To step up the Voltage on an very long underground Cable run, is it possible to install an step up transformer, or would the Load continue to brown out from an undersized cable Feeder that feeds the transformer trying to step up the Voltage? Thanks for any feedback!
Voltage drop Solution ?
- Thread starter powerplay
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If a big voltage drop is outside the part of the circuit that you run at higher voltage you will not change that part of the totsl voltage drop.
If you look at just boosting the voltage at the load with a boost transformer or a tap change, you will still have the same swing between loaded and unloaded condition, the average and minimum voltages will just be higher.
For a motor load that might decrease the load current enough to slightly reduce the voltage drop in that part of the circuit only.
If you do not change the voltage on the feeder you will not change the voltage drop on the feeder.
If you look at just boosting the voltage at the load with a boost transformer or a tap change, you will still have the same swing between loaded and unloaded condition, the average and minimum voltages will just be higher.
For a motor load that might decrease the load current enough to slightly reduce the voltage drop in that part of the circuit only.
If you do not change the voltage on the feeder you will not change the voltage drop on the feeder.
1) the Voltage is 240 volt
2) distance is apparently 500'
3) the Load is apparently 22.3kVA
I head to the Project Monday, but they say the Cable is rated for 200amps and had been calculated. I believe it is 3 conductor 250KCMIL Cable underground. They had mentioned putting in an step up Transformer and Step Down at the Load to prevent the Brown Out. Would running an parallel cable in the same Trench reduce the Voltage Drop?
kwired
Electron manager
- Location
- NE Nebraska
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- EC
single phase or three phase. Copper or aluminum conductor?
without doing any VD calculations seems like it would be pretty reasonable even on aluminum at single phase - but if you had a heavy surge from motor starting it would still result in a temporary voltage sag that would be noticeable to users. 23.3 kVA single phase would only be about 93 amps if three phase it would only be about 54 amps.
...sounds like this answers my question about running a parallel cable to attempt reducing the brownout by reducing the resistance?
oops.. single phase, and assuming it is aluminum Conductors.
...stepping up the Voltage is the Solution?
JFletcher
Senior Member
- Location
- Williamsburg, VA
Figure out which is less expensive; stepping up/down voltage using existing 250 mcm or running additional set of 250 mcm.
If they buy a few shovels and work the next year digging, the extra cable would be half the price of the two Transformers installed
Is that discounting the labor? (i.e. no-cost labor) :?
That was an attempt at humour.. Haha
I haven't costed options thoroughly, but a friends suggestion to parallel cable would save electrical cost if it reduces brownout, but it sounds possibly that the voltage needs to be changed to prevent voltage drop
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
At 500' wouldn't a single larger cable be cheaper?
they apparently upgraded the cable once with calculations, but it sounds like the resistance is going to create the sag in voltage unless it is stepped up..
Without assigned parameters, mitigating voltage drop by stepping up/down of voltage or decreasing conductor impedance, or a combination thereof, there can be no comparison.
Stepping up voltage to double, using existing cable, the stepping down voltage at the other end is approximately just as effective (considering physical properties only) as reducing conductor impedance to one-half (i.e. parallel existing cable). This is where actual cost enters the picture...
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Not so. Doubling the voltage will reduce the % voltage drop by a factor of 4. (As noted indirectly by Ingenieur.)
Or were you figuring in estimated transformer impedance too?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Key factor here. What impact does the 4% VD we presently have on any of the load, and is it worth the cost to make any changes?
Most installations I have ever done what is existing would be fine. Most places I work at the unloaded supply voltage will be near 250 as well so that helps a little on actual voltage after the long run - though that is at the lower end of what I might call a long run.
Agree
Need load details
also most 240 stuff will run fine at 220 and 120 at 110
Factor in likely closer to 245-250 than 240 and even better
how stiff is the supply
if the service is 100 kva and long load 20 kva not bad
if service is 50 may be an issue
Yes... that's why I said approximately. The point was to not speculate about which method is better. A more comprehensive analysis is required.
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