boB,
To add to Drake's wonderings, I've had a few SMA TL-40
inverters trip with an AFCI fault. Significant hassle to get onsite and
deal with it. Some with metal roofs some without, may have been
lightening in the area.
Bill
On 10/9/2018 2:02 PM, Drake wrote:
Hi boB,
I will keep putting an SPD on each string and on the AC line.
Sometimes my systems end up with a lot of blue lights hanging from a
wiring gutter!
Have you ever heard of any problems using the Midnite SPDs with Sunny
Boy TL series inverters? So far, I don't think I've had a problem,
although one TL-22, on a large metal roof, had arc fault protector trips.
Thanks,
Drake
Drake Chamberlin
/Athens Electric LLC
OH License 44810
CO License 3773
NABCEP Certified Solar PV
740-448-7328
/http://athens-electric.com/
At 01:39 PM 10/9/2018, you wrote:
Content-Type: multipart/alternative;
boundary="------------98C0DCEF93B9ECF248E0580B"
Content-Language: en-US
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 or grid 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/
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