[RE-wrenches] Fault Current

[Chris Mason]

The Available short-circuit current (SCA) of utility transformer is in the
range of 100,000+  Amps. I still don't see a single phase solar
installation being a large part of that so I doubt that is the issue.
I (partially) understand the issue of reverse current detection in
paralleled utility feeders, but it would require a detailed examination of
the utility system by an a HV experienced Electrical PE to determine the
possible implications of your solar system on that protective equipment. It
would probably be money well spent to engage such an engineer before buying
a three phase feed. Usually any reverse detection is on the three phase
lines anyway.


On Thu, Mar 27, 2014 at 4:15 PM, Dave Click <daveclick at fsec.ucf.edu> wrote:

>  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<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>
> 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] *On Behalf Of *Dave Click
> *Sent:* Thursday, March 27, 2014 1:29 PM
> *To:* 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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-- 
Chris Mason
President, Comet Systems Ltd
www.cometenergysystems.com
Cell: 264.235.5670
Skype: netconcepts
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