Yes. It happened to me on a recent SB 4000US installation. SMA knows of the
problem but doesn't know the cause. It's shown up in about 20 of 4000
(that's quanty of 4000) inverters sold. SMA did not tell if its unique to
the 4000US or other models as well.
But you can get the inverter to boot up properly by changing the jumper to
pos gnd, and move the gfi fuse to the positive gnd fuseholder. Then power up
the inverter and let it run for 1/2 hour. Then shut it off and change the
jumper and fuse back to a neg gnd. Then power up and it will boot properly.
This is the recommended work around by SMA and it worked for me. BTW, I
tried the pos gnd thing for only 15 minutes the first time and it did not
work, so do 30 minutes as recommended.
Kirk Herander
Vermont Solar Engineering
802.863.1202
fax 802.863-7908
NABCEP(tm) Certified Solar PV Installer
Xantrex Certified Dealer Charter Member
NYSERDA-eligible installer
VT Solar Incentive Program Partner
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Jeff
Clearwater
Sent: Sunday, September 21, 2008 2:42 PM
To: RE-wrenches
Subject: [RE-wrenches] Getting "GFDI Open" Message When It's Not
Good Day All,
I'm getting a "GFDI Fuse Open" message on a SB3000 and the fuse is good.
What I've checked:
1) I've checked POS to GND and NEG to GND both floating and when
connected to the integral DC Disco both for continuity and voltage .
I show expected Voc on both strings and no continuity to GND nor
voltage to GND when the fuse is pulled. There appears to be no
ground faults or miswiring.
2) I've visually inspected all array wires - no pinching can be
seen. I've checked for Voltage and Continuity to GND from both the
array side and the inverter side to isolate the wires in the conduit
- no problems there either.
3) I've replaced the fuse even though it shows good with a good fuse
with no change.
4) I've cycled the SB several times - no change.
5) I've run through John B's method below twice - no change.
6) I've confirmed that the GFDI fuse is in the top position of the
two possible GFDI position - the one for negative ground.
About the only thing I forgot to do was check if the Jumper for
Negative or Positive GND was in the correct position - it dawned on
me after coming home that if somehow that got set wrong at the
factory that it would perhaps show a fault but not blow a fuse?
Could this be it? (I hope!)
Anyone experience this condition before?
Next step is to just swap out the inverter but as it's Sunday SMA
tech support is probably not open so I hesitate to do that without
their go ahead.
Thoughts?
Thanks!
Jeff C.
At 12:18 PM -0800 11/21/07, John Berdner wrote:
Subject: RE: SMA Ground Fault troubleshooting advice. [RE-wrenches]
Dave/Wrenches:
Locating ground faults in the array is fairly straight forward albeit a
little dangerous.
A DVM and some spare fuses (just in case) is all you really need.
>Be very careful when you are doing all of this because you will be
working with live wires hanging in space and PV negative is no longer
necessarily at ground potential. If the equipment grounding on the
array is not up to snuff it is also possible to see hazardous voltages
on the module frames or structure so measure everything and be really
careful. Treat everything as hot and potentially lethal until your
meter says otherwise. Remember each time you disconnect something the
>whole situation can change so measure again to be sure. Also, depending
where the ground fault is and the order in which you pull the wires out
of the inverter (or disconnect) it is possible to see double the array
Voc. This can be a very bad thing since the spacing on all components
was designed for 600 Vdc max and you could be at double that. A 960 Vdc
arc at 5 to 8 Amps is pretty ugly.
Start by opening the DC disconnect and removing the GFDI fuse in the
inverter.
Measure the array open circuit voltage form the PV plus in the dc
disconnect to the PV negative in the inverter.
Lets say it is 480 Vdc.
Now measure PV positive to ground and then the PV negative to ground.
An array without a ground fault should give you roughly equal values of
around 240 Vdc but the measurement should decay down towards zero. What
you are seeing is a discharge of the capacitive coupling between the
array and ground.
In an array with a ground fault you will measure a fixed voltage to
ground on both the PV positive and PV negative.
The sum of the PV positive to ground and PV negative to ground
measurements should equal the open circuit voltage.
The difference in this case is that the voltage will be fixed and will
not decay towards zero.
The voltages you measure actually tell you where to start looking for
the ground fault.
For example: with 12 modules in series and an open circuit voltage of
480, each module is equal to 40 Vdc.
If you measure PV positive to ground and get 0 volts then you should
see a PV negative to ground voltage of - 480 Vdc. This tell you the
ground fault is in the PV positive output conductor.
Alternatively, if you were to see PV positive to ground at 400 Vdc and
PV negative to ground at -80 Vdc this tells you the ground fault is
between the 2nd and 3rd modules "up" from the PV negative.
To figure out which string the ground fault is in, isolate each string
(remove the wires from the disconnect/inverter) and repeat the PV
positive to ground and PV negative to ground measurements. On one
string the measurement will float around and the other will give you a
fixed measurement to ground. The fault is in the string that has the
fixed measurement to ground. My suggestion is to pull both positive and
negative wires for string 1 and measure. If you are lucky you picked
the right string the first time out and you don't need to pull the
second string at all.
It is unlikely but also possible to see a ground fault in the "middle"
of a module. In this case you might see 380 Vdc from PV positive to
ground and -100 Vdc from negative to ground. This would indicate a
fault in the middle of the third module "up" from the PV negative.
Normally this means the module itself has a ground fault due to a nick
in the backskin, fault in the edge seal, etc. You can verify this by
isolating (unplugging) the suspect module then measuring PV positive to
ground and PV negative to ground for that isolated module.
Lastly, In some very rare case the ground fault will actually be in the
string combiner, dc disconnect, or (heaven forbid) in the inverter
itself. You can verify this if the array voltage measurements show a
ground fault when connected to the combiner/disconnect/inverter and then
both strings float when measured in hanging in free space. While
unlikely, if you find this situation reconnect the PV back up then
disconnect one thing at a time and measuring relative to PV positive and
PV negative to ground until you find where the fault is.
Best Regards,
John Berdner
[EMAIL PROTECTED] 11/21/2007 07:40:51 AM >>>
>
Wrenches,
I have a grid tied system with a SB3800U inverter being fed by 2
strings of
(12) Evergreen 180's (4.32kW). UniRack rail mounted on garage roof.
Good
installation all wiring neat and well supported. Only DC bond to ground
is
in the inverter etc. And no external monitoring equipment.
The system has been operating very well (over 5,000 kWh over 2 months
in
Northern Vermont), this is the first problem.
We are in the middle of a snowy spell and the array is covered in snow,
>but
I should be able to check out the array within a few days. According to
the
error message on the Sunny Boy the GFDI 1 amp fuse is open. The array
has
made it through lots of rain, ice and snow over the past year.
My suspicion is in the MC connector(s) themselves. We had a bad batch
of MC
cables purchased from a large distributor 12 to 18 months ago. The MC
connector would pull off the wire when tested. Of course not all of
them
where tested before they got into the field, so one could be on this
roof.
Obviously I will check connections in the combiner, the dc disconnect
etc,
could be a moisture issue. Of course it could be a squirel I guess.
Any advice on troubleshooting this ground fault would be appreciated.
Safety
wise do we need to cover the array with a dark tarp?
Dave
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Village Power Design
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