- Technical Blog From My Notebook

Friday, February 19, 2016

Physical significance of power factor

What is power factor?
Power factor = cosine of the angle between voltage and current= cosθ . This is the instant answer from all. The other definitions are , cosθ= ratio of active power to apparent power or it is the ratio of Resistance to the impedance in the circuit.

   These all are definitions and expressions that we all know. But, actually what is the physical significance of power factor? What does it actually mean?

  " Power factor is the measure of effectiveness of utilization of available power."

The power in an ac circuit is mainly of three types.Apparent power, Active power and Reactive power.
Apparent power is the total power supplied to the circuit . It is given by,

S= VI  Volt Ampere
  But  actually the circuit does not utilizes the applied power completely (if it is not a purely resistive circuit). The part of the applied power which is actually consumed by the circuit is called active power and it is given by,

 P= VI cosθ watts

The rest of the applied power is circulating in the circuit with out doing any actual work. It s called reactive power and is given by,
 Q=  VI sinθ Volt Ampere Reactive (VAR)

Thus, the power factor is the measure of  percentage of the  power consumed .

 i.e,   " Power factor is the measure of effectiveness of utilization of available power."

The power factor can be also measured in terms of percentage.

  In a purely resistive circuit, the power factor is 1, or 100%. This means that, in a pure resistive circuit, the applied power is completely utilized by the circuit. (Reactive power is zero)

  If  in a circuit, the power factor is 0.5, or 50 % it means that only 50% of the applied power is utilized by the circuit.

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