Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
150,000W / (480 x 1.732) = 180 amps
(1.732 x 21.2 x 180 x 2000) / 14.4 = 917,960mcm AL
(1.732 x 21.2 x 180 x 2000) / 14.4 = 917,960mcm AL
Mitigating voltage drop on a 2,000' 480 V feeder
- Thread starter MRKN
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winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Oh, the OP asked about 'tap changing transformers' as a possibility for compensating for voltage drop. While it is probably not a good solution (read expensive and reduced efficiency), there are devices known as 'voltage regulating transformers' available.
These are transformers where part of the core operates in saturation, or other non-linear aspects of the steel and an external circuit, are used to actually regulate the output voltage. They are generally used when you have loads which require much tighter than normal voltage regulation (+-1%), but could be used for 'normal' loads when you are dealing with excessive voltage drop issues.
You could design your 2000 foot feeder with excessive voltage drop, and then use a voltage regulating transformer to compensate. This would reduce the cost of the wire, but add the significant cost of the transformer and also add the ongoing cost of power lost in the wire.
-Jon
These are transformers where part of the core operates in saturation, or other non-linear aspects of the steel and an external circuit, are used to actually regulate the output voltage. They are generally used when you have loads which require much tighter than normal voltage regulation (+-1%), but could be used for 'normal' loads when you are dealing with excessive voltage drop issues.
You could design your 2000 foot feeder with excessive voltage drop, and then use a voltage regulating transformer to compensate. This would reduce the cost of the wire, but add the significant cost of the transformer and also add the ongoing cost of power lost in the wire.
-Jon
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I noticed that. It's usually pretty close. I will have to investigate where you guys are screwing up.
I know there have been some discussions in the past about significantly different results from different VD calculators......I used the southwire one should be more on the worst case side bc they sell wire and it assumes .9 power factor.
dmsv10
Member
- Location
- Frisco Texas U.S.A.
That's a long run, is this in a commercial area, large residential? It might be cheaper depending on the clients needs to install a new service entrance and pole mounted xfmr closer to the load. If an option, utility companies normally have options for new meters where the startup cost is absorbed over time and or associated discounts.
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ptonsparky
Tom
- Occupation
- EC - retired
i fixed it.
I noticed that. It's usually pretty close. I will have to investigate where you guys are screwing up.
I'm getting 620,000 CM range for copper. Threw the paper away...
2 350 MCM copper in parallel will do it at 3%.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
One more thing I would add for the OP: Might want to confirm what the actual load is. If that 150KW was calculated or nameplate, the actual load could be quite a bit less.
kwired
Electron manager
- Location
- NE Nebraska
If load remained constant, could possibly work. But remember you will have an overvoltage at no load/low load conditions.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
why would you use 2 transformers? Just run the 480V, use the smallest cable for 200A and then bump the voltage back up at the other end.
If you use #3/0AWG you'll get an 11.38% voltage drop for 200A @ 2000' (in conduit)
By a 400 to 480V step up transformer, and set the taps to +5%. This will give you stiff 480V on the step up side.
If you use #3/0AWG you'll get an 11.38% voltage drop for 200A @ 2000' (in conduit)
By a 400 to 480V step up transformer, and set the taps to +5%. This will give you stiff 480V on the step up side.
ptonsparky
Tom
- Occupation
- EC - retired
We frequently see 500 volts with no apparent ill effect on equipment.
kwired
Electron manager
- Location
- NE Nebraska
Same here, but if you are boosting volts by 15 volts for VD compensation, that means if you start with no load volts of 500 it jumps to 515 with no load. May not cause immediate failure of anything but may not be helping life of certain components either.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
that is only 4% over voltage.
