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Generators and transformers are always designed in kVA because designers never know about the load it will provide power to. Then how do we know the wind turbine generator will deliver 1500 kW or 2 MW etc?

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    \$\begingroup\$ Jason, can you check your post and clarify or fix "aur 2 MW"? If English is not your first language then please mention this in your user profile. Note: small "k" for kilo, so 'kVA'. 'K' is for kelvin. \$\endgroup\$ – Transistor Jul 14 '18 at 18:01
  • \$\begingroup\$ Could you clear up the question a bit. What are you really asking about? The units of kVA and kW basically mean the same thing -- the maximum amount of measured energy the generator can produce. The difference between them depends on how reactive the load is. For a fully resistive load kVA and kW is exactly the same. Maybe you want to ask about kWh, that is how much energy the generator can produce over time. \$\endgroup\$ – ghellquist Jul 14 '18 at 19:20
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    \$\begingroup\$ @Ghellquist No, when transformer is designed its rating is given in kva. The same is true for generators. It is so because the designer dont know about its power factor. Then how do we know about kw ratings of wind turnines? Some turbines are 2MW and some are 1.5MW. Why are they not rated in kva? \$\endgroup\$ – Jason Jul 14 '18 at 20:05
  • \$\begingroup\$ @ghellquist: kVa and kW are units of power, not energy. \$\endgroup\$ – Eric Duminil Jul 14 '18 at 20:08
  • \$\begingroup\$ Agreed. power, not energy. Happens when you leave your home territory in a second language. \$\endgroup\$ – ghellquist Jul 14 '18 at 20:13
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In most practical contexts, the load of a wind turbine is pretty well specified: It will be connected to a regional power distribution grid. For the relevant purpose here the grid can be considered an ideal AC voltage source -- pushing 2 MW into it will not affect its voltage amplitude or waveform much.

It is therefore reasonable to design the generator to work in that specific electrical environment -- and, in particular, to avoid delivering significant reactive power to the grid (which would tend to make distribution companies unhappy). So specifying its capacity or operating limits in watts is appropriate.

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Generators are designed for a specified capacity that includes both a kVA and a kW capacity. Wind turbines are designed for a specified capacity to drive a turbine that would include the torque that can be provided at a given speed over a specified range of wind speeds and rotating speeds. What is known is the power that can be delivered at any wind speed. A generator of a given capacity will not be installed unless there is a reasonable expectation that there is sufficient demand for power to make the installation economically advantageous.

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