[RE-wrenches] Smart grid grid-connected compatibility
Kent Osterberg
kent at coveoregon.com
Mon Jul 9 07:46:38 PDT 2012
Chris,
Enphase has the ability to remotely adjust the voltage and frequency
operating windows. They have adjusted them as far as they can, or will.
I have some SMA Sunny Boy inverters in locations that recently have
TWACS remote reading systems installed. Most don't have remote data
monitoring. At least one does but the TWACS meter was just installed
there last week. I'll know more about that one after I have a chance to
confirm that the TWACS system has been activated.
I agree with you that the TWACS signal shouldn't be sent to the
customer, but it is generated in the utility meter so it's going to both
the customer and the substation. Also, the TWACS signal can be adjusted
if necessary to generate a bigger signal. I guess that would be their
first step in handling a site with a large capacitive load.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
t: 541-568-4882
On 7/9/2012 6:05 AM, Chris Mason wrote:
> Yes, I expect they can. The greater issue is going to be whether the
> other inverters are going to react also. Have you had any experience
> with other inverters in this scenario?
> I don't undertand why the meter manufacturer can't ensure the burst is
> filtered out of the load connections. They have to know it can mess up
> devices behind the meter.
> Large capacitors on the load side should not stop the utility reading
> the meter. If it does, any consumer with a large UPS will kill it.
>
> In the SMA firmware, there is the ability to adjust some of the
> parameters such as the Vmax to adjust the system to local variations,
> which we often have to do here. Can you adjust the size of the
> frequency window in the Enphase system settings? If you can make the
> inverters look at a longer window of cycles that may eliminate the
> problem.
>
> Chris
>
> On Sun, Jul 8, 2012 at 8:40 PM, Kent Osterberg <kent at coveoregon.com
> <mailto:kent at coveoregon.com>> wrote:
>
> 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 <http://www.bluemountainsolar.com>
> t:541-568-4882 <tel: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>
>>
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>> --
>> Chris Mason
>> President, Comet Systems Ltd
>> www.cometenergysystems.com <http://www.cometenergysystems.com>
>> Cell: 264.235.5670 <tel:264.235.5670>
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> --
> Chris Mason
> President, Comet Systems Ltd
> www.cometenergysystems.com <http://www.cometenergysystems.com>
> Cell: 264.235.5670
> Skype: netconcepts
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