Why do street lights flicker in snowy weather?



Last night we had lightning, not flickering street lights -- and there were power cuts also. Do you live near any rail system? The shoe on the third rail makes some pretty impressive lightning which lights up the clouds - especially in a fog or snow storm.
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Because of utility privatisation they don't service the lights, exchanging blown bulbs with fresh ones?
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Tzortzakakis Dimitrios
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Tzortzakakis Dimitrios wrote:

I don't think they ever did. They did a planned maintenance thing which was replacing all the bulbs whether working or not. I saw a private contractor doing that the other day.
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I'm not apathetic... I just don't give a sh** anymore

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Eddie wrote:

When I lived in Massachusetts, the only times my lights flickered was during lightning storms. Most of that occurred when demand was almost equal to capacity.
Can you describe the flickering? Were the lights really flickering or was the snow so bad that snow blown sideways blotted out the light momentarily?
/BAH
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Demand is always almost equal to capacity. If it would be more, it would be a waste, if less there would be serious stability issues. That's the problem with wind turbines, you just don't know when the wind blows, and you have to cover each MW of wt with at least of 700 kW conventional reserve, because when the wind stalls what? Stop everything?

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----------------------------- Please check the definitions of demand and capacity - as the above is nonsense.
Ideally the capacity should exceed the demand by some optimal margin but as adding and dropping on line capacity is in blocks corresponding to the capacity or rating of individual generators, and demand is up to the customers (predictable but not controllable) the capacity will normally exceed the demand by a fairly large margin at times- there is no "stability" problem. As for waste by having extra on-line generation- economic dispatch optimization is a common procedure. If demand exceeds capacity, then problems can occur- not necessarily stability problems. As for the wind turbine reserve, you are being a bit over optimistic. You are assuming 30% availability of wind capacity. In practice, from recent data it appears that 10-15% is a better figure and this is a statistic based on an annual average, which means nothing if wind fails. In other words. reserve capacity must be available for the worst case situation- 100% failure of any generation source, concentrated as in a 500MVA fossil plant or distributed as in 500-1MVA wind units in a region where wind diversity is small.
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Most of the generators have variable power output, not simply on or off.

Frequency drops below nominal, and conversely when supply exceeds demand, frequency increases above normal. There's a requirement in the UK for frequency to average out correctly long-term (so things like synchronous clocks don't drift long-term), consequently, supply has to exactly match demand long-term. However, since the demand and supply can't exactly track each other short term due to inherent lags, there are periods of both demand exceeding supply, and supply exceeding demand. These are both inevitable due to the supply lag with different types of plant and unexpected plant failures on some occasions, and deliberately forced to correct for earlier drifts on other occasions.
There is contingency reserve in addition to the supply - additional plant spinning sychronous online ready when needed due to either an increase in demand or an unexpected loss of supply, and yet more plant offline ready to run up and cut in with a bit more notice.
A longer article I wrote on this some years back, with some examples of how it was applied in the UK to some specific historic events, and how it went wrong on one occasion... http://groups.google.co.uk/group/sci.engr.lighting/msg/99b03c9711a4f753?hl=en

The BBC did a programme about the wind power in Denmark, one of the highest users of wind power. In spite of installing lots of turbines and being able to point to all the power they get from them, they haven't been able to spin down any conventional generating station, because they need them when the wind stops. When the wind blows, they have an excess of conventional electricity which they sell, but for their neighbours, it's effectively as unreliable as the wind, since its export stops as soon as the wind stops, so it only commands a low price as an unreliable source. This combined with a failure of a transmission circuit, plunged much of central Europe into darkness a couple of years ago when supply suddenly fell well short of demand, and emergency load shedding was initiated.
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Andrew Gabriel
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-------- In no way did I imply otherwise. However a generator is either on line or off line as a unit so that the system "capacity" changes in blocks depending on the rating of the machine added or removed from the system. The system "demand" depends on the load and this demand is split between the units on line- generally through some economic dispatch scheme.
>

-------------------- I am quite familiar with the concepts and practice involved. -----------------

------------------ Again I have no problem with this- this is normal . Possibly there are some word usage problems
I take capacity as the total available generation on line That is, (ignoring power factor as it affects unit capability), if there are 2- 100MW units and a 50MW unit on line the capacity is 250MW . The load and losses (again ignoring pf) may be 200MW leaving 50MW on-line reserve. I take demand in this case as the load +losses 200MW which has to be delivered to the system. Except for transient periods when loads change the supply and demand are the same. Only during acceleration or deceleration will they be unbalanced. Typically generator droops, essential to proper load sharing between units, will result in speed changes. These lead to frequency errors and the need to correct the long term average frequency. -----------------------------------------

--------------------------
In my opinion, wind is to be used when available- reducing the load on other sources at that time- but it doesn't replace the other sources for the good reasons that you have given. The fact that wind energy is available on nature's timetable, not man's, is one that many wind advocates appear to ignore.
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*plonk*
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Excellent eco-weeny response there. Stick your fingers in your ears and refuse to listen to hard fact.
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The refutation of his, and any windmill enthusiast's claim that windmill are going to reduce CO2 emissions is to look at countries which have an aggressive policy of installing windmills. Say Germany.
Compare Germany (lot so windmills) to France (very few windmills, lots of nuclear power). Germany emits about 10 tonnes of CO2 per person per year. France about 6.5 tonnes per person per year.
Similar levels of industrialisation, similar climates, similar everything. What the Germans have found (surprise, surprise) is that wind power is unreliable and must be supplemented by conventional generating capacity.
The UK could meet all its Kyoto obligations by going nuclear to the same extent as France. Politicians in the UK are too wet to go for it.
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British citizens nowadays carry drugs into China to get themselves executed; they have good ol' Gaelic, Cymru or Anglo-Saxon names like "Akmal Shaikh". I'm surprised Gordon Brown isn't wearing a turban to get himself re-elected.
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I know this is going to be hard for you to understand. But the use of the plural in that phrase was inappropriate, and the use of "citizen" is dubious. I think the term you were looking for was "subject", singular.

I think you will find his aim was to make lots of money, not to get executed.

As opposed to good old American names like "Nidal Malik Hasan", "Mohammed Ali", "Barak Obama" or "Androcles" you mean?

Turbans are worn by a very small proportion of the UK population, notably Sikhs who are not Moslems and who are not even the majority in the immigrant population. Your own coutnry appears to have an immigrant population of about 250 million. So if you're one of those tossers who bases their entire politics on the status of someone as "an immigrant" then I suspect you'll have to start by hating yourself.
Oh look. You already do.
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Mr Shaikh was a subject. Perhaps you should try to remember what you are talking about?
I see you dodged away from the fact that he was an individual, not a group. Is coping with the difference between singular and plural something that confuses you?
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Shouldn't you be busy cutting holes in your bedsheet now?
BTW, only fuckwits piss about with follow-ups.
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If you read my signature, at the bottom is my real email address. So far, almost nobody from any newsgroups have sent me a direct email (except a couple of people), and I've been posting since 1999.
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Tzortzakakis Dimitrios
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And the relevance to sci.physics is what, exactly? Seems to me everyone and his dog uses sci.physics as the default flaming and shit dumping ground.
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