Transcript

Introduction

Hi, everyone. Welcome to today’s Ask a Pro Session. I’m Andrew Kornfeld, one of the software engineers here at PMI, and I’m the author of this paper. Today, we’re gonna be talking about COMTRADE in PQ Canvass.

In this presentation, we’re gonna cover what the COMTRADE format actually is, the structure of a COMTRADE record, the four companion files, and the newer single file CFF format, how to import a COMTRADE record into PQ Canvass, the analytical capabilities you get once a record is loaded, and if you have any questions or comments as we go, just type them in chat, and we’ll go through them at the end.

What Is COMTRADE?

COMTRADE stands for the Common Format for Transient Data Exchange. It’s defined by two standards: IEEE C37.111 and IEC 60255-24. It’s a file format for storing high resolution, voltage and current waveform records, and is most commonly produced by protective relays and digital fault recorders. Some power quality monitors also support it, but the center of gravity for COMTRADE is really on the protection side.

Recordings are typically used by power quality and protection engineers to review disturbances, faults, and other system anomalies. The important thing about COMTRADE is that it is defined by a public standard, and that means that a record produced by one vendor’s device could be opened by any conforming analysis tool, including PQ Canvass.

Why COMTRADE in PQ Canvass

Protective devices typically capture only short windows around a trip event, and importing these COMTRADE records into PQ Canvass lets engineers analyze that protection side data alongside the broader continuous monitoring provided by PMI instruments. This is also part of a larger PMI effort to let customers bring data from common industry formats into PQ Canvass alongside their native reports.

Contents of a COMTRADE Record

A COMTRADE record traditionally contains up to four companion files.

• The header file, which ends in .hdr, is an optional plaintext file. Engineers use it to add human readable context like a substation name, the length of a faulted line or line identification.
• A configuration file, .cfg, is required. This is the structural definition of the record, the number and type of channels, sampling rates, units, channel names, scaling factors, and the date and time of the event.
• The data file, .dat, is also required. This contains the actual sample values themselves. It can be read in either ASCII or binary. ASCII is easier to inspect by hand, but binary is much smaller and faster to load, which is what you want for high resolution or long duration records.
• The information file, .inf, is optional, and it was added in the 1999 revision of the standard, and gives you a structured place to stash additional metadata that doesn’t fit naturally in the config file.

The Combined File Format (CFF)

The combined file format, .CFF, was added in the 2013 revision of the COMTRADE standard. This consolidates the header, the configuration, data, and information files into one single file rather than requiring four separate files. Inside a CFF, each section is delineated by a header marker that identifies the section type. For the data section, the marker also tells you whether the contents are stored in ASCII or binary.

The big practical advantage is that it eliminates a very common source of import errors, mismatched or missing companion files. With a CFF file, everything that belongs together stays together.

Importing into PQ Canvass

PQ Canvass supports three ways of bringing a COMTRADE record: a single file CFF, multiple individual files which, at minimum, needs the .CFG and the .DAT file, or a zip archive containing either of the above. The upload flow is a four-step wizard, and we’re actually gonna walk through it.

If you go to the Recordings tab on PQ Canvass, up in the top left corner, there is an Upload button. You can click on that, and then you can click either PMI Recording or COMTRADE. Since you’re uploading your COMTRADE, we’re gonna select COMTRADE.

Step two is the package screen. Here, you can choose how your COMTRADE recording is packaged. You can choose a zip archive, multiple files, or a single CFF. In my case, I’ve got a zip archive that I’m gonna use.

Step three is the upload screen. You can drag and drop, or you can click to browse and pick the files off your file system. I’m going to go ahead and drop in my zip file. I’ve got a demonstration COMTRADE file.

Then on step four, this is the import screen. You can give the record a name, and you can pick the folder that you want it to live in. All the COMTRADE recordings are gonna end up in the Uploaded folder or one of its subdirectories. I’m going to just go ahead and leave it in the Uploaded folder. And success, my upload’s complete.

Reviewing the COMTRADE Record

On here, we’ve got the overview page. Once the recording is uploaded, it’ll give you a quick overview of all the metadata. You’ve got the station name, sampling rate, total samples, number of analog and digital channels, start and trigger times and so on. This is all pulled from the config file.

