Voltage Drop Formula

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The complete voltage drop formula is as below

VD = (1.732*I(RcosO + XSino)*l*100/(1000*380)......(i)

in this formula

R = Resistance ohm/km/per
X = Reactance ohm/km/per
O(Tetha) = ArcCosin(p.f)
I=Ampere
l=length
380 = line to line Voltage and we know that

220 line to neutral = 380/1.732 (line to line voltage) it is substitude because of impedances are per phase so we must use line to neutral voltage (220) or 380/1.732 volt.

The above information is a real formula for voltage drop calculation.

But if you want to make your work easy or do it fast we can substitude the following as below

From cable catalog we take Resistance per km and Reactance per km
and make a factor

factor(k) = 1.732*(RcosO + XSinO) we make this factor for each cable size.

In formula (i) there length and current are two variable which varies every time. but factor(k) remains constant for a specific cable size.

So, formula number (i) changes as below for a specific cable size


VD = k*I*L*100/(1000*380)

So, in your formula the factor 2.K.I.D = CM

can be a constant

If it is DC wire then reactance is zero and the power factor will be one and there will be only resistance


Hope it is done.
 
Found this info in some reference material I had.

k = resistivity of conductor metal (circular mils);

values for k: 12 for copper circuit conductors loaded between 50-100% of their allowable carrying capacity; 11 for circuits loaded at less than 50%;

k = 18 for aluminum conductors at 30 degrees C.


The above k values are general approximations.

Hope this helps.
 
K in the above formula represents the resistance in Ohm's for 1000 circular mils, 1000 feet long.

So for Copper, K would be 12.9 and for Aluminum K would be 21.2 based on an ambient temperature of 75 degrees C.

Chris
 
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