Apparent Power (VA) is the product of the RMS Current and the RMS voltage.
True power is the time integral of the (product of instantaneous current and instantaneous voltage) divided by the time period.
Energy (KWH) is the same as above, except that the integration is over an indefinite period of time, and you don't divide by a time interval. If you're working with Volts, Amperes and seconds, then you must multiply the result by:
~ (.001KW/Watt)(1/3600 Hours/Sec) to get KWH. A KWH meter performs this integration.
.
For sine waves, the calculation of reactive power and true power is simpified.
Pr = VIsin(Theta)
Pt = VIcos(Theta)
Pa = VI
Where
. V = RMS Voltage
. I = RMS Current
. Theta = phase angle between voltage and current.
. Cos(Theta) is the power factor (PF).
. In general, PF = (True power)/(Apparent Power)
Regards,
Kral