Power quality, earthquakes, and oil spills...
Power quality, earthquakes, and oil spills...
On Sunday, April 4, a major earthquake hit California. It was named after a nearby Mexican town called Mexicali, which is right on the border between Mexico and California; and just across the border is the town of Calexico, so who says geographers don't have a sense of humor? The earthquake caused few injuries, and provided a beautiful demonstration of the fact that the entire electrical grid is one single machine. The earthquake knocked a major generator off-line abruptly, and that caused the entire western United States grid to drop in frequency, simultaneously. It's a perfect example - here's a little 2-page report: Mexicali_Earthquake_and_the_Western_Grid.pdf.
(The earthquake map above is from the United States Geologic Survey, the government organization responsible for mapping these things. Somehow, the notation on it that it was "Not reviewed by human" tickles me - in this computerized age, it's good to see that human judgement is still good for something.)
While we're on the topic of disasters, the big oil spill in the Gulf of
Mexico has an interesting
power quality angle. The remotely-operated submarines that you see in
all the news reports doing everything from photographing the well-head
flows to carrying and operating the hydraulic shears are equipped with
PQube power monitors. These submarines are
"flown" from a ship-board control room - those of you familiar with
ship-board power quality and grounding issues will know what that
implies.
In addition, the submarines are dangling at the end of a 3,000-meter
power cord, which incorporates several slip-rings so it doesn't get
tangled.
The submarines have all sorts of on-board sophisticated navigation, propulsion, and instrumentation systems, all of which rely on good power... There's a beautiful multi-channel fiber-optic ethernet link back to the ship. When something goes wrong with the power -- and it does -- the PQube immediately reports the problem, complete with waveforms for rapid diagnosis.
I'm starting to see the platforms themselves equipped with PQube monitors, which I think is a good idea. The AC power is questionable, and there are a lot of very sensitive, critical instrumentation and control systems. In the context of offshore preemptive safety, it makes perfect sense to monitor the platform's power quality disturbances.
We're glad to be helping clean up the Gulf spill a little, and wish we could help more. It's a pretty sad situation.
Visit Power Standards Lab at Semicon West in San
Francisco!
If you're in San Francisco on July 13-15, stop by SEMICON and see the latest power technology at PSL's Booth 2712. We're in the South Hall right across from our friends at Applied Materials. We will be showing off some impressive new features in the PQube. (I would tell you what they are, but then it wouldn't be as exciting to come visit us, right?)
Question: Same cable size for AC and DC power? (Uwe
Haller)
My old friend Uwe Haller, one of the best electrical engineers I know, asks an interesting question: Given that skin effects increase with the frequency squared, is it really necessary to use the same size conductors at DC as at 50/60 Hz AC?
Of course, the skin depth at 60 Hz is about a centimeter, so we both realize this question doesn't really apply to smaller cables. But this could be a very important question for bigger cables and bus bars. These days at photovoltaic installations we're moving megawatts of DC at fairly low voltage, and copper is expensive - could society save scarce resources by using less copper than the standards require for 50/60 Hz?
Maybe there's some effect that I haven't thought of, but it seems to me that requiring the same cross-sectional area for DC and 50/60 Hz might be wasting copper.
Any ideas?
(And if you ever get a chance, ask Uwe to tell you some of his travel stories, and show you some photos. He has trekked to some interesting places!)
Question: Capacitor lifetime calculation? (Alex
Baitch)
Another old friend, Professor Alex Baitch, writes from the euphoniously-named University of Wollongong in Australia, where (at least in my experience) the single-phase line voltage can be surprisingly high...
He writes:
I was wondering whether you can help me with some investigations that
I am presently undertaking. I am looking for knowledge regarding the
effect of steady state voltage (or more particularly overvoltage and
undervoltage) on electrical components. The body of knowledge is
essentially with manufacturers as they tend to do accelerated aging
testing using the technique of application of overvoltage. However, it
is hard to find analytical data.
I have recently come across information from a capacitor manufacturer who provides the following relationship for metalised film capacitors: Service lifetime = (Normal voltage / Excess voltage) **9 x Service lifetime at nominal voltage. Accordingly a capacitor rated at 230V would have a life of 42% if operated at 253V instead of 230V. Intuitively sounds about right.
Assuming that a similar function applies to other types of capacitors, this has major implications for the expected service life of many devices. In particular, the present drive for energy efficient compact fluorescent lamps must have adequately rated components to ensure adequate expected life.
Are there other widely-accepted lifetime adjustments for electronic components, resulting from sustained over- or under-voltage?
Regards
Prof Alex Baitch e-mail baitch[at]besaust.com.au
(A note from Alex McEachern: Prof Baitch sent me this question several months ago, and I have been slow to include it in the newsletter - my apologies!)
Voltage sag immunity testing - still a great idea!
We've been doing it for years, all over the world, and it's still a very useful idea: test and certify equipment for voltage sag immunity.
It's probably the cheapest, most effective way to solve power quality problems. The standards are readily available -- SEMI F47, IEC 61000-4-11, and 61000-4-34 -- and the test equipment is portable and easy to use.
Here's a nice e-mail this week from someone who just purchased one of PSL's voltage sag generators, the Industrial Power Corruptor: Dave Layden, Electrical Power System Engineer at TomoTherapy writes "What a well-thought-out piece of gear. Quite happy with it, for sure. Especially love all the channels of monitoring available. That’s it; again, a most impressive machine! Helped us out tremendously." (Thanks, Dave!)
If you'd like to test the sag immunity of almost any electronic device (VFD's, chillers, wind turbines, auto welding robots, semiconductor tools, power supplies, routers) almost anywhere in the world (North America, Europe, Saudi Arabia, Japan, China, etc.), please contact Andreas Eberhard or one of our Test Engineers. They will help, test and certify anywhere you are around the world.
Thousands of PQube power monitors are now in use all over the world. I love these little guys. They really are incredible little instruments -- 0.05% accuracy, full energy and power disturbance event recording, and -- best of all -- absolutely no software required. Everything is stored in standard GIF picture files and CSV Excel files on a standard digital camera SD card.
Some new developments:
We continue to expand our list of world-wide distributors. If you know an organization that you think might be a good fit with PSL products, or if your own organization is interested, please contact Andreas Eberhard or Marco Mancilla. We're always open to suggestions, especially in countries where we aren't represented yet!
In the past few months, I've met with engineers in England, France, Denmark, Germany, Holland, Croatia, Italy, China, and Japan; in the next few weeks I will be in Quebec, Purdue University in the U.S., Vienna, and Florida.
Do let me know if you would like to get together at any of these locations - my detailed calendar is at Alex.McEachern.com.
I hope you have 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 -
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Alex McEachern
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(I have sent this e-mail to you at 'hohoking@sbcglobal.net', because you are on my personal world-wide list of 17,611 engineers, educators, and students interested in power quality. If you no longer wish to receive it, please let me know.)