On 12/10/2020 09:00, 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.

All rotating generators are AC, and DC is obtained from them either by
mechanical rectification (commutators) or via silicon diodes.

Only constant speed turbines running at some sub-multiple of 50Hz (3000
rpm) can generate synchronous mains frequencies.

Wind turbines by their nature are not constant speed devices and
gearboxes to push than from a few revs per minute up to synchronous
speed would be lossy fragile and expensive. And locking their blades to
a constant speed would probably destroy them.

So its AC=DC=mains freq AC via two pieces of power electronics


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more than peace. Those who seek battle despite peace. Those who thump
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battle dance and dream of glory €¦ The good of dead warriors, Mother, is
that they are dead.
Sheri S Tepper: The Awakeners.