Sag waveform
Sag RMS
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| PQube Sag waveform |
PQube Sag RMS |
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.
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...
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:
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:
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!
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:
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 ! |
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With my best Summer wishes for you -
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Alex McEachern
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