30 Replies Latest reply on Dec 5, 2020 5:23 PM by ipv1

    Suggestions Needed for Monitoring Line Voltage Glitches

    jw0752

      For the last couple weeks I have been getting power line glitches in my home. It was first noticed as a flickering of the lights. The kind of flicker that is just bad enough to catch ones attention. I have 5 UPS power line protection systems around the house and the glitches are enough to trigger the switch mechanism in the UPS systems about 50% of the time. I have put my FLUKE multimeter across the 240 volt line and another meter across one 120 volt phase and set them both on MIN/MAX. I have had the power company out and they did some stress tests on the system exterior to the house and could not see a problem. I have checked the circuits inside the house and all the connections in the breaker box. Since the phenomena is seen on several circuits and in both 120 Volt phases I am convinced that the cause of the glitches are external to the house wiring. My meters are showing Max voltages of roughly 120 volts and 240 volts and Min voltages of 110 volts and 220 volts. Tomorrow the power company is returning with a chart recorder so that should give a good picture of what is going on.

       

      This situation has me thinking and trying to imagine how I would build a circuit that would watch the power line and detect these low voltage spikes that last only milliseconds. It doesn't have to be anything fancy. Perhaps just a beep from a sonalert whenever a glitch passes. I have been experimenting off and on today without much luck.

       

      Can anyone throw some ideas at me on how to detect a 10 % voltage millisecond drop in a mains line.

       

      Thanks

      John+

        • Re: Suggestions Needed for Monitoring Line Voltage Glitches
          lui_gough

          Well, being lazy, I built a "power line to sound card" interface to analyse the waveform offline to try and find off-peak mains signalling (https://goughlui.com/2014/02/02/project-analyze-mains-power-flicker-issue-ripple-signalling/ ). It's basically just an isolated transformer and a voltage divider. I didn't develop much in the way of software applicable for your situation, but I suppose that's one approach you might think about by defining a "mask" and comparing samples for each cycle by looking at zero-crossings. It's a lot cheaper than a cycle-by-cycle capable power analyser or using an oscilloscope and trying to capture every cycle with it, but perhaps may need a little "calibration".

           

          - Gough

          6 of 6 people found this helpful
            • Re: Suggestions Needed for Monitoring Line Voltage Glitches
              jw0752

              Hi Gough,

               

              Thank you for the link and the extremely interesting exploration of the noise you had on your power line. You always do such an awesome thorough job with every presentation.

               

              John

                • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                  lui_gough

                  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

                  4 of 4 people found this helpful
              • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                kmikemoo

                jw0752  Please forgive the slight side track.  I'd recommend that you also check your neutral to earth voltage. Infrequently, the neutral connection can become loose or corroded and what should be zero isn't.  It exhibits itself as flicker, dim and/or bright, in the early stages.  If the neutral floats... stuff burns up.  I know that you checked all the connections in the breaker box.  I hope that included the white and green - especially the main bonding jumper - the one connection between the neutral buss and the ground/earthing buss.  At work, we see it every so often.  Oh yeah... happened to me, also.

                5 of 5 people found this helpful
                  • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                    lui_gough

                    Great point kmikemoo! Definitely worth checking especially for split-phase 120/240V installations, perhaps depending on where the earth-neutral bond is, it could also be on the transformers on poles and have broken off there (I think I remember videos from Bobsdecline's YouTube channel mentioning this for Canada).

                     

                    Things are different down-under where I am, where 3-phase distribution and 1-phase/3-phase supply is the norm. Our main earth-neutral bond is in the meterbox usually, losing it just means potential safety issues (e.g. tingles when touching electrical devices and taps) but rarely results in voltage issues for the device itself as houses usually get a neutral wire and don't depend on earth connection except for safety.

                     

                    - Gough

                    1 of 1 people found this helpful
                    • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                      jw0752

                      Hi Mike,

                       

                      this is a good insight and I will check it out. I do have one of my meters set to Min Max set between Neutral and one Phase just so I could see if I was getting glitches there and not across the two phases at the same time. So far it looks like a glitch on a phase to neutral happens at the same percentage drop as the drop across the 240 volts.

                       

                      John

                      • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                        BigG

                        Yep, something similar happened to me only last week. Air gap in old fuse (more likely) or possibly loose connection had caused flickering but could smell some ozone too (usually the sign). Failure triggered due to higher than normal current as had a couple of electric heaters on for a change (one was also my fan heater) and then the wife put the kettle on...

