Voltage Drop

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Sajid khan

Sajid khan

Senior Member
Location
Pakistan
Measured voltage drop thru calibrated fluke analyzer is occuring too much high as compare to calculated voltage drop.

What could be possible reasons; negative Ferranti, Aged cables, power factor or any other possible reason???

Analyzer reading on 2 sets 240 1C PVC/PVC: 115 Amps ,372 Volts at 260 meters..

The calculated VD at 400V is 3V only while the actual measured at analyser is 28V.

The load is being by a generator.


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Z

zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
(what is "negative Ferranti"?)

I'd start with checking on whether the calculation is correct. At 400v a 3 volt drop is under 1%, which most people would consider unrealistic and unnecessary. A 28v drop is 7% so a little over what's usually considered acceptable but not too bad for 260m/850ft. To get only a 1% drop would require some right heavy cables - the Southwire calculator tells me two sets of 600kcmil copper, which is HUGE and EXPENSIVE.)
 
Sajid khan

Sajid khan

Senior Member
Location
Pakistan
zbang said:
(what is "negative Ferranti"?)

I'd start with checking on whether the calculation is correct. At 400v a 3 volt drop is under 1%, which most people would consider unrealistic and unnecessary. A 28v drop is 7% so a little over what's usually considered acceptable but not too bad for 260m/850ft. To get only a 1% drop would require some right heavy cables - the Southwire calculator tells me two sets of 600kcmil copper, which is HUGE and EXPENSIVE.)
Click to expand...

Negative Ferranti effect is opposite of ferranti i.e Less voltage receive at the end of a long cable length.
1% VD is obviously very good but 7% drop is at higher side. Why the meter is showing higher VD compare to the Calculated VD of 1%?


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zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
Or because the conductors are smaller than planned, or because the terminations are bad, or..... but I'd look at the calculation first.

And by my understanding the Ferranti effect applies to long lines and under 1km is nowhere long enough. Look for simple causes first and tell us about the actual installation; other than suggesting two parallel sets of conductors "2 sets 240 1C PVC/PVC" isn't clear in US electrical terms.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Sajid khan said:
Measured voltage drop thru calibrated fluke analyzer is occuring too much high as compare to calculated voltage drop.

What could be possible reasons; negative Ferranti, Aged cables, power factor or any other possible reason???

Analyzer reading on 2 sets 240 1C PVC/PVC: 115 Amps ,372 Volts at 260 meters..

The calculated VD at 400V is 3V only while the actual measured at analyser is 28V.

The load is being by a generator.


Sent from my iPhone using Tapatalk
Click to expand...
Is the VD being measured a result of losses in the conductors or is impedance of the source a factor as well? Or maybe even plain and simple too much load for the source or it's controls are not functioning properly? More load means controls need to provide more fuel to maintain output, at least until some upper limit is reached then it may simply be overloaded.
 
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