Strange observations during a power outage

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The other night our power went out here in Oakland. Was watching teevee when the lights went out all of a sudden. Then they came back on. Then they flickered a bit and went out again. Came on again, there was a muffled "BOOM!", whereupon they went out, this time for good.
It was the first power outage we'd had here in a long time. And I noticed some really strange things.
First of all, the "BOOM!" turned out to be a transformer which exploded rather spectacularly right outside the building I'm in. Some neighbors down the street said they actually saw the thing go, sparks and all.
Turns out there were several other transformers all over town that blew at (about) the same time. Power was out to 4,500 customers at the peak of the outage, in an area covering many square miles. But walking around, I'd see blocks on end without power and with no streetlights. Then there'd be a block with power. And some of the blacked-out areas had working streetlights. The local power grid must be a crazy quilt of wiring.
Regarding the cause of the outage, when I got ahold of PG&E (Pure Greed and Extortion), the guy said it was due to "equipment failure". Talking with my neighbor, though, he said he though it was human error: someone threw the wrong switch or something.
And really, how else could a transformer fail spectacularly, other than an overload, except by there being some kind of massive overvoltage surge (what people incorrectly call a "power surge")?
OK, so for the rest of the evening we were without lights. Sort of.
Sort of? I though power outages were pretty much black and white: either the power is on or it's off.
Not so, grasshopper. I stuck my VOM into an outlet and monitored the line voltage. The reason I did this was that after the power had been off for a good long time, I heard my microwave squealing a high-pitched whine. And there was noise coming from the fridge motor. At that point, I could see that there was about 60 volts on the line, enough so that when I turned the lights on, they came on, sorta dimly.
After that, the line voltage fluctuated wildly, going from a low of about 45 volts all the way above 80. My guess is that they (the power co.) were switching things in and out, and that was causing the ups and downs. Another unusual thing I noticed was that my neighbor's diesel generator kicked in when the power went out (they have a small server farm they like to keep alive). But every time the voltage went above 80 volts, the thing would turn itself off--which meant that they were running on low voltage for at least part of the time.
I found out that my TV (old analog) and DTV converter work fine on about 75 volts. I didn't want to find out about my computah, so I turned it off. Also turned off the fridge because I didn't like the sounds I heard coming from the compressor.
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the on off on off on off was a power company circuit breaker trying to reset. most will try 3 times then quit and in newer areas report back tripped
i keep my satellite receivers on a UPS to protect them. undervoltage is espically bad
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bob haller wrote:

Some of the high voltage fusible circuit breakers sound like an explosion and I've seen one set the pole on fire.
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wrote:

I actually witnessed a transformer on a pole explode once as i was driving by. scared the ...... out of me. before cell phone i stopped at the next pay phone and called it in.
exploded in a ball of fire, from side then flames.
i will ask a retired buddy of mine he was a power lin transformer engineer designer at one time. he has amusing stories of transformers failing testing.
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Nebenzahl wrote in part:

Low frequency power transformers in this power class have "E-I" cores, with E and I "laminations" alternating/interleaved. The "I pieces" are adjacent to the 3 tips of the "E pieces". The alternation has E's sandwiched between I's, and I's sandwiched between E's.
The "center leg" of the "E pieces" has width twice that of the 2 "outer legs", that of the "backbone of the E", and that of the "I pieces".
Unlike what you said, both the primary and secondary windings are around the "center leg of the E's".
If an E-I core is used for a transformer requiring some DC in the primary (such as a "vertical output transformer" of a mostly-tube TV or output transformer of a single-ended vacuum tube audio amplifier), then there is likely need for a gap in the core. In that case, the E's are stacked together pointing the same way, the I's are similarly stacked into a rectangular block, and some layer of paper or cardboard or whatever is typically used to space the I's from the E's. The windings are still around the center leg of the E's. 2-lead fluorescent lamp ballasts (for lamps at most 22 watts in USA) and "reactor" type ballasts for other lamps and "filter chokes" for some power supply designs generally have similar E-I core with an "E stack" and an "I stack" and a gap of some sort.
Lamp ballasts with more than 2 leads (excluding any used by starting circuitry) and "neon sign transformers" (which are actually ballasts) get different by using more complex core designs with "magnetic shunts".
- Don Klipstein ( snipped-for-privacy@misty.com)
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On 3/30/2009 9:25 PM Don Klipstein spake thus:

Yes. I realized that was wrong after I sent that message.
So do you know the construction details of utility power transformers?
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On Mon, 30 Mar 2009 17:02:57 -0500, snipped-for-privacy@invalid.com wrote:

I saw a recent episode of "How It's Made" and they showed the construction of a power transformer.
G.S.
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On Mar 31, 1:57�pm, snipped-for-privacy@invalid.com wrote:

how its made, dirty jobs, air emergency, deconstruction some of my favorite shows.
all on cable networks...........
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bob haller wrote:

I still remember that summer afternoon in 1985 when a young IRS gal was sitting in our third floor offices conducting an audit. She had been there a couple of days and "so far so good". We were getting along fine, perhaps because in chatting we'd learned that her dad was an alumnus of the same college I'd graduated from.
Anyway, a window was open next where she was sitting. The skies darkened, followed shortly by a a crack of lightening and a "boom" as a pole transformer not far from that open window exploded. The building lights went out and some sort of alarm started howling.
It was the Devil who made me do it, but I stuck my head out the window, looked up and yelled, "About twenty feet to the left, God."
(Yes, we passed the audit with flying colors.)
Jeff
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Actually, transformer cores do "wear out". And when then do, they do overheat which can lead to spontaneous fire/explosion.
However, if multiple transformers failed in the same area there was clearly some precipitating event. Most likely a lighting strike but there are many other potential causes.
Fortunately, it's rare to experience the kinds of fluctuating voltages you observed. The system is generally designed to deliver a relatively clean supply or none at all. And it does work that way most of time.
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On 3/29/2009 5:34 PM Malcolm Hoar spake thus:

Absolutely clear weather all around. So it must have been some kind of cascading failure, and once again, I say the only way transformers can blow up under such circumstances has to be overvoltage.

And how do you know this for sure? Have you monitored your line voltage during an outage? Could yield some interesting results ...
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Yes, at various times in the past I have done main voltage monitoring professionally.
I don't do that now but the computer into which I am typing this post is connected via a UPS that does record most mains voltage variations -- sags, surges, spikes, outages, over-under voltage and more.
And I too am in PG&E land -- not many miles south of Oakland.
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Care to elaborate?
Mark
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snipped-for-privacy@yahoo.com wrote:

These large capacity transformers typically last 10-30 years and fail for many reasons (other than overload). Some of the issues:
* Ingress of air and water. This changes the dielectric properties of the core and can, of course, lead to corrosion problems.
* Problems related to the coolant (typically oil). The oil can break down, there can be ionization, production of gasses and more.
* Laminated cores can delaminate.
* Insulation can break down over time.
* The magnetic properties of the core change over time making the transformer less efficient leading to the production of more heat.
Often what starts out as a minor problem creates a hot spot within the core. This deteriorates further leading to a more catastrophic (and spectacular) failure of the device.
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well ok,,,
those certainly are failure mechanisms, but I wouldn't call them "wear out" ,,, but that's just me...
Mark
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snipped-for-privacy@yahoo.com wrote:

I did put the "wear out" in quotation marks.
Having said that, after checking, my use of the phrase does seem fairly consistent with most dictionary definitions.
1. To make or become unusable through long or heavy use. 2. To use up or consume gradually. 3. To exhaust; tire.
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wrote:

Oh right, I guess my tires, shock absorbers, wiper blades, tooth brush, computer monitor, fence, water heater, etc. all required repacement because of worn bearings. NOT.
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wrote:

That's a load of balls ;-)
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wrote:

Slightly OT - The transformer serving my house, about 40' away, was struck by lightning a few years ago. The noise of the lightning/explosion was breathtaking. After the storm let up I went out to see what happened. The pole was splintered and the largest piece of transformer was about 1/2 sq. foot, and was in the nearby woods. Lotsa oil too. WOW!
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David Nebenzahl wrote:

The cans are filled with oil acting as a coolant. If the can leaks, and the transformer's under full load, it will melt, igniting the remaining oil, and blow that sucker into the bay!
Or it could be part of the plan concerning the candlelight vigil for the dear departed, Lovelle Mixon. The man had "Love" in his name and was lifted into the arms of baby Jesus just this past week.
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