UFC 3 -520-01
June 10, 2002
temperature). The line current is calculated based on the expected real power
requirement and phase angle. The following equations show the calculation of line
current:
Single -Phase Circuits
P
IL =
V cos θ
where,
IL
=
Line current in amperes
P
=
Real power, in kW
V
=
Voltage, RMS--in kV to match power units
?
=
Phase angle between voltage and current
Three-Phase Circuits
P
IL =
3 VL cos θ
where,
IL
=
Line current in amperes
P
=
Total three-phase real power, in kW
VL
=
Line voltage, RMS--in kV to match power units
?
=
Phase angle between voltage and current
B-2.3
If comparing voltage drops across different nominal voltages, reference
voltage drop calculations to a 120 volt base to allow ready comparison of the voltage
drops throughout the system, regardless of the actual voltage level. Use the following
expression to convert a voltage drop at some nominal voltage to a 120 volt base:
Actual Voltage Drop 120
Actual Voltage Drop (120 V Base) =
System Nominal Voltage
B-3
TRANSFORMER RATED CURRENT.
B-3.1
Transformer rated secondary current is calculated by dividing the rated kVA
capacity by the rated secondary voltage. The following examples illustrate the rated
secondary current calculation.
B-4
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