> I don't know about the US, but in Sweden, the frequency of the A/C mains, are
> guaranteed to be exactly 50 Hz. If the frequency drops a little during high load
> times, they make up for it during the night. So over 24h, it should be as
> accurate as anything you can think of.
>
US line frequency of 60hz is held to a very tight standard. IIRC VAX-11/780 used a clock based on the line frequency. Alphas generally use a common clock chip, which is why they need leap ticks.
Your joking, right?
bill
No joke. They need perfect synchronisation so that each generating plant provide power to the grid at the exact same phase of the 60hz. A generator that would off by a 120th of a second (half a phase) would in essence reduce the grid's power.
There are , if I recall properly, 2 main grids in north america, on for the east and one for the west. Within each region, all 60hz is synchronised, even between different grids inside the region. And power exchanges between east and west grids is done via AC-DC-AC converters to ensure the power at the other end matches that grid's phase.
How is it distributed on the grid? When I lived in Los Altos there were
110KV lines nearby and I thought they were 3 phase.
They are. That's why that the HV power lines always* have 3 or a multiple of 3 main conductors (not counting neutral or lightning arrester wires)
Are you SURE about that? The last I heard DC was dead except for a very small area in New York City which was the reason for AC/DC radios and TV sets. I think that area may have finally been converted to AC fifteen or twenty years ago.
DC is very awkward to use for power transmission since they can't use transformers to step up the voltage and step it down again. Electric power is normally AC and is transmitted at high voltage to minimize "I squared R" losses and stepped down to 440, 220 or 110 volts at the place where it's consumed.
Yes NYC no longer supplies DC to end users, although there still is some very old DC equipment (often elevator motors) that have to run off AC/DC converters.
That's true, but DC is overall more efficient in the transmission line portion, because it can carry more power for a given peak voltage. It's not hard to go from AC to high voltage DC, just transformers followed by rectifiers not unlike what's in any electronic device other than the size. Getting from DC to AC is much more difficult. This requires fancy converters/switching stations, but they become feasable once you're dealing with large amounts of power that's cheap but not near consumption (like James Bay, lots of hydropower, hardly any people around) as well as interties between different grids that aren't in synch or are even of different frequencies (like in Japan as well as Brazil and I think Paraguay)
Thomas Edison gets the last laugh after all.
I live not too far from the receiving end of the Hydro Quebec DC link that JF mentioned. There is a huge DC/AC converter station there (Sandy Pond, Ayer Mass.) where 900kV DC (+/- 450kV) from Canada goes in, and several
345kV AC lines come out. I see the DC pylons coming from the north often, they have two main conductors with huge insulators as well as a smaller insulated one (purpose unknown to me).
Would that smaller line be the topmost by any chance? If so, it might be a "lightning rod".
I didn't mention the two uninsulated "lightning rod" wires above the mystery conductor.
This is that line in Londonderry NH.
Possibly it could be the return line? (DC "Neutral") So, it's +/0/- with the two live conductors having a positive and negative potential of 450 kV from the "neutral", respectively.
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