Voltage Drop and Power Formulas for Electrical Engineers

Custom Search
Working with single phase, three-phase and DC (direct current circuits) and you quickly need to reference formulas for voltage drops and power calculations for a given conductor? The table below provides a quick reference for these calculations.

Voltage Drop and Power Calculation Formulas For Single Phase Circuits

Electrical Parameters Formulas
Voltage Drop $∆V = 2*I*L*(rCosՓ + xSinՓ)$
% Voltage Drop% $∆V  =  \frac{∆V}{V_r}*100$
Active Power $P = V*I*CosՓ$
Reactive Power $Q = V*I*SinՓ$
Apparent Power $S =  V*I = \sqrt{{P^2} +{Q^2}}$
Power Factor $CosՓ = \frac{P}{S}$
Power Loss $P_L = 2*L*r*I^2$


Voltage Drop and Power Calculation Formulas For Three-Phase Circuits
Electrical Parameters Formulas
Voltage Drop $∆V = \sqrt{3}*I*L*(rCosՓ + xSinՓ)$
% Voltage Drop% $∆V = \frac{∆V}{V_r}*100$
Active Power $P = \sqrt{3}*V*I*CosՓ$
Reactive Power $Q = \sqrt{3}*V*I*SinՓ$
Apparent Power $S = \sqrt{3}*V*I = \sqrt{{P^2} +{Q^2}}$
Power Factor $CosՓ = \frac{P}{S}$
Power Loss $P_L = 3*L*r*I^2$



Voltage Drop and Power Calculation Formulas For Direct Current (DC) Circuits
Electrical Parameters
Formulas
Voltage Drop
$∆V = 2*I*L*r$
% Voltage Drop
% $∆V = \frac{∆V}{V_r}*100$
Active Power
$P = V*I$
Reactive Power
$ - $
Apparent Power
$ - $
Power Factor
$ - $
Power Loss
$P_L = 2*L*r*I^2$


Meaning of symbols used in the formulas above:
$L$       =   Total length of conductor
$r $       =    Resistance of conductor per unit length
$x$       =    Reactance of conductor per unit length
$∆V$    =   Voltage drop 
$P$       =   Active power
$Q$      =    Reactive power
$I$        =   Current