Power Quality Newsletter - May 2009(from Alex McEachern)
Medium frequency emissions - reports of problems
In my last newsletter, I asked if anyone knew about practical problems caused by emissions in the 2-9 kHz range -- a frequency range that is above the traditional harmonics limits, but well below the usual range for high frequency noise. (The question originated with Ed Yandek of General Electric.)
Thank you for all of your replies!
Colin Hargis of Emerson Industrial Automation pointed out several examples of acoustic problems, which makes perfect sense: acoustic noise in light fixtures, and electrical noise coupled into acoustic systems such as telephones and audio amplifiers. He also pointed to equipment problems: UPS trips, which didn't surprise me, and malfunctioning hand dryers of various types, which did.
Marcel Tremblay discussed how noise in this range can cause increased earth currents. These increased currents flow through the phase-to-earth capacitors in noise filters, and also through cable-to-earth capacitance (a new idea to me, but it makes sense). Marcel recommended "EMI Emissions of Modern PWM ac Drives" by Skibinski et al., in the Nov/Dec 1999 issue of IEEE Industry Applications Magazine. It's a compilation of 17 papers on this topic from 1996 - 1999, so we're going back 13 years to learn about this!
My friend Naoki Kobayashi of Tokyo Electric Power sent in a fascinating and detailed report. He tells us that there have been hundreds of incidences reported to branch offices about earth leakage breakers opening, or abnormal acoustic noise from appliances, associated with 5kHz emissions from a particular type of vacuum cleaner. This vacuum cleaner had digital (dc brush-less) motor technology, and consequently drew significant current at 5kHz. There were no official limits in any applicable standards, so the utility's technicians could only recommend that customers not use the cleaner and consult to its manufacturer. As a result of these incidents, Japan is now studying this problem in detail, and discussing the need for a standard.
I am grateful to everyone who wrote with their experiences - it sounds (pun intended) like emissions in this range can be a serious problem. If you're interested in this problem, I suggest you contact IEC Technical Committee 77A, Working Group 1, through your National Committee.
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Upgraded ultra-low-cost PQube monitor available
I love this little instrument!
I've been using the PQube myself all over the world - it captures sags, swells, interruptions, frequency variations, RMS flicker, 1-microsecond impulses, unbalance, THD, plus daily, weekly, and monthly trends and statistics, and it connects directly to any voltage from 100V to 690V, at 50/60 Hz. And it's a full energy and carbon meter, too, with lab-grade accuracy and a NIST-trace certificate for every PQube. Built-in e-mail, web server, FTP, and now PQDIF and Modbus too.
All this with no software required - if you can use a digital camera, you can use a PQube.
And now, at last, PSL has caught up with demand and we have hundreds in stock for immediate shipment. Maybe you need a few? Or even one or two, just to try out the PQube?
We're seeing these little PQubes installed everywhere: in medical equipment, hospitals and clinics, airports, food processing plants, auto factories, military bases, semiconductor fabs, sewage treatment plants, wind turbines, telecom offices, universities, automated industrial equipment, radio and television studios, transit systems, shipboard power, biotech, pharmaceutical plants, military bases, elevator/lift controls, data centers, offshore platforms, petrochemical plants, pulp and paper factories - the list just goes on and on.
Details at www.PowerStandards.com/PQube.htm.
Questions? Please contact:
|Marco Mancilla (English,Espa˝ol), mobile ++1-415-297-9796, e-mail Marco@PowerStandards.com, Skype: marcoii2005|
|Andreas Eberhard (English, Deutsch, Franšais), mobile ++1-510-919-4369, e-mail AEberhard@PowerStandards.com, Skype: andreas_eberhard|
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Questions about electric power around the world
If you have thoughts on any of these questions, please send me an e-mail - thanks!
Are there any electric companies that offer incentives or payments for improved power factor? Many electric companies charge power factor penalties, of course, but Dan Greenberg of E-source was wondering if any power companies offer rewards, or help pay for power factor correction. Do you know?
How does your country generate electricity? What percentage comes from coal, from hydroelectric, from renewables, from nuclear, etc.? It probably varies by region, but what are the rough percentages? (I have useful numbers about Great Britain from John Sinclair, and the U.S.A. from our Department of Energy, and China from James Wang. Now I'm looking for approximate numbers from other countries. Can you help?)
Does flicker cause equipment problems? Any published papers on this topic? I wonder about this, because the flicker standards are so closely tied to incandescent light bulbs and human perception. If I remember correctly, Terry Chandler (Thailand) has informally told me about an automatic welding control that was affected by flicker, and James Wang of China told me about a glass rolling plant whose quality was affected by flicker caused by a nearby arc furnace. But I can't seem to find any publications. Any ideas?
Jan van Nassau asks an interesting question about SPD's (surge protection devices): is there any way to predict SPD lifetime? The question reminded me of Francois Martzloff proposal for a marvelously simple device to measure the surge intensity of an environment: just connect a bunch of SPD's to the local grid and make sure they have different thresholds and energy-handling capabilities, then, after a year, examine them and see which ones have been damaged. Here at Power Standards Lab, we do equipment tests with surges up to 6000V and 5000 amps. Quite often, the transient protection device explodes, which can be very exciting. When we're running these tests, we have to warn everyone else in the lab. Bringing this back to Jan's question, it's obvious that after the SPD explodes in the course of doing its job, it is no longer capable of doing its job. Anybody know how to predict when this will happen?
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Last month, I got to study and discuss power quality problems in Dubai, Beijing, Nanjing, and Tokyo.
In May and June, I plan to visit Pittsburgh, New Jersey, Knoxville, and San Diego in the U.S., as well as Toronto, Singapore, Kuala Lumpur, and possibly Poland and Romania. 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 to see you somewhere!
With best wishes -
(I have sent this e-mail to you at '[recipient]', because you are on my personal world-wide list of 14,493 engineers, educators, and students interested in power quality. If you no longer wish to receive it, please let me know.)