재신정보 > 전기품질,에너지측정,진단,절감분야 > (from Alex McEachern) Electric Power Quality Newsletter


	PQube Sag waveform	PQube Sag RMS

Power Disturbance near London Olympics

My old friend and colleague Ian Murdoch of IMH in England (www.imh.co.uk) sent me this interesting voltage sag, recorded by a PQube a few kilometers from the Olympic Stadium in London on the first day of Olympic competition.

It's an interesting sag! Clearly, it took place on an 11 kilovolt delta distribution line early in the morning. Based on the voltage and current waveforms, I'd guess that we're looking at a fault downstream from the PQube monitoring point. There are some interesting phase shifts in the current. (The change-in-frequency on the RMS graph is a measurement/definition artifact caused by the phase shifts in voltage.)

This sag was recorded by a PQube in London. The PQube then generated these graphs without any outside software, and emailed them through a wireless 3G modem to Ian in Essex, England. Then Ian emailed them to me in California. These high-tech communication systems sure work well, don't they?

But I confess that I don't understand the strange voltage waveform during the sag. Any ideas?

Let me know if you would like the raw data recorded during this sag by the PQube for your own analysis. I'd like to know what you think.

PQubes and SpaceX

SpaceX recently completed the first non-government space flight, delivering supplies to the International Space Station. Here at PSL, we're very proud that they used 20 PQubes to keep track of power quality in their control center, in their launch center and in their test and qualification lab for their flight electronics. Congratulations, SpaceX!

I recently visited SpaceX's California headquarters. It's an astonishingly practical place: the flight hardware is assembled right out in the open, by regular people using regular tools.

Seeing it gives me great hope that space flight could soon be far more "ordinary" than it is today.

And PSL is standing by, ready to help SpaceX with their next flight in any way we can...

Answers: What is the English name of this cable transition?

In my last newsletter, I passed along this question from Lothar Fickert. To my surprise, there doesn't seem to be a single name in English. Here are some of the comments I received:

Professor Luis Pedro Alcantar Baz?a says that in Mexico, "transici?n a?rea-subterr?nea", wich stands for Air-Underground transition, in pr?ctice we call it transition.
Sebastian Jaroszewski suggests "cable entry point".
Leamon C. Calloway of Southern California Edison reports "Overhead to Underground Riser".
Wyatt Pierce, P.E., of Pacificorp writes: "In my area (central Oregon), we typically call these riser poles. As for direction of the coupling, the term "reverse riser" is used here for the underground to overhead transition. While this may seem counterintuitive, I would suggest that the term riser is much older and therefore applies to the more traditional (here anyway) OH to UG transition. As more UG has been constructed, UG to OH transitions have become more necessary and a new term has become necessary for them. I cannot back up that deduction. I do hear "dip pole" used occasionally for overhead to underground transitions. I rather like that term since the power flow "dips" underground; however I cannot say that I am in the majority on this preference. "Reverse dip" does not really roll of the tongue, and I don't think I've ever heard it used." A comment from Alex: a "dip", in British English, is a brief reduction in RMS voltage - myself, I wouldn't want to see the term "dip" used in the context of pole transitions...
My structural engineering colleague Joe Ungerer writes "In the building trade, the horizontal part of a stair is called a tread, and the vertical part is called the riser. Also in plumbing, the vertical pipes in a building that distribute to the floors are called risers. There are hot water risers, fire risers. But vertical waste pipes are called stacks. Go figure."
Stefan Fassbinder, who has a great sense of humor, writes "German is a difficult language. So long I have been unaware 'we' have a dedicated phrase 'Kabelauff?hrung'! Adopting into English is difficult already because of the '?'... 'Auff?hrung' also means 'theatre performance'. Have you tried an auto translator yet? 'Conductor cross sections' once turned out as 'Dirigentenquerschnitte'. Well, right, 'Dirigent' is the conductor of an orchestra..."
On a more serious note, Rob Kersten writes "The proper name seems to be "Riser Pole" and / or "Aerial-to-Underground Transition", and even provides a useful citation: http://www.sandia.gov/engstds/ConstSpecs/Div_16/16401_Electrical_Distribution_System_Aerial.pdf
Gero Bauser of Camille Bauer suggests "I would suggest to use the term cable lead-up (and cable lead-down in case of: Kabelabf?hrung)."
Edward Barrett, currently working in Dubai, suggests " It's not quite a landing gantry as used for landing HV transmission lines, so let's call it a landing pole."
Richard Massitti writes "Hydro-Quebec simply uses 'cable pole' as the standardized english term for this transition (and the more detailed 'poteau de liason a?rosouterraine' as the standardized French term)." Ref: ISBN 2-550-02730-2;HQ publ.963-2157
Carl Benner at Texas A&M University writes: "To add to your list of names for this riser, some years ago we did some work with the US Navy, and they called similar installations (on a ship) 'down comers'."

