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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?

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    \$\begingroup\$ 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. \$\endgroup\$
    – Bimpelrekkie
    Commented Mar 3, 2021 at 16:21
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    \$\begingroup\$ 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. \$\endgroup\$
    – Bimpelrekkie
    Commented Mar 3, 2021 at 16:27
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    \$\begingroup\$ 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). \$\endgroup\$
    – user16324
    Commented Mar 3, 2021 at 16:36
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    \$\begingroup\$ @BrianDrummond That's true. The minister might just confused frequency control with voltage control. \$\endgroup\$
    – AlexVB
    Commented Mar 3, 2021 at 16:44
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    \$\begingroup\$ @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!) \$\endgroup\$
    – user16324
    Commented Mar 3, 2021 at 16:50

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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

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