[RE-wrenches] Smart grid grid-connected compatibility

Mon Jul 9 11:59:51 PDT 2012

Kent,
Typically the manufacturer is not to anxious to change the parameters
outside those set out in the UL 1742 standard. However, for this, I suspect
that is what is needed. They will probably need you to sign a waiver first,
which is what we had to do with SMA.

Do you have a scope to look at the waveform of the signal? With a scope and
a few capacitors, you could see what it took to clean up the waveform
reaching the inverters.

On Mon, Jul 9, 2012 at 10:46 AM, Kent Osterberg <kent at coveoregon.com> wrote:

>  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>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
>> 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>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
>>> t: 541-568-4882
>>>
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>>
>>
>>  --
>> Chris Mason
>> President, Comet Systems Ltd
>> www.cometenergysystems.com
>> Cell: 264.235.5670
>> Skype: netconcepts
>>
>>
>>
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>
>
>  --
> Chris Mason
> President, Comet Systems Ltd
> www.cometenergysystems.com
>  Cell: 264.235.5670
> Skype: netconcepts
>
>
>
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-- 
Chris Mason
President, Comet Systems Ltd
www.cometenergysystems.com
Cell: 264.235.5670
Skype: netconcepts
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