[RE-wrenches] Inverter 1741 Listing Process

Matt Lafferty gilligan06 at gmail.com
Wed Oct 20 12:20:56 PDT 2010


Thanks Guys,
 
Here's an update for anyone who cares. 
 
The specifics I was looking for are included in IEEE 1547.1, which is
inherently included in UL 1741. In other words, since 2007, if you have an
inverter listed to UL 1741, it must also meet (by certification) the
requirements of IEEE 1547 and 1547.1. In fact, the sections of UL 1741 that
formerly applied to the Utility Compatibility functions have been removed.
Voido. They are now replaced by IEEE 1547 & IEEE 1547.1. 
 
IEEE 1547.1 is clear and precise about the production test requirements I
was looking for. UL 1741 is weak on the issue. In general, utility companies
rely on IEEE documents and requirements for their guidance. I see why some
of them require field verification of the non-islanding function by flipping
the AC switch off with the inverter running... Well, not exactly.
Technically, the non-islanding function is something else. The
"Cease-to-energize" function is what they are actually verifying in the
field. Here's a short rundown on the issue....
 
IEEE 1547.1 (Clause 6; Production Tests) requires production tests for
response to abnormal voltage, response to abnormal frequency, and
synchronization. Combined, these would constitute production testing that
confirms the non-islanding functions that are Type tested on a sample unit.
And there's more. This section also requires that the documentation of these
production tests be provided with the equipment.
 
IEEE 1547.1 (Clause 7; Commissioning) requires some verification and testing
steps. These are allowed to be performed by a qualified person and the
utility may require that they witness the process (at their option).
Inherent to this section is a requirement that there be a commissioning
report generated which contains data related to the process. "A
commissioning test report shall be produced and shall contain the results of
all tests and a listing of the final ICS settings."
 
The required steps involved in Commissioning include: Verification and
Inspection, Identifying any required Type and Production tests that were not
performed and performing them in the field; Unintentional Islanding
functionality test; Cease-to-energize functionality test; Documentation of
revised settings. 
 
Understand that all of these steps are REQUIRED AS PART OF THE COMMISSIONING
PROCESS, per IEEE 1547.1. 
 
My focus is primarily on the Commissioning procedure... I'll skip the
inspection and verification steps for this post.
 
Note that Clause 7.3 of the Commissioning section requires field performance
of any Type or Production tests that have not been performed. When the
manufacturer fails to include the Documentation of Production Tests with
their product, the commissioning technician has no choice but to do them in
the field.
 
(NOTE TO INVERTER MFRS: INCLUDE CLEAR DOCUMENTATION OF YOUR PRODUCTION TESTS
WITH EACH INVERTER, PER IEEE 1547.1 Clause 6.4; NOTE TO INSTALLERS: HAVE
THIS DOCUMENTATION HANDY AND LEAVE IT WITH THE INVERTER.)
 
Clause 7.4 is the Unintentional Islanding functionality test. If the unit is
connected to the grid via reverse-power or minimum-power protection
equipment (commonly referred to as non-export or zero-export; relatively
rare) instructions are given for testing. This test is waived if the
inverter is certified to Clause 5.7, the Type test for Unintentional
Islanding. (Check) If the unit is not certified to 5.7 and not connected via
zero-export protection equipment, this function is to be tested according to
procedures provided by the integrator or the manufacturer. UL 1741 Listed
inverters should be certified to Clause 5.7, which makes them eligible for
the waiver.
 
Clause 7.5 is the Cease-to-energize functionality test. This tests that the
inverter does not energize the output (AC) terminals on loss of grid AC. It
also checks that the restart/reconnect time delay (5-minute wait) functions
as required. The test is simple. Run the inverter at any power level and
open the ungrounded AC phase conductors. Verify that the output terminals of
the inverter are not energized. Apply AC power. Verify that the unit waits
the required amount of time to reconnect. 
 
There are two important sentences in this Clause to know about. The first is
that "An ICS that meets the requirement so 5.9 (open-phase type test) and
7.4.1 (zero-export) satisfies the requirements of this subclause." This
means that a UL 1741 Listed inverter interconnected via zero-export
equipment is exempt from this test.
 
The second sentence to know about is this one: "The following procedure may
be adjusted dependent on an agreement between the area EPS authority
(electric utility) and the system installer." This means that, every time
the utility does not require you to test this function, they are agreeing to
"adjust" this procedure, even if they don't tell you they are. You are
getting a free pass.
 
Let me repeat that another way... IEEE 1547.1 REQUIRES that this test be
done unless the above-mentioned exemptions are met. As an installer, you
must be prepared for and expect to do this test. 
 
Nowhere in the Commissioning section of IEEE 1547.1 does it exempt
performing the Commissioning steps or producing the Commissioning test
report.
 
