[RE-wrenches] Smart grid grid-connected compatibility

Mon Jul 9 06:05:05 PDT 2012

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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