On 10/13/2018 11:32 PM, Wayne.B wrote:
On Sat, 13 Oct 2018 21:28:35 -0400, "Mr. Luddite"
wrote:
On 10/13/2018 8:32 PM, wrote:
On Sat, 13 Oct 2018 19:49:25 -0400, "Mr. Luddite"
wrote:
The equipment we built was generally custom in nature and, as a system,
was not subject to URL certification, although many of the standard
components ... valves, contactors, motor starters, etc., carried
their own URL certs. Only had one case in 30 years of designing
and building this type of equipment that the city ... not the customer
... required the system to be inspected by URL. It wasn't a
certification of any type. It was just a look over to ensure that
the components used were mostly URL certified. It was in Chicago
in a Honeywell plant that was very close to O'hare Airport.
In fact, many of the electrical subsystems, how they were used
and installed were in direct violation of some of the NFPA National
Electrical Codes or were simply not covered by the Code at all.
Good example is the 10-12 Kw high voltage (10,000 volts) power supplies
used to operate a device called an electron beam gun. An electrician or
electrical engineer following "the book" would freak out if unfamiliar
with it and it's use. There's a governing rule that applies and we
included it in all of our technical proposals as did all manufacturers
of equipment like this. Read something like:
"When a conflict exists between an applicable code and the system
requirements, the requirements of the system shall apply and prevail."
I am surprised you did not run into a building department that
insisted on a listing.
I did once. Not the building department and not a URL listing but the
local electrical inspector in Rochester, NY caused an issue once.
We built a large thin film deposition system for the University of
Rochester, Laboratory for Laser Energetics. Part of a major project
funded by several government agencies including the DOE and DOD and had
very high "visibility".
These systems create a high vacuum condition in which a "process" takes
place. Part of that process involves heating the optics to be coated to
200 degrees C or more. To accomplish this in a vacuum, radiant
energy in the form of many, 1000 watt quartz lamps are used because
there is no convective or conductive heat transfer in a vacuum.
The lamps run on 240 volts (controlled by an SCR) and that voltage
is enough to ionize any remaining gas molecules (mostly water vapor)
that may exist in the vacuum. This causes an arc and nuisance
blowing of the fast acting SCR fuse or sometimes the SCR itself
which was an expensive unit.
To prevent this an isolation transformer (1:1 winding ratio) is used
to remove any ground reference to the arcs.
The isolation transformer is a very large, potted type that has a
temperature rise rating of 120 degrees C above ambient. No typo there.
120 degrees C rise above ambient. It gets *hot* but it's designed to
get hot. We purposely oversized the transformer and it's current rating
so it never got near it's temperature rise rating but it still got very
warm. It's protected so nobody can burn themselves.
So, the local electrical inspector comes by after the system was
installed. It was running at the time and he noticed how warm the
transformer was. He made a big deal about it, declaring it should
never get that hot and ended up getting the Director of the Laboratory
involved. Next thing I knew I received a panic phone call from the
engineer in charge of the lab and I agreed to fly up the next day.
I met with the Director of the Lab, the lab engineer and the electrical
inspector. The Director was a retired Navy commander of a nuclear
submarine, known at the lab as "the Captain" and of his demanding
personality. He read me the riot act about the report the electrician
had filed. I tried to explain to them that all was ok. It is *supposed*
to get hot. Told them why and explained that it's not unique to this
system. All systems of this type use the isolation transformer for the
reason described.
This caused a debate with the electrical inspector who had become
somewhat embarrassed. It ended when I told them that if he believed it
was unsafe, I'd shut the system down and disable any further operation
until the issue was resolved.
As I mentioned, this was a high profile project and they couldn't
afford to have the system shut down needlessly and the electrical
inspector was now under the gun. By now the "Captain"
understood the issue but he had to appease the electrical inspector
because a lot of new equipment was being installed at the Lab to support
the project.
So, he "ordered" that we Hi-Pot test the transformer windings. A megger
was located and I tested the leads/windings with the electrical
inspector, "Captain" and lab engineer watching.
All was fine, the electrical inspector grunted "ok" and he left.
Last I ever heard of that issue.
That system was installed in 1994 and is still in daily operation today
with the original isolation transformer. Last I heard it was being used
to coat the laser optics for the "NIF" program at Lawrence Livermore
Laboratory.
===
Interesting stuff. Did you ever consider water cooling it? When I
worked at the synchrotron lab at Cornell U we had a lot of high
powered electrical gear that was water cooled, including a magnet ring
that was a half mile in circumference.
Many components were water cooled including the large (72"), stainless
vacuum chamber itself. Never thought or considered water cooling the
isolation transformer because it was used well within it's ratings,
power-wise and temperature wise. The total quartz lamp load was
typically 8Kw or 10 KW. We used isolation transformers rated at 15-20 kw.
But yes, water cooling of components was a big deal. Each system we
built had a "water panel" containing about 20 flowmeters for various
components that interlocked their operation.
Over the years we built well over 100 of these systems for the thin film
deposition of optical coatings and they were almost always inspected by
the local electrical inspector. This was the one and only time an
inspector had anything to say. Most just checked the power service
for the system if newly installed.