Fault Current Calculator | Kewo Engineering

System

Source

Primary voltagekV Primary system

System voltage Voltage, line to lineV Configuration

Infinite source

Three-phase faultkA X/R Phase-to-ground faultkA X/R

Phase-to-phase faultkA X/R Phase-to-neutral faultkA X/R

Transformer

Rating Secondary voltage Rating, otherkVA Secondary, line to lineV Configuration Impedance%Z X/R Primary winding Primary connection Impedance tolerance Reduce impedance by%

More transformer settings

Zero-sequence ratio Z0/Z1 Half-winding R multiplier Half-winding X multiplier

Secondary cable

Conductor Size Installation Cables per phase Lengthft Insulation Conductor spacing (GMD)in

Drag to turn. Double-click to reset.

More cable settings

Neutral size Conductor temp., faults°C Conductor temp., voltage drop°C Enter the cable impedance instead R per conductor at 75 °CΩ/1000 ft X per conductorΩ/1000 ft

Equipment rating at the end of the cable

Short-circuit ratingkA

Finds the shortest cable that keeps every fault at the end within the rating.

Load

for voltage drop

Load Power factor, lagging Load connected

Report details

Location Prepared by Reference

Available fault current

Fault current

Symmetrical rms, bolted faults

Voltage drop

Fault current along the cable

Inputs

Impedances and asymmetry ohms at the secondary voltage

Basis

Bolted, symmetrical rms faults by the ohmic method with complex impedances; prefault voltage at nominal; no motor or inverter contribution.

Source impedance from the three-phase and phase-to-ground fault currents and X/R. Transformer impedance from %Z and X/R; single-phase 120 V faults use 1.5R + j1.2X of the full winding (half-winding approximation).

Cable R and X from NEC Chapter 9 Table 9 (conduit); for direct buried and overhead cable, R from Table 9 and X from the geometry of the cable drawn. R corrected for temperature; phase-to-ground and phase-to-neutral faults return on the neutral.

Voltage drop by the IEEE Std 141 formula; transformer regulation at nameplate impedance with the primary at nominal voltage.