Wagner Lipnharski wrote:

> Paul, what you say, is that if I create a device and install it
> between the electric meter and all my house wiring, and by any way
> this device cause a strong shift in current angle, say 90¡ to Voltage,
> reflected to the meter, and correct it back to my house wiring, I
> would be paying almost zero of power consume?

  The suggestion as I heard it was that most appliances are either
pure resistive or inductive.  Domestic fluorescent lamps rarely have
correction capacitors (just another part that sometimes goes "bang" and
emits pungent smoke).

  It is therefore argued that the meters are compensated for inductive
loads but not a strongly capacitive load and indeed have a design
limitation there (related to the motor requiring a "lag" circuit to make
it rotate).

  No alteration to fixed wiring is involved.  The supposed "cheat"
device is merely a (switched) gang of induction motor run capacitors
plugged into any power outlet to over-compensate the whole system (which
depends on what you are doing already) so that at light loads, the meter
runs backward.

  Such is the claim, I have not tried it.  It is pertinent to note that
capacitors are somewhat unfriendly devices to switch into circuit (and
inductors are correspondingly unfriendly devices to switch *out* of
circuit too!) and should have bleeder resistors.  Imaging pulling the
plug out...

> so probably that "free" angle should be not exactly 90¡.

  It may be as little as 45¡ capacitive.

> Question:  Why should a meter take current *AND* voltage to calculate
> my house's power consume?

  Because they are required to be *fair*.

>  Reading just current should be enough, since voltage is a known
> element

  No way!  Surely you realise that the line voltage is anything *but* a
known constant.  20% variation is quite common (100 to 120V on a 110V
line).  The meter must accurately measure power to within a few percent,
(under *reasonable* loading conditions - and there is the trick) and
unless the contract states penalties for reactive loading (see the
website I gave for specific metering of reactive power!), this most
certainly means real and not imaginary power!

> and by this way they can avoid problems with power factor messing with
> their measurement...

  Indeed it is necessary to measure the voltage and current to determine
the in-phase product for this very reason - to *avoid* power factor
"messing with" the true power measurement.
-- 
  Cheers,
        Paul B.