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