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 <k...@coveoregon.com
<mailto:k...@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
<k...@coveoregon.com <mailto:k...@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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