Voltage Drop Factors

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Line current may be expressed in terms of kilowatts and voltage as follows:
kW

I
=
(kV) (COS A) (P)
Where:
kW = Circuit load in kilowatts
kV = System nominal phase-to-ground voltage in kilovolts
P  = Number of phases
Voltage drop referred to at a 120 V Base (VD) is expressed as follows:
Actual Voltage Drop (120)
= 
VD
System Nominal Voltage
Using the preceding equations for line current and voltage drop referred to at a 120 V Base (VD),
the equation for voltage drop becomes:
(kW) (r cos A + x sin A) (120)

VD
=
(kV) 2 (cos A) (P) (1000)
The equation for (VD) expressed in per mile units is written as follows:
(kW) (R cos A + X sin A) (s) (120)

VD
=
(kV) 2 (cos A) (P) (1000)
Where:
R = Resistance in ohms per phase mile of line
X = Reactance in ohms per phase per mile of line
S = Line distance in miles
Letting the following factor be designated the voltage drop factor (VDF):
(R cos A + X sin A) (120)

VDF
=
(kV) 2 (cos A) (P)
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