On Mon, 25 Mar 2002, Bill Hooper in USMA:19071 wrote:
. . . > The watt is also equal to a volt-ampere but that is not it's original > definition. The watt is originally defined as a joule per second. Since the > volt (V) is a joule per coulomb (J/C) and the coulomb (C) is defined as an > ampere-second (A�s), it is easy to show that the volt-ampere equals the > watt: > 1 V�A = (1 J/C)�(1 A) = (1 J/A�s)�(1 A) = 1 J�s = 1 W . . . That of course being the case, could someone please explain why serious power equipment often uses VA (kVA, MVA, etc.) as distinct from W ? I recall recently seeing some small computer UPS (or some other equipment) that was rated in both VA and W, with *different* numerical values given for each. (Is this an RMS-vs-peak kind of thing?) This has always perplexed me when I see VA used on utility transformers, etc. Bruce H.
