Load KVA vs kw

Dodgydave

Joined Jun 22, 2012
11,284
KVA is the AC version of KW. Kva is the total power drawn from the mains what you're paying for!!, KW is what is being done by your equipment.

then you have a power factor loss if less than 1 for Inductive and Capactive loads, , you will get a smaller KW output, which is wasted power!!, The smaller your power factor the more wasted electricity you're paying for!!

KW = KVA x PF.


In DC there is no wasted power factor.
 
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nsaspook

Joined Aug 27, 2009
13,081
USA residential services typically don't pay for (or cause much) reactive power so billing is by kilowatt-hours (real power). The large AC induction motors seen in industrial sites will cause significant reactive power loads on the utilities if not PF corrected so they get billed for both KWh and KVArh consumption.
 

WBahn

Joined Mar 31, 2012
29,978
Why do we use kVA instead of kW to rate alternators and transformers?
To some degree, it is an indirect way of specifying amperage capacity. The heat and stresses in a transformer are primarily functions of the current in the windings, independent of the voltage. If you have a low power factor, you can have a large current but be delivering a lower real power -- but the windings see the current and don't really care about the phase relationships. Since the RMS voltage across the transformer is essentially fixed, the kVA is proportional to the RMS current. Having said that, there are other losses that really only depend on the voltage, largely independent of the current. So kVA is a way of taking both into account in a reasonable way.
 

dendad

Joined Feb 20, 2016
4,451
In DC, power = amps x volts. so 10amps at 100Volts = 1KW
In AC too, but only if the load is resistive , and that will have the current and voltage in phase.
BUT, running AC into a capacitive or inductive load will have the current and voltage out of phase to varying amounts depending on the capacitive or inductive reactance (like resistance) so there will need to be a triganomic calculation to determine the Volt/Amp value, and that will not be the same as the Watts.
There may be more info ...
https://www.allaboutcircuits.com/textbook/alternating-current/
(I have not read it myself).
 
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