How Everything Works
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QUESTIONS AND ANSWERS
 
Question 879

With reference to power generation and transmission, can you please explain "Volt Amp Reactance" (VAR, kVAR, MVAR). What is meant by "importing/exporting VAR's"? What is meant when a plant is "consuming/producing VAR's"— ID, Northern Territory, Australia
In most situations of AC electric power generation or AC electric power consumption, the current flowing through the circuit is in phase with (or, more simply, directly proportional to) the voltage across the circuit. But that isn't always the case. In situations involving reactive components (e.g., capacitors and inductors), it's possible for the current and voltage to be out of phase with one another. If the current and voltage are a full 90° out of phase, there is no average power flowing through the circuit. I believe that VAR is a reference to this portion electricity in the circuit—the portion for which the voltage and current are 90° out of phase. While this portion of the electricity doesn't transfer any power, it does place demands on the power transmission system. I think that the distinctions between "importing" and "exporting" and between "consuming" and "producing" are related to the phase ordering of the current and voltage (whether a device is acting as a capacitor or an inductor). In one case, the voltage leads the current by 90° and in the other the current leads the voltage by 90°.
         

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