Electrical guru's?

[John]

OK, not DIY but interesting anyway.

Yesterday, I was sat at my computer at about 3.00pm and suddenly the computer and the wireless router went off, I was listening to the radio tuner of the hi-fi and that went off, but at the same time I was using the DVD/HDD recorder to dub some stuff from the hard drive to DVD (with the telly on so that I could see what was going on, but the sound turned down) and that *remained on* and OK - all of these being fed on the same ring main.

Meanwhile, my wife was in the kitchen (which is on a seperate ring main) and she came in to say that her telly had gone off but the kettle was still on. I looked at the consumer unit, not really knowing what to expect - MCBs couldn't have tripped or everything on those circuits would be off, but they weren't. As expected, nothing was untoward. Then a neighbour came knocking to say that something similar had happened at their house and was wondering if we'd noticed anything.

Just been talking to a mate of mine on the phone and he said, "Did your lektrickery go off at about 3 o'clock yesterday?" Apparently, he was in town shopping and various shop lights and stuff went off. Half an hour later, he rings his wife at work and she says that she'll not be home on time as

*some* of the computers (not all) had thrown a wobbly - her office is in town.

When he got home, he found that his kitchen fridge was off and that a clock/radio in the bedroom had gone off (because the display was flashing). His beer fridge in the garage was OK though (PHEW!!! :o))

Now, my house, his house, and town are roughly in a triangle geographically, with each side of the triangle being about 3, maybe even 4 miles. How the hell could this have happened and more to the point, just exactly *what* happened??

John (this is in Preston, Lancashire, BTW)

[Robin]

possibly relevant

Is the kit which went off now working again or dead or a mixture?

[The Wanderer]

Probably a fault at a higher voltage (33kv or even higher) some long way from you pulled the volts down enough for a 'brown out'.

Fault protection for predominantly overhead systems have both an instantaneous element and a time-delayed element. The instantaneous element trips the circuit in a matter of a very few milliseconds and is intended for transient faults, like wind-borne material, birds flying into and clashing the wires, tree branches, which can cause a very short duration fault but which then clears itself, so the circuit can be re-energised after a few seconds delay. In the event of a sustained fault the time-delayed protection operates. At 11kv, that time delay is still very small, typically 350-400 milliseconds.

On underground systems, there isn't usually any need for instantaneous protection, as a fault will be sustained anyway. The higher the voltage the longer the (relative) time delay, to get discrimation between voltages - you don't want the protection at, say, 33kv or 132kv recognising and operating with a fault at 11kv, so the time delay to operate could be two or three seconds.

So, a fault at a much higher voltage, and quite possibly some distance from you will be pulling down the voltage for perhaps two or three seconds where you are until the fault is cleared. Some equipment at home will be more sensitive to (severe) voltage fluctuations than others, hence some items affected, some not.

[Dave Baker]

Obviously due to deployment somewhere of an EM pulse weapon. A no-brainer for Stargate SG1 watchers.

[John]

Ha, that'll be it Robin. We get the LEP delivered but it only arrives at about 5.30ish - hadn't thought about looking at the online version :o)

Everything working as it should, it was only off momentarily. What I couldn't understand was that it only affected some things in the house and not others.

John

[John]

Brilliant explanation Wanderer, thanks very much.

John.

[John]

Must admit, that hadn't really crossed my mind Dave :o)

[Dave Plowman (News)]

You had a voltage reduction and those things sensitive to this shut down while others - like a kettle - carried on. Some devices with a clever power supply can cope with a much greater voltage reduction than others and carry on working normally. Had it been dark and you'd had lights on you'd have noticed a reduction in brightness. Probably.

[John Rumm]

Yup, very useful. ;-)

I would add to that, IT equipment in particular will respond to these things in different (and sometimes surprising) ways.

Most PC power supplies have enough internal capacity to ride out short interruptions of several hundred ms. So a short glitch that affects some equipment may go unnoticed by the PC. However as the duration increases more and more will reset (hence the "some computers in the office" problem). The reverse can also be true, the PSU in the HDD recorder may be able to cope with longer interruptions than the (typically more heavily loaded) computer PSU can.

Brownouts (sustained low volts) pose a different sort of problem - how it copes with this will depend on the PSU technology. Most IT kit will have switch mode PSUs, and some have very wide ranging input capabilities (laptop PSUs for example are often happy with anything from

90V up), and may carry on with half mains voltage and not bat an eyelid. Others may treat it as an interruption and shut the machine down. What happens on power recovery is controllable in the BIOS on many PCs now. So you have have them stay off, or start, or return to whatever state there were in at the time of interruption. Most non IT kit will just run dimmer / slower or not work at all on low volts. Although some things like fridges are actually at risk of being damaged by persistent low volts.

For IT kit a UPS is your friend!

(and if you power is anything like ours, gets well used sometimes!)

[John]

Again, very good, interesting info - thanks John

[The Natural Philosopher]

"Brownout". Voltage dropped enough to trip some stuff but not others.

[Roger Mills]

Not quite a "blackout" - but bad enough to require a change of underwear?

[tony sayer]

In article , John writes

More then likely it went low volts which we have had a few times recently. On one transmitter site dropped to around 120 volts affected some gear and not other stuff. One unit will work on anything, literally from 70 up to 300 odd the others are far more fragile!....

[The Natural Philosopher]

[The Natural Philosopher]

Lost a SCO unix box to a brownout once. It had two big disks and a tape drive in it..too much for the power supply capacitors to keep going on. It rebooted, and we got another one as it was reloading all its operating system. Crashed the most critical part of the disk. Never worked again.

No other computer batted an eyelid.

[John Rumm]

We had about half a dozen power cuts last Monday during the day - only lasted at most a couple of mins each so the UPSs rode though them without any difficulties. The last one however came at about half seven, and it stayed off. After 15 mins or so I though it was time to power down before the batteries ran out. Then we though ok, now what? Decided a cinema trip was about the only thing to do, so fired a computer up again long enough to book tickets (made it with 30 secs of battery to spare!). Buggered off to see Shrek the third. Phoning home at 10:00 revealed still no power (this power cut affecting only 300 meters square of the village it seemed). So got a takeaway on the way home. Apparently the power came back about 10 mins before we got home ;-)

[mike]

"Dave Plowman (News)" wrote in news: [e-mail]:

Had it been dark and you'd had lights on

Absolutely.

I sit up late with the cat and a lager and watch old films on the telly with houselghts dim and surround sound through a separate unit. (On Saturdays I have some cheesy biscuits - that's living all right!)

My lights, (overhead supplied) are always dimming, but the telly, HDD player, and audio unit don't give a damn.

Neither does my PC if on, or anything else that I can see.

mike