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 8.4.4 Short Range System Planning. For every electrical distribution plant, short range
system planning is imperative to achieve the orderly expansion of the system to accommodate the
load growth.
8.4.4.1 Voltage Drop Study. Short range system planning is achieved by performing a
voltage drop study. The voltage drop study reveals the strong and weak points of the system by
measuring the load at various points on the system. An example of a voltage drop study is
represented below.
Voltage drop calculations are referred to as a 120 V Base.
Voltage Drop (120 V Base) = Actual Voltage Drop x 120
System Nominal Voltage
For Example:
Nominal System Voltage
= 12.47 grounded wye/7.2 kV
Actual Voltage Drop
= 360 V
Voltage Drop (120 V Base)
= 360 x 120 = 6V
7200
8.4.4.2 Voltage Drop Factors. The study analyzes voltage drop factors for the different
conductor sizes on the system. The development of voltage drop factors is illustrated below.
The voltage drop for known source-end and lagging power factor conditions may be calculated
from the following equation.
Voltage Drop = I (r cos A + x sin A)
Where:
I
=
Line current in amperes
A
=
Phase angle between voltage and current
r
=
Resistance of line in ohms
x
=
Reactance of line in ohms
This equation provides an estimate of the voltage drop resulting from normal system designs.
8-21
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