What is Power Factor and Why is it important?

 

We would discuss about Power Factor in this article. We discuss so many questions about Power Factor like, what is Power Factor? Practical significance of Power Factor, types of Power Factor, why do we need to improve Power Factor? Methods of Power Factor improvement and so on 

 

 

Power Factor

 

There are so many definition of Power Factor which introduced in so many books some of are given below

 

1) Power Factor is defined as the ratio of Active Power to Apparent Power and it is represented by cos@. Let us understand by Power Triangle

S = Complex Power or Apparent Power         

P = Active Power

Q = Reactive Power

J = complex Operator

 

S = P + jQ   _(KVA)

S² = P^{2 +} Q²

P = S*cos@  _(watts)

 

Q = S*sin@  _(VARs)

 

So cos@ = P/S

 

                                                     OR

 

2) Power factor of an electrical circuit is the cosine of phase difference between the voltage and current applied them.

 

                    Cos(_{phase difference  btw voltage and current})

 

@ is the phase difference between voltage V and current I.

 

Power Factor cos@ lies between 0 to 1

 

 

Practical Significance of Power Factor

 

Practically we can say P.F. is the degree of complex power which we used actively. Means , let us consider P.F. is 0.8 means 80% of total power used actively and rest of 20% energy stored in inductor and capacitor in the form of magnetic energy and electrostatic energy respectively.

 

 

Types of Power Factor

• Lagging Power Factor

• Leading Power Factor

• Unity Power Factor

Lagging Power Factor

 

Lagging power factor indicates those loads which absorbs reactive power (lagging VARs). For such kind of loads load current is lagging from supply voltage. This property indicates that load is inductive in nature. The inductor stores the energy in the form of magnetic energy. To maintain this magnetic domain inductor absorbs lagging VARs.  So we can say the power factor of inductive circuits is lagging.  

                             

Leading Power Factor

 

Leading power factor indicates those types of loads which supply reactive power (lagging VARs). For such kind of loads load current is leading from supply voltage. This property indicates that load is capacitive in nature. The capacitor stores the energy in the form of electrostatic energy and it supplies lagging vars.  So we can say the power factor of capacitive circuit is leading. 

Unity Power Factor

 

In a purely resistive ac circuit the current and voltage are in same phase and phase difference between current and voltage is zero.

 

 

Power Factor = cos0 = 1.

 

So we can say that the power factor of pure resistive circuit is unity. Unity power factor indicates that it neither supply reactive power nor absorbs reactive power it use 100% of apparent power.

Why do we need Power Factor improvement?

 

 

P = VIcos@

I = P/Vcos@

 

• I is inversely proportional to cos@. If  cos@ is increases then current I decreases means I²R losses decreases then efficiency increases.

• As I is inversely proportional to cos@. Higher the power factor lower the current flow means low cross sectional area conductor is required and thus it saves the money 

• Higher Power factor means fraction of useful power is high.

• As Cos@ increases Sin@ decreases means reactive power burden on generator reduces

 

 

 

Power Factor Correction / Power Factor Improvement Method

 

• Power factor improvement by Capacitor bank

• Power factor improvement by Synchronous condenser/Synchronous phase modifier

 

Power factor correction by Capacitor bank

 

Since most of the practical load is inductive in nature. An inductor requires power (reactive power) to maintain magnetic domain. If generator can’t able to supply the reactive power demand then capacitor bank is connected in parallel to the load. This capacitor bank fulfils the reactive power demand.

 

 

 

Synchronous Condenser/ Synchronous Phase Modifier

 

Synchronous phase modifier is an overexcited synchronous motor on no load. Synchronous machine can operate on all Power Factors like leading, lagging, unity according to their excitation. By controlling the excitation of synchronous motor reactive power demand and supply can maintain.

 

An overexcited synchronous motor supplies lagging VARs (reactive power) which helps to improve power factor

 

An under-excited synchronous motor absorbs lagging VARs which helps to reduce Ferranti effect.

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