Voltage Drop Techniques on Low Voltage System

[buddy91082]

Hi there. I have a 240v, 1200 amp single phase service for a residence. The length of run is about 1000 feet from the utility transformer to the home. The utility has stated they do not have taps on their transformer. Stepping the voltage up to 480v and then back down to 240v is not an option. If I can boost the voltage to 252v that would reduce the amount of copper in the ground to the home. In lieu of installing massive amounts of copper underground to the home I am considering:

1. Using a buck boost transformer to boost voltage 252v (5%)
2. Using a 1:1 transformer with tap setting up to 5%

Any other techniques to compensate for voltage drop? Voltage regulator?

Thanks.
b

 

[itsmoked]

Why is 480 or better yet 600 "not an option"?

You're going to have horrid regulation.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I hope that you are not in North America. Under North American codes, increasing the supply voltage is not acceptable to reduce voltage drop.
Under our codes, the maximum allowable voltage drop is measured in percentage, not Volts.
I suspect that the utility is using a pad mount transformer to service your project.
Is it possible to locate your own pad-mount step-up near where the supply crosses your property line?
Another advantage of the transformer option is that you won't need to run a neutral for a further saving of copper.
Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[buddy91082]

There is no room indoors to install a transformer. The Owner doesn't want a transformer sitting around in his front or back yard. Unfortunately a step up and step down option isn't an option. In addition, if installed outdoors the transformer would need to be installed 4'-0" above grade to be above the local design flood elevation.

 

[electricnewbie123]

A stupid question: If the point of metering is home, then wouldn't it be the responsibility of the utility to provide the cable to home?

I totally agree with waross, the best option is a transformer. If you do the cost calculations, it may seem comparable between installation of heavy cables vs a transformer. Who knows, the distribution company may chip in the transformer and transmit at medium voltage up to the property boundary if there is potential for more load growth in the area.

 

[waross]

By my voltage drop tables and Canadian code;
200 Amps, 3% drop, 4 x 3/0 cable per line. You may be able to deduct the 240 Volt loads to reduce the neutral size somewhat.
Note: 10,000 feet is based on 100 Amp loading on the neutral. If you calculate 200 Amps on the neutral, or 100% unbalanced loading,
Then you are looking at over 20,000 feet of 3/0 as the voltage drop must now be a percentage of 120 Volts rather than 240 Volts.
Show your customer the price of 10,000 feet or 20,000 feet of 3/0 copper cable. He may change his wants a little when he sees the cost.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Not following you Bill. OP states 1,200A for a 1,000foot run.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I did a bad and assumed.
1200 Amps for a residence?
I took that as a typo and worked with 200 Amps. If it is 1200 Amps for 1000 feet, the cost gets really crazy. Book a tropical vacation on the profits from this job.
For 200 Amps at 240 Volts, my table shows 4 x 3/0 per line.
In the worst case, if all the loads are 120 Volt loads, the maximum possible unbalance is 200 Amps. So we have to consider the voltage drop based on 120 Volts. That takes us up to 6 x 3/0 per line.
A couple of things that will help;
Rather than using 1200 or 200 Amps, we should be using the calculated demand as per code. This will probably drop the current 25% or more.
Demand factors may be applied to the minimum ampacity of the neutral.
If this is really a 1200 Amp service and the customer is adamant that there be no transformer, take the money!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

I see what you did.. Makes sense. True take the money.
At some point you have to tell the customer "no" can't be done. Just because they want their house to float on air doesn't mean they get that.. Tiz interesting.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jghrist]

With this large a service, I'd consider 3Ø. This would reduce voltage drop and losses. 120/208 V might be a problem if there are already 240 V appliances.

 

[waross]

Another option that may be economically feasible, given the ridiculous amount of copper involved with a 240 Volt or even a 120:208 Volt service;-
A higher voltage cable to an underground vault and an underground transformer close to the residence. This would keep the service length shorter and greatly reduce the amount of copper needed.
Is this a 1200 Amp service or was that a typo?
At 1200 Amps the vault will almost be mandatory.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

The OP said it was a flood plain so no underground vaults. I wonder if full solar would be on par with the cost of cable? Probably not especially if we're talking 1200A.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

Underground vaults and flood plains are not incompatible. Any electrical equipment suitable for vault installation is intended for submersed installation; typically with a maximum depth. If the design flood provides less than the maximum depth, there wouldn't be any issue.