Irish LaidE said:
i've just started to read about imaginary or reactive power my text
book doesn't seem to cover to much information on this subject.
any additional information on this subject would be greatly
appreciated
IL,
There probably is a book, somewhere, with an explanation that will make it
clear to you. I've never read one that really explained it well, to me.
Capacitors and inductors (perfect ones, that is) do not dissipate power as
heat (or light), although they will dissipate some power due to radiation
(as a function of the driving source frequency or as a function of their
self oscillations). Ignoring the radiations effects, capacitors and
inductors are energy storage / energy release devices.
When a sinusoidal signal is applied to a capacitor or an inductor, the
resulting current through the device is 90 degrees out-of-phase with respect
voltage across the device. The voltage "lags" the current in a capacitor (it
takes time for the charge to separate across its plates (I * t), so the
resulting voltage (Q/C) builds up as time goes on (it lags). The opposite is
true with an inductor. It takes time for the current to change in an
inductor.
Here are two things to remember:
1) you can never instantaneously change the voltage across a (perfect)
capacitor, and you can never instantaneously change the current through a
(perfect) inductor.
2) a (perfect) capacitor or inductor will never get hot. In the real world,
however, this is not the case -- due to parasitic impurities.
The "so called" real component of power is that component that dissipates
power. The reactive/imaginary component is that which is being transferred
back-and-forth between inductors and/or capacitors in the circuit and its
driving source.
If you apply a sine wave to a circuit of R's and C's and L's, and look at
the resulting source's current's phase (with respect to the driving voltage,
you can always separate the current into two components: the "in phase" part
of the current and a part which is 90 degrees out of phase (either leading
or lagging). The heat generated by the circuit will only be due to the
applied V and its "in phase" component of current. This is the "real"
component of power. The balance is the "imaginary" component of power (the
portion that is transferred back-and-forth to/from the source.
This is probably a pretty good start, for you. Ask more questions after
you've thought about this.
Bob