Suggestions Needed for Monitoring Line Voltage Glitches

Decided to write a quick follow-up - thanks for the kind words jw0752. Perhaps if you aren't bothered to write some software, you might build it anyway and just use a sound recording app to record the waveform over a long period. Then you could try various filters on a copy of the file to see where things are suddenly different - e.g. perhaps you can try a notch at 50/60Hz then normalize to 100% (or even above) and then see if there are any "spikes" that remain. Transients usually have high frequency components as they have a sudden onset - so they may leave a tell-tale spike after filtering. Then you note down the time, go back to the original file and study the waveform carefully.

Another way which I forgot to mention, assuming you have a decent oscilloscope that can ride through the power interruptions, is to use that with a high voltage differential probe (for safety) - something like these which I reviewed earlier: https://goughlui.com/2018/12/16/review-eevblog-hvp-70-70mhz-micsig-dp10013-100mhz-high-voltage-differential-probes/

The idea would be to get the screen to capture a few cycles, triggered across the zero crossing, under a "mask test" set-up where you may capture a good set of waves from the mains as a reference, "increase" the mask around it say by a few percent, and set the oscilloscope to beep and capture screenshots/waveform files to USB when it violates this mask. Of course, this is not a feature all oscilloscopes have.

If you have the scope but not the probe, assuming you get the polarity of live/neutral right, you could get away with the 10x probe but you would be violating the safety CAT ratings of the oscilloscope and potentially put things in danger. If you get it wrong, you'd be shorting live to earth which is a terrible thing to do in general. Instead, you could take the hybrid approach and just use a linear brick transformer like I did before and scope the output of that. It should be noted that the transformers themselves may have resonance/distortion due to the core materials and inductance properties, so I would be less inclined to trust the absolute reading/waveform shape after it goes through a magnetic transformer compared to a high-voltage differential probe.

What you might be suffering from is some loose connection or intermittent shorts somewhere which is causing some short periods of "notching" on the waveform, or a short dip which is not going to easily be caught by a DMM that might only sample at about 4Hz. In the very catastrophic case, it could even be a sign of arcing somewhere in the network which happens transiently (e.g. bats hanging across phases, trees clashing with wires in the wind occasionally, failed ceramic insulator on a pole, high-resistance cut-out contact, a minor partial discharge inside a transformer perhaps?). Other causes may be more mundane - a weak/failing fuse, breaker contact, perhaps even a surge protective device going a bit funny and "clamping" during higher-voltage peaks (rather than surges) as the MOV wears out.

- Gough

  Whoa!  Glad you found that before it got uglier.

I'm a certified installer. First home I did was my parent's, 1983 - 4.

30 years later they had issues. A differential interrupter (loss detector)  was defect. When I opened the cabinet, I saw that there had been a small fire inside (smoke, but plastic not molten).

Turned out it was the utility entry cable that got somewhat loose, gave an interrupted contact. I still think it was me not fastening the thick cable enough, or not revisiting the cabinet after a few days to retighten the screws after the thick wires settled. ...

I remember being on the train into London a number of years ago, absentmindedly looking out of the window and suddenly a whole substation exploded - it was quite spectacular but I could tell it wasn’t going to bode well.  Actually, I don’t know what they are, it’s what I all them, but it’s a number of very large electrical machines fed by, or feeding, the overhead power cables.  A few seconds later the train ground to a halt.  The whole of the West Coast main line into London was out, and stayed out for the best part of 24 hours.  We had to get off the train and walk along the tracks.  Getting home was interesting!!

Our hydro provider have units they leave on-site to record and monitor. I'm not sure if that was available or offered by your provider.

I did a work tour in the high arctic community that got it's power from diesel generators. The electronic equipment I services, was located at the very end of the power-line. I experienced a week of equipment switch-overs from mains to standbys. The time of day was the only thing that was in common.

The hydro provider changed the tap on the transformer at the site. I never did get an answer to why it had worked for years without a problem. I suspect the town draw had increased to the point that the far end customers just got dregs.

The troubleshooting consisted of a line monitor supplied by the provider. I twigged to line power might be the issue when I was measuring 110/109 AC at times.