Apparently to match the demand at given instance electricity plants rotate their turbines a bit faster or a bit slower instead of switching a complete plant on and off[edit: this is not exactly right, see the reply below], which results in slight deviations from the 50Hz standard but it is fine as long as it stays between the limits.
At the end of the day, as the demand increases and decreases, the average frequency would be 50Hz and engineers took advantage of that fact to create clocks that may not be accurate to the second but accurate on average. How do they do that? They count the change in the electricity and assume that 50 changes are exactly 1 second.
Unfortunately, due to political issues in the Balkans, the grid was undersupplied or oversupplied for a prolonged period and this created a deviation from the average of 50Hz and the clocks that depend on this average to be 50Hz also lost accuracy that currently amounts to 6 minutes.
This is slightly imprecise. It actually works the other way round: the demand is "communicated" through the network by slight changes in the frequency.
This can be described best for the example of steam-based generators, as they are typical for the majority of coal/gas/oil/nuclear power plants. When demand for electricity grows, for example because a new factory is powered up, the turbines in the power plants are experiencing larger forces attempting to slow them down, starting with the power plant closest to the new factory.
The speed (and thus the frequency) is constantly measured, and if it drops, the steam valve is opened just a tiny bit more to counteract the drop. If this is not possible because the power plant is already at maximum output, either other power plants have to take the load (and the electricity is then routed through the network to the factory) or additional power plants may have to be added to the network.
The important thing is: the frequency change is a means of communication, it originates from demand changes, and because the entire network is kept in sync, it works to communicate demand changes across the entire network. Power plants providing energy to a sub-part of the entire network always attempt to run their turbines with the exact same speed of 50 rotations per second, which should ideally always conform to the frequency in all other sub-networks that a specific sub-network is attached to.
If just one of these sub-networks does not perform its duty of re-establishing 50 Hertz by powering up their own plant output, the rest of the network must either channel enough power into this sub-network to allow its local generators to re-establish 50 rotations per second by taking some of the load off of them or - if that is not possible or decided against - must also deliberately drop their frequency (and thus the rotational speed of their generators) to match the sub-network that is deviating.
The only alternative to this would be to drop off the deviating sub-network entirely, but that is usually only done in extreme cases of deviation.
If the USA's power grid is about 4,000,000 meters wide, and the electric signal propagates at roughly the speed of light (3 x 10^8 m/s) (https://physics.stackexchange.com/questions/358894/speed-of-...), then it will take roughly .013 seconds for the electrical signal to reach from one station to another. This is a lot out of phase! (the period of 60 Hz is .016 sec) How is this managed?
If two generating stations on opposite ends of the country are both contributing to the electrical signal, how is this time lag accounted for? I have two guesses:
1. The power network is "mapped" such that there is one central generating station and all other generating stations are time lagged based on their graph distance from this generating station
2. All stations try to generate simultaneously, with their output signals interfering with eachother to a certain degree. This might not matter much because their local loads dampen the strength of their signal.
Either way seems to introduce inefficiencies.
Imagine you are on half a tandem bicycle. You are in a room with the chain of the tandem vanishing beyond the wall. You can't see, but clearly someone else is pedalling the thing as the pedals are rotating. Getting on it is tricky, as you have to rotate your feet at the right speed, but once you're on you can sit there and let it carry them round - or you can start applying pressure through your feet to do work and accelerate the chain system.
At this point you discover the thing on the other end of the chain is not a person but a 60Hz synchronous motor-generator. Congratulations, you are in sync with the grid and (when pushing on the pedals) contributing power.
(A corollary of this is that if your grid connection is down or the grid is split into two pieces, you can't start up again until you get a grid input to know you're in phase. See "black start" for details on this.)
It's like a very long pipe with standing water in it. AC power is like attaching a pump column at one point and adding/removing pressure at just that point. This creates a /wave/ of energy that propagates, but the actual water (electrons) do not. It's more accurate to say they vibrate.
