Doug Miller wrote:
In article iUMDh.1122344$5R2.839435@pd7urf3no, Tony Hwang wrote:


Many loads are not pure resistive. There is always inductive/capacitive
component.


Really? Always? What's the inductive or capacitative component in a light
bulb?

Hi,
Filament has an amount of inductance/capacitance. it is very fine coil.
Even piece of wire has finite capacitance and inductnace. Why do you
think there is a surge current when light bulb is turn on? Ever heard of
phase compensating capacitor or lump inductor. Or go inside a power room
in any big commercial building, what do you see there? Do you know why
electric cable is some times criss crossed or twisted?
Simply to answer your question, Yes, really, always. It becomes very
critical on high frequency. Todays florescent bulbs are driven by 44KHz
current. Pure resistive circuit in real world is problably near none.
Z^2 is combination of R and j(Xl-Xc). Remember HS physics class?
Xl and Xc cancels each other, equal value, whatever left is either Xl,
or Xc. In real world most load is inductive. In inductive circuit
voltage is leading and current is lagging. This phase difference
produces wasted power which does not do any work. Ideally the phase
difference should be zero.
That is why KVA is not equal to Watt rating of a device.(efficiency)
I spent my working life on RF telecommunication(mobile and fixed base),
UPS, MG, Antenna farm, stuff like that.