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COMTRADE (Common format for Transient Data Exchange for power systems) is a file format for storing oscillography and status data related to transient power system disturbances.

COMTRADE files are typically generated by Intelligent Electronic Devices (IEDs), such as an electronic protective relay, in electrical substations during power systems disturbances. These IEDs are monitoring the electrical characteristics of the power system by digitally sampling measurements of the current, voltage, power, frequency, etc. at a high speed. The IEDs then use digital signal processing algorithms on that data to detect abnormal conditions in the power system so that automated control actions can be taken to prevent damage to the power system. When faults are detected, the IEDs will record the digitized transient fault data that was used during processing into a file using the COMTRADE file format. Analysis tools can then download the COMTRADE file and calculate useful information related to the disturbance. For instance, a COMTRADE recording of the fault current absorbed by a transformer prior to the circuit breaker opening can be used to calculate the total energy dissipated by the transformer which helps the utility to more accurately estimate the impact of that fault on the lifetime of the transformer. COMTRADE files from multiple substations can be used collectively to perform forensic analysis of large scale power disturbance events (e.g. blackouts) to determine the root cause of the disturbance, help improve system protection and guide future mitigation strategies.

The COMTRADE file format has been standardised by the Power System Relaying Committee (PSRC) of the IEEE Power & Energy Society as C37.111. The most widely used version of the COMTRADE standard is C37.111-1999. This version specified a file format that consisted of multiple file types designated by the assigned file extensions of *.CFG, *.INF, *.HDR, and *.DAT. The *.DAT file contains the digitized sample data in an ASCII text format. The *.CFG file contains configuration data on what is in the *.DAT file including information such as signal names, start time of the samples, number of samples, min/max values, and more. Only the *.CFG and *.DAT files were mandatory. Although the values of the digitized samples in the *.DAT file are viewable without the *.CFG file, the value of the data is greatly diminished as it would be very difficult to fully reconstruct the meaning of the data without the *.CFG file.

As applications for using COMTRADE grew the limitations of the file format begin to cause problems. For instance, the North American Synchro Phasor Initiative (NASPI) sponsored by the North American Electric Reliability Corporation (NERC) wanted to use the COMTRADE file format to exchange synchrophasor data. The C37.111-1999 version of the COMTRADE format only supported ASCII encoded data, supported limited analog and digital status data types, and did not convey any power system configuration information. This would have made large scale exchange of synchrophasor data more difficult. Beginning in 2011, the IEEE PSRC began work on a new version of the COMTRADE standard that has been published as C37.111-2013. Also known as IEC 60255-24 Ed.2, this standard defines a format for files containing transient waveform and event data collected from power systems or power system models. The format is intended to provide an easily interpretable form for use in exchanging data. The standard is for files stored on currently used physical media such as portable external hard drives, USB drives, flash drives, CD, DVD. It is not a standard for transferring data files over communication networks.[1]

This version of the standard supports a variety of new features including XML encoding configuration and data, a single file type (*.CFF) that combines all the C37.111-1999 types into a single file, additional data types for 32 bit binary and floating point values and a partial binary encoding to reduce file size.

The IEEE Power Quality Subcommittee of the IEEE Power & Energy Society has also developed a file format called the Power Quality Data Interchange Format (PQDIF) that is similar to COMTRADE in structure but is used primarily to convey power quality data instead of transient disturbance data.

There are numerous COMTRADE viewers available from many commercial companies as well as free viewers like ComCalc Pro, TOP, GTPPLOT and others. Viewer functionality varies.

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