add capital costs and introduce a new point of failure, but also add losses. Someone will be paying forever for the iron losses in the transformers. That could amount to $100 a year or more. Over the life of the installation that could pay for thicker wire.

What is the nature of the load ? Could it be specified for 240 volt operation instead. If a large number of small 120 volt loads are involved, could a 3 wire supply at 120/240 volts be used instead.
Click to expand...

This works depending on the installation. If this would be a long run in public right of way that is accessible to the public, I'd be hesitant to placing larger conductors as copper theft in my area tends to shape some designs and coming back to reinstall a long run with copper conductor every month is not sustainable.
 
electrofelon said:
I think you will find using transformers in this situation to be more expensive than just using the appropriate aluminum wire. A "compromise" option perhaps worth investigating is to send 240 to the load (assuming you have 240 available at the source end) and just use one transformer at the load end.
Click to expand...

I suspect you are probably correct, given the 20 amp/120 volt. But your compromise solution is a good thought.
Been my experience that when these questions come up and cost comparisons are being made between larger conductor or transformer(s) all to often the true cost of a transformer solution are overlooked. Things such as ongoing operating losses, the real cost of all the required OCPD devices, a GES, labor, space, etc. tend to add up.
 
For a situation where transformers are justified in lieu of larger conductors this is the most efficient design I have seen.
 

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texie said:
For a situation where transformers are justified in lieu of larger conductors this is the most efficient design I have seen.
Click to expand...

Yeah that is the ticket, nice diagram. Avoids both a neutral (assuming 3 wire is needed) and an egc - just two wires, one of them a grounded conductor. That is what I have at my house, 1900 feet, 2400 volts. I find it odd they still have that "rebonding" exception for sds despite getting rid of it for feeders.
 
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