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I was listening to an interview (sorry don't have the source) from the Mexican's minister of energy, where he mentioned 'Wind turbines are useful even when the wind is not blowing because they can be used as frequency regulator'. Now I understand the need for ancillary systems to regulate frequency swings, but I'm not sure I understand how a turbine can be used to do so.

Can a wind turbine consume energy (reducing frequency on the grid)? Is there any way for a wind turbine to increase the frequency of the grid without the wind blowing?

winny
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Snick
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  • False ......... they can draw power which may cause a reduction in grid frequency – Tony Stewart EE75 Mar 03 '21 at 16:07
  • Sorry, why 'False'? It looks like the statement is correct. By consuming energy, they can reduce the frequency on the grid' – Snick Mar 03 '21 at 16:11
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    Don't trust the any politician's technical remarks unless you know that politician is an engineer. Since wind turbines rotate at different speeds depending on the wind, their rotation cannot be coupled to the mains frequency (like is the case for a conventional power plant). So these wind turbines use **electronics** to adjust the frequency of their output to the grid. If the reverse were true then the grid's frequency would vary **a lot** and many clocks would tell the wrong time (many clocks use mains frequency as a time reference). So that's not the case. – Bimpelrekkie Mar 03 '21 at 16:21
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    *Can a wind turbine consume energy?* No because that would be silly, where would the energy go. OK, we could use them as a **fan** but that would be stupid. *reducing frequency on the grid?* That has nothing to do with wind turbines. **If** the mains grid is overloaded then the frequency could drop as the generators turn slower, normally this should not be allowed to happen, the generators should turn at the correct speed. – Bimpelrekkie Mar 03 '21 at 16:27
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    It's possible (as I understand it) to drive DFIG (doubly fed induction generators) used in most large turbines, so that they appear as an inductive or capacitive load - i.e. a reactive (lossless) load - so they can perform power factor correction. This may improve grid stability (though it doesn't directly affect the frequency). –  Mar 03 '21 at 16:36
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    @BrianDrummond That's true. The minister might just confused frequency control with voltage control. – AlexVB Mar 03 '21 at 16:44
  • @Bimpelrekkie afaik I believe wind turbine are connected to the grid and in a forced frequency sync. All wind turbines rotate at the same speed, what changes is the torque on the rotor (based on the wind). – Snick Mar 03 '21 at 16:47
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    Frequency regulation without any wind isn’t possible but there is significant research in using wind turbines with VSC (pretty much all of them these days) as FACTS and/or reactive power control which don’t need any wind if you have enough DC link capacitance. – winny Mar 03 '21 at 16:50
  • @BrianDrummond and Winny, I think you might have actually hit the right point. I assume if you can control voltage, there are ways to control the frequency (although I don't know what those systems are). Follow up question, what practically (from a mechanical standpoint) does it mean that they are deployed as reactive loads? Do they actually start rotating ? – Snick Mar 03 '21 at 16:50
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    @Snick No, their speed is not forced to be all the same. Bimpelrekkie is correct that electronics is involved ... normally a DFIG uses electronics to synthesise a rotating field that will, for the turbine's actual speed, provide a mains frequency power output. I'll let the usual sources explain how DFIG works! The benefit over an inverter is that the electronics only need to handle the field power, a tiny fraction of the rated power. (And as a reactive load, no they won't rotate!) –  Mar 03 '21 at 16:50
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    @Snick True synchronous wind turbines are very rare and old. You can assume pretty much all built after 2000 have power electronics in between the turbine and the grid so their speeds are allowed to vary. Newer ones are full on VSC. – winny Mar 03 '21 at 16:55
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    _” Do they actually start rotating ?”_ Depends on how much DC link capacitance they have. If “too” little, then they need the turbines inertia as energy storage which needs to be rotating at some minimum speed. Also, if they are rotating, there is also research in using the stored energy in the inertia for fast frequency regulation. This puts significant mechanical stress on everything but FFR is very expensive in some parts of the world so may be worth it to take the initial cost to sell FFR during the turbines lifetime. – winny Mar 03 '21 at 16:57
  • @Bimpelrekkie It’s not that silly if you could have a wind turbine which could act as a chopper for the grid, but the situation is usually the opposite - local wind farm looses part of or the entire link and drives the then local frequency too high and you need a chopper for a few seconds. – winny Mar 03 '21 at 17:06
  • False .. it cannot increase grid f but any load of GW proportions may slow down the grid by accelerating to speed with no wind and lots of drag – Tony Stewart EE75 Mar 03 '21 at 19:57

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It seems likely that the quoted statement is related to supplying reactive volt-amperes to the grid. Only wound-field synchronous generators can supply reactive volt-amperes. All other generating sources need to have capacitors to supply reactive volt-amperes. Grid operators tend to accept connection with supply their "fair share" of the reactive volt-ampere load connected to the grid. That means that wind turbines and other sources that are not wound-field synchronous generators would likely have capacitor banks connected to the grid either directly or through a grid-tied inverter. A grid-tied inverter for a wind turbine could supply reactive volt-amperes without the turbine operating. They would not really be operating as "frequency regulators," but they would prevent the frequency from varying due to the reactive volt-ampere demand on the grid exceeding the supply capacity of other connected generating sources.

Other questions here answer questions about reactive volt-amperes they will have the [power-factor-correction] tag. For example: Power factor correction of predominantly inductive load component with capacitor