[RE-wrenches] Smart grid grid-connected compatibility
Kent Osterberg
kent at coveoregon.com
Sun Jul 8 17:40:09 PDT 2012
Chris,
SCRs are capable of creating voltage spikes that cause noise well into
the radio frequencies. But with TWACS there is an inductor in series
with the SCR that is tuned such that the pulse caused when it fires is
0.5 ms to 1.0 ms wide with very little high frequency content. Because
the frequency content is very low, it difficult to filter out. Ferrite
toroids are of no help and large capacitors will prevent the utility
from reading the meter too. The pulse location is near the zero crossing
so it makes for a dirty looking waveform for about 8 seconds while the
meter is sending data. Never-the-less, it's actually easy to make a
reliable frequency measurement by shifting the measurement threshold off
zero far enough that the TWACS signal doesn't interfere. The Enpase
folks should be able to do that with a firmware change.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
t: 541-568-4882
On 7/8/2012 4:47 PM, Chris Mason wrote:
> Kent,
> I haven't any direct experience with the smart meters tripping
> inverters, but the issue of SCRs and generators is well known. I
> suspect you understand the problem, but to recap it, the problem
> revolves around the way SCRs make a sine wave.
> A motor driven generator controls the alternator output by increasing
> or decreasing the DC excitation level. It does that by sensing the
> "zero crossing", or point in the sine wave at which the voltage is
> zero. This happens 120 times a second on a 60Hz system.
> When the source of the electricity is electronic, the waveform will
> sometimes be messy around the zero crossing. That gives the voltage
> control circuit problems to detect the zero crossing We see this a lot
> when trying to drive a UPS from a generator, it can drive the
> generator crazy.
>
> I suspect your problem is the same. The SCR in the meter disturbs the
> waveform and the inverter thinks it is a faulty waveform.
> I would try a low pass filter between the meter and the inverter. A
> properly sized capacitor ought to remove any noise above 60hz and
> present a clean waveform to the inverter.
>
>
> On Sun, Jul 8, 2012 at 7:06 PM, Kent Osterberg <kent at coveoregon.com
> <mailto:kent at coveoregon.com>> wrote:
>
> Wrenches,
>
> There weren't very many replies to my question about
> grid-connected inverter compatibility with utility remote meter
> reading systems so I'll explain my recent experience with hope
> that this information may be of assistance sometime.
>
> Last fall I installed an Ephase system for a customer. Soon after
> it was on line he complained that the inverters were dropping off
> line frequently. Since we had a lot of cloudy weather in northeast
> Oregon all winter, it wasn't easy to see what was going on. In the
> spring we had some clear days and noticed that the inverters were
> dropping off line several times a day at exactly the same time
> every day. It didn't take very long for our suspicion to turn to
> the utilities new remote meter reading equipment. Because our
> weather has been so cloudy it took a while to find clear days
> where the utility could provide assistance. But with their help by
> reading the meter on demand and temporarily disabling the meter
> communications we were able to finally prove the remote meter
> reading system is tripping the inverters offline for five minutes
> every time the meter sends a data packet.
>
> Recently the remote meter reading system has expanded to more
> areas so we have now observed this problem with both Enphase M190
> and M215 inverters. The system we've observed that is in town is
> seeing many more dropouts, so we think every kWh meter on the same
> service transformer and maybe some beyond it are causing trouble too.
>
> The remote meter reading equipment is made by Aclara and uses
> their TWACS technology. This isn't new technology and with more
> remote meter reading systems going in all the time there will be
> more occurrences of incompatibility. Certainly more between
> Enphase and TWACS. And possibly more between other inverters and
> other communications systems.
>
> At present I'm really dissatisfied with Enphase's support on this
> issue. All they've done is point out that only a few systems have
> been affected and put us in the position of telling customers that
> they'll just have to live with the lost production time. Until
> Enphase comes up with a fix, I won't install any more Enphase
> inverters.
>
> --
> Kent Osterberg
> Blue Mountain Solar, Inc.
> www.bluemountainsolar.com <http://www.bluemountainsolar.com>
> t: 541-568-4882 <tel:541-568-4882>
>
> _______________________________________________
> List sponsored by Home Power magazine
>
> List Address: RE-wrenches at lists.re-wrenches.org
> <mailto:RE-wrenches at lists.re-wrenches.org>
>
> Options & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> List-Archive:
> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
> <http://www.re-wrenches.org/etiquette.htm>
>
> Check out participant bios:
> www.members.re-wrenches.org <http://www.members.re-wrenches.org>
>
>
>
>
> --
> Chris Mason
> President, Comet Systems Ltd
> www.cometenergysystems.com <http://www.cometenergysystems.com>
> Cell: 264.235.5670
> Skype: netconcepts
>
>
>
> _______________________________________________
> List sponsored by Home Power magazine
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Options & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
>
> Check out participant bios:
> www.members.re-wrenches.org
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20120708/bb1d211c/attachment-0003.html>
More information about the RE-wrenches
mailing list