Mains power voltage drop to reduce usage? (2023 Update)

Why would an invertor disconnect at lower frequency? It should be able to match any frequency.

Its a regulatory requirement.

John

That is not an explanation. There's no reason to disconnect.

But you can drop it to 49 for a while then put it up to 51 when there's plenty power.

It is to me... If I am the engineer designing or installing an inverter, I have to follow the law and regulations.

And do it in the entire Europe, simultaneously?

System frequency is maintained within very tight tolerances - - for a variety of reasons. Large thermal generators are quite fussy about frequency. Alarms will sound at less-than .5 Hz +/- ; automatic load shedding and/or generator rejection and other significant control measures will happen at ~ 1 Hz. +/- < or even less >. System frequency variations are a sign of problems / instability / unbalance etc. which can cascade and cause system separation islanding and complete system shut-down. The adjustments that are made to maintain clocks are in the range of .05 Hz. . John T.

Why are the generators fussy to 1%?

We're linked by DC, so no.

No, you're *supposed* to.

Anyway, that doesn't explain why the regulation is there. Surely an invertor is capable of producing a sine wave at any frequency?

Big generators are synchronous generators and the question is how do you connect a large number in parallel (in the national grid) and how properly share the generated power between them. The power delivered depends on the _phase_difference_ between generators i.e. a constant phase difference.

If there would be even a small _frequency_ difference between generators that would cause a constantly variable phase difference. If the phase difference would grow above 90 degrees, a catastrophic situation would occur.

Note that this method of synchronizing generators several hundred kilometers away from each other has been used for well over a century without any other synchronization connection, just the power grid.

Messing up with the frequency would also mess up the phase protection systems.

Wrong.

Well said, downunder. As a result, there cannot be a _frequency_ difference _anywhere_ in the net. The entire net must change frequency.

Most parts of continental Europe are connected to a single 50 Hz synchronous network (UCTE). UK is connected to this network with under sea DC cables. Scandinavia is also connected to this UCTE network with DC cables. All these three networks are nominally 50 Hz but there are phase differences varying all the time.

Due to the AC/DC/AC connection across the Channel UK could do some strange thing with their network without affecting the continental Europe.or Scandinavia.

They strive to keep the generators perfectly in phase with the rest of the network. Allowing a phase difference would cause reactive power, which is wasteful. The power delivered is adjusted by regulating the field excitation. The input for the regulator is the mains frequency. There are set limits to that process, of course, to protect the installations.

The overall coupling constant for the European network is about 20GW/Hz, IIRC.

Jeroen Belleman

That can in fact be done. And was done. And it wrecked equipment in German factories, so they installed their own exactly 50Hz inverters.

I think the problem originated in one of the ex eastern bloc nations.

Yes, the European mainland grid whilst it is not all of Europe, is synchronised. I believe Norway, the UK and Ireland, are definietly totally separate.

Yes. Unfortunately if the UK grid frequency drops too far, those inverters feeding it from the undersea DC will disconnect, as will all the wind farms and the solar panels, making everything worse.

It has already partially happened. Fortunately a large section of grid could be isolated and blacked out saving the rest.

There cant be. In practice if the generator isn't being fed enough torque, its phase lags and the grid drives the generator!

Its very simple. You run your generator with no load. match the phases and connect to the grid. The generator is now locked to the grid as surely as any other synchronous motor is.

Then when you push the steam into the turbines all that happens is that the current rises and the phase advances slightly. Very slightly.

Don't think you really understand how it works.