                         

                        2 of 2 people found this helpful
                      • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                        genebren

                        John,

                         

                        I know how frustrating it can be when you see glitches in the lights, but you can't determine the source or quantify the severity of the events.

                         

                        Many years ago, almost in another life, I worked for a company that built very high power inverter systems.  One of our clients wanted to use our inverter in a grid power quality system.  The idea of the system was to stand in between the grid and a remote factory.  The system would monitor the grid voltages on a cycle-by-cycle basis, measuring the amplitude, frequency and phase of the grid.  From these readings we would generate a signal that was a mirror of the grid voltages, that we could use to create a envelope (very similar to the mask test that that lui_gough describes, except active through the entire cycle) we could compare (instantaneously) against the incoming readings, giving us a go/nogo decision on the incoming signal.  If the grid dipped (brown out), we would fire up the inverter to support the grid voltages.  The cool part of this system is that the power needed to support the grid through a brown out came from a massive superconducting magnet.  We could stand in from the grid and support a load of 1.2MW for about a minute.   Btw, the client for this system was an outfit in Madison, WI.

                         

                        This was task required quite a bit of computing power (and custom electronics), so it is not too likely that you would want to try this at home, although I guess most PC and such today could likely do as much as the floating point DSP (TI) that we were using back then.

                         

                        Good luck with you search with glitches!

                         

                        Gene

                        2 of 2 people found this helpful
                        • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                          jw0752

                          The power company just stopped by to tell me that the neighbors have started to also complain and that they think the neighborhood transformer is starting to fail. Looks like we get a new transformer on Monday. Hopefully this will solve the problem.

                           

                          John

                          • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                            shabaz

                            Hi John,

                             

                            Interesting problem, I hope it gets resolved for you soon.

                             

                            I asked a family friend, and he pretty much echoed some of the other comments here, such as it could be a neutral feeding issue if it's not grounded well, may need checking of tightness of connections, old fuseholders (if there's no tension in the spring contacts then it can arc) or if you're by heavy machinery or an industrial estate, heavy loads switching.

                            A 10% voltage drop doesn't sound unreasonable perhaps? The UK tolerance is quite large (-5% to +10%).

                             

                            Anyway your dilemma got me thinking how to monitor it using household tools (for engineers!), and I was thinking one approach could be to have a chain of series resistors to drop the mains voltage, followed by a large ferrite transformer. That could potentially be flat enough over a low frequency region of interest. And it would be safe, since it's fully isolated. And then attach a sound recorder or PC or any custom circuit. Some handheld recorders are quite low-cost and even timestamp., and create a .wav file that can be then post-processed.

                            However, I didn't have any suitable ferrite to try it out.. I just now tried a type 43 toroid since that was the largest I had, and wound about 100 turns on the primary and half of that on the secondary, but although it was really flat from about 5 kHz to beyond 1MHz, unfortunately it then tailed off a lot all the way down to 60 Hz. It would require some experimenting with different materials (hard to do here ferrites are more difficult to obtain in the UK), but I guess that's not possible in a useful time anyway, if the electricity company will install their recorder tomorrow. Anyway it will be great to find out how it goes, and what they identify.

                            3 of 3 people found this helpful
                              • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                                ipv1

                                A little late to the party but my solution would be a similar transformer isolation but using an ADC to capture the value after a rectifier. Running an ESP32 with a DCT and monitoring for changes in frequency peaks does the job nicely. Send alerts over MQTT to your favourite Service, Webapp or RPI or even another ESP8266/esp32 would display the data on a cheap I2C LCD.

                                 

                                Easily doable over a weekend though some here would be able to do it over the night.

                                 

                                Just my two cents worth.

                                3 of 3 people found this helpful
                              • Re: Suggestions Needed for Monitoring Line Voltage Glitches
                                kmikemoo

                                jw0752  Thanks for sharing this.  I'm always intrigued by the odd problem and its solution.  AND... you got it addressed before anything went catastrophic.  Murphy has been thwarted.  The good guy wins.  I love a happy ending.

                                Of course, in lui_gough's story, the Death Star actually explodes.  Let's hope for a quite weekend for you.

                                1 of 1 people found this helpful