For an inverter with two MPPT inputs, you will need to treat the
negatives and positive lines separate unless
the manufacturer says something else. That means one SPD per array
unfortunately. Negative and positive connect
to separate leads of the SPD and then ground in the middle. As both
positive and negative PV lines rise together
relative to ground, the SPD is supposed to clamp that rise to below the
equipment's hi-pot voltage that they test
to at the factory. (i.e. common mode voltage rise) All wires except for
ground (chassis) of the equipment are tied
together and the hi-pot machine (sort of like a Megger ?) applies the
high voltage between all those wires on one
side and ground on the other to make sure the insulation doesn't break
down inside the equipment.
This hi-pot test goes for AC utility input/output connections and DC
from the PV input side.
The SPD has to clamp plus and minus and AC inputs to a lower voltage
than this hipot rating but higher voltage
than lines will see differentially in voltage. Remember that in a
3-wire SPD, there is two sets of MOVs in series and
the center is tied to ground. If one MOV starts conducting at say, 500
volts DC then you can apply up to 1000
volts between the hot leads. Each plus and negative line can rise up
to 500 volts from the lightning before they
start to clamp. The bigger the lightning strikes effect, the more
current will be applied to the MOVs though and
the clamp voltage will rise somewhat. That's why the SPD arrestor
voltage should be well below the hi-pot voltage,
whatever that is... Hi-pot voltages are quite a bit higher than the
operating voltage. For example, All Classic CC's
are tested to 2270 volts DC from hot lines to ground. It's something
like double the operating voltage plus 1000V
and multiply by 1.414 for DC rating..... I'm going off memory so don't
quote me on that but something like that.
I think that Ray has the right idea about short connections like from
the local generator. Battery also.
Just apply SPDs to anything that goes outside like an antenna.
boB
On 10/9/2018 8:26 AM, cwarfel wrote:
I think something on the order of 90+% lightning strikes come from the
utility feed, not the dc side. That has to be ignored if in a high
strike area orgrid isolated.
On 10/8/2018 10:37 PM, Ray wrote:
I believe you can use the SPD 300 AC on 2 strings, if PV neg is
grounded. You would connect the green to ground (or PV neg) and then
connect the red to one string pos, and connect the black to the other
string pos. This would be limited to 300 v also. I haven't tried
that exact configuration, but I have used the 300 AC to protect both
the AC in and AC out on 120 vac inverters. I also believe you can
use a 600 DC version, and wire as I mentioned, but the LEDs won't
light. If you are using ungrounded inverters, then I think you would
need an SPD for each string in order to protect both the pos and neg
of each string, like you've been doing.
Maybe someone from Midnite can clarify this.
As far as it being worth it, I haven't had lightning related damage
since I started using the Midnite SPDs, and I used to have system
damage every year. If you are not in lightning country, or the
install is in a low spot with less likelihood of taking a hit, you
might be able to skimp. But for some of these off grid ridge top
installs, I consider it a must. Some times I don't install one on the
gen circuit, if its really close.
Ray Walters
Remote Solar
303 505-8760
On 10/8/18 4:03 PM, Drake wrote:
Hello Wrenches,
Do you use surge arrestors with multi MPPT input string inverters?
Do you put a separate arrestor on each MPPT input? I find it sort of
pricey using a Midnite Solar arrestor on each string, but have been
doing that. Is there a less expensive approach that is effective?
I believe the Midnite units are the best. Are they worth the expense?
Thank you,
Drake
Drake Chamberlin
/Athens Electric LLC
OH License 44810
CO License 3773
NABCEP Certified Solar PV
740-448-7328
/http://athens-electric.com/
_______________________________________________
List sponsored by Redwood Alliance
List Address:[email protected]
Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive:http://www.mail-archive.com/[email protected]/maillist.html
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out or update participant bios:
www.members.re-wrenches.org
_______________________________________________
List sponsored by Redwood Alliance
List Address:[email protected]
Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive:http://www.mail-archive.com/[email protected]/maillist.html
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out or update participant bios:
www.members.re-wrenches.org
--
Christopher Warfel, PE
ENTECH Engineering, Inc.
PO Box 871, Block Island, RI 02807
(401)466-8978
EEI logo <http://entech-engineering.com>
_______________________________________________
List sponsored by Redwood Alliance
List Address: [email protected]
Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive:
http://www.mail-archive.com/[email protected]/maillist.html
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out or update participant bios:
www.members.re-wrenches.org
_______________________________________________
List sponsored by Redwood Alliance
List Address: [email protected]
Change listserver email address & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive:
http://www.mail-archive.com/[email protected]/maillist.html
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out or update participant bios:
www.members.re-wrenches.org