Continuing the metaphor, power plants increase the amplitude of this sloshing wave, and must be synchronized to the phase of the wave /where they connect/ (in order to be additive instead of subtractive). Consumers of the power are always subtractive, '(active/passive) power factor correction' in switching power supplies is about attempting to keep the consumption timed for efficiency. AC Motors are continuous users and mostly just draw all the time.
In early days of electrification the physical topology usually was spanning tree and in fact this was the motivation for research into minimal spanning tree algorithms at the time.
Think of the phase as a distributed signal that indicates the current state of the local system taking into account all connected generators. It's weird but true!
This makes it sound more complex than what I learned when I last tried to figure it out =)
They seem to be describing that where two grids meet they go through a synchronizer that disconnects one or the other if they aren't in sync, so implies manually disconnections throughout the network as needed locally.
If instead of a tandem bicycle, it is a very long rope that someone is moving up and down, then when I try to join some distance away there will seem to be a wave passing me. Even if I join in at the correct phase, I will also be generating a wave traveling back to the first 'generator' and interfering with the existing wave along the way. With the right distance and relative strength then we will produce a standing wave between us. Is there an apparent 'direction' to the wave of electric potential in a large grid?
Then there is the issue of triangular arrangements the sibling comment raised, when the radial distances and relative phases don't align.
Maybe my issue is always trying to think through physical analogues I can 'see'.
The nearest I can think to "direction" is "reactive power", or the phase angle between voltage and current at any particular point.
There very definitely are loops and multiple paths to a particular point, it's not called a "grid" for nothing. This little map of the UK grid is interesting: https://www.nationalgrid.com/uk/about-grid/our-networks-and-...
Edit: Aha, further reading - systems for altering the phase angle: https://en.wikipedia.org/wiki/Quadrature_booster
I'm also wondering since a couple of years about the same question.
Once the generators are switched in, they'll inherently maintain sync, as even if there's too little motive power being supplied by the station's turbines, the difference will be made up by the power grid itself, which will drive the generators round like an electric motor. (Typically this would happen for a brief period after coming online, after which the station would throttle up and start helping to push the generators round.)
If you think of two generators connected together in a power grid, they need to have the same frequency and the same phase. If one of the generators slows a little bit, it begins drawing current from the other. It in effect becomes a motor. Power flows as a proportion to the difference in phase angle.
Perhaps they're not using just frequency to coordinate (solar/wind perhaps needs a sidechannel?), and someone on their grid in a politically unstable area is using power without reporting on the side-channel. Hence the frequency drops due to the unaccounted load.
But the effect is as you say: something goes bang.
Yes, east coast and west coast are out of phase, but only to a perfect observer who can see phase value on both coasts instantly (without a propagation delay). However in reality information about the phase cannot travel faster than speed of light, so to any real observer anywhere between east and west coasts both sides appear to be in sync.
Going forward it may not be a good idea to rely on the grid's timebase as there's talk as well as an NPRM out there to do away with the standard. https://www.federalregister.gov/documents/2010/03/29/2010-64...
All power grids are connected, so there is just one frequency.
and here is a commercial example:
This is actually quite handy. When demand locally exceeds supply, the phase will lag (this is how generators work), and power will flow toward the excess demand.
More advanced grid operators use various devices to intentionally shift the phase to control the flow of power. 
 Actually calculating this is surprisingly complicated. You can integrate the Poynting vector; you can model the inductance and capacitance of the line, calculate the current, and use P=I*V; or you can probably do it in several other ways. You might even be able to model it as little packets of energy moving along at the group velocity.
 This ability is important for economic and engineering reasons. Imagine you connect two cities with two parallel, competing transmission lines. One has 100 MVA capacity, and one has 10 MVA capacity, but they have the same impedance. (This is a bit farfetched, but capacity is related to impedance, heat dissipation ability, and the ratings of whatever equipment is at the ends of the lines.) Without some kind of active control, to much power will flow through the 10 MVA line and it will fail.
> The electrical grid that powers mainland North America is divided into multiple regions. The Eastern Interconnection and the Western Interconnection are the largest. Three other regions include the Texas Interconnection, the Quebec Interconnection, and the Alaska Interconnection. Each region delivers 60 Hz electrical power. The regions are not directly connected or synchronized to each other, but there are some HVDC interconnections.
