Naked Science Forum
Non Life Sciences => Technology => Topic started by: Chemistry4me on 01/02/2009 01:58:34
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What are the usual causes of power cuts? [???]
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Ummm, someone didn't pay the bill? [;D]
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Of course not!
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Some burk did something stupid.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.millan.net%2Fminimations%2Fsmileys%2Felectricf.gif&hash=9e88a244e16ac606ab69a0f6c6f044bb) (http://www.millan.net)
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I don't know the statistics related to local power cuts, but these are often due to local equipment failure which, in turn, can be related to the weather (lines down for example). Often, cuts due to such effects can be kept to a short period by the nature of the grid system that allows re-supply via a different route.
The bigger problems arise due to the very nature of this grid system. It can happen that local problems can contrive to overload particular power stations. Usually this needs some unfortunate coincidence, but it happens. If a power station gets overloaded (usually the generators cannot maintain the 50Hz, or 60Hz in the USA frequency) they have to be shutdown, Clearly this can, and does, result in a cascade failure over a wide area which can take quite a while to sort out.
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Locally, probably the biggest cause of power-cuts is road-works and other types of engineering that involve digging up the top few feet of the ground.
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I guess the answer to the question will depend upon which part of the World you happen to be in. It could be Israeli shelling, under some circs.
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It can happen that local problems can contrive to overload particular power stations. Usually this needs some unfortunate coincidence, but it happens. If a power station gets overloaded (usually the generators cannot maintain the 50Hz, or 60Hz in the USA frequency) they have to be shutdown, Clearly this can, and does, result in a cascade failure over a wide area which can take quite a while to sort out.
The only thing is that the power plants are not shut down, but disconnected from the grid. These accidents are avoided by equipment that compares the grid frequency with the power plant frequency, after the frequencies are equal the synchroscope allows the breakers to be close.
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mmm...
doughnuts synchroscopes
http://en.wikipedia.org/wiki/Synchroscope (http://en.wikipedia.org/wiki/Synchroscope)
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Well, there wasn't a cloud in the sky the other day so I don't think it was caused by the weather.
I don't know the statistics related to local power cuts, but these are often due to local equipment failure which, in turn, can be related to the weather (lines down for example). Often, cuts due to such effects can be kept to a short period by the nature of the grid system that allows re-supply via a different route.
How short is a "short period"?
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"How short is a "short period"?"
From a fraction of a second (a brownout) to a few minutes.
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erickejah, it is not an accidental loss of synchronism that is the problem. When a generator is sufficiently overloaded it cannot maintain the rate of rotation and then has to be disconnected from the grid. This removal of supply to the grid then affects other generators trying to take up the load, which then also have to be disconnected potentially resulting in a cascade of failing supply. This can be initiated by a power station fault because a station has to be shut down, though usuually there is sufficient capacity designed in to cope. The problem arises if two power stations simultaneously have a problem.
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[:I] yes, you are completely right. [:D] nevertheless, desynchronizing failures still make people think that there is no power, because fluctuations of the frequency that causes equipment to not work at the specified requirements.
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Another one today, although not at my house. Said on the news that it was caused by a transformer fault, what ever that means...
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Another one today, although not at my house. Said on the news that it was caused by a transformer fault, what ever that means...
it means that the voltage lines feeding that community need maintenance. i think that the transformers that they are saying is of this kind:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fblog.oregonlive.com%2Fbreakingnews%2F2007%2F09%2Fmedium_IMG_3988.JPG&hash=ffa65aaa131ce259327becf815dd5614)
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Thanks dude [:)]
But that transformer looks really ancient!
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there are also transformers like this:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.electricityforum.com%2Fimages%2Felectrical-transformers.jpg&hash=9819727135c910e7d52795933b905b8e)
If they break more people is affected. [:-\]
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Well, it has left 74000 people without power!
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Well, it has left 74000 people without power!
i bet it is a 22,000v transformer.
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How do you know that?
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In the UK, and to affect 74000 people, it would more likely be a 200-400+ kv transformer.
I just downloaded a nice pdf showing the UK national grid, from the BBC at
http://news.bbc.co.uk/1/shared/bsp/hi/pdfs/14_06_06_powerstations.pdf (http://news.bbc.co.uk/1/shared/bsp/hi/pdfs/14_06_06_powerstations.pdf)
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Here in the US from about Oklahoma to the Atlantic coast it is ice storms. Tree branches that overhang power lines get loaded with ice and break off onto the power wires. There is a big push going on right now to keep the tree limbs trimmed.
Trees in home owners yards used to be off limits, but a new ruling allows power companies to trim all they want. I hope it works.
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We had major power outs in South Africa last year, and it's still not over. The company, Eskom, was informed years before that the more power stations were needed, but the new management ignored it because no one wanted to make a desicion. So now we're in the dark. Often. There's talk of nucleur power which is awesome.
I hate you Eskom.
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wow! that must be great to avoid power consumption energy loss. What is the frequency in UK? is it 50Hz?
I observed that some coal plants have been close, why is that?
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Yup, the UK frequency is 50Hz.
Lots of coal plants have been closed, mostly for economical reasons i.e. the price of coal, but it also looks good for environmental reasons too. The pollutants from coal fueled power-stations could be recovered and prevented from reaching the atmosphere but that then effects the economics, reducing the profits. We have quite a few mothballed coal mines around the UK and when the technological/economical climate is right I have little doubt that they'll be re-activated.
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There can be all sorts of reasons for power-cuts, and it does depend where you live - even within the UK.
The most drastic case is a major failure in generation somewhere (or a completely unexpected or excessive surge in demand) which causes demand to greatly exceed supply. If this arises, the power companies have little choice but to employ "load shedding" where houses/businesses are deliberately cut off so as to make demand equal supply. This is fairly rare in the UK, but has happened once or twice in the past 18 months or so when there were a couple of simultaneous serious generation-failures.
If you live in the countryside with electricity delivered via long lengths of low and medium-voltage powerlines on poles (240/415V, and 11kV) then windy weather and/or overhanging trees can cause the wires to short resulting in flickering lights followed by the eventually tripping of a fuse or circuit-breaker.
If living in more urban areas, then I'm sure contractors digging holes and cutting through cables is a significant cause of power-cuts.
In urban areas there is sometimes redundancy where the low-voltage (240/415V) circuit can be fed from more than one transformer and upstream supply. A few years ago a fairly significant local transformer in my area failed for some reason, and several hours later the engineers came round opening up manholes and patching in new fuses to make a different circuit. They did this with the power 'live'. Was very tempted to switch on every single device in the house to ensure they got the biggest spark when they put the fuse in!
There's not much to go wrong with transformers, although if something happens to the coolant oil then they can overheat and fail.
In the event of solar storms, the earth's magnetic field can be disturbed and this can induce huge DC currents in very long-distance powerlines. This can cause big transformers to go into magnetic saturation and then they become hugely lossy and will rapidly overheat if you still try and force AC power into them. This caused widespread blackouts in the USA and Canada a few years ago.
So lots of causes.
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In the event of solar storms, the earth's magnetic field can be disturbed and this can induce huge DC currents in very long-distance powerlines. This can cause big transformers to go into magnetic saturation and then they become hugely lossy and will rapidly overheat if you still try and force AC power into them. This caused widespread blackouts in the USA and Canada a few years ago.
interesting [:o]