POWER FACTOR AND COMPLEX POWER

POWER FACTOR


The power factor is the cosine of the phase difference between voltage and current. It is also the cosine of the angle of the load impedance.

The average power is a product of two terms. The product Vrms Irms is known as the apparent power S. The factor cos(θv − θi) is called the power factor (pf).

S= Vrm Irms

The apparent power(inVA ) is the product of the rms values of voltage and current.

The apparent power is so called because it seems apparent that the power should be the voltage-current product, by analogy with dc resistive cir- cuits. It is measured in volt-amperes or VA to distinguish it from the average or real power, which is measured in watts. The power factor is dimensionless, since it is the ratio of the average power to the apparent power.

COMPLEX POWER

Considerable effort has been expended over the years to express power relations as simply as possible. Power engineers have coined the term complex power, which they use to find the total effect of parallel loads. Complex power is important in power analysis because it contains all the information pertaining to the power absorbed by a given load.



Complex power(inVA) is the product of the rms voltage phasor and the complex conjugate of the rms current phasor. As a complex quantity,its real part is real power P and its imaginary part is reactive power Q.

 Given two of these items, the other two can easily be obtained from the triangle. , when S lies in the first quadrant, we have an inductive load and a lagging pf. When S lies in the fourth quadrant, the load is capacitive and the pf is leading. It is also possible for the complex power to lie in the second or third quadrant. This requires that the load impedance have a negative resistance, which is possible with active circuits.

LEARNING:

The apparent power(inVA )is the product of the rms values of voltage and current.

The power factor is the cosine of the phase difference between voltage and current. It is also the cosine of the angle of the load impedance.

Apparent Power is simply:   P_apparent= V_RMS I_RMS

Therefore we can express Average Power as:    P_average= P_apparent × pf

We can also say:    pf = P_average/P_apparent

In other words, the power factor is the percentage of Apparent Power
that is actually being absorbed by the load.