재신정보 > 전기품질,에너지측정,진단,절감분야 > PSL사 알렉스 회장의 뉴스레터 - Electric Power Quality Newsletter

OK, here's my personal favorite.

Click on map.pqube.com, and you'll have immediate access to dozens of PSL's tiny PQube monitors around the globe. Click on one of the PQubes, and you're connected directly to that PQube's built-in web server... well, almost directly. The PQube's internal server has limited connections, so you're actually connecting to a server in the Cloud that mirrors those PQubes. But what you see is straight from the PQube's internal server - there's no software involved.

What can you see? If English is your first language, I suggest starting in California at Lawrence Berkeley National Lab, where you can see everything from energy consumption, to unbalance, to a large impulse on December 25 http://tinyurl.com/46paalw.

If you're up to it, you can follow the progress of the whole Fukushima nuclear problem by watching it through a PQube on an outlet in Tokyo (it started at about 3:00PM local time on March 11 http://tinyurl.com/5u44yxw, but you can see it affect frequency through the next few days).

Zoom in on Slovakia, and you can inspect a PQube connected to a 1-megawatt solar array. Check out the effects of cloudy days on PV arrays http://tinyurl.com/3fput6y, or see how fast the inverter drops off line when there's a voltage sag http://tinyurl.com/6bxby2a. Or check out the frequency stability in, say, Vietnam, and see how it compares to the Dominican Republic.

If you poke around map.pqube.com a little, you'll quickly find that you can get all of the raw data in Microsoft Excel (CSV) files, for your own analysis... Everything's free, and everything's public. You're welcome to use the 50 gigabytes of data any way you like, and about 100 megabytes more are added every day.

Isn't that great?! And if you find something interesting that you want to share, you'll find a "Tiny URL" link at the top of each page - just copy it, and send it to a friend. Here's a one-page descript-xion of map.pqube.com - please feel free to copy it and distribute it. I'm just tickled by this site, and I'm learning a lot from it. I hope you do to.

(If you're interested in buying some of these tiny, lab-grade, low-cost PQube monitors, please reply to this e-mail, and I will get you in touch with the right people.)

Question: Budeanu VAR's or fundamental VAR's?

There are two kinds of Volt-Amp-Reactive definitions out there: the good old power triangle (or Budeanu) version of VAR's, which is the remainder when you geometrically subtract watts from volt-amps; and there's the fundamental version of VAR's, which is the volt-amps times the sine of the angle, at the fundamental frequency, between the voltage and the current.

The two definitions are equivalent if you don't have any harmonics, and you can use either one safely. But these days, of course, there are almost always lots of current harmonics, and the two definitions produce different readings. That's why we include both definitions in the little low-cost lab-grade PQube monitor.

But I'm still scratching my head about this. For what applications does the power triangle definition make sense, and when does it make more sense to use the fundamental definition? Any ideas? I've heard some arguments that the Budeanu definition is "more complete" because it includes harmonic VAR's; and I've heard arguments that we ought to choose the fundamental definition of VAR's because that's what is needed for correctly choosing power factor correction capacitors.

Ideas?

PQube recorders for photovoltaic applications

I'm seeing lots of our PQube energy-and-power-quality monitors being included in the design of photovoltaic installations. It makes sense. The PQube can monitor the DC voltage and current from the PV array, and simultaneously monitor all aspects of the AC output of the inverter. Including a monitor like the PQube is a great way to avoid service calls when the inverter shuts off due to grid disturbances. And it's a great way to accumulate revenue-grade energy data, as well as carefully calculate avoided CO2 emissions. Here's a great new Application Note for photovoltaic installations.

More information? PSL's Thomas Pua -- email thomas@powerstandards.com -- is the right guy to ask.

Questions: RVC monitoring? How to measure in the 2kHz-150kHz region?

My IEC SC77A Working Group 09 is taking a shot at defining how to measure Rapid Voltage Change, which seems to be an increasing concern at some utility companies - perhaps because it can reduce the lifetime of tap-changing transformers. If you have any ideas about how to measure RVC, they would be welcome.

I'm also beginning some work on measuring noise in the 2kHz-150kHz region. There have been some reports of meter malfunctions due to events or noise in this part of the spectrum, but given the lack of details about the problem, I'm not sure how to measure this. At this frequency, it's almost certainly conducted rather than radiated, so should we measure phase-to-phase, phase-to-neutral, or phase-to-earth? Should we just measure the energy over the whole spectrum, or should we divide the spectrum up somehow? Should we average over some time interval? A second? A cycle? This kind of measurement is necessary for creating immunity and emissions standards, so we'll have to move ahead quickly.

Please send me your ideas - they would be welcome.

Good article in EC&M about PQube monitoring

I liked this article in Electrical Construction & Maintenance magazine. It's about a manufacturer of carbon fiber devices, and the power quality problems they were struggling with. My sense is that the problems were partly technical, and partly a difficult communication challenge, and they figured out how to solve both.

(There's a useful, and probably correct, comment from Carl Benner at the bottom of the article.)

The Smart Grid and spacecraft power systems - a useful analogy from Harold Kirkham

At PNNL last week I was chatting with Harold Kirkham, a wise Fellow of the IEEE, about our mutual days back at JPL in Pasadena, where a lot of the American spacecraft are still designed. Harold made an interesting link between spacecraft power system design and the "Smart Grid".

He pointed out that spacecraft power systems have always been designed with fall-back modes that are triggered by various failure sensors. And every spacecraft power system includes an ultimate "safe" mode which is usually very, very dumb but very, very reliable. Harold suggested that the present grid, our "dumb grid", might be thought of as the safe mode of the Smart Grid; and that it would be worthwhile thinking about exactly how to transition back to the safe, dumb grid if (or when) the Smart Grid hits a problem: equipment failures, information hacking, etc. An interesting idea, and he encouraged me to share it, so here it is!

I hope you are having a warm summer if you are in the Northern Hemisphere, and a good winter to my friends in the Southern part of the globe!

With best wishes -

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

(I have sent this e-mail to you at 'jaeshininfo@korea.com', because you are on my personal world-wide list of 23,136 engineers, educators, and students interested in power quality. If you no longer wish to receive it, please let me know.)

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

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