[time-nuts] Logging the grid frequency....
shalimr9 at gmail.com
Sun Feb 24 10:48:11 EST 2013
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.
Sent from my Droid Razr 4G LTE wireless tracker.
From: David <davidwhess at gmail.com>
To: Discussion of precise time and frequency measurement <time-nuts at 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 <nerd at verizon.net>
>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.
>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.
>> Sent from my Droid Razr 4G LTE wireless tracker.
>> -----Original Message-----
>> From: Gabs Ricalde <gsricalde at gmail.com>
>> To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>> Sent: Fri, 22 Feb 2013 9:01 PM
>> Subject: Re: [time-nuts] Logging the grid frequency....
>> 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.
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