COMTRADE Viewer & Fault Analyser

Open a disturbance record (IEEE C37.111 / IEC 60255-24 COMTRADE, 1991, 1999 or 2013; ASCII, BINARY, BINARY32 or FLOAT32) and read it like a protection engineer: waveforms and digital channels, pre-fault and fault phasors, fault type, trip and breaker times, clearance time, apparent impedance of the faulted loop and the distance to the fault.

After every trip the relay's disturbance record answers the key questions: what kind of fault, how much current, how fast the protection tripped and the breaker cleared, and where the fault was. Vendor tools read only their own relays and are not on every engineer's laptop; COMTRADE is the common format, so one viewer works for every relay.

Standards followed

IEEE C37.111-1999 / -2013 and IEC 60255-24 (COMTRADE: configuration, data, scaling, sample rates)IEC 60255-121 (distance protection: loop impedance, residual compensation k0 = (Z0 − Z1) / 3Z1)Fortescue symmetrical components

What it can do

Reads .cfg + .dat pairs and 2013 single .cff files; ASCII, BINARY (16-bit), BINARY32 and FLOAT32 data; channel scaling a·x + b, primary/secondary conversion, multiple sample rates or time stamps.
Plots currents, voltages and digital channels with inception and clearance markers.
Detects fault inception (step change against one cycle earlier), computes one-cycle DFT phasors before and during the fault, classifies the fault (A-G … ABC) from phase and residual currents.
Trip and breaker times from the digital channels, clearance time from the currents, apparent impedance of the faulted loop (phase-earth with k0, phase-phase), distance to fault from the line impedance; warnings for clipping, missing samples and neutral mismatch.

Example problem

The sample record of the S13 Q01 line fault (P132_Q01, 1600 samples/s).

A-G fault at 06:12:31.200 UTC: IA = 5.00 kA, 3I0 = 4.88 kA.
Trip 31 ms after inception, breaker 52a changes at 81 ms (operating time 50 ms), current cleared at 81 ms.
Loop A-G with k0 from Z1 = 0.08 + j0.40 Ω/km and Z0 = 0.25 + j1.20 Ω/km: 4.07 Ω ∠ 78°, about 10 km from the substation.

A zone 1 earth fault 10 km down the line, cleared in 81 ms — the same story as the SOE time line.

The record is generated for the sample; on real records compare one reading with the vendor's tool once. Apparent impedance assumes a solid fault fed from the relay end; fault resistance and remote infeed shift it (mainly in the resistive part). Files are read in your browser.

Disturbance record

Open .cfg + .dat (or .cff)…

Line data (for distance to fault)

R1 (Ω/km)

X1 (Ω/km)

R0 (Ω/km)

X0 (Ω/km)

Z1 = 0.408 Ω/km ∠ 78.7°, k0 = 0.668 ∠ -0.7°

Result

Open a COMTRADE record or load the sample.

Tool guide · know before you use

What this tool is, how it works and how far to trust it

A COMTRADE disturbance record viewer that classifies the fault, measures protection and breaker times and computes the fault impedance and distance.

Read this before relying on a result. Every method, formula, assumption and limit is stated here, so you can check the answer yourself instead of accepting it blindly.

What it can do

Read .cfg + .dat pairs and single .cff files (1999 and 2013) in ASCII, BINARY, BINARY32 and FLOAT32, with channel scaling and primary / secondary conversion.
Plot analog channels and digital signals with markers at fault inception and clearance.
Detect inception, compute phasors before and during the fault, classify the fault (A-G … ABC) and give the phase and residual currents.
Measure trip time and breaker time from the digital channels and clearance time from the currents.
Compute the apparent impedance of the faulted loop (phase-earth with k0, phase-phase) and the distance to fault from the line constants; warn for clipping, missing samples and neutral mismatch.

Why you need it

After every trip the record answers the key questions: what fault, how much current, how fast the protection and breaker were, and where the fault was.
Vendor tools read only their own relays; COMTRADE is common to all, so one viewer works for every relay in the substation.

Understand this first

A record is a .cfg (channels, scaling, rates, start time) and a .dat (samples); the .cff (2013) packs both in one file.
Phasors are computed over one cycle; the 'during fault' window is taken one cycle after inception, when the DC offset and transient have mostly settled.
Phase-earth loop impedance = Vph / (Iph + k0·3I0) with k0 = (Z0 − Z1) / 3Z1; distance = loop reactance / line reactance per km for low fault resistance.
Trip time is from inception to the trip output; breaker time from trip to the breaker auxiliary contact; clearance is when the current reaches zero.

What you need before you start

The disturbance record (.cfg and .dat together, or the .cff).
For the distance: the line R1, X1, R0, X0 per km (or k0) and the line length.
A current browser (Chrome, Edge, Firefox or Safari). Nothing is installed and your data is never uploaded; it is processed on your own computer.

How to use it

Open both .cfg and .dat at once (or the .cff), or load the sample.
Check the channel assignment of currents, voltages, trip and breaker contacts; enter the line constants.
Read the summary, then check the plots and the phasor table.

What you get

Fault type, fault currents, trip, breaker and clearance times, loop impedance and distance; findings and warnings.
Waveform plots, digital channel bars and a phasor table before and during the fault.

How to read the results

Distance close to the relay's own fault locator: both are consistent; a big difference suggests fault resistance, infeed or wrong line data.
Breaker time above its rated value: check the breaker mechanism (see the breaker wear analyser).
3I0 present without a phase current rise: CT or wiring problem, not a fault.

Technical basis

IEEE C37.111 / IEC 60255-24 COMTRADE; one-cycle DFT phasors; Fortescue symmetrical components.
IEC 60255-121 loop impedance with residual compensation.

Limits: when not to rely on it

The single-ended reactance method is affected by fault resistance with remote infeed and by mutual coupling of parallel lines.
Channels are identified from their names and units; check the assignment for unusual naming.

Sample files for this tool

Download, open and compare with what the guide says you should see.

S13_Q01_fault_P132_Q01.cfg — Disturbance record of the Q01 line fault — configuration
S13_Q01_fault_P132_Q01.dat — Disturbance record of the Q01 line fault — data

All sample files and what to expect →

For preliminary engineering use. Results must be checked by a qualified engineer against the project's standards. How results are checked · Terms & disclaimer · Privacy · Build 7cfcbe2 · 2026-11-14