EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: JonM on September 21, 2017, 02:39:29 am
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In the past I have experienced plenty of power line noise, voltage sags, and once the loss of one phase of a three phase feed (causing three phase motors in a lab to stop turning and fry). However, I do not know that I have ever been affected by a "power surge" from the power company. I do remember how much marketing effort went in to pushing surge protectors in the past, and I still have a lot of power strips with MOV, etc protection.
I am away from home at the moment, but tonight I got an alert from my county about a power surge causing 44 calls to the fire department and two buildings to catch fire:
http://wydaily.com/2017/09/20/fire-officials-multiple-structure-fires-caused-by-surge-in-kingsmill-grove-areas-nws/ (http://wydaily.com/2017/09/20/fire-officials-multiple-structure-fires-caused-by-surge-in-kingsmill-grove-areas-nws/)
All of my test equipment is currently unplugged, and most of my computer and network equipment is on UPSs with good protection (I think...). This event was not in my neighborhood, but not far away and it's my power company.
In any case, I guess that the possibility of a "surge" from "the power company" is still a real possibility, even in a US city. If any interesting details appear later I will post them.
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I've heard of one case* where powerlines that fed a tram line made their way into the local phases (240/415V), the end result was 750V DC blowing up ever electrical device in a street. When the surge reached the end of the street, that house caught fire and burnt down in <5 minutes. Amazing to consider how huge power surges are still subject to line termination effects.
* was written up in The Serviceman in a 1990's silicon chip if I recall.
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A primary-secondary short on one of the transformers can also cause that.
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Last one I heard of was workers digging up a high power line and shorting it. Lots of AC things plugged in were blown. Some melted. I think the melted stuff was more in the line of motors and/or transformers on things. That's probably what causes a fire.
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Yeah, I've seen some nasty stuff when poles that have both LV & MV are hit and wires break/touch. It's certainly not part of normal day to day operation, but the results can be catastrophic because it's not a little spike, it's suddenly several KV with a very low source impedance.
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We had a customer where a digger on the road outside shorted out a kv supply with their 230v. The building had a fully protected UPS supply. Except the one computer with our software, which happened to be plugged into the only socket in the place with no protection.
Not only did the computer no longer work, the metal parts inside had fused together.
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Disconnecting the neutral in a three phase system will also kill stuff. I still have some devices with blown fuses or transformers because someone did this.
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I once caught a repair crew about to connect two phases of our three phase supply together so as to get the power back on within some allowed time to repair criteria (I think I had the only building on the street that actually used all three phases).
I 'Politely' pointed out that neither our three phase pumps not our delta/star transformers would appreciate them doing this, and that they actually needed to fix it properly.
Lost neutrals are a fairly popular game at music festivals, it causes all kinds of weird voltage excursions, but they are usually constrained to no larger then the line to line voltage of the three phase supply, still a good way to get a million dollar insurance claim going tho.
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Had it 2 times already of the neutral bus bar ( plus all the earth wiring) being stolen in the substation across the park, and the local mains voltage going up to over 280VAC, with the UPS beeping and bucking the incoming mains down for me. Went to the meter room, measured all 3 phases and turned off the big red switch, then called the Metro and informed them of the loss of neutral in the system.
Too bad for the rest of the street, they either lost every thing plugged in ( anything in standby basically) from the high voltage, or they blew out geyser elements as tyhey kicked in and cooked, or they had only dim lights in the phase winning the competition. Too bad for the coffee shop, turns out that the coffee machine heaters won the first few rounds, but the lights, the POS system and the fridges lost them, then other loads kicked on and did the coffe-o-matic in as well. I went out and came back later to turn on the building, only had 2 people lose TV sets and decoders that were plugged in.
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There was an update on the cause:
"Dominion Energy has traced the cause of a power surge in the Kingsmill area to a “software issue,” according to a Dominion official."
Not a lot more in the article:
http://wydaily.com/2017/09/22/dominion-cites-software-issue-in-power-surge-that-caused-fires-nws/ (http://wydaily.com/2017/09/22/dominion-cites-software-issue-in-power-surge-that-caused-fires-nws/)
Some of the replies reminded me of another story. A large site where I worked had an annual power shutdown for maintenance (checking transformers, etc). I was always on-site for the power-up to re-start vacuum systems, computers, and electronics. One Saturday night I heard the site engineer call out over the radio "OK, smoke it" (meaning re-connect to the sub-station). Well, smoke it did. Sparks erupted out of a manhole, and the maintenance window moved into Sunday...
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That is the exactly problem. Electrical building maintenance is done -for obvious reasons- on weekends or holidays.
What that means is that sometimes there could a lack of senior and experienced individuals on the crew performing a "routine maintenance".
There is never anything resembling routine when dealing with these types of maintenance.
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They probably have to give a reason but for liability reasons they will say as little as they can get away with.
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That is the exactly problem. Electrical building maintenance is done -for obvious reasons- on weekends or holidays.
What that means is that sometimes there could a lack of senior and experienced individuals on the crew performing a "routine maintenance".
There is never anything resembling routine when dealing with these types of maintenance.
That annual power shutdown did not suffer from lack of experienced personnel. The head site engineer was running the show, a well known third party electrical testing company was doing most of the work, and the two full-time site electricians were on-hand. PhD scientists were standing by to bring equipment back up. It did not matter that it was a weekend.
An interesting contrast from that event (25-30 years ago) it that it was caused by some mechanical / electrical error. This recent event in my town was caused by a "software error" at the power company. Seems too easy to recur, and I will once again pay more attention to surge protectors.
