Power cut

[The Natural Philosopher]

yes.

If not, how does it all work?

>

[The Natural Philosopher]

make sure they are all rotating at te same speed. Typ[ically 3000 RPM

They (mostly) run through electronic switched mode inverters that deliver at whether the mains is at - unless it drops frequency and then they disconnect..as they did...

Note that's the same for windnills, solar panels, and HVDC links to France etc...

[The Natural Philosopher]

in general just three lightbulbs is pretty good

Exactly. the grid will drive a generator as a motor

[The Natural Philosopher]

its not a simplification. Its exactly what would happen

[charles]

I know we did this as a university practical, but it was in 1962 and I can't rememebr much about the process.

[Bob Eager]

This is an amusing read (and on topic, as you will see).

Tiny version:

[Max Demian]

I heard on a radio programme recently that the generator people are relaxed about the overall synchronisation and they don't have clocks saying "electric time" and "actual time" in the power stations so that "cooker clocks" might not be reliable. Does anyone know if this is true? There must be loads of synchronous timeswitches about, and quite a few clocks - I think I saw one in a local hospital.

[Max Demian]

I don't doubt it: it's more like believing that big metal things can fly.

[Andy Burns]

AFAIK exactly the opposite, they make sure there are exactly 4,320,000 cycles per 24 hour period.

[The Other Mike]

The interconnector HVDC links, or at least the ones we have right now will always operate at the local frequency and disconnection will only occur at or around the same frequency for rotating heavy plant, so they will always operate down to at least 47.5Hz. Technically 45Hz is possible with 55Hz at the other end.

[Martin Brown]

They are legally bound to keep the twenty four hour average extremely close to 50Hz - ISTR the exact tolerance is still an official secret.

Excursions 0.1Hz either way are not uncommon at times of heavy or light loading. They play catchup in the night and run slow in daytime.

A synchronous motor mains clock could be running 0.2% slow for most of the working day so in an 8 hour shift it could drift by about a minute in the employers favour. These days most modern systems are crystal controlled and drift around 15s a month or less if trimmed.

Cooking wouldn't notice a 0.2% error in timing. GPS would!

[tabbypurr]

the output of them all connect together, so if they're not in sync a massive short happens.

NT

[The Natural Philosopher]

Thanks. I didnt know that.

So tehy wont dosconnecte but they wont help stabilise frequency actively, either

[The Natural Philosopher]

There are specifications. Long term ferquency drift is zero. So clocks may run fast or slow for a while, but it always ends up back on time

[Max Demian]

That's what I thought. (The programme was the last edition of BBC Inside Science from Radio 4 BTW.)

[tony sayer]

Do that many clocks use the mains these days?, went to the leccy wholesalers the other month quite a good range, all battery Radio ones and aren't they using much the same or quartz on cookers and the like a lot nowadays?..

[Steve Walker]

Probably any mains powered clock. Why bother using the crystal, when mains frequency (over time) is more accurate? The crystals are then only used for battery back-up.

SteveW

[Martin Brown]

Any connected to the mains are probably using the 50Hz reference unless they use MSF Rugby or the DCF77 German equivalent atomic clocks.

You could test it experimentally. A rule of thumb would be any with a wallwart with a DC output are quartz crystal. The rest are most likely mains. If they keep time to much better than 15s/month then they are almost certainly using mains as their frequency reference.

[newshound]

Part of the reason it was so bad was that about 500 MW of "embedded generation" dropped off the system automatically because of the phase shift following the two "main" trips. Lots more detail here

[newshound]

Very detailed analysis of it all here