Why do street lights flicker in snowy weather?

Sigh... too bad.

Don's quite right on the matter. 'Capacity' is not the current production, but the current maximum possible by on-line equipment. So it is always kept greater than demand. 'Production' is matched to demand by a variety of techniques. Most notably, manual operation of base load settings and governors of regulating units.

'Spinning reserve' is kept on line to respond to sudden losses in capacity by a unit trip. Most system operators are required to maintain enough spinning reserve available for the tripping/loss of the largest generating unit. So if the system has a very large unit on line (say,

1000 MW), they must have at least that much spinning reserve. So you could say the system has a 'capacity' that is kept 1000 MW higher than demand.

daestrom

That would be the start of the sequence and, if the fault was transient, it would result in the line being reconnected. However, if, say, a line had been brought down, then the load would be shifted to minimise, as far as possible, the area affected.

They needn't be, unless you haappen to be within an area that ends up disconnected as a result of the power switching. However, I do recall one incident around 35 years ago, when a fault at a time of high demand resulted in cascading overloads that blacked out much of SE England.

Colin Bignell

The plonk went to:

This is an attack ad hominem. I should check the definitions? Nobody forces me to read plain insults.

Ï "Androcles" Ýãñáøå óôï ìÞíõìá news:S6L_m.23186$ snipped-for-privacy@newsfe02.ams...

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.

Generating capacity, maybe? I think it's installed power. I might be wrong, of course (since many people seem to forget) I am greek and have gotten my degree in Greece. My English is acceptable, but only God is always right.OTOH, we mere mortals...

As long as base units are synchronised, their most efficient use is to operate 24/7 at full load. When they need to reduce output at night, they might eg reduce coal supply

Here, in Crete, we have fast units (gas turbines) that synchronise in 11-12 mins. Even the (small) steam units, 3-4 hours and the 2-stroke diesels 1/2 an hour. I think hydro can synchronise in quite fast, too.

No it's not. You don't appear to understand the term "ad hominem".

Yes. If you're going to pontificate about something which can be measured objectively then you would do well to check your sources before you start to talk about the subject. Otherwise you could end up looking like someone who doesn't know what he's talking about. You were being given good advice which you respond to like a child throwing a rattle out of a pram.

No one posted an insult, plain or flowery. No one can force you to read anything. You chose to read the post, you chose to flounce.

I thought this might be the root of the issue. You are normally quite knowledgeable about such matters. I wondered why you went for 'plonk' so quickly on Don's post.

Although it might be the most economic operating point for a single plant, demand of course does not change in such increments. So some units operate as 'regulating units' and must 'throttle' their output to match demand.

As Don pointed out, in a traditional system a technique called 'economic dispatch' is used to decide which plants to control in this way. Typically this works out to those with the highest fuel costs. Plants with the lowest marginal cost are kept on line as long as possible as demand drops, and those with higher marginal costs are the first to cut back or be taken off completely.

Of course the choice to leave a plant on line at very low power or shut it down completely is another issue. Cost / time to re-start, expected schedule for re-start and fixed operating costs to name a considerations.

In an unregulated system, the choice is made simply on the bid price of each generator (not counting long-term purchase agreements).

Yes, we have 'peaking plants' that can be remotely started and auto-synch and load in a matter of minutes (gas turbine or diesel). And some plants schedule up/down based on predictions of demand.

But if you've lost a large plant's output due to a trip, even 10 minutes is too slow. Every moment that demand exceeds actual production means frequency is dropping. So the combination of the on-line spinning reserve units and the excess capacity in regulating units (sometimes counted in the 'spinning reserve' summary) has to respond within seconds.

Here in the US the FERC (Federal Energy Regulatory Commission), along with NERC, has specific guidelines / requirements to maintain a certain level of reliability in the transmission system. This

daestrom

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.

*plonk*

Do not reply to this generic message, it was automatically generated; you have been kill-filed, either for being boringly stupid, repetitive, unfunny, ineducable, repeatedly posting politics, religion or off-topic subjects to a sci. newsgroup, attempting cheapskate free advertising for profit, because you are a troll, because you responded to George Hammond the complete fruit cake, simply insane or any combination or permutation of the aforementioned reasons; any reply will go unread.

Boringly stupid is the most common cause of kill-filing, but because this message is generic the other reasons have been included. You are left to decide which is most applicable to you.

There is no appeal, I have despotic power over whom I will electronically admit into my home and you do not qualify as a reasonable person I would wish to converse with or even poke fun at. Some weirdoes are not kill- filed, they amuse me and I retain them for their entertainment value as I would any chicken with two heads, either one of which enables the dumb bird to scratch dirt, step back, look down, step forward to the same spot and repeat the process eternally.

This should not trouble you, many of those plonked find it a blessing that they are not required to think and can persist in their bigotry or crackpot theories without challenge.

You have the right to free speech, I have the right not to listen. The kill-file will be cleared annually with spring cleaning or whenever I purchase a new computer or hard drive. Update: the last clearance was 25/12/09. Some individuals have been restored to the list.

I'm fully aware that you may be so stupid as to reply, but the purpose of this message is to encourage others to kill-file fuckwits like you.

I hope you find this explanation is satisfactory but even if you don't, damnly my frank, I don't give a dear. Have a nice day and f*ck off.

------------------ That is rarely the most efficient situation. In Crete, it may be the best approach because you may have some large fossil units and, apparently some hydro and the rest is high fuel cost gas turbines and diesels so that it is sensible. Since the 1930's the process of economic dispatch at any load is to load all generators on line (where possible) to the point of equal incremental cost per Kw modified for losses. This was first done intuitively by operators and later proved to be the optimum loading distribution. A further and more complex addition is to optimize unit commitment considering the costs of shutdown and restart of units.

That's right but if you lose a major generation, do you simply drop loads and wait for more generation to come on line or do you have enough reserve capacity in on-line units to pick up the load if, for example, the largest unit on the system fails?

I would suggest that capacity is not installed power but the available power that can be generated by the units which are on-line. If you bring up and synchronize a100MW machine, you have then increased on-line capacity by

100MW.