Here’s some visualizations of that (see the linked movies) from a cool project called FNET/GridEye:
But the answer is contained in the parent comment. Each plant generates more power if the phase lags and produces less if the phase leads. Basically, electricity consumers drag on the phase and the plants use this to control output power, so that the phase matching can be done purely locally.
But it is a lot simpler if you use high voltage DC! If you do that you can connect networks with entirely different phases!
So that takes care of some of it.
Anyway, synchronization is actively managed, when a generator starts up, it is synchronized to the grid adaptively.
So there must be some accounting for this propagation error, either as losses, or engineering.
What I suspect (totally not my field) is that the high power interconnects between large generators do have this triangular lag (the incoming lines lag from the plant's reference frame), but they use quadrature boosting or similar to match that particular interconnect.
T&D (transmission & distribution) result in ~6% of the net energy being wasted. I imagine phase lag "feels" like impedance, with the real component acting as resistance.
Also, it's worth noting part of the appeal of HVDC, aside from line reactance and skin effect, is you get to choose your output frequency.
Maybe active synchronisation solves this, but to my (inexpert) mind the network would still suffer from interferences at various points between power plants.
BTW North America actually has eight transnational (USA/Canada) interconnection authorities or "regions" in which power distribution is managed; it's not a unitary entity.
For example, there was a big power outage in Florida in 2008 that caused a generator to suddenly go offline, and several orgs had a couple dozen power frequency meters running on the grid at the time, so they were able to make an animation of the east coast power grid "ringing" over the course of about 10 seconds as the load changed rapidly throughout the grid.
The animation for that is here: https://www.youtube.com/watch?v=bdBB4byrZ6U
Do you know how the power plant's control loops are tuned? It seems like just tuning your plant to be properly damped isn't enough, because there's also lots of feedback from other power plants.
(And really, the load changes are typically more gradual. Even "everyone just got home from work" is a fairly spread out event, compared to, say, the sudden loss of a few hundred MW of generating capacity...)
> TV pickups [...] are a surge in demand caused by the flushing of toilets (leading to a surge at the pumping stations) and the opening of fridge doors by millions of people. There is a common misconception that the number one driver of TV pickup is the boiling of kettles. In fact, this only creates a pull on the local network for a short period of time until the water has boiled, and can therefore be managed relatively easily, whereas flushing the toilet causes a longer surge at the water and sewerage pumping stations, and opening the refrigerator lets the chilled air escape, causing the compressor to run.
Personally I'd expect a shortage to result in a lower voltage, not a lower frequency.
I'm also rather surprised that the correct functioning of my clock depends on the political stability of a politically unstable part of the continent.
The opposite is also true, if you suddenly increase the load on the generator, the generator will start spinnging less fast and the frequency drops to say 49.9Hz.
This is all very carefully monitored, and there are multiple automatic (massive) power breakers throughout a power network to detect these changes. Imagine all power lines of a large part or entire country suddenly dropping away. The network outside of that country would suddenly experience a large decrease in load and its frequency would go up, while inside the country the load would have a large increse, reducing the frequency in that country. If the change is so large that the frequency goes above 52.5Hz or below 47.5Hz, then the automatic circuit breakers trigger to prevent damage to the entire network (basically adjusting the load of the network). If it can't adjust enough, more circuit breakers will trip, causing larger outages.
Example of these are the 2003 Italy blackout and 2003 US/Canada Northeast blackout.
Reconnecting a blacked out part to the grid isn't easy either. People tend to leave things on during a blackout, such as airconditioners and TL lights. Now when the power comes back, these things draw a low of power for a short period of time during startup. Normally this isn't bad, but when they all do it at the same time the load is massive (think of a power spikes of 7-8x the normal usage), usually tripping the same huge circuit breaker again.
As for the clock deviation, apparently running below 50Hz for a longer period of time has been condoned by the people in charge of the EU power grid. Maybe for too long. There are two solutions:
- generate more power in the EU, but that costs money. They could sell the power to the slackers (which I guess they don't want to pay for)
- cut the slackers off (which is very drastic and does not help the EU's idea of looking out for each other).
