Higher voltage grids can't "feed in" from domestic networks

I don't see why, as its not high voltage when its on the domestic network, and one still needs to synchronise the 50 or 60Hz before you can do it in any case. I think we had a long discussion on this not long ago. Brian

Yes, there may be more current carrying capacity needed, but what I read seemed to suggest the HV transformers were somehow one way.

There is nothing to prevent an HV network transformer being used in 'step -up' mode. Most windfarms feed in to the grid via a normal HV transformer in 'step-up' mode.

What gets complicated is when you have a simultaneous step down-and step up requirement.

The turbines certainly do not. They use high speed semiconductor inverters Cant answer for the wind farm as a whole

They output 415kV straight onto the national grid? That's some inverter.

Why? I've got a transformer sat here. If I put 240V in one side, I get 12V out the other side. If I feed 12V in the other side, I get 240V out the first side.

You should have read what I wrote more carefully, I did not claim the turbines individually fed direct to the grid but the windfarm i.e a collection of turbines does.

Each turbine normally has a transformer either inside the tower or close by which is connected to an HV cable network which goes back to an HV substation which then has a step-up export HV to grid transformer

That is not analagous to how a power networks operate. Discreet generation facilities can export by step-up transformers to the grid no problem. Likewise normal distribution systems operate by step-down Tx's to local networks.

The complications come when you try to do both at the same time.

No. It doesn't. Each turbine has a semiconductor HF inverter.

But not 415kV.

Why? As I said, my transformer is happy to go either way with no adjustment. So will the 415kV to 11kV transformers.

That doesn't happen in the scenario above.

Yes as long as the power is flowing one way or the other but not both simultaneously.

Have you tried applying inputs to both sides of your 240 to 12v Transformer?

Well they have on every windfarm installation I have worked on (in the UK). The turbine output voltage may be different on different makes of turbine but it has to be transformed up to the grid voltage somewhere along the line, Canadian practice may differ.

I don't think that the individual wind turbines are outputting at 400kV though. Very likely at 11kV, then the whole farm stepped up for export.

Exactly.

Don't be stupid. Imagine a town being fed by one of those beasts. Only one of two things can be happening, either the town is generating more than it needs, or it's using more than it's generating.

Your idiocy is like saying what happens if it's colder outside my house at the same time as it's warmer outside my house?

I'm surprised there's such a thing as a 415kV inverter. Transistors can cope with that?