Chris Hogg wrote:
On Mon, 12 Oct 2020 03:19:43 -0400, Paul
wrote:

Scott wrote:
I visited the UK's largest on-shore wind farm this afternoon. Some of
the turbines were running and others were not. I assume this was
simply a factor of demand.

There was one turbine we watched (turbine 40). It was running as we
arrived, then it stopped, then it restarted (all as others in the same
section continued to run). Why would they stop and start one turbine?
Do they need to be rested or tested or rebooted periodically?

How do they maintain the frequency if the rotation speed can vary with
the wind? I know they can adjust the angle of the blades but it was
clear the turbines were not all running at the same speed.
https://www.lagerweywind.nl/wp-conte...LW_L147_en.pdf

GENERAL

Nominal power 4.3 MW
Rotor diameter 147 m
IEC class IIA

Turbine concept Direct drive, variable speed,
variable pitch, full power

Power control Electric pitch control

GENERATOR Lagerwey multi-pole
synchronous generator
Field generation Permanent magnet

Cooling Based on air flow around
the outside of generator
(cooling fins)

CONVERTER
Type Full power AC-DC-AC
Control system IGBT-Control
Cooling Water-cooled

OPERATIONAL DATA

Cut in wind speed 2.5 m/s
Cut out wind speed 25.0 m/s
Power factor Regulated

SAFETY SYSTEM 3 independent pitch control
systems with emergency
power provision

OTHER

Service brake system Standard
Lubrication system Automatically controlled
bearing and gear lubrication

The AC-DC-AC part, the output AC side matches the grid frequency.
The output side could be single-phase or three-phase, whatever
the customer wants.

Paul

So, for the benefit of my understanding, they generate AC of variable
frequency depending on wind speed, rate of rotation etc. This is then
rectified to DC, which is then converted back to AC of frequency
corresponding to the grid frequency and locked in to it. Is that a
reasonable summary?


Yes, that's it.

Just don't underestimate the complexity of that converter
though. It's got a lot to do, to prevent the tower
from toppling over, the blades from flying off, and so on.
Since the document above claims an ordinary "generator" with a
permanent magnet rotor is being used, there are some
dangerous conditions involved there if the generator
is under-loaded. Part of what the converter has to do
is "get rid of the energy with haste". Transferring
it to the grid, helps keep down the terminals voltage
on the generator part.

They could use a generator, an alternator, a magneto.
Each has different properties. On something like
this, maybe they're shooting for decent efficiency.
I don't know if the alternator is the best choice
for that. Your car uses an alternator, because
it's "dead easy to control". But it also happens
to run at a rather impressively high temperature.
Even generators get warm. That's why the 97% number
in that spec sheet is pretty amazing.

Paul