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What is Power Factor (Cosθ) ? Cos fi or P.f Definitions & Formulas

Power Factor (Cosθ) – Cos fi or P.f –

In electrical engineering, power factor is only and only related to AC circuits i.e. there is no power factor (P.f)  in DC circuits due to zero frequency.

What is Power Factor?

Power factor may be defined by three definitions and formals as follow.

1).  The Cosine of angle between Current and Voltage is called Power Factor.


  • P = Power in Watts
  • V = Voltages in Volts
  • I = Current in Amperes
  • W = Real Power in Watts
  • VA = Apparent Power in Volt-Amperes or Watts
  • Cosθ = Power factor

2). The ratio between resistance and Impedance is Called Power Factor.

Cosθ = R/Z


  • R = Resistnace in Ohms (Ω)
  • Z = Impedence (Resistance in AC circuits i.e. XL, XC and R known as Inductive reactance, capacitive reactance and resistance respectively) in Ohms (Ω)
  • Cosθ = Power factor

3).The ratio between Actual Power and Apparent Power is called power factor.

  • Cosθ = kW / kVA


  • kW = Real Power in Watts
  • kVA = Apparent Power in Volt-Amperes or Watts
  • Cosθ = Power factor
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  1. Simple and easy to understand, thanks

  2. Dattatrirao Kulkarni

    i too expected same example from you<br />

  3. I want to download free e-books. so plz invite me to do so.

  4. the total power factor in actual is a product of the displacement power factor(cos[fi]) and the distortion power factor.the distortion power factor is a function of the total harmonic distortion,hence the total power factor of the system decreases on in actual practice on account of the presence of harmonics and other non linearities.

  5. REALY GOOD EXPLICATION…Thanks!!<br />

  6. its banificial for us that’s why thanks

  7. sir plz upload 3 phase transformer 25 kva step down oil immresd self cooled core and winding calculation.

  8. sir plz answer the question its about control i know you can answer it …. which transform we use for convergence ? Laplace transform or Fourier transform or Z transform

  9. Its very simple to understand.I never understand about these three power concept.

    Thanks sir.

  10. plzz tel me how to reduce to kvah

  11. Nice article and well explained!

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