Re: [time-nuts] Logging the grid frequency....
We had a problem some time ago with a large power system where I work. It would shut down every day around 7:00AM. It turns out that is when the power company switches large capacitors in to correct the poor power factor caused by inductive loads that are turned on when businesses start the work day. It took a while but after we convinced ourselves it had to be a line transient, we ended recording the transient with a Dranetz. It was only once a day, so it would probably not have affected ADEV significantly, but it sure caused havoc with our equipment. It caused ringing that would definitely have affected a zero crossing detector. Didier Sent from my Droid Razr 4G LTE wireless tracker. -Original Message- From: David davidwh...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sat, 23 Feb 2013 4:14 PM Subject: Re: [time-nuts] Logging the grid frequency That was on my mind when I suggested a sampling phase comparator with the sampling time adjusted for noise rejection. Of course since I have been doing a lot of research recently on sampler design, every problem looks like a nail. :) Thyristor commutation into a reactive load can be nasty but I have heard horror stories about inverters as well. On Sat, 23 Feb 2013 14:05:36 -0500, Peter Gottlieb n...@verizon.net wrote: Some grid connected inverters have a LOT of noise around the zero crossings, so much so that certain digital power meters won't function as they can't get frequency lock. I've seen this on the large Parker units as well as the low bid units out of China. So if you have solar or wind farm alternative energy projects nearby you may indeed see excessive noise. Excess noise and high order harmonics from such inverters has on occasion caused capacitive line filters on nearby equipment to overheat and catch fire. Peter On 2/23/2013 7:53 AM, Didier Juges wrote: I am curious how this compares with the zero crossing method. I suppose it should work much better because this method will not be so sensitive to noise around the zero crossings. It will use the entire waveform. Didier Sent from my Droid Razr 4G LTE wireless tracker. -Original Message- From: Gabs Ricalde gsrica...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Fri, 22 Feb 2013 9:01 PM Subject: Re: [time-nuts] Logging the grid frequency Hello, I also don't have a Picotest or similar equipment but I've done similar things by using the line input of a soundcard. Multiply the recorded signal with a 60 Hz quadrature oscillator, apply a low pass filter then do some analysis on the resulting phasor. The stability of the sound card oscillator should be enough for this purpose. You can measure the frequency difference w.r.t. the 60 Hz oscillator by taking the slope of the phasor angle (be careful with phase wraparounds) and you can do this as often as you like. I'm curious how this compares with the zero crossing method. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Logging the grid frequency....
On 02/23/13 12:01 PM, John wrote: All, If you want a reason for logging the mains frequency, see the following link to a news item which appeared on a BBC news program a few weeks ago here in the UK. http://www.bbc.co.uk/news/science-environment-20629671 There was also a full program about it which you can listen to at the following link http://www.bbc.co.uk/programmes/b01p7bxw John G3UUT Interesting. I never realized the UK national grid was just one grid, all running at the one frequency. I wonder if there are small variations in frequency at a local level due to all these wind-turbines that seem to be cropping up everywhere? I doubt they will generate a voltage at exactly the same frequency the voltage is coming into them, especially as it is not a constant. I personally object to funding these things so others can make a huge profit from them. Perhaps I can argue they are a threat to national security! Dave -- Dr. David Kirkby Ph.D C.Eng MIET ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Logging the grid frequency....
By their nature, these distributed generation devices operate in current injection mode. That is, they are synchronized to the line and inject enough current at whatever voltage the line is at (subject to IEEE 1547 provisions, e.g., -12% to +10% of nominal) to transfer the power they need to. So yes, they generate their power at the exact frequency the line is at. They are all four-quadrant devices and can also generate quadrature (imaginary) power as well so can correct for power factor problems. All the decent sized inverters I have seen are tightly phase locked to the line. Now here's a fun thing to think about: due to safety concerns the power company does not want any of these things to generate power if a line goes down. They call this a power island. So every inverter must have detection for this condition. It's trivial to detect if the load on the island is different than the inverter output - the voltage will immediately go out of bounds - but not so easy to detect if the island load matches the inverter output. so, what to do? One thing manufacturers do is to wiggle the Q (imaginary power) output and see if it shows up. If they're connected to the grid, well, they're way too small to move the overall power factor but if they're the only source, it shows right up! So many of these inverters are actually creating a small amount of phase noise onto the mains. In terms of powering things it is insignificant and of no consequence, but when you get to time-nut accuracy and measurement capabilities, I'd bet you can actually see such modulation! If you are out on a long run from the nearest substation it could even throw off your measurements as it will be non-steady and depend on insolation or local wind conditions of the source inverter. As for huge profits, well, not in that industry. Peter On 2/24/2013 11:01 AM, Dr. David Kirkby wrote: On 02/23/13 12:01 PM, John wrote: All, If you want a reason for logging the mains frequency, see the following link to a news item which appeared on a BBC news program a few weeks ago here in the UK. http://www.bbc.co.uk/news/science-environment-20629671 There was also a full program about it which you can listen to at the following link http://www.bbc.co.uk/programmes/b01p7bxw John G3UUT Interesting. I never realized the UK national grid was just one grid, all running at the one frequency. I wonder if there are small variations in frequency at a local level due to all these wind-turbines that seem to be cropping up everywhere? I doubt they will generate a voltage at exactly the same frequency the voltage is coming into them, especially as it is not a constant. I personally object to funding these things so others can make a huge profit from them. Perhaps I can argue they are a threat to national security! Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] OT: Robot Watch
Hi, I was just given an Anarobo Quartz writwatch, like this: http://www.listia.com/auction/1183485-robot-watch-with-turquoise-blue-clock Honestly, it is THE cutest trhing I've see in ages, and made of solid stainless steel. Does anybody know anything more about it? Was it a promo of some kind? Thanks, -John = ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] OT: Who needsa a Spectrum Analyzer anyways
Just use your scope Sorry about the noise but you gotta see this http://www.eevblog.com/forum/testgear/agilent-dsa-x93204a-33ghz-80gss- teardown/ CFO ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OT: Robot Watch
John, You know, it looks sort of like that robot cartoon Instructables.com uses for their logo. You might check there. 73, Todd K7TFC / Medford, Oregon, USA / CN82ni / UTC-8 QRP (CW SSB) / EmComm / SOTA / Homebrew / Design ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