There are all kinds of things that can be done. some version of the transformer idea is usually the most cost effective. people claim it uses power forever but the amount of power it uses just sitting there will likely never exceed the cost savings on the capital side.
and in most cases, the amount of juice a feeder like this uses is highly variable. it rarely if ever uses the full amount available. often it is running at 10 or 20%. I would be looking at voltage drop in a realistic way as opposed to assuming it will be fully loaded 100% of the time when it will probably (almost) never see full capacity.
drktmplr12
Senior Member
- Location
- South Florida
- Occupation
- Electrical Engineer
step up to 4.16kV, step back down to 480V or increase conductor size if facility manager doesn't want to deal with 4.16kV. anything else is a band-aid in my opinion.
dealing with 4.16kV can be as simple as hiring a company to inspect and adjust once a year. how often does the padmount or pole mount outside your house need attention? i would say never.
The other option is a stepped capacitor bank with load monitoring to make sure it doesn't over correct. i think that is equally dangerous to 4.16kV and will require more intelligence (electronics) and replacement/service sooner (8 year life on electrolytic capacitors vs 30+ for a padmount)
dealing with 4.16kV can be as simple as hiring a company to inspect and adjust once a year. how often does the padmount or pole mount outside your house need attention? i would say never.
The other option is a stepped capacitor bank with load monitoring to make sure it doesn't over correct. i think that is equally dangerous to 4.16kV and will require more intelligence (electronics) and replacement/service sooner (8 year life on electrolytic capacitors vs 30+ for a padmount)
dmsv10
Member
- Location
- Frisco Texas U.S.A.
I had a large property where the running loads on the building during the day with 1700+ people, started bringing down the voltage on the secondary side of our 16kv/480v 2500 KVA Xfmr. As far down as 460vac. Our solution with the electrical companies blessing was to change the internal secondary tap on the transformer to D-Tap, this effort brought our daytime running voltage up to 480/485 vac.
When the Transformer was unloaded and everybody left for the day air handlers turned off big equipment not running the 500 volt output of the Transformer was closer to 499 when unloaded with a standard 5% impedance for a Transformer that size so yes to your comment about seeing 500 volts did not affect any of the critical UPS equipment or generator operation, gave us are 480 volts perfectly all the time when loaded.
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kwired
Electron manager
- Location
- NE Nebraska
Around here unloaded 480 volt services usually will run about 500 volts, 240 volt services about 250 and 208 services about 216 volts. Those are all within 5% of nominal.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
Standard deviation according to C84.1 for a 480Y/277V system is 504Y/291 (Max; service and utilization voltage) to 456Y/263V (min-service voltage) and 440Y/254V (min-utilization voltage)
Which corresponds to why transformers have standard taps of +/- 2 x 2.5% taps; i.e. 5% tap gets you to 504volts on a 480V system.
Which corresponds to why transformers have standard taps of +/- 2 x 2.5% taps; i.e. 5% tap gets you to 504volts on a 480V system.
dmsv10
Member
- Location
- Frisco Texas U.S.A.
Sounds normal for totally unloaded, the property I was referring to had a minimum running load 24/7 of 1000 KW. Data center load plus cooling. So the building was never unloaded. I'm sure with no load on D tap it would have been much higher. Building loaded during the day was running at 1750kw [MENTION=63279]480[/MENTION]vac when dropped to 1000 at night it was up to 500 vac. So we used the buildings constant load + people load to maintain that range of 480/499.
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kwired
Electron manager
- Location
- NE Nebraska
Intentionally boosting voltage makes sense if you are never unloaded to any significant level. What may be undesired is to do something to boost voltage so you see 490-500 while under full load but then end up with say 515 to 520 during periods of minimal load.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I guess it is perfectly reasonable to boost voltage to the limits of normal operating tolerance at no load, to give a bit more wiggle room for voltage drop under load.
But I would not want to boost voltage above normal tolerances at no load.
-Jon
But I would not want to boost voltage above normal tolerances at no load.
-Jon
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
Equipment at 480V is rated for 600V. What is going to be the problem if you are 10% above at 528V unloaded.
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