Fault Current & Short-Circuit Simulator

Model three-phase, SLG, LL, and DLG faults across a four-bus radial system using the per-unit method — with configurable source impedance, transformer, cable, and relay — and a clear statement of what a code-grade study includes that this educational tool does not.

AVAILABLEAUTOMATED CHECKS ONLYSTANDARDS-AWAREADVANCEDIEEEIEC 60909WHAT DO THESE STATUSES MEAN?

4 FAULT TYPES4 BUS LOCATIONSPER-UNIT METHODX/R ASYMMETRIC MODEL

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Overview

Short-circuit studies are the foundation of equipment selection, protection coordination, and arc flash analysis — yet the per-unit method, X/R ratio, asymmetric DC offset, and sequence network behavior that drive those studies are poorly understood without a tool that shows all the variables interacting. This simulator builds a four-bus radial system: source (0.4–500 kV, Zs 0.01–1.0 pu), transformer (1–100 MVA, 1–15% impedance, with Delta-Wye Grounded, Wye-Wye, or Delta-Delta configuration), cable (0.1–20 km), and a relay (pickup 100–10,000 A, trip time 0.02–2 s). Fault location is selectable across Bus 1 (Source Terminal), Bus 2 (Transformer Secondary), Bus 3 (Feeder Mid), and Bus 4 (Load End). Fault type is selectable: Three-Phase (LLL), Single Line-to-Ground (SLG), Line-to-Line (LL), and Double Line-to-Ground (DLG). Base MVA (10–1,000 MVA) and X/R ratio (1–50) are adjustable for asymmetric first-cycle calculations. The tool computes symmetrical fault current, asymmetric peak, and relay operating time, and shows the per-unit impedance network. The educational content section explicitly states what the tool does and does not model — including no protective device coordination, no arc-in-a-box correction, no motor contribution, and no code-compliant label output — making it honest about its role as a learning tool rather than a study replacement.

App preview

A live look at the app you'll launch — every control on the left drives the visualizations on the right in real time.

Inside the lab

Example data — not a real field report

Short-circuit simulator with four-bus system and fault results — Simulator — configure source, transformer, cable, and relay, then pick a fault type and bus to see symmetrical current, asymmetric peak, and trip time update on the four-bus one-line.

Per-unit impedance network and sequence analysis — Analysis — inspect the per-unit impedance network from source to fault, with Zs, Zxfmr, Zcable, and Zf laid out to show how each element contributes to the total.

Preset short-circuit scenarios — Scenarios — load the Default Industrial Bus Fault and other presets to compare fault types and locations without rebuilding the system.

Learn tab covering fault theory — Learn — per-unit system, symmetrical components, X/R and DC offset, transformer zero-sequence behavior, common misconceptions, and what a code-grade study models that this tool does not.

What you'll do

01Convert system impedances to a common per-unit base and compute total impedance from source to fault location
02Calculate symmetrical three-phase fault current and explain why it sets the upper bound for equipment interrupting ratings
03Predict how transformer configuration (Dy vs. Yy vs. Dd) affects zero-sequence current path and SLG fault magnitude
04Explain X/R ratio and calculate the asymmetric peak multiplier for first-cycle fault current
05Determine how fault current magnitude changes as fault location moves from Bus 1 to Bus 4 due to additional series impedance
06Identify what a code-grade short-circuit study includes that this educational tool does not, including motor contribution, arc-in-a-box correction, and coordination modeling

Try a guided scenario

Run a sensitivity study on available fault current.

Available fault current · Power Systems Analysis

No sign-in required. Progress is saved on this device.

What this lab is not

Not a design document, stamped calculation, or approval record.
Not a substitute for engineering analysis by a licensed professional.
Not connected to live equipment and not a safety device.

Calculation basis

References IEEE, IEC 60909. Results are computed from the entered inputs and cited back to the referencing clause or table number — no code text or table is reproduced verbatim.

Simplifying assumptions are stated in the lab itself; where a model is intentionally conceptual, the lab says so rather than implying study-grade accuracy.

Standards basis: Standards-aware. Validation state: Automated checks only (last checked 2026-08-15).