But a decision has to be made. Looks like more power is currently being generated, as the frequency is now on 50.010Hz.
If the problem is that the frequency is too high, i.e. power load is too low in that coubtry, why would tripping a break help? Wouldn't that very suddenly aggravate the problem and create even higher frequencies?
"On a level road it is easy to maintain speed. On reaching a gradient, however, the rider needs to make more effort to achieve the same speed. Going downhill, the rider needs to apply the brakes to keep the same speed.
In the entire European network the electrical generators are set up in such a way that they automatically and immediately respond to a change in grid frequency. Depending on the level of consumption they increase or lower their capacity. This ensures that the frequency remains stable. This automatic adjustment can be compared with the cruise control in a car."
And very interesting thoughts come up, especially when you add newer developments like non-rotational-mass-based power sources (solar power, batteries, stuff like that) into the mix. Because at the moment with the high number of traditional steam-powered generators, the rotating mass of the turbines and their inertia serve as a kind of buffer against sudden swings in electricity demand with an ultra-quick response time of "basically no time". As a second buffer stage we have the steam supplies in the plants, which can be quickly accessed just by opening a valve, thus the response time is non-zero, but still quite short.
Now replace all those generators with some other power sources without those inherent balancing capabilities (that probably weren't explicitly built into them, but that just happen to be there because of their construction) and you'll get a network that is much more vulnerable to sudden changes on the demand side. Now, explicit mechanisms of storing energy in a way that can be accessed in literally zero time need to be introduced into the network, just to keep it stable and to provide other regulation mechanisms (of which a lot of them also have to be re-thought) with enough time to do their job.
I wouldn't wonder if there were already plans for building large rotating masses with motors on them that are kept at network frequency, with the motors switching over to serve as generators when the frequency drops.
The question of "how can we build a large and stable grid without thousands of tons of rotating mass?" is an area of very active research I've been told.
(It should be noted that other motors, including asynchronous machines, contribute as well)
AIUI the HPR has reaction times on the order of a few seconds.
Flywheels? Yes: https://en.wikipedia.org/wiki/Flywheel_energy_storage#Grid_e....
It was also built to be able to do a black start (startup after a total grid outage).
Aren't all stations?
Some coal plants had gas turbines fitted solely to allow a black start, others a ton of diesel generators. Some plants need power from the grid to kick off - nuclear for instance. Only some percentage of the grid needs cold start capability, and the rest of the grid is bootstrapped from that.
 (edit) Think aero engine. Rolls Royce Avons were used at Didcot A, and the industrial Avon is still available after 60 years. That's the same basic engine found in the Hawker Hunter and EE Lightning.
For that reason, all the equipment in the generator building ran on 48V DC, supported by a large bank of batteries.
Somewhere there will be a manual for the unfortunate operators who will have to restart the whole grid in the correct order, relying on the telephone company's backup generators to communicate.
Now that a bunch of wind and solar is being added to the grid with completely different control schemes, there’s a lot of concern about whether the system will continue to stay reliably synced.
Only when people started interconnecting these generators in a grid did the need to settle on a single frequency arrise.
How does the demand affect the frequency ? Is there a logical unit, somewhere, responsible of "communicating" through the network ? Or is it a physical effect ?
> When a factory is powered up, the turbines in the power plants are experiencing larger forces attempting to slow them down.
How does something like a higher demand, a drop in frequency, translate to a larger force attempting to slow down the turbines ?
If this was not the case, we could basically generate arbitrary amounts of power from nowhere, as there was no resistance and we could thus just spin a generator forever with zero power necessary (except for the little bit required to overcome friction) once it is set in motion. The Lorentz force makes sure that's not the case by slowing down the movement, and it slows it down more if more electric power is pulled from the generator.
There is websites such as https://www.swissgrid.ch/swissgrid/en/home/experts/topics/fr... that track and display the deviation.
When the alarm went off the following morning, I proceeded to get ready for lectures (This clock was my only means of telling the time, there were no phones or computers in my room) and after having showered I switched on the TV (which could only receive 3 channels at the time!) where I was met with unfamiliar programmes. This confused me for a long while until I realised the time was about 40 minutes later than the clock told me. I missed my first lecture.
