Power Factor
In general power is the capacity to do work. In electrical domain, electrical power is the amount of electrical energy that can be transferred to some other form (heat, light etc) per unit time. Mathematically it is the product of voltage drop across the element and current flowing through it.
Considering first the DC circuits, having only DC voltage sources,
inductor is like short circuit
capacitor is like open circuit
in steady state.
Hence the entire circuit behaves as resistive circuit and the entire electrical power is dissipated in the form of heat . Here the voltage and current are in same phase and the total electrical power is given by
Electrical power = Voltage across the element * Current through the element
Its unit is Watt = Joule/sec.
Now coming to AC circuits , The inductor stores electrical energy in the form of magnetic energy and capacitor stores electrical energy in the form of electrostatic energy. Neither of them dissipates it. Further there is a phase shift of 90 degree between voltage and current. Hence when we consider the entire circuit consisting of resistor, inductor and capacitor, there exists some phase difference between the source voltage and current. The cosine of this phase difference is called electrical power factor .
This factor (0<cos<1) represents the fraction of total power that is used to do the useful work.
The total power in this case is , Total electrical power = voltage across the element * current through the element. This is called apparent power and its unit is VA (volt amp.) and it is denoted by S.
A fraction of this total electrical power which actually does our useful work is called as active power . It is denoted by P
P= Active power = Total electrical power cos and its unit is watt .
The other fraction of power is called reactive power . This does no useful work, but it is required foe the active work to be done. It is denoted by Q and mathematically is given by,
Q= Reactive power = total electrical power sin and its unit is VAR (volt anp reactive)
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This reactive power oscillates between source and load.
This factor (0<cos<1) represents the fraction of total power that is used to do the useful work.
The total power in this case is , Total electrical power = voltage across the element * current through the element. This is called apparent power and its unit is VA (volt amp.) and it is denoted by S.
A fraction of this total electrical power which actually does our useful work is called as active power . It is denoted by P
P= Active power = Total electrical power cos and its unit is watt .
The other fraction of power is called reactive power . This does no useful work, but it is required foe the active work to be done. It is denoted by Q and mathematically is given by,
Q= Reactive power = total electrical power sin and its unit is VAR (volt anp reactive)
\
This reactive power oscillates between source and load.
Mathematically S2 = P2 + Q2 .
