[RE-wrenches] Surge arrestors on strings
bob at midnitesolar.com
bob at midnitesolar.com
Wed Oct 10 13:05:49 EDT 2018
The SPD-600 is evidently the one to use on the SMA TL inverters.
In older grounded PV systems, if the negative or positive is grounded
directly to ground, then you could get by without
an SPD connected to that grounded conductor because it is, well, already
grounded and that line will rise in voltage along with
the ground voltage from the strike. However, if this grounded PV
conductor is connected through one of the r ground fault interrupters
that has a 1/2 amp or slightly higher ground bonding connection, (not
permanently bonded), like the Classic or MPPT-60 and
some other controllers with internal GFIs then I would think that a
separate SPD line be used for positive and negative PV lines on that array.
We don't want that ground bond to open on that line and risk internal
arcing in the equipment.
As for arc faults, SPDs are a passive type protector and should not make
any noise that might be interpreted by the sensor as arcing.
Lightning itself may very well be interpreted as an arc. I think that
the Bird-House system which has a switcher supply up-stairs
in the Bird-Next might have been an arc fault culprit for some TL
inverters. Sometimes it is hard for a AF detector to tell the
difference. Hopefully they are better now.
"I have clients who have covered the SPD's in tape to keep the light
from attracting small flying insects to the electronics area. "
I hear you there, Dave ! We are working on being able to coordinate the
lightning strike with the insects so that the SPD also
works as a bug zapper ! :) :-)
Just kidding...
boB
On 10/9/2018 3:10 PM, Dave Angelini Offgrid Solar wrote:
>
> We have been using Midnite SPD's since they came out. The one
> suggestion I have is the light is too intense. I have clients who have
> covered the SPD's in tape to keep the light from attracting small
> flying insects to the electronics area. Some places just have too many
> bugs :( The blue seems to bring them. I saw an inverter fan filter
> that was an 1/8 of an inch thick with gnats.
>
> Fly paper will help but the battery circuit and AC panel SPD's need
> some help here.
>
> *Dave Angelini Offgrid Solar "we go where powerlines don't"
> http://members.sti.net/offgridsolar/ e-mail offgridsolar at sti.net
> <mailto:offgridsolar at sti.net> text 209 813 0060*
>
" 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 Tue, 09 Oct 2018 17:02:32 -0400, Drake
> <drake.chamberlin at redwoodalliance.org> 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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>> --
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>> Christopher Warfel, PE
>> ENTECH Engineering, Inc.
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