Looking at other comments, it seems that we're a little weird down under and most places don't track the drift.
It scrapes the swissgrid.ch page (with something like "curl | grep | sed > csv" in a loop), so the data is only as accurate/current as theirs…
Edit: here's the actual sheet in case you want to "fork" it – https://docs.google.com/spreadsheets/d/1i9cLeKb5Eq1IoZFOUoOk...
If you want a free source of mostly-reliable oscillations, and it doesn't have any real impact if it falls out of sync, sure go ahead and use something like this. But in the case of time, if you want to sync a clock in Western Europe with something that is free and non-internet based, you're much better off using DCF77 , which is specifically designed to synchronize time and comes with specific uptime and quality promises. Still ultimately susceptible to political actions, of course, in extreme cases, but at least you know its primary purpose is to transmit time information, and it is in the control of only one (relatively) stable government as opposed to being subject to the unpredictable changes brought about by interactions between multiple interconnected systems.
DFC77 doesn't solve the same problem as using AC as an oscillator, of course, since you still need an oscillator to keep your clock going during the downtimes that are permitted to the radio signal.
I would disagree. You don't get it for free, you pay for that. The Grid frequency is regulated and the powergrid providers have, IIRC, even legal obligations on how far they are allowed to deviate the time.
Using AC as clock signal is good enough if being wrong by a few minutes is not mission critical. If you absolutely do need accurate time use DCF77 or GPS.
That is not entirely true. The TSO is committed to keeping the average frequency of the power grid at 50Hz and has always communicated that. It tries to keep grid time within 20 seconds of UTC, and has historically achieved this. So it is reasonable to use the grid as a time source where high accuracy is not required. The current situation is highly irregular. Using the grid frequency for time keeping is a secondary function of the electricity grid, but it is not merely an unintended side-effect.
I agree with the rest of your points about using a different time source where high accuracy is required.
When living at what was then often quoted as the extreme fringe of the coverage area - Trondheim, Norway, on 63,5 degrees of latitude - I had reliable coverage as long as the clocks were kept in window sills (hence, effectively outdoors)
However, just moving down to my current home (on 62 degrees, or -roughly speaking- 11% closer to the transmitter site), I now have reliable coverage everywhere (granted, in a wooden house - but the DCF77 alarm clock in the basement synchs every hour, too)
Or one can use a PC to transmit the DCF77 signal locally (it could be illegal) to a clock using a pair of headphones, I've seen at least a couple of examples but never tried them.
Edit: found the photo http://forums.watchuseek.com/f17/possible-method-improve-ato...
You can find more details in the second page of this datasheet
This is completely outside of my area of expertise, but doesn't the radio signal strength decrease exponentially? So that last 11% could be a big deal?
Line-of-sight attenuation of an EM wave in the empty space is quadratical, whilst - for example - attenuation of an electrical signal in a wire is exponential.
Obviously this is a super simplification...
On a only barely related note, I've been playing with the idea of implementing a NTP synced clock on an ESP8266. It'd wake up, join wifi and sync NTP every few hours, then keep time on its internal crystal in between. It should be a good deal cheaper, work anywhere in the world, and have better indoor coverage (I have a DCF77 clock in an interior bathroom in London, and it never syncs. Kind-of defeats the purpose that I have to move it to a south-facing room for the day to get it to sync).
Even with that, a clock generally runs for months, even years, on a single battery. Not exactly phone territory, but might be feasible on the ESP8266, depending on how the oscillator behaves in deep sleep mode.
TI's bq32000 is $0.55@1K, is 3.3V for easy interface to the ESP, and takes just over 1 microamp in backup power mode. That's just one that I quickly poked at.
(Side note: at this point, I'd think I'd want to be using an ESP32 in any new designs.)
He solved this problem by making gifts of his clocks to executives of the local power companies, and as if by magic, the timekeeping of all his clocks soon improved.
Several fascinating points:
- Denmark is split between the Nordic (Sjaelland and Lolland) and continental systems. Anyone know why?
