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What is Kilo-Volt_Ampere used for? What is kW used for?

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closed as unclear what you're asking by ACuriousMind, user36790, knzhou, Diracology, Gert Jul 13 '16 at 1:48

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    $\begingroup$ There is no difference. A Watt is equivalent to a volt-ampere - the unit of power. $\endgroup$ – lemon Jul 12 '16 at 14:59
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    $\begingroup$ @lemon Yes there is. A coil with 14mH inductance and zero resistance will draw a current of 50A when connected to 220V 50Hz mains, enough to blow a domestic fuse. Yet the coil itself doesn't dissipate any power (0W), the (220*50) 11kVA is reactive power. $\endgroup$ – Previous Jul 12 '16 at 17:29
  • $\begingroup$ I do not have enough rep to vote to re-open, but it's pretty clear what the OP is asking. The question is straightforward and is in the title, and the body is about as clear as it could be. I'm not sure how anybody couldn't be clear on what is being asked. That said it might be a better question for EE than physics. $\endgroup$ – Jason C Jul 16 '16 at 18:47
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VA is used for apparent power and reactive power. Watt is used for active power. An inductor or a capacitor in an AC circuit does not dissipate energy, because the current and the voltage are 90° out of phase: energy flows into them during half the cycle, but it flows back during the next half cycle.

The power lines have to supply that current however, and they have transport losses since their resistance is not zero. The dissipated power in a supply line is equal to I²R: if the current is I+d during the first half of the cycle and I-d during the second half, the dissipated power during the whole cycle is: (I+d)²R/2 + (I-d)²R/2 = (I²+d²)R.

The rated VA of a load also determines the required current capacity of the line, the fuse needed to protect it etc...

The ratio of active power to apparent power in a circuit is called the power factor, or sometimes the "$cos \phi$". Large customers (factories,...) may be charged extra when their $cos \phi$ is too low. Usually there is an excess of inductive load (electric motors for example), and the $cos \phi$ will be corrected by adding capacitive load.

Power ratings for transformers, AC motors, AC motor controllers are usually expressed in (k)VA. Purely resistive loads like heating elements will have a rating in (k)W.

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You can reference these links: https://en.wikipedia.org/wiki/Volt-ampere

https://en.wikipedia.org/wiki/Watt

The prefex Kilo simply means 1000. So a Kw is 1000 watts and a KVA is 1000 volt-amperes.

Hope this helps!

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