Waveform Capture View

To actually look at the waveform, we’re gonna click on the Waveform Capture button up here at the top left, and this is the standard time domain view. There’s a few things you can do here. You can click and drag over a portion of the waveform to zoom in, just like this. You can toggle between channel view and phase view using the three-phase icon down here on the bottom toolbar.

You can also add annotations on the waveform by using the pencil icon in the bottom right corner. And then you can toggle their visibility after you’ve added it. So let’s go ahead and add one. And you can toggle its visibility here with the eye, with the pencil view. You can view line-to-line voltage by clicking the triangle button here.

Harmonics View

We can take a look at the harmonics graph. You can click the bar graph icon to switch to the harmonics view. There’s a couple useful shortcuts here. You can press F or click the Hide Fundamental button, which hides the first harmonic, and that rescales the Y-axis, so you can see smaller harmonics in detail.

You can click the 51+ button, which shows higher order harmonics. There’s one caveat: the ability to do this depends on the sampling rate of the recording. At lower sample rates, the button is disabled, because the Nyquist limit prevents accurate resolution of these higher harmonics. As you can see here, you can see all the way up to the hundredth harmonic.

Phasor Diagram

If you click the vector arrows icon, you can see the phasor diagram. This shows the magnitude and phase angle of each voltage and current channel at any selected point. You can use the up and down arrows to view at each harmonic.

Meter View

The meter icon gets you a tabular view of derived metrics. You can see phase angle, crest factor, K-factor, unbalanced and symmetrical components. Key thing to know about the meter view is that these values are computed for the cycle currently highlighted in the cycle selection window.

You can slide this selection window to any point in the waveform capture to see how these metrics evolve over the duration of the recording. This makes it especially useful for investigating how conditions change during a transient or a fault. You can watch K-factor or unbalanced shifts cycle-by-cycle as the event unfolds.

RMS and Symmetrical Components Views

If you click the RMS view, you can see the waveform as a running RMS trace. This is useful when you care more about the envelope of the event rather than the cycle-by-cycle waveform shape. The SYM icon in the toolbar shows symmetrical component magnitudes over time.

If you want a deeper dive on what symmetrical components are and why they matter for your power system analysis, PMI has a separate white paper called Understanding Symmetrical Components that walks through it.

Recap

COMTRADE is a public standard format that is primarily produced by protective relays and fault recorders. PQ Canvass reads it in all three of its packaging forms: single CFF, multiple companion files, and zip archives.

Once a COMTRADE record is loaded, you get the same waveform capture toolkit you use in a native PMI recording: time domain view, harmonics, phasors, meter view with derived metrics, RMS, and symmetrical components. The big takeaway here is that COMTRADE support lets you analyze protection side captures alongside continuous PMI monitoring data in a single platform without needing the original vendor’s software.

Additional Comments

COMTRADE is very common in the protection world: relays and substations, digital fault recorders. Those types of devices that are only capturing waveform-based, typically based on events, use COMTRADE natively, and their software is oriented towards that single purpose.

If you wanna do something more with that waveform, like look at the harmonic content, look at a sliding RMS graph to analyze it from a power quality standpoint, PQ Canvass is a much more powerful platform for that. With Andrew’s COMTRADE import, you can now use the power of PQ Canvass for that data where you were typically limited by that other vendor’s software, because it’s focused on protection for fault clearance. Having this data in PQ Canvass gives you a lot more powerful tools and allows you to combine this with the other power quality data from PQ reports.

Automated COMTRADE Import

Should this be configured to automatically import COMTRADE files? That’s something we’re working with utilities now to set up automated acquisition of this type of data. If that’s something that you would like to do, we’d be happy to work with you to set that up, stage that, and pilot that in your system so that you can use PQ Canvass to automatically ingest this sort of data on a continuous basis to allow you to have a much deeper view into what’s going on in your system.

Closing

All right. Well, that just about does it for today. Be sure to check out the links for additional information. And as always, thank you to everyone for tuning in, and have a great rest of your day.