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from the you're-not-just-bored:-the-wall-clock-IS-slow dept.
Electric clocks on continental Europe that are steered by the frequency of the power system are running slow by up to 5 minutes since mid-January according to a news release from the European Network of Transmission System Operators for Electricity ('entsoe'). The transmission system operators (TSOs) will set up a compensation program to correct the time in the future.
Many electric clocks rely on the transmission system frequency to provide a source that minimises long-term drift. Quartz crystals have good short term stability, but dreadful long term stability, so plant and machinery that requires power to be turned on or off at a specific time each day without maintenance over a long period historically used clocks slaved to the power-system frequency, which is kept long-term stable by the system operators to prevent problems in power generation and transmission across national and supra-national grids - for example, attempting to switch supplies to generators that are not synchronised to the grid frequency can severely damage the generator.
It is normal for transmission system operators to allow the frequency to drop slightly at periods of high demand, thus slowing clocks, but usually, the frequency is increased during periods of low demand to ensure the long-term average frequency remains stable.
(Score: 2) by Grishnakh on Tuesday March 06 2018, @11:07PM (4 children)
However, DC is very ineffective for local distribution because the losses for DC-DC and DC-AC conversion are higher than AC-AC transformations and it is a lot more expensive too.
I'm pretty sure this is no longer true. AC-AC transformation requires transformers, which are large, heavy hunks of iron and copper, both of which aren't that cheap (esp. copper). DC-DC conversion uses semiconductors, electronic control circuitry, and not so much metal, mainly some relatively small inductors. Take a look at the power supply in any computer now; it's really a DC-DC converter with a rectifier for the AC side (which is why it doesn't care if you feed it 120VAC or 240VAC).
Basically, AC is obsolete thanks to modern power electronics. Your post sounds like it would have been exactly right circa 1990, but things have changed a lot since then.
(Score: 3, Disagree) by jdccdevel on Wednesday March 07 2018, @12:40AM (2 children)
I'm not an electrical engineer, but my understanding is that a PC power supply built that way works because the wattages required are relatively low, such that semiconductors can handle them without burning up.
Try running a whole house's, (or an entire neighborhood's!) worth of power through a cheap semiconductor and I'm pretty sure you won't even be able to find the pieces after it explodes.
I know high voltage, high amperage DC to DC is possible, but it's still very expensive. Economies of scale may fix that... but that is nonetheless the case today. And there's no escaping the fact that high-voltage, high amperage currents would be required to provide enough wattage to run a house.
Even something as simple as a switch will wear out faster when used for DC current (AC current reduces contact wear due to arcing.)
Saying AC is obsolete flatly ignores all the uses for AC power that primarily don't involve electronics. (Appliances, heaters, machine tools, welders, fans, etc)
(Score: 4, Interesting) by RS3 on Wednesday March 07 2018, @03:52AM
Actually PC power supplies are DC to DC switching supplies _because_ of the power required. An iron-core transformer that can handle 200-400 W (VA) would be quite large and heavy.
I'll put it in perspective: a typical house has 240V 200A service (some are 400A...) so ~50KW (or 100KW). A typical electric car motor is 150-250KW and is controlled by, yep, semiconductors, often handling 350-500VDC. So you could easily run a house on semiconductor systems.
In fact, that's why Tesla makes the PowerWall https://en.wikipedia.org/wiki/Tesla_Powerwall [wikipedia.org] - they're already making power storage: Li-ion batteries, and controllers that handle similar power levels.
(Score: 2) by Grishnakh on Wednesday March 07 2018, @04:25PM
I'm not an electrical engineer
This is the first problem right here. You're commenting on something you don't understand.
Someone else already responded pointing out that a typical electric car handles more power with semiconductors than your house does, so I won't comment on that.
Saying AC is obsolete flatly ignores all the uses for AC power that primarily don't involve electronics. (Appliances, heaters, machine tools, welders, fans, etc)
The reason for this is because we already have an AC power system, so those devices were designed for that. There's nothing inherent about AC that makes those things work better on it, given modern technology. In the past, many machines did indeed use AC motors that were cheap and worked well with the AC power system. But washing machines, for instance, now have ditched their AC motors and use DC motors (usually brushless DC 3-phase motors actually, which are in reality AC but you don't drive them with household AC power) which are electronically commutated and controlled so they can be run at different speeds and in both directions. Welders don't use AC directly either, they have to step it up or down, and be switchable between AC (of varying frequency, depending on what you're welding) and DC (aluminum, I believe, needs to be welded with DC unlike iron/steel). Heaters can be run with literally any kind of electricity, they're just big resistors. Machine tools again use variable frequency drives to run their motors at different speeds and directions. Some fans do use simple inductive or even cheaper switched-reluctance motors, but the cheap-o fans in your PC for instance are actually brushless DC.
There's really no reason I can see any more to keep using AC, except the obvious fact that we already have an enormous global power system that works that way so there's a huge amount of inertia.
(Score: 3, Informative) by RS3 on Wednesday March 07 2018, @03:34AM
I pretty much agree with you. I'll augment your post by saying: we had good efficient switching supplies in the 1970s, and they've gotten better and better ever since, due to better semiconductors (faster switching, lower "on" resistance). My only beef with them is the filter capacitor failures. I'm fully aware of the "capacitor plague" due to faulty / cheap / fake / poor quality, but even good low ESR caps have a limited lifetime spec. under heavy switching currents (due to design compromises).