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buddy91082 (Electrical) (OP)
23 Feb 10 10:18
Looking to calculate voltage drop on a 12kV ciruit that is a few miles long. Is the voltage drop formula for medium voltage the same as low voltage. Anyone know of a link to an online voltage drop calculator?

Thanks.
b
rbulsara (Electrical)
23 Feb 10 10:28
The Ohm's law, V=IZ is the formula, which remains the same. You need to get the right impedance (X and R) data.  Use per phase values.

Just be careful as to what formula you use, as some 'customized' formula would ignore reactance for smaller size wires at low voltages and you cannot ignore that at higher voltages.

You may want to visit some MV cable manufacturer's website such as okonite.com to get some assistance and data.

As for the link, your web search would be as efficient as mine.

Rafiq Bulsara
http://www.srengineersct.com

jghrist (Electrical)
23 Feb 10 10:57
for balanced loads, the voltage drop formula is the same:

VD = I·(R·cosø + X·sinø) where power factor = cosø

If your phases are not balanced, things get more complicated.  You can account for the imbalance by using a sequence phase impedance model as described in "Distribution Feeder Line Models" by W.H. Kersting of New Mexico State University.  This model correctly accounts for the effect of unbalanced loading and mutual coupling for fully transposed lines using standard equations for sequence impedances.
 

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