- Even North Africa is synced to Europe.
- A corner of northeast Poland is fed by Belarus.
- Cyprus is disconnected, and northern Cyprus apparently has no network to speak of.
- You can see the DC links to the other systems, and e.g. a back-to-back converter at Alytus, Lithuania, that isolates the European from the ex-Soviet system. But I see no such arrangements at the Belarusian and Ukrainian borders, or at the borders with Syria and Iraq. Is this just missing information, or are these countries also synced in some way?
The Jylland-Fyn grid and Sjælland grid was developed in parallel so we ended up with a grid containing 400kV and 50kV cables West of Store Bælt and 60kV East of Store Bælt.
According to sources I've found (all in Polish, so I'm not linking them here), this 220kV line Between Bialostok and Rossj was built in 1962 and is out of use since 2004. The power to the region is delivered by 100kV lines which are not shows on this map.
There was an idea to build a new one double 400kV line to import energy from Belarus but nothing going on so far.
North Cyprus does not surprise me but Crete apparently has no power distribution to speak of or only 50kV lines for transmission.
From memory they were planning to have a subsea interconnect installed.
You mean Kaliningrad? Because that is not Poland but a Russian exclave
Looking at the map it's clear that OP means Białystok.
Best I've got is an offhand sentence that Kosovo is using more power than it produces and Serbia refuses to balance that consumption.
Since the end of the Kosovo war in 1999, the four northern Serb-majority municipalities have not paid Pristina for their energy consumption.
To make up for the shortfall, people from other areas of Kosovo had a percentage added to their bills to pay for the north’s electricity.
In December, the Energy Regulator’s Office announced that electricity bills will be reduced by 3.5 per cent as consumers will no more cover the cost of the four municipalities’ power as they have done for the past 19 years.
Source: I live here.
raising this issue now (rather than earlier in the year) in response to the near-end of the syrian pipeline proxy war, bulgarias mysteriously financed repurchase of it's own gas lines from czech holding co, lavrov and gazprom ceo in belgrade unveiling giant mosaic, etc etc etc...
edit: I stand corrected, we are in the same frequency domain with Sweden and Norway. I must have confused myself with the DC submarine cables under the Baltic.
In high school, I was told that a lot of the power for Minneapolis was sent over high tension DC lines from coal power plants in the neighboring Dakotas for this reason. This was part of the lesson about how the lakes in northern Minnesota had very little pH buffering capacity due to limestone being scraped down to bedrock by glaciers and therefore being particularly sensitive to SO2 emissions from coal power plants in the Dakotas, but most of the electrical demand for that power also coming from Minnesota.
I took the frequency data from the last 1200 days, and calculated the cumulative drift. The raw drift graph, assuming 50Hz is nominal, is here:
This seems bogus; there's a constant drift.
If I compensate for that drift by assuming the nominal grid frequency is 49.9972Hz, the data looks a little more sane.
You can clearly see the 6 minute deviation this year - it's pretty striking, and certainly nothing this drastic has happened in the last three years. But what's with the positive offset over the previous year? Not entirely sure how much I trust the RTE data.
I have no evidence to back this claim, only anecdotal info as I know some people in the area:
The Serbian minority in the north does not pay for electricity in Kosovo due to a long standing disagreement with Pristina. The Kosovo government so far managed to find ways to compensate for that, either through loans or by charging more people in other areas.
However, I'm guessing, the bills skyrocketed when the crypto mining craze started so Pristina decided to stop footing the bill.
I've heard of thousands of mining rigs being set up in the area, largely due to the free electricity.
So now there's no more free electricity but there is a huge demand and nobody is paying. Hence the deviations.
When I read about the power shortage today, I was kinda relieved to get the confirmation, that my own pattern recognition was very fine, but that my theories where just not elaborate enough :-D
If you are on a tandem bike, all occupants notice the decrease in speed and add power to get up to speed.
Unless one of them doesn't, and then you have to add even more power to also carry their feet through the rotation...
Yeah, that swissgrid website linked in the parent comment even has a "Everyday comparison with a bicycle" section. :)
- Stored capacitance of the distribution lines (sub-ms response time).