I am of the strong opinion that having the manufacturer's Production Test
Documentation on-hand will go a long way toward gaining the utility's
acceptance of the system without performing the Cease-to-energize
functionality test. I believe that most of our modern inverters will meet
one of the exceptions to the Unintentional Islanding functionality test. I
believe that it is best practice to perform comprehensive commissioning on
all systems, and record the relevant data. I have always found that doing
this and having your documentation together gains respect from AHJs and
utility inspectors. I believe that by doing this, we demonstrate
professionalism and responsibility. Working with utilities in a manner that
demonstrates professional, knowledgeable, and responsible behavior can only
benefit our respective organizations.
 
Happy commissioning!
 
Matt Lafferty
  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Exeltech
Sent: Tuesday, October 19, 2010 12:20 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Inverter 1741 Listing Process


boB covered the main points perfectly.

Manufacturers of UL-certified products are subject to unannounced
spot-checks several times a year by the issuing NTRL to verify the products
coming off the production line are absolutely identical to the products
submitted for UL testing.  Any major deviation in the production units from
lab-tested units can result in immediate de-certification and possible
recall of any affected product(s).  "Major" in this case could be different
software, mechanical changes, or a substitution of any components that
affect safety or unit operation in any manner with unauthorized components
.. for openers.

By the way .. for anyone who's not met boB in person .. I had the good
fortune to do so at the Midwest Renewable Energy Fair in Wisconsin this past
June.  Great guy.

Dan


--- On Tue, 10/19/10, boB Gudgel <boB at midnitesolar.com> wrote:




From: boB Gudgel <boB at midnitesolar.com>
Subject: Re: [RE-wrenches] Inverter 1741 Listing Process
To: gilligan06 at gmail.com, "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Date: Tuesday, October 19, 2010, 12:42 AM


On 10/18/2010 9:53 PM, Matt Lafferty wrote: 

Thanks for the info Dan and boB.
 
What production tests required to maintain listing? Do you happen to know if
there is a different regimen for micro vs string vs central inverters? 



You mean, a difference between the two when UL, ETL, CSA comes by for their
pop inspection ??

Off hand, I don't  see why one inverter would be given any different kind of
attention than the other
type.  The UL/ETL followup inspections are basically to make sure you are
following the proper
manufacturing and testing processes such as, software version, verification
that you are using
UL recognized  sources of parts and materials, hi-potting at the correct
voltages, etc.


They are both grid-tie inverters so the testing processes are very similar.

 I'm sure that Dan will pick up on anything  important that I forgot.

boB




 
I'm working on developing a detailed commissioning procedure. Detailed yet
generic. There will be at least two versions for inverters. One for string
and one for central. In my book, central inverters have re-combiners
(standalone or integral) and string inverters don't. I'm trying to
understand which functions are tested in the factory on every unit so I can
avoid unnecessary duplication by the commissioning people.
 
Thanks in advance for any light you can shed on the subject!
 
Matt Lafferty
  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Exeltech
Sent: Monday, October 11, 2010 10:04 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Inverter 1741 Listing Process


Matt,

The 5-minute delay is verified in the group of inverters sent to the test
laboratory.  Then, as long as the software and hardware don't change, it's
presumed the delay in all production units meets the value(s) measured in
the tested units.

An alteration in either hardware OR software can result in a unit being
required to completely re-test (as Bob pointed out).  NRTLs get copies of
the source code and can and do periodically compare their copy as submitted
with the original test units to the software being programmed into the
inverters during production to verify it's the same.

NRTLs conduct unannounced "field audits" by simply showing up on site and
randomly selecting various aspects of the product for verification --
including the software.

The overall UL1741 certification process is extremely complex, very time
consuming, and quite expensive.


Dan



--- On Fri, 10/8/10, boB Gudgel <boB at midnitesolar.com> wrote:




From: boB Gudgel <boB at midnitesolar.com>
Subject: Re: [RE-wrenches] Inverter 1741 Listing Process
To: gilligan06 at gmail.com, "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Date: Friday, October 8, 2010, 9:26 PM


On 10/8/2010 6:04 PM, Matt Lafferty wrote: 

Hola Wrenches,
 
Does anybody know off the top of their head if the
"5-minute-wait-to-interconnect" function is tested on 100% of inverters
produced? (i.e. every single inverter is tested with AC & DC within the
start parameters of the unit for at least 5 minutes)
 
Thanks!
 
Matt Lafferty


Good question.  I bet it's not 100% tested because if the software does not
change, then they may just not wait the extra 5 minutes in order to save
money on testing.

Or, maybe they do a random sampling for this test.

Theoretically, it shouldn't matter as long as the software does not change
and the hardware is tested enough in other ways, like, timers and clocks
etc.

BTW, Nowadays, there are two options for manufacturers of grid interactive
inverters....

And the UL spec has gotten more stringent.

One option  is that you have to have  the  code (software) blessed by the
NRTL in a separate process (another UL specification, (UL 1998 -Software in
Programmable Components")

OR, if they don't go for that option, then if software changes need to be
done to the inverter, the inverter must (technically) go through the UL1741
listing process all over again.

boB

 


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