COMTRADE in PQ Canvass

Abstract

The Common Format for Transient Data Exchange (COMTRADE) defined by IEEE C37.111 and IEC 60255-24 is a file format most commonly produced by protective relays and digital fault recorders, though some power quality monitors also support the format. Records are typically used by power quality and protection engineers to review disturbances, faults, and other system anomalies. Because the format is defined by a public standard, records produced by one device can be opened by any conforming analysis tool. This paper describes the structure of a COMTRADE record, including the header, configuration, data, and information files, as well as the Combined File Format introduced in the 2013 revision. The workflow for importing COMTRADE records into PQ Canvass is presented, followed by a detailed discussion of the analytical capabilities available once a record is loaded. COMTRADE support is part of a broader PMI initiative to allow customers to bring data from common industry formats into PQ Canvass alongside native PMI recordings.

Contents of COMTRADE Records

Each COMTRADE record contains up to four companion files, or a single consolidated CFF file introduced in 2013.

1. Header File. The header file (*.hdr) is an optional ASCII text file used by PQ engineers to add human-readable context (ex: substation, length of faulted line, line identification, etc.)
2. Configuration File. The configuration file (*.cfg) is an ASCII text file that provides the structural definition of the record, including number and type of channels, sampling rates, units, channel names, scaling factors, and the date and time of the event.
3. Data File. The data file (*.dat) contains the sampled values themselves and may be written in either ASCII or binary format. ASCII data files offer human readability and ease of inspection, while binary files provide significantly reduced file size and faster loading times, which makes them preferable for high-resolution or long-duration records.
4. Information File. The information file (*.inf) is an optional ASCII text file that was introduced in the 1999 revision and provides a structured location for additional metadata that does not fit naturally within the configuration file.

The 2013 revision of the COMTRADE standard introduced the Combined File Format (*.cff), which consolidates the header, configuration, data, and information sections into a single file rather than requiring separate files. Within a CFF file, each section is delineated by a clearly defined header marker that identifies the section type and, for the data section, indicates whether the contents are stored in ASCII or binary form. This unified structure preserves all of the information available in the traditional multi-file format while eliminating the risk of mismatched or missing companion files, which often causes import errors during record transfer. 

Importing COMTRADE Records into PQ Canvass

PQ Canvass supports single-file COMTRADE records (.cff), multiple file uploads (which require at minimum .cfg and .dat files), and a zip archive of either. Users can click the Upload button in the top-left of the recordings tab. Select COMTRADE on the Source screen (Figure 1) and choose the record format on the Package screen (Figure 2). On the Upload screen (Figure 3), users can select the appropriate files from their file system to be uploaded. On the Import screen (Figure 4), users can enter a name for their file and choose a folder to put the COMTRADE record in. All COMTRADE recordings will exist in the Uploaded folder or within one of its subdirectories.

Visualization of COMTRADE Data and Analytical Capabilities

After a recording is uploaded, users can click on the recording to view a brief overview of metadata about the record (Figure 5). 

To view waveform captures of COMTRADE data, click the Waveform Capture button in the top-left corner.

Figure 6 shows the standard time domain view of a waveform capture. To zoom in on a subsection of data, click and drag over a portion of the waveform. Waveforms can be viewed by channel or by phase, which can be toggled by clicking the 3 phase icon on the bottom toolbar. To make annotations on the waveform, select the pencil icon in the bottom-right corner. These annotations can be seen on the graph by clicking the eye and pencil icon. Users can click the triangle icon to view line-to-line voltage. 

Users can click on the bar graph icon to switch to the harmonics graph (Figure 7). Pressing the ‘F’ key or clicking the ‘Hide Fundamental’ button removes the fundamental harmonic which recalculates the auto-scaling for the y-axis, allowing the user to see the remaining harmonics in higher detail. Clicking the ‘51+’ button allows users to view higher order harmonics. Availability of this option depends on the sample rate of the recording; at lower sample rates the button will be disabled because the Nyquist limit prevents accurate resolution of those harmonics.

Users can click on the vector arrows icon to view the phasor diagram, which shows the magnitude and phase angle of each voltage and current channel at any selected point in the recording (Figure 8). Users can view phasor diagrams for harmonics using the up and down arrows on the bottom toolbar. 

Users can click on the meter icon to access the meter view, which presents tabular data including phase angle, crest factor, K factor, unbalance, and symmetrical components for each channel. These values are computed for the cycle currently highlighted by the cycle selection window. Users can slide that selection window to any point in the waveform capture to observe how these metrics evolve over the duration of the recording, which is particularly useful when investigating how conditions change during a transient or fault event.

Users can view the waveform as a running RMS trace by clicking the RMS icon on the top toolbar.

Users can view symmetrical component magnitudes by clicking the SYM icon in the toolbar. To learn more about symmetrical components and why they are important to power system analysis, see PMI’s ‘Understanding Symmetrical Components’ whitepaper.

Conclusion

By supporting COMTRADE imports in multi-file, single-file CFF, and zip-archive forms, PQ Canvass allows engineers to apply the same waveform-capture capability to records originating from any conforming device, allowing engineers to apply the same analytical tools used for native PMI recordings. This complements PMI’s broader effort to support common industry data formats within PQ Canvass, so that engineers investigating disturbances on systems with mixed monitoring equipment can work from a single platform.