[RE-wrenches] Fault Current

[Dave Click]

The "explanation" you quote doesn't make any sense to me. If the 
engineer is concerned about fault current, the primary source is going 
to be through the utility transformer, and it will be on the order of 
5,000 - 10,000A depending on the transformer's impedance. The fault 
current contribution from the inverters will be much less than that (an 
SB8000 fault current is all of 61.7A) and it will last for a much 
shorter duration. Be nice-- some engineers think by default that all 
generation acts like a rotating machine, which can contribute quite a 
bit of fault current. Not so for PV, so hopefully this engineer will see 
the light with a bit of help from you.

A few questions for your engineer then:
1) These inverters will be exporting power, not drawing it; why are the 
inverters not considered a negative load in this installation? [I assume 
you're not installing batteries]
2) What is the "500A fault current limit" that was taken into account in 
the site design? The service size is ___A.

A 167kVA transformer at 240V has a rated current of about 700A, which is 
another reason why the "500A fault current" doesn't make sense.

DKC



On 2014/3/27, 15:28, Karl Jaeger wrote:
>
> Nathan,
>
> The only explanation the electrical distributor provided is seen 
> below. They are really skirting a thorough explanation...
>
> /The distributor engineer does not view the inverters as a negative 
> load, and states they will exceed the 500A fault current limit the 
> site is designed for./
>
> Thanks,
>
> Karl
>
> *From:*re-wrenches-bounces at lists.re-wrenches.org 
> [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of 
> *Nathan Charles
> *Sent:* Thursday, March 27, 2014 2:03 PM
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] Fault Current
>
> Karl,
>
> Can you give us some more details on their concerns?  I've done some 
> very large single phase ag installs and the only time I've had issues 
> is when we exceed the 80% of minimum load on the medium voltage feeder.
>
> Best,
>
> -N
>
> On Thu, Mar 27, 2014 at 2:51 PM, Karl Jaeger 
> <kjaeger at lightwavesolar.com <mailto:kjaeger at lightwavesolar.com>> wrote:
>
> Dave,
>
> We are about as rural as we can get here.... farm land. Very good 
> document, nonetheless.
>
> Karl
>
> *From:*re-wrenches-bounces at lists.re-wrenches.org 
> <mailto:re-wrenches-bounces at lists.re-wrenches.org> 
> [mailto:re-wrenches-bounces at lists.re-wrenches.org 
> <mailto:re-wrenches-bounces at lists.re-wrenches.org>] *On Behalf Of 
> *Dave Click
> *Sent:* Thursday, March 27, 2014 1:29 PM
> *To:* re-wrenches at lists.re-wrenches.org 
> <mailto:re-wrenches at lists.re-wrenches.org>
> *Subject:* Re: [RE-wrenches] Fault Current
>
> Karl, you're interconnecting into a spot/area network, right? It's a 
> real concern; some solutions and background on the issue here:
> http://www.nrel.gov/docs/fy09osti/45061.pdf
>
> DKC
>
> On 2014/3/27, 14:05, Karl Jaeger wrote:
>
>     Esteemed Wrenches,
>
>     We've recently run into an issue with a local distributor citing
>     network fault current on a split-phase service as a reason to
>     prevent interconnection of our customer's solar array. They've
>     given us the options of reducing our system size from 36.5kW-DC to
>     15kW-DC, or having the customer upgrade to 3-phase at a soft price
>     of $20-30K. We're looking at 32kW of inverters on a 167kVA
>     transformer.
>
>     Does anyone have experience on circumventing the issue of network
>     fault current? Any experience with Fault Current Limiters?
>
>     Much appreciated,
>
>     *Karl Jaeger*
>
>     *Design/Build Engineer*
>
>     *LightWave Solar Electric LLC*
>
>
>
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> -- 
>
> Nathan Charles
>
> Engineer
>
> NABCEP Certified PV Installation Professional #042013-20
>
> Paradise Energy Solutions
>
> (717) 283-2021 direct
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