voltage drop and buck boost transformers 1

[kurtmyr]

I've got a 3000' run to an out building that I have to feed with a 2-pole 100A feed. Because of the voltage drop, I'd need to go up to 600MCM ! My question is can I use a buck/boost transformer, either at the line side or at the load side to boost the voltage back up, so that I don't have to use such large conductors. Nearly 10K' of 600MCM is a ball buster. I'd rather use a buck boost, or a combination of buck/boost and larger wire. Any insight would be greatly appreciated. Kurt

 

[dpc]

The boost transformer can increase the voltage, but you will still have to live with the voltage drop in the wire which will vary with the load, so your regulation may be poor. If you calculate the voltage at no load then the voltage at full load, you will see how much the voltage will vary with the load.

The better (and more expensive) solution would be to step up the voltage to a much higher voltage on the sending end, then step it back down at the receiving end, so 2 fully-rated transformers would be required. But if you increase the voltage, the required wire size for the 3000' feeder goes down, so you would have savings on the wire.

You don't mention the voltage you are using, so it's hard to be more specific.

 

[kurtmyr]

I'm just talking about 240V 1Ph. It just might be cheaper to transform up to 480 and back down again to 240, taking advantage of the multi-taps at the secondary side. I'll have to price out the difference in the savings using smaller wire vs. the price of two transformers. Thanks again for your thoughts, Kurt

 

[mc5w]

If you want to run 120/240 volts using fat wires you can get lugs from

http://www.sefcor.com

that you would weld onto the ends of aluminum wire. This would allow you to run say 1,500 KCM aluminum using 3x500 KCM or 2x750 KCM. You would need to use a tungsten-inert-gas welder that is powered by an engine. The lug series are WFC for 1 wire per lug and WFC-2 for 2 wires per lug. You can get lugs as small as 3/0 aluminum and as large as 3,500 KCM. The maximum size aluminum wire for 600 volts is 1,000 KCM. Anything over 500 KCM is a real %#@*& to install not that you need a forklift truck to pull even 4/0 into a conduit.

Have you also considered a combination of wind and solar power? Also, a conventional generator would work for occasional use and if it has wheels you can use it during a blackout.

However, transformers also have voltage drop particularly when motors start. To be effective at 3,000 feet of distance you would have to step up to 2,400 volts or better yet 4,800 volts or 7,200 volts.

An oil distribution transformer of this size has 2% impedance so you have 4% impedance plus the voltage drop of the wire plus the voltage drop in your supply system. To get reasonable voltage drop youn would need to buy 2 50 KVA padmount transformers that step up to say 4,800 volts and bury some 5 KV or 15 KV cable. You would have 3 transformers in series counting the local distribution transformer.

For what that costs you could have your utility run a primary line extension and put in a second meter. You would only need to pay them for a 15 KVA or 25 KVA transformer depending on how much load you are actually running. This is the only solution that I would consider.

Also, the newer electronic meters have enough sensitivity to low amperage loads that some utilites have been able to do primary metering for residences that are far from the road or just have a large lot. So, there is a way for you to do this with 1 meter.

All of these solutions depend on how much load you want to run and how many kilowatthours you will use.

 

[dpc]

If you go with two transformers, you can step it up to 600V and go with even smaller wire.