- Stored kinetic energy of the spinning machines, both generators and loads (sub-cycle response time).
- Automatic throttle management (sub-second response time).
- Spot market for electricity (intervals vary, but 15 min is typical).
- Futures market for electricity (up to a year in advance).
Not all suppliers bid for the frequency control market. Those that do are paid to adjust their throttle back and forth automatically, providing what's known as primary frequency reserve. Normally, every hydrocarbon power plant is bidding for primary frequency reserve. Typically all of the supplier bids for for short-term frequency control have the same ramp rate for automatic throttle management, set to provide a 100% power step per 5% frequency deviation. It makes up the difference between what the spot market cleared and what customers actually demanded during the interval.
Normally, (in deregulated electric markets in the US anyway), a frequency decrease translates directly into a higher price for power, which is cleared by the spot market to return frequency back to 60.0 Hz. A sustained frequency decrease, combined with a net sink of power into this particular geopolitical region, is caused by suppliers in that region failing to provide enough power to clear the spot markets. The difference is being made up by the PFR suppliers throughout the rest of the grid.
S is "complex power", meaning it includes both the real (resistive) and imaginary (reactive) parts. It is measured in volt-ampere, and is calculated as S=I_z x V, where I_z is the impedance current ("complex current").
P is "real power" (resistive) measured in watts, and is calculated as P=I_r x V or P=S x cos(φ), where I_r is the resistive current ("real current"), S is the complex power, and φ is the phase angle or "power factor"—the delay between voltage and current as an angle.
In a pure DC system (think "incandescent bulb on a battery"), the phase angle φ is 0 making P equal S, as cos(0) equals 1. However, in real life, it is only a vague approximation. Electronics switch currents and have reactive components, giving them a non-zero phase angle. They're more complicated to calculate on than an pure sine-wave AC system, not less.
(I apologize for any hiccups above. I stopped being an electrician a looooong time ago.)
Both the weight of the stone and the height have an impact on the energy required to do the lifting.
Now imagine you are lifting and lowering it repeatedly. It should be intuitive that doing so 50 times a second requires more power than doing it 25 times a second (One being more lifts than the other, in the same time period).
As a matter of fact the average DC power does not depend on frequency.
You could posit a system where g is alternating between positive and negative values and the h reacts to it (phase-shifted). You'd quickly come the conclusion that the potential energy (averaged over a period of oscillation) does NOT depend on the frequency. (The kinetic energy does, but that's where your analogy breaks).
This is false. In the toy system, weight is current, height is voltage. A stone that stays still has constant voltage, not zero voltage. Thus, it would have a 'power'.
What the system lacks is to define the stone as a capacitive load. Then it would sorta make sense.
It is a hypothetical system, so you can only reason about the aspects the author defined. Tying potential energy in the toy system to real-world potential energy doesn't work.
(Btw, potential energy is not power, it is work. Power is work over time.)
> As a matter of fact the average DC power does not depend on frequency.
Uhm. "DC power" stops existing if the frequency ≠ 0, so in that sense it does depend on frequency.
It's true that power itself is not frequency dependent. However, any load is, as reactive losses (parasitic or not) are a function of the frequency. As the power is a function of the load, power ends up being directly tied to the frequency.
(A resistive load cannot exist outside of a perfect DC system, so reactive loads will exist).
If you define mass/inertia as capacitance, then the resistance to changes make sense. A pure resistive load (which cannot exist, but lets ignore that) is not frequency dependent.
It's incredible how connected and interdependent we have become as a society and how we only notice this if things start to break (or at least run out of spec); even if it only impacts such supposedly minor things as a clock on a baking oven.
Using AC as a clock is not the worst and most of the time extremely reliable.
This seems to be the primary issue, not the minor drift in cheap clocks.
Also, the press release says nothing about "energy war" so that kind of hyperbole does not add anything of value.
What is going on here is akin to someone tampering with their electrical meter, except done by a state electrical company, so on a somewhat grander scale.
1 GWh = 1,000,000 KWh and in Serbia/Kosovo the price is around €0.07/KWh so the retail amount of this theft is around €8 million. It is significant enough to make an issue of it, but not really a big deal.
