1. Low-Voltage Feeder Fault Analysis
Electrical Design EngineerBackground
An engineer needs to verify if a downstream distribution panel rated for 10 kA breaking capacity is safe from faults occurring after a 400V transformer and a short cable run.
Problem
Calculate the symmetrical and peak short-circuit currents at the end of a cable run with known transformer and line impedances.
How to use
Set the system voltage to 400V, select a voltage factor of 1.05, enter 0.005 Ω for transformer resistance, 0.015 Ω for transformer reactance, 0.01 Ω for line resistance, and 0.005 Ω for line reactance.
systemVoltage = 400, voltageFactor = 1.05, transformerR = 0.005, transformerX = 0.015, lineR = 0.01, lineX = 0.005Outcome
The calculator outputs an initial symmetrical short-circuit current of approximately 9.70 kA and a peak current of 15.41 kA, indicating the 10 kA panel is barely adequate for symmetrical faults but requires careful review of peak withstand ratings.