Kent,
Life should be so easy as to be able just to tweak the firmware and
make things all better.
The moment a change is made to the firmware where the zero-crossing
detection is involved .. UL safety standards mandate the inverters must
undergo re-certification to the applicable aspects of UL1741. In this case,
it would mean retesting to IEEE 1547 (anti-islanding) to prove the change
in the firmware hasn't affected any aspect of the inverter disconnect under
abnormal line conditions -- and possibly other retesting as well.
Such a firmware change may also render all modified units incompatible
with the manufacturer's communication schemes presently in place.
Not to defend a competitor .. but likely every grid-tie inverter maker would
be in the same situation here if the TWACS system causes inverters to see
what's perceived as an abnormal line condition, and they cease producing
power as a result.
Likely an engineering solution can be found, but it would extend beyond
what even most advanced installers would be able to derive (though there
may be a rare few out there who could solve this on their own...).
This now becomes a situation where our industry needs to sit down
with the monitoring industry to create a workable answer.
Dan
--- On Sun, 7/8/12, Kent Osterberg <k...@coveoregon.com> wrote:
From: Kent Osterberg <k...@coveoregon.com>
Subject: Re: [RE-wrenches] Smart grid grid-connected compatibility
To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org>
Date: Sunday, July 8, 2012, 7:40 PM
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 <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
t: 541-568-4882
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches@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