My conclusion: There isn't a "correct" name for this transition. When writing in English, call it what you like, but make sure it's clear to the reader from the context - maybe a picture would be nice.

Power Standards Lab Hosts IEC PQ Instrument Standard Meeting

Edition 3 of the IEC's Power Quality Measurement Method Standard for instruments is under way!

The IEC SC77A Working Group (WG09) meeting was held at PSL in late June. Experts traveled from Italy, Croatia, Germany, Austria, France, the United States, England, Australia, Canada and Belgium to PSL in California, with dozens of other countries participating electronically.

Several important changes were decided:

we're adding measurements for 2kHz-150kHz emissions, a problem I discussed in my last newsletter
we're adding current measurements to the existing voltage measurements
and we're moving Class B measurements to an informative annex.

It's a cheerful, hard-working group. We were forced to take one break during our 3-day meeting so the colleagues could watch Italy vs. Germany in the Euro 2012 semi-final football/soccer match. (Italy won, so we all enjoyed an Italian dinner in San Francisco.)

After the meeting, several members joined me on a trip to California's beautiful Gold Country, and Yosemite Valley ( picture 1) (picture 2). It's always a treat to work with this group, but this time it was a special pleasure for me to spend time with other engineers who like to stop and look at electric power views, like this one of a pumped-water energy storage station near Yosemite. Thanks for the nice trip!

FIDVR - an interesting new power problem

Fault Induced Delayed Voltage Recovery is an interesting problem -- and a great example of the law of unintended consequences.

High-efficiency residential heat pumps are much more energy efficient that old-fashioned air conditioners. But it turns out that many of them are susceptible to motor stalling, even during normal voltage sags. When they stall, they draw much more current than normal for several seconds (after a few seconds, their thermal protection generally takes them off-line).

This isn't a problem unless you have a big number of these heat pumps on a single distribution line. A simple voltage sag, a few stalls, and the additional current pulls the voltage down further, causing more stalls... You wind up with an extended voltage sag for several seconds, possibly followed by a voltage swell because the sag lasted long enough to trigger voltage increase at the substation.

We're seeing problems like this in hot regions of the United States this summer. And we're slightly worried that the problem could cascade beyond the original distribution line.

Joe Eto of the Lawrence Berkeley National Lab organized an interesting meeting a few weeks ago that gathered significant researchers on this topic. There's a lot of good research going on. Oak Ridge National Laboratories has a FIDVR lab. Lawrence Berkeley National Labs is working with Southern California Edison; NERC is sponsoring research at universities, modeling FIDVR and gathering data to confirm the models.

But gathering real-world FIDVR data presents its own problems: Communications are almost always affected by the event itself - all the routers go down. And there are lots of questions about triggering event recorders and how much data needs to be gathered.

We've been thinking about this at PSL and we think PQubes offer some real advantages for grabbing FIDVR data:

No communication required - all the data is captured and stored in the unit on a SD card
Voltage sag triggering can be set for RMS current, rate-of-change in current or wave shape change
Pre- and post-trigger recording
Data recorded in GIF (for quick viewing) and CSV (detailed analysis)
Low cost per node - design to be left in place
Easy to locate along distribution feeder and at residences

The FIDVR problem is real and is in need of a solid solution. Some possible solutions include changing the protection settings on the units (not likely); installing undervoltage trips on the units; designing a system to randomly restart units like this after a sag event.

Any ideas out there?

If you write to me, please forgive me if I don't reply right away -- Red and I are getting married this Saturday, and we're going to take a few days off in Hawaii !

With my best Summer wishes for you -

Alex McEachern
Alex@PowerStandards.com
Power Standards Lab
2020 Challenger Drive
Alameda, California 94501 USA
TEL ++1-510-522-4400
FAX ++1-510-522-4455

ㅇ 핵심 기술 (전기품질, 누전분석, 축전지셀진단) 제안, 세미나 자료 다운로드 서비스 (2009.06 버전)

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