Voltage drop Solution ?

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powerplay

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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!
 
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GoldDigger

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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.
 
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powerplay

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Ingenieur said:
It is a common practice
works fine if designed correctly
what
voltage
distance
load in va
Click to expand...


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

kwired

Electron manager
Location
NE Nebraska
powerplay said:
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?
Click to expand...

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.
 
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powerplay

Senior Member
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In front of a computer.
GoldDigger said:
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.
Click to expand...

...sounds like this answers my question about running a parallel cable to attempt reducing the brownout by reducing the resistance?
 
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powerplay

Senior Member
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kwired said:
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.
Click to expand...


oops.. single phase, and assuming it is aluminum Conductors.

...stepping up the Voltage is the Solution?
 
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Ingenieur

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500'
95 A at 240
250 Al mcm
4% drop

what load profile
continuous?
what % motors?
how sensitive to drop, rated for 220?
what is the actual source v > 240? Often is
etc
 
Smart $

Smart $

Esteemed Member
Location
Ohio
powerplay said:
...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
Click to expand...
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...
 
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Ingenieur

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Earth
Double the v and you 1/2 the current
so 10 v drop is now only 5
5/480 ~ 1%
new v drop ~ 1/2 x 4% /(480/240) ~ 1%

double conductor
drop is 5 v or 5/240 ~ 2%

you may be fine as is
without load details only a guess
 
G

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Smart $ said:
...
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...
Click to expand...
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

kwired

Electron manager
Location
NE Nebraska
Ingenieur said:
Double the v and you 1/2 the current
so 10 v drop is now only 5
5/480 ~ 1%
new v drop ~ 1/2 x 4% /(480/240) ~ 1%

double conductor
drop is 5 v or 5/240 ~ 2%

you may be fine as is
without load details only a guess
Click to expand...

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.
 
I

Ingenieur

Senior Member
Location
Earth
kwired said:
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.
Click to expand...

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
 
Smart $

Smart $

Esteemed Member
Location
Ohio
GoldDigger said:
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?
Click to expand...
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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