[RE-wrenches] Troubleshooting Stumper - Resolved

Wed Sep 28 12:28:58 PDT 2016

I wanted to send a quick email and thank everyone for their suggestions
and help.  Dan at Exeltech ultimately spent some time on the phone with me
and his technical acumen was much appreciated - albeit not completely
understood.

We tried just about every solution suggested without any luck.  The only
solution that was successful (beyond wires in free air) was running a
second set of conduit from the roof to inverter and grouping the positives
in one conduit and negatives in the other conduit (a string in each
conduit resulted in same inverter failure mode as before).

Dan's explanation:

'This now has all the symptoms of a resonance condition in the inverter
front end .. which points to a design characteristic in the inverter...

...[The solution] hasn't eliminated the source of the issue .. but has
simply prevented the circumstances that trigger it from being present.

You'll want to get back to the inverter manufacturer and suggest to their
engineers look for an unwanted resonance / oscillation condition at the DC
input.  Despite your having turned off the MPPT function in the inverter,
and the condition still existed .. this hasn't eliminated the inverter as
the culprit.  For example, there is still the consideration of the ramp
rate, which in of itself limits the
slope on the power increase.'

I have installed a lot of Solectria 3800s without seeing this before,
including identical systems.  It sounds like just an unfortunate
circumstance that hopefully we will never encounter again.

Thanks again,

Matt

On Wed, September 7, 2016 11:33 pm, Matthew Sirum wrote:
> Greetings Matt,
>
>
> I like the troubleshooting thoughts others have given.  If all else
> leaves you with the issue persisting I would also consider checking for
> current on the grounding system and on bonded conductive materials/items
> on the property.  It may be helpful to see if there is any current on the
> Equipment Grounding Conductors, Grounding Electrode
> Conductor(s), metallic conduits & raceways, PV mounting system, and
> etc.  If the inverter in this system has an AC Neutral connection intended
> only for instrumentation and L1 & L2 voltage reference it would be
> interesting to measure the actual current on it.  It is good you have a
> similar system installed next door, you may need to compare test
> measurements and readings.  If you run out of tests and troubleshooting
> ideas it may be helpful to open (turn off) all the circuits in the
> house/on the service and see how the PV system performs while being the
> only item connected to the service.
>
> The "smart" modules/optimizers may be making system troubleshooting
> more challenging.  I wonder what Trina & Tigo has/can offer(ed) to assist
> with troubleshooting?... and if there is an approved/safe megger
> (insulation resistance) test for these modules?  This is an
> interesting case.  I'll be continuing to follow the thread.  I hope we can
> all learn something from this.
>
> Best regards,
>
>
> ----MATT
>
>
> Matthew Sirum
> P.O. Box 1227
> Greenfield, MA 01302-1227  USA
> phone: +1.413.773.0611
> email: MatthewSirum at gmail.com
>
>
> Date: Wed, 7 Sep 2016 17:45:32 -0400
> From: "Matt Partymiller" <matt at solar-energy-solutions.com>
> To: re-wrenches at lists.re-wrenches.org
> Subject: [RE-wrenches] Troubleshooting Stumper - Homerun Interference
> in Conduit/Inverter Turning Off/On Rapidly
>
> Wrenches,
>
>
> One of our systems is having an issue I have not encountered before
> where the inverter switches between nighttime mode and interconnection
> every few seconds.  I am hoping for some technical wisdom from the
> community.
>
> We have an array of 20 TrinaSmart modules in two strings of 10.  The
> array is connected to a Solectria 3.8 kW inverter.  The conduit run is
> simple, all four homerun wires (#10 PVwire) in 1" EMT down to the
> proximity of the Solectria inverter where the conduit switches to 1" LFMC
> before entering the inverter.  The run is about 20', straight down the
> side of the wall before hitting the inverter.  A 600V jacketed
> communications wire was also in the conduit but has since been removed and
> run separately.
>
> Our inverter is starting up, running for a few seconds, giving a low
> voltage error, briefly showing nighttime mode, then going into startup mode
> again.  Solectria was gracious enough to send us a new inverter but we
> have the exact same issue.  They tell us their error codes (266, 274)
> indicate 0 volts.  The transition between low voltage error and startup is
> almost instant.  Basically we have 20 seconds of start up, 5 seconds of
> run, 5 seconds of error then repeat.  This is not a grid problem, the
> identical system next door works fine.
>
> In the process of troubleshooting, our technician pulled all four homerun
>  wires out of our conduit and meggered them.  They all tested fine so he
> connected to the inverter.  The inverter worked fine.  The technician
> verified grounding of the array and conduit, pulled new homeruns back
> through the conduit, and reconnected to the inverter.  He had the same
> error as before.
>
> He connected each string separately to the inverter by removing the
> string fuses.  Either string will operate fine independently.  With string
> one in conduit and either homerun of string two in conduit (but not both)
> the inverter operates fine.  With string two in conduit but string one
> outside of conduit, the inverter does not operate.
>
> I was certain the error had something to do with homerun roof wiring so I
>  went out with the technician and removed and checked pretty much every
> module.  Everything appears fine, all connections solid, all homeruns have
> been remade at least once at this point.  Now I am stumped and lack the
> technical knowledge to diagnose the problem.  I would be extremely
> grateful if an esteemed wrench can provide technical support/advice.
>
> Thanks,
>
>
> Matt
>
>
> Matthew Partymiller
> Solar Energy Solutions LLC
> (877) 312-7456
> matt at solar-energy-solutions.com
> _______________________________________________
> List sponsored by Redwood Alliance
>
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
>
> Change listserver email address & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
>
> List-Archive:
> http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.ht
> ml
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
>
> Check out or update participant bios:
> www.members.re-wrenches.org
>
>

Matthew Partymiller
Solar Energy Solutions LLC
(877) 312-7456
matt at solar-energy-solutions.com