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Software error is not going to cause overvoltage, unless they have no interlocks to prevent putting 33kV onto a 11kV line, or to turn a tap compensator to max load setting on minimum load level. This smacks of a poor design, or the error was a wrong connection and applying the incorrect supply to a distribution transformer.
Software error like the Therac is not really something you want to apply to the power grid.
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Not sure whether this should go here or in the 'design a space station power bus' thread.
Anyway it's interesting.
https://www.youtube.com/watch?v=8EPbJRsN1Zk (https://www.youtube.com/watch?v=8EPbJRsN1Zk)
Salyut 7 - The forgotten rescue of a dead space station
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JonM:
Not saying that this particular instance was caused by less-than-competent individuals.
I was only saying that there have been industrial accidents, in places with lax regulations, that have occurred.
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There was an update on the cause:
"Dominion Energy has traced the cause of a power surge in the Kingsmill area to a “software issue,” according to a Dominion official."
Not a lot more in the article:
http://wydaily.com/2017/09/22/dominion-cites-software-issue-in-power-surge-that-caused-fires-nws/ (http://wydaily.com/2017/09/22/dominion-cites-software-issue-in-power-surge-that-caused-fires-nws/)
Some of the replies reminded me of another story. A large site where I worked had an annual power shutdown for maintenance (checking transformers, etc). I was always on-site for the power-up to re-start vacuum systems, computers, and electronics. One Saturday night I heard the site engineer call out over the radio "OK, smoke it" (meaning re-connect to the sub-station). Well, smoke it did. Sparks erupted out of a manhole, and the maintenance window moved into Sunday...
Interesting , thankfully nothing affected us across the river.
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Perhaps the software in question was that doing work assignment scheduling, which assigned unqualified personnel to do some maintenance or repair operation. This has happened a number of places and times. And fits with saying something for public consumption that sounds like it means something, and sort of does, but is misleading as it can possibly be.
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A bit of new info...
http://wydaily.com/2017/09/27/dominion-after-power-surge-fires-residents-may-file-damage-claims-nws/ (http://wydaily.com/2017/09/27/dominion-after-power-surge-fires-residents-may-file-damage-claims-nws/)
The power and voltage issues were caused by a “software issue,” Dominion spokeswoman Bonita Harris told WYDaily last week. The surge sparked 44 fire department calls, including two structure fires, two transformer fires, 13 alarms and 27 calls for electrical shorts or the smell of smoke.
The Dominion representative, David Vanderbloemen, told supervisors Dominion was working on the Kingsmill substation upgrading the operating system of a transformer when the power surge happened.
They “identified a programming error” that caused the surge after it happened, the official said, adding it was a “human error.”
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@JonM
Do you live in Williamsburgh/Yorktown?
Kingsmill has a nice golf course.
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Yes, I recently moved to Eastern Virginia from New Jersey. Luckily golf is not a time / money sink that I have. I am busy enough with my daughters farm, a sailboat, computers, and (of course) test equipment!
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working on the Kingsmill substation upgrading the operating system of a transformer when the power surge happened.
I would love to hear the details of this. :palm:
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working on the Kingsmill substation upgrading the operating system of a transformer when the power surge happened.
I would love to hear the details of this. :palm:
I thought I had seen it all, until I read about Bluetooth enabled smart toilets
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working on the Kingsmill substation upgrading the operating system of a transformer when the power surge happened.
I would love to hear the details of this. :palm:
Yes, I thought that people would get a kick out of the transformer OS upgrade issue...
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There was a guy in my yard a while back that was sitting by the transformer in the enclosure on the ground behind my home and I walked over to see what was going on , the guy said the local utility requires them to check out the transformers once ever two years. I had never had that experience with other places I lived, but this is a co-op run utility and he said they are really good about maintenance. He was measuring the voltages and looking for any signs of potential failure.
Nice to know they don't just drive by and look at the transformers and assume all is well like everywhere else I have lived.
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The Metro does a 6 month cycle of checking, and at home they changed out the 500kVA transformer for a refurbished one, as the one flange had a leaking gasket. Change out the transformer rather than the gasket, so they can do the whole set and test them all, along with a high pot test and internal check on the then 60 year old unit. One going is is also 60 years old, was at another location.
At work they are planning to replace the 55 year old 200kVA unit with a 500kVA unit, and use a mostly unused backfeed to feed the rest of the load off another transformer in the next building over, that they want to remove. Next one to the other side is a 1MVA unit, running at around 300kVA or so load normally, this 200kVA runs at a peak of 150kVA, I did measure the phase currents one evening at 6PM, peak load time. Our feed off it peaks at 200A in mid summer, with all AC running, and in winter is a lot less.
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Hearing stories like that makes me realize I'm probably not all that well prepared myself for if that were to happen. Even the whole house surge suppressors you can buy would probably not save you from that, as they don't even physically disconnect the feed, they just rely on shunting to ground, that's not going to work for long when it's on a 15 amp breaker. That breaker will pop and the surge will continue throughout the rest of the house.
One thing I always envisioned is some kind of spring loaded lever switch is released if the voltage exceeds a certain threshold. It would sit between hydro feed and the panel. Essentially it would be setup so that if there is a surge it electromagneticly releases a pin that causes the switch to slam open. There would need to be some beefy MOVs to capture the brunt of the initial surge though as a mechanical device on it's own would not be fast enough. Idealy it would need to be rated for about 15kv so it can survive a high voltage transformer bypass. Most residential HV lines are probably 7200v but good to overrate to be safe. TBH I'm surprised a device like this is not a standard thing to have, it could perhaps even be built into the meter base. Kinda like how line carbon protectors are standard on phone lines.
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In power transmission class I learned that they have to 'extinguish the arc' in high voltage disconnects because breaking the contacts doesn't stop 'arc over'.