what is the cause of power factor? what is RMS(root mean square)?

Answer 1

OK...power factor is not only because of phase shift...

Power factor is the ratio of real power P as measured in watts to apperent power S as measured in volt-amperes.

which in simple, time-inverant, linear systems (circuits) which can only have the following items:

1. resistors
2. capacitors
3. inductors.
power factor reduces to VI cos(theta).

if there are any non-linearities in you circuit (such as transistors, diodes, scr's, transformers, etc.) your power factor will not be different.

Note: the core of a transformer is nonlinear and as such your power factor is off from the convention of VI Cos(theta). This is generally taken into account with the "stray losses" of your transformer.

Answer 2

The illustrated link may help. Power factors are involved generally when a circuit contains components (capacitors and reactors) that can draw electrical current to set of fields (stored energy) but give the energy back as opposed to pure resistors that dissapate the energy which is lost as heat. RMS is a way of averaging sinusoidal voltages where you square the positive and negative voltages to make both positive, find an average value of that then take its square root (to undo the initial process of squaring values). For example house voltage may have peak values of +/- 170 volts buts performs as though it was steady (average) 110 volts DC when it heats a resistor such as a portable electric heater. Hope this helps a little.

Answer 3

A waveform's RMS voltage produces the same heat in a load resistor that an equal DC voltage would produce. Power factor relates to inductive or capacitive loads that cause the voltage and current to be out of phase.

Answer 4

Kes says "RMS is a way of averaging sinusoidal voltages "

No it isn't.

The average value of a sine wave is one thing, the r.m.s. value is another.

And the peak value of 110Vr.m.s. is 155.54