Same info for November 2014 : 49,99994706 Hz.
(edit:Apparently, the emergency broadcast system.)
Leads to interesting questions such as how the (time-based) metering is affected in this situation.
Modern ones are networked SPSes or small industrial PCs.
Even many consumer grade clocks will sync to the radio signal once a day and use a quartz otherwise.
Source (in Dutch):
I am sure I set it correctly after the end of the latest daylight savings period (which they also should forbit, different subject).
It seems getting worse over time. It now runs behind for guess what.. 6 minutes ;)
I guess a lot of clocks use a crystal now so they're less dependent on the grid frequency.
Also don't buy an alarm clock in the US and bring it to Europe and vice versa, unless it is user adjustable (or you are comfortable with a soldering iron)
Then again, what kind of more dependent systems or companies would have negative effects due to this? Besides bedside alarm clocks.
It's actually moderately annoying.
It was a fairly well reviewed (cheap) machine from Wilkinsons, a budget brand. Perils of cheap electronics.
EDIT: Well sounds like it's not the case, TIL, not sure where I picked that up from.
The voltage is usually 240 volts rather than 230, but within the acceptable range (which can be as high as 256).
Higher voltage is good. The kettle boils faster.
After last week where demand was very heavy and frequency was below 50Hz, the frequency is currently the highest I have ever seen (50.107Hz)
You can also see the French grid using the same site. This shows the European frequency at 50.024Hz, so perhaps corrective action is being taken.
Edit - as you were, 5 minutes later UK frequency is 49.902Hz and European frequency is 49.993Hz
It is? What does the UK use?
I'm not sure if that is the case.
And they cannot set it higher than 50.01 because at that point mechanisms for bringing the frequency down to 50 would automatically kick in.
They seem to go well above 50.01 for significant periods. Data from http://www.gridwatch.templar.co.uk/
For the Continental European grid, the article links to https://www.swissgrid.ch/swissgrid/en/home/experts/topics/fr... which states that in the case of a time drift of more than 20 seconds the frequency will be shifted to 49.990 or 50.010 to correct it.
As of a few years ago the best was Germany, where the average customer had about 15 minutes per year without power due to unplanned outages (excluding outages caused by exceptional events). (For comparison, the best quartile of utilities in the US averaged about 90 minutes/year for their average customer).
If you look inside a cheap mechanical timeswitch , you'll find a synchronous motor the size of a sugar cube, turning 50 or 60 times a second, then half a dozen plastic gears reducing the rotation to 1 turn per day. AC wall clocks follow the same principle, but with a slightly different gear ratio.
This means you don't need a printed circuit board, or any integrated circuits, or anything like that. Such efficiency is how you make a profit, if you're selling timers on Aliexpress for $3.50.
If you're making a digital timeswitch, a quartz crystal might be cheaper, or might not - it depends on the insulation/isolation you think your product requires.
"I didn't notice until now" is quite the opposite of happenstance, on par with the PHB mantra "what do we need devops for, anyway, the network seems to be up!" Well it's up because devops is keeping it up. Likewise, the grid doesn't just magically self-balance around 50 Hz.
EDIT: Nevermind, sounds like there are precision concerns that justify using the power grid for timekeeping.
leftpad would like to have a word
Edit: NPM has engineering challenges, and Node as well...but I would be extremely hesitant to call a library of ~ten LoC "engineering."
UK and EU grids have websites letting you look at frequency history.
There's still an awful lot of infrastructure keyed off having an accurate synchronous time, including billing systems, traffic lights, street lights...
A clock using the power grid as reference might be off by 4 minutes over the day but on average it will be perfectly on time.
You can use a resistor to lower the voltage and plug in a stepper motor and there is your clock.
When the idea was initially proposed quartz generators were also a bit more expensive so using the grid to synchronize was not a bad idea at all.
Even today it's not the worst idea since it's being kept very close to 50hz. Close enough that you can safely operate an alarm clock from it without being off to far by the end of the day.
There's probably thousands of electrical panels with old DIN rail timers that don't get replaced until they die.