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AC BASIC AND NETWORKS

How to find out of Apparent Power, True Power, Reactive Power and Power factor?

The product of rms values of current and voltage, VI is called the Apparent power and is measured in Volt-amperes or kilovolt Ampere (KVA).

The true power in an AC Circuit is obtained by multiplying the Apparent power by the power factor and is expressed in Watts or kilowatts (KW).

The product of apparent power, VI and the sine of the angle between voltage and current, sinΦ is called the Reactive Power. This is also known as wattless power and is expressed in reactive Volt-amperes or kilovolt Amperes ( kvar).

i.e., Apparent power,
                                               VI
S = VI Volt-amperes or --------- kVA
                                            1000

True power, P = VI COS Φ  watts or 

                 V I CosΦ
              ------------------ KW
                  1000

Reactive Power, Q = V I SinΦ VAR or

                   V I SinΦ
                ----------------  KVAR
                   1000 

And KVA  =  √ ( kw)^2 + (kvar) ^2

Power factor may be defined as 

I)  Cosine of the phase angel between voltage and current 
Or 

II) the ratio of the resistance to impedance or 

III) the ratio of true power to apparent power.

The power factor can be greater than unity. The power factor is expressed eighter as fraction or as a percentage. It is usual practice to attach the word "lagging" or "leading" with the numerical value or power factor to signify whether the current lags behind or leads the voltage.

1) Active Component of current.

The Current component which is in phase with Circuit voltage
( i.e., ICosΦ) and contributes to active or true power of the Circuit is called the Active ( wattful or in phase ) component of current.

2) Reactive component of current.

The Current component which is in quadrature ( or 90° out of phase ) to Circuit voltage ( i.e., I sinΦ ) and contributes to Reactive Power of the Circuit, is called the Reactive ( or wattless ) component of current.

Q- Factor of Coil.

Reciprocal of power factor is known as 
Q-factor of the coil. It is also called the quality factor to figure of merit of a coil.

Mathematically Q - factor

                   1                        1             Z
 =   ------------------------ = ------------- = ------
      Power factor         CosΦ          R

If   R  is very small in comparison to 
Inductive reactance XL , the 

                           XL           2πfL
Q- factor  =  ----------  =  --------
                            R               R

                         Maximum Energy stored
Also Q = 2π× ------------------------------------
                      Energy dissipated per cycle


                    



     

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