[RE-wrenches] Utility transformer limitations
Christopher Warfel
cwarfel at entech-engineering.com
Mon Dec 26 05:17:15 PST 2022
Wouldn't the microinverters shut down if the voltage rose? They
wouldn't be able to raise voltage about PUC/DPU limits I would think.
They would shut down on high voltage. I am saying this because of an
experience this fall where our infamous Block Island Power Company
raised the taps on a local xfmr due to their "secret heat pump program"
that was dragging down local voltage. They claimed solar was a burden,
but were quiet on the load building program they embarked upon without
any disclosure. When the cooling loads disappeared, the voltage went
above our grid tied systems set points and they shut down. We told the
utility they had a high voltage problem and they adjusted the taps. Of
course they did not acknowledge or thank us. It seems our little coop
which is now head from a guy from the Vermont Electric Coop is taking an
old utility approach instead of cooperation, integration and
maximization of performance and economics.
I'd think you be able to ask how the supply can raise the voltage when
there is so much diversified load on the same device. Electricians
have to do a diversity calculation, and I know a utility has to conduct
them as part of these studies. Worse case of no load and all generation
is such a low probability that to design for it, when/if it occurred, is
not a danger and of no material consequence makes little sense. But,
we've been dealing with that ever since this person arrived in our neck
of the woods.
Chris Warfel
On 12/25/2022 5:21 PM, Garrison via RE-wrenches wrote:
> Hi William,
>
> One possible path forward would be to ask the utility co what AC
> inverter capacity would be allowed. Maybe the solution would be to
> unplug a micro or two if you are just over the limit. Even better,
> maybe they would allow you set an export limit on the micros you have
> installed.
>
> I had a recent situation where a 40kW DC system had exceeded a utility
> transformer by only 2kW AC, so a simple redesign avoided an $8k
> invoice from the utility. The utility was not transparent about this
> option at first and only made it clear after some persistence.
>
> Good luck,
>
> Garrison Riegel
> Celestar Solar
>
>> On Dec 25, 2022, at 3:14 PM, Darryl Thayer via RE-wrenches
>> <re-wrenches at lists.re-wrenches.org> wrote:
>>
>>
>> It is common practice for the utility to overload the transformer a
>> lot for the potential load. They expect no one will use their
>> service at maximum, furthermore, they expect non coincidence of
>> loads. Look at the transformer most have a label as to the kW or the
>> unit, and the utility should give you that number along with the
>> impedance. Note I have had area engineers not understand that solar
>> reduces the load on the transformer. They have two concerns, you
>> will overload and you will raise the voltage to other customers.
>> Overload is ridiculous; the transformer must be at least 20 kW if a
>> 15 kW concern is valid. However, raising the voltage is not. If all
>> the customers shut off their power, the voltage would rise to the
>> inverter limit,and/or feed current back on the distribution line
>> raising up/downstream customers voltage. I have had this problem, on
>> three occasions discussions with the utility upper engineering, not
>> local engineer, i prevailed, one case I did not. In one cast
>> utility allowed connection and put a voltage monitor on secondary
>> voltage, then later allowed permanent connection.. Good luck
>>
>> On Sun, Dec 25, 2022 at 1:16 PM William Miller via RE-wrenches
>> <re-wrenches at lists.re-wrenches.org> wrote:
>>
>> Wrenched:
>>
>> Merry Christmas to those of you that observe such traditions, or
>> substitute the winter festivity of your choice.
>>
>> I helped a previous employee install an Enphase IQ8 system on his
>> home. He applied for the utility approval concurrently with his
>> building permit The day he got his final inspection the utility
>> contacted him and claimed "The aggregate generation exceeds the
>> identified transformer rating" and refused him a Permission to
>> Operate letter.
>>
>> Adding up the service ratings of the homes on his secondary we
>> get about 336 kW of potential consumption. Adding the grid-tied
>> systems on his secondary we get about 16.5 kW. How is it that
>> the back-feed exceeds the transformer rating?
>>
>> I would appreciate any insight on how to consider this situation
>> and how to fight it.
>>
>> Sincerely,
>>
>> William Miller
>>
>> Miller Solar
>>
>> 17395 Oak Road, Atascadero, CA 93422
>>
>> 805-438-5600
>>
>> www.millersolar.com <http://www.millersolar.com/>
>>
>> CA Lic. 773985
>>
>> _______________________________________________
>> List sponsored by Redwood Alliance
>>
>> Pay optional member dues here: http://re-wrenches.org
>>
>> List Address: RE-wrenches at lists.re-wrenches.org
>>
>> Change listserver email address & settings:
>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>
>> There are two list archives for searching. When one doesn't work,
>> try the other:
>> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/
>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>
>> List rules & etiquette:
>> http://www.re-wrenches.org/etiquette.htm
>>
>> Check out or update participant bios:
>> http://www.members.re-wrenches.org
>>
>> _______________________________________________
>> List sponsored by Redwood Alliance
>>
>> Pay optional member dues here: http://re-wrenches.org
>>
>> List Address: RE-wrenches at lists.re-wrenches.org
>>
>> Change listserver email address & settings:
>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>
>> There are two list archives for searching. When one doesn't work, try
>> the other:
>> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/
>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>
>> List rules & etiquette:
>> http://www.re-wrenches.org/etiquette.htm
>>
>> Check out or update participant bios:
>> http://www.members.re-wrenches.org
>>
>
> _______________________________________________
> List sponsored by Redwood Alliance
>
> Pay optional member dues here:http://re-wrenches.org
>
> List Address:RE-wrenches at lists.re-wrenches.org
>
> Change listserver email address & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> There are two list archives for searching. When one doesn't work, try the other:
> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/
> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> http://www.re-wrenches.org/etiquette.htm
>
> Check out or update participant bios:
> http://www.members.re-wrenches.org
>
--
Christopher Warfel
ENTECH Engineering, Inc.
PO Box 871, Block Island, RI 02807
401-466-8978
<http://entech-engineering.com>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20221226/908cdb9c/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: EEIlogolong.jpg
Type: image/jpeg
Size: 17117 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20221226/908cdb9c/attachment.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: cwarfel.vcf
Type: text/vcard
Size: 203 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20221226/908cdb9c/attachment.vcf>
More information about the RE-wrenches
mailing list