why does a core creates a power factor and how does it happend?
power factor is not a physical term. Its hypothetical. It says how effectively power is used. What i understand from your question is why some amount of power is utilised to magnetise the core.. Is it what you want to know..? if yes, the answer is; allmost all cores are made of some materials which has certain properties of resistance and inductance/capacitance. to overcome these factors some mmf is required which is pulled from supply power.
Power factor results from the inductive nature of a coupling system. To overcome thiis negative effect, capacitors are used to balance the inductivity. Usually sytems rated in VA shall be multiplied by a factor, often between 0.8 and 0.9, to calculate the usable power in Watts.
why does a core creates a power factor and how does it happend?
The core of the tx is made up of material having some hysteresis loss and eddy current loss.To supply these losses ,a working component of no load current.no load current has to supply magnetic current also to magnetise the core which is 90 degree out of phase with v(lagging ).This gives rise to no load power factor angle which is @ 70-80 degree.