What is a free COMTRADE viewer I can use without installing anything?

A browser-based viewer: SagSwell, Detego, ZeroRiskk and Pragmasoft OscilloViewer all open a .cfg and .dat pair in a web browser. Which one fits depends on the question you are asking of the record: power quality (sags, swells, ITIC, harmonics) or protection (fault location, distance, differential).

Can I open a COMTRADE file on a Mac or a Chromebook?

Yes, with a browser viewer, because it runs in the browser rather than on Windows. Most vendor viewers are Windows programs.

Can I open a COMTRADE file in Excel?

Not directly: the .dat holds raw counts that need the scaling in the .cfg. Convert it first, for example with the free COMTRADE to CSV converter, which applies the scaling and writes primary or secondary values.

Which COMTRADE viewer should I use for a relay from one vendor?

The relay vendor's own software usually reads its own files best and knows its own channel naming. A vendor-neutral viewer is useful when records come from several manufacturers or when you cannot install the vendor tool.

Is my file uploaded when I open it in a browser viewer?

It depends on the tool. SagSwell reads the file in your browser and keeps nothing unless you save it to your account; Detego and Axon say their viewers keep files on your machine too. Check each tool’s own privacy statement before opening sensitive records.

Free COMTRADE viewers compared (2026): browser, desktop and code

The COMTRADE viewers you can use today, side by side: browser viewers that need no install, desktop software from relay and test-equipment makers, and libraries for scripts, with what each one costs and what it is built for.

Updated 21 October 2026 · SagSwell

Written by SagSwell, which makes one of the tools below. Every row says only what that product’s own website says, as read on 21 October 2026, and links to it. Prices and features change; if something here is out of date, write to sagswell.app@gmail.com and we will correct it.

The short answer

To look at a COMTRADE record without installing anything, use a browser viewer. To work inside one relay manufacturer’s ecosystem, use that vendor’s desktop software. To process many records in a script, use a library such as the Python comtrade package. Among the browser viewers, the main difference is the question each is built to answer: what did the disturbance do to the supply (power quality: sags, swells, ITIC, harmonics) or what did the protection do (fault location, distance, differential).

Browser viewers

Open a .cfg and .dat (and in some cases .cff or .zip) in a web browser, on any operating system.

Tool	Cost	Sign-in to view	What its site says it does
SagSwell SagSwell (this site)	Free; Pro plan for diagnosis, replay, archive and reports	No (account to save records)	.cfg + .dat, .cff and .zip. Power-quality focus: IEEE 1159 sags and swells, ITIC (CBEMA) and SEMI F47, harmonics and THD, phasors. Files are read in the browser.
Detego Detego	Free plan (3 recordings, 1 AI analysis a month); Pro US$79 a month	No (account to save recordings to its cloud)	Protection focus: waveforms, phasors, fault identification, harmonics, distance and overcurrent tabs, AI analysis. Says files stay on your machine.
ZeroRiskk COMTRADE viewer ZeroRiskk	Viewer free; AI fault report paid per report	No for viewing; free account for saved records and advanced views	Relay evidence focus: A/B cursors, frequency and df/dt; with an account phasors, fault location, R-X and differential review. 1991, 1999 and 2013 records.
OscilloViewer Pragmasoft	Free	No	Plots analog and digital channels in separate charts with zoom. The site says the current version accepts binary COMTRADE.
Axon COMTRADE viewer Axon Group	See the site	See the site	Spanish-language tool page; says the tools run locally in the browser without sending data to the cloud.

Desktop software

Windows programs, mostly from relay and test-equipment manufacturers. They read their own manufacturer’s files best and often add features tied to that equipment.

Tool	Cost	Sign-in to view	What its site says it does
WaveWin Softstuf	Check the vendor for current editions	–	Fault data manager and analysis: waveforms, phasors, sequence of events, harmonics, single- and double-ended fault location.
SIGRA Siemens	Commercial	–	Fault record evaluation that ships with the SIPROTEC engineering tools.
TransView OMICRON	Check the vendor	–	Transient record visualisation and analysis, used alongside OMICRON test sets.
SEL-5601-2 SynchroWAVe Event SEL	Check the vendor	–	SEL's event and COMTRADE analysis software.
COMTRADE viewer Elspec	Free	–	Reads COMTRADE, PQDIF and Elspec formats; trend, spectrum, phasor and event charts.

Libraries for scripts

Tool	Cost	Sign-in to view	What its site says it does
comtrade (Python) open source, MIT licence	Free	–	Reads 1991, 1999 and 2013 records: .cfg + .dat (ASCII and binary), .cff, BINARY32 and FLOAT32, into arrays.

How to choose

A quick look at one record, any computer: any of the browser viewers. If the file will not open, the free COMTRADE file checker lists what in the .cfg is unusual.
Power quality: was it a sag, a swell or an interruption under IEEE 1159, where does it sit on the ITIC (CBEMA) curve, what is the THD. SagSwell is built around these questions.
Protection analysis: fault location, distance zones, differential and overcurrent review. Detego, ZeroRiskk and the vendor tools are built around these.
Many records, or your own analysis: a library, or export to CSV with the COMTRADE to CSV converter.
No record to hand: try any viewer with the free sample COMTRADE files.

What every viewer has to get right

Whatever the tool, the numbers on screen are only as good as its reading of the .cfg: the scaling factors a and b, the primary and secondary ratios and the P/S flag, the sampling rates and the time stamps. When two viewers disagree on a value by a large factor, check those first; the .cfg line-by-line guide shows where each one is.

Questions people ask

What is a free COMTRADE viewer I can use without installing anything?: A browser-based viewer: SagSwell, Detego, ZeroRiskk and Pragmasoft OscilloViewer all open a .cfg and .dat pair in a web browser. Which one fits depends on the question you are asking of the record: power quality (sags, swells, ITIC, harmonics) or protection (fault location, distance, differential).
Can I open a COMTRADE file on a Mac or a Chromebook?: Yes, with a browser viewer, because it runs in the browser rather than on Windows. Most vendor viewers are Windows programs.
Can I open a COMTRADE file in Excel?: Not directly: the .dat holds raw counts that need the scaling in the .cfg. Convert it first, for example with the free COMTRADE to CSV converter, which applies the scaling and writes primary or secondary values.
Which COMTRADE viewer should I use for a relay from one vendor?: The relay vendor's own software usually reads its own files best and knows its own channel naming. A vendor-neutral viewer is useful when records come from several manufacturers or when you cannot install the vendor tool.
Is my file uploaded when I open it in a browser viewer?: It depends on the tool. SagSwell reads the file in your browser and keeps nothing unless you save it to your account; Detego and Axon say their viewers keep files on your machine too. Check each tool’s own privacy statement before opening sensitive records.

References

IEEE Std C37.111-2013 / IEC 60255-24:2013, Common format for transient data exchange (COMTRADE)
Each tool’s own website, as linked in the tables, read on 21 October 2026