Anti-Islanding Re-certification and CYA [RE-wrenches]

jberdner at sma-america.com jberdner at sma-america.com
Thu Oct 24 10:43:51 PDT 2002


Bill:

There is a simple switch on every installation to check anti-islanding.
It is called the ac circuit breaker ;-)  This is how several utilities
in Texas verified things after forcing us to jump through lots of
expensive and unnecessary hoops.

To verify trip times (a few cycles) and the other Anti-islanding
parameters at the needed accuracy is not a trivial matter.  Our
suggestion to the utilities is for the inverter to display it's measured
values for voltage and frequency. This can be compared to a calibrated
instrument, e.g. DVM, and used to verify all of the analog conditioning
circuitry.  Other schemes where you change the set points to the nominal
value, e.g. 60 Hz, 240 Vac do not represent an accurate test.  The
behavior of the inverter while adjusting a set point are likely to be
very different than when they are operating normally. In our case it is
a completely different mode.

If you have any questions, or if I can be of any further assistance,
please do not hesitate to contact me.

Best Regards,

John Berdner

SMA America, Inc.
12438 Loma Rica Drive, Unit C
Grass Valley, CA  95945
530.273.4595 (voice)
530.274.7271 (fax) 


-----Original Message-----
From: Bill Brooks [mailto:billb at endecon.com] 
Sent: Thursday, October 24, 2002 10:24 AM
To: RE-wrenches at topica.com
Cc: Chuck Whitaker
Subject: RE: Anti-Islanding Re-certification and CYA [RE-wrenches]

Travis,

This is not a new issue. We have been 'round and 'round with utilities
on
this one. Utilities routinely test relays because historically they were
analogue devices that tended to drift in their settings over time. Most
new
equipment now is digital. They still do periodic testing, but their test
intervals are significantly longer than for older equipment.

Islanding capabilities are programmed in software so it either works or
it
doesn't. Voltage settings of an inverter are the most likely to drift if
a
sensor starts to drift, but at some point it will cause the inverter to
shut
down since the voltage has to be in a defined window just to run.
Periodic
testing can be very expensive or it can be easy, depending on the
requirements of the test and how readily testable the inverter is. I
would
like to see self-test features built into every inverter so that the
system
owner can push a button, similar to a GFCI, and the unit will test
whether
everything is operating properly.

Not many people test their GFCIs like they should, but it doesn't cost
anything either to test. It does have to be built into the unit,
however, so
redesign can be expensive for the manufacturer.

Bill.


-----Original Message-----
From: Travis Creswell, Ozark Solar [mailto:ozsolar at ipa.net]
Sent: Wednesday, October 23, 2002 9:54 PM
To: RE-wrenches
Subject: Anti-Islanding Re-certification and CYA [RE-wrenches]


My local utility engineer called me today and asked me a very
interesting
question that he thought of after a recent "event".   I believe the
"event"
****snip****

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