COMTRADE Files: .cfg, .dat, .hdr and .inf Format

Short answer

COMTRADE is the common format for exchanging fault records, test results and simulations of the power system, defined by the dual-logo standard IEC/IEEE 60255-24:2013, also published as IEEE C37.111-2013. A classic record has a configuration file (.cfg) that describes channels, scaling, sampling and time, and a data file (.dat) with the samples, plus two optional files (.hdr and .inf). Since 2013 all four can be combined in a single .cff file.

What COMTRADE is

COMTRADE (Common Format for Transient Data Exchange) is the standard format for storing and exchanging power system time-series data: fault records from relays and recorders, test results and outputs of transient simulation programs. Thanks to it, a record taken by one manufacturer’s relay can be opened in another’s software, compared with the record from the other end of the line or replayed with a secondary injection test set. How to get that file out of each brand of relay is covered in downloading events and oscillography from a relay.

The current version is the dual-logo standard IEC/IEEE 60255-24:2013, identical to IEEE C37.111-2013. Before it came the IEEE revisions of 1991 and 1999 and the first IEC edition of 2001. The 2013 revision added:

The single .cff file, which gathers the content of .cfg, .inf, .hdr and .dat in sections.
Two new data types: binary32 (4-byte integers) and float32 (4-byte reals).
Two new lines at the end of the .cfg: one with the time code and the difference between local time and UTC, and another with the time quality of the samples.
Support for UTF-8 Unicode characters.

It is the central piece of power system fault analysis: almost everything you see in an oscillography comes from a COMTRADE file.

The parts of a record

File	Mandatory?	What it contains
.cfg (configuration)	Yes	Text that describes the record: station, device, channels, scaling, frequency, sampling, dates and data type
.dat (data)	Yes	The samples: sample number, time stamp, analog values and digital states, in ASCII or binary
.hdr (header)	No	Free text from the record’s author: event description, network data, notes
.inf (information)	No	Additional information in public sections, readable by any program, and private sections specific to each manufacturer
.cff (single file)	Alternative	Since 2013, the four files above in a single file

The .cfg and the .dat must have the same base name. If someone renames one and not the other, the record stops opening. The IEEE C37.232 standard (COMNAME) proposes a convention for naming files with date, time, substation, circuit and device, useful when you handle hundreds of records.

What the configuration file describes

The .cfg is a text file that any editor can open. Line by line, it defines:

Station, device identification and revision year of the format (1991, 1999 or 2013).
Number and type of channels: how many analog and how many digital (status).
Each analog channel: name, phase, circuit, units, conversion factors a and b (value = a·sample + b), channel sampling time skew, minimum and maximum values, primary-to-secondary ratio and whether the resulting value is primary or secondary.
Each digital channel: name, phase, circuit and normal state.
Nominal frequency of the network (50 or 60 Hz).
Sampling rates: how many different rates the record has and up to which sample each one is used.
Time stamps: the time of the first sample and the time of the record’s trigger point.
Data file type: ASCII, BINARY, BINARY32 or FLOAT32.
Time stamp multiplication factor.
In the 2013 revision, the time code and local-to-UTC offset, and the time quality of the samples.

The primary-to-secondary ratio and the P/S flag in the .cfg prevent one of the most common analysis errors: comparing primary currents from the record with a setting in secondary amperes, or the other way around.

Sampling and resolution

Each device records with its own sampling rate, expressed in samples per second or samples per cycle. A dedicated fault recorder usually samples faster than a relay, because it is designed to see transients; the relay records what its function needs. The standard includes an informative annex on sampling rates for data exchange and a sample program to convert the sampling frequency.

For the analysis, these matter:

Samples per cycle: with few samples the fundamental magnitude is well seen, but high harmonics and the details of current extinction are lost.
Pre-fault and post-fault duration: without a few cycles before, you cannot see the load or the voltage before the fault; without post-fault, you cannot see the reclose.
Digital channels: the resolution of a binary input in the oscillography is that of the sampling, but its real instant also depends on the device’s debounce filter.

An ASCII record can be inspected with a text editor; a binary one takes less space and is the most common in modern devices.

What software reads COMTRADE

Practically all record analysis software supports it. Some examples:

Relay manufacturers’ viewers: Siemens SIGRA analyzes records from protections and recorders with time-domain signal views, phasors, circle diagrams and tables, and calculates impedances and symmetrical components. SEL SYNCHROWAVE Event displays and analyzes event reports from SEL relays and COMTRADE files. The other major manufacturers have equivalent tools. This is complemented by analyzing fault records with SIGRA.
Secondary injection test set software: lets you replay a COMTRADE record on a relay to check how it responds to the real fault.
Analysis and programming tools: third-party libraries and programs exist for reading COMTRADE in spreadsheets or in programming languages.

Before blaming the file, check that the software supports the record’s revision and data type.

COMTRADE in testing

Replaying a COMTRADE with a test set is one of the most valuable tests for understanding a doubtful operation: you inject into the relay exactly what it saw during the fault, with its settings, and observe whether it trips the same way. It is also used in commissioning to test functions that are hard to simulate with simple states, such as out-of-step. See secondary injection.

How a device delivers these files over telecontrol is covered in files and fault records over IEC 104 and disturbance records in IEC 103.

Common mistakes with COMTRADE files

Sending only the .dat or only the .cfg.
Renaming one of the files and not the other.
Comparing primary values with secondary settings.
Trusting the record time without checking whether the device was synchronized or which time zone it records in.
Mixing records from two line ends with different sampling rates without aligning them.
Exporting from the manufacturer’s software with a revision the recipient does not support.

Send us your records

If you have COMTRADE records of a trip and need to know what happened, our team analyzes them remotely together with the relay settings, for any of the main brands. When the problem is in the parameterization, we correct it with our remote relay configuration, and when it is in coordination, with a protection coordination study. Write to us through our contact page.

References

IEC/IEEE 60255-24:2013, Measuring relays and protection equipment – Part 24: Common format for transient data exchange (COMTRADE) for power systems (IEEE Std C37.111-2013).
IEEE C37.232: common format for naming time sequence data files (COMNAME).
IEEE C37.239-2010: common format for event data exchange (COMFEDE), inactive-reserved.

Frequently asked questions

How do I open a COMTRADE file?

You need at least the .cfg and the .dat with the same name in the same folder, or a single .cff. They open in the record viewers of relay manufacturers, in the software of secondary injection test sets and in other analysis programs that support the file's format revision.

Why won't the COMTRADE file open in my software?

The most common causes are a missing .dat or one with a different name, software that does not support the 2013 revision or the binary32 and float32 data types, or a file left incomplete by the download. Check the first line of the .cfg: it holds the format revision year.

Are the COMTRADE values in primary or secondary terms?

It depends on how the device generated it. The .cfg of each analog channel carries the primary-to-secondary ratio and a flag that says whether the values converted with its scaling factors are primary or secondary. Check it before comparing with the relay settings.