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The Power Factor

The Power Factor. What is the power factor?. A number that represents the portion of the apparent power dissipated as true power. (Number represented as a decimal fraction or percentage.). Eq. 24.22 PF = TP/AP AP= Apparent Power TP= True Power or Real Power.

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The Power Factor

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  1. The Power Factor

  2. What is the power factor? A number that represents the portion of the apparent power dissipated as true power. (Number represented as a decimal fraction or percentage.) • Eq. 24.22 PF = TP/AP AP= Apparent Power TP= True Power or Real Power

  3. In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. • The higher currents increase the energy lost in the distribution system, and require larger wires and other equipment. • Because of the costs of larger equipment and wasted energy, electrical utilities will usually charge a higher cost to industrial or commercial customers where there is a low power factor. • An automatic power factor correction unit consists of a number of capacitor that are switched by means of contactors. These contactors are controlled by a regulator that measures power factor in an electrical network.

  4. More Equations • Substituting the equations for TP and AP in the Power Factor equation will yield: IR2R / IT2Z = PF

  5. For Series Circuits Only!! In series circuits, the current is the same, and IR equals IT. Therefore this power factor equation becomes: • Eq. 24.23 • IR2R / IT2Z R / Z = PF

  6. For Parallel Circuits Only Eq. 24.23 is modified as: Eq. 24.24 IR / IZ = PF (Note: IZ = IT)

  7. Eq. 24.25 PF = Cos θ S= Apparent Power P= True Power Q= Reactive Power

  8. Problems • Find the power factor of a series circuit when R=5kΩ, Z=7.07kΩ, θ= 45°, VS= 20V, and IT = 2.82mA

  9. Example Find the power factor of a series circuit when R=5kΩ, Z=7.07kΩ, θ= 45°, VS= 20V, and IT = 2.82mA PF = (2.82mA)2*5kΩ/(2.82mA)2*7.07k Ω = .707 PF = 5kΩ/7.07kΩ = .707 PF = Cos 45° = .707

  10. Last equation to know Combining the previous equations gives us an equation for true power that is universal. Can be used for any type of circuit. • Eq. 24.26 • TP = ITVS Cos θ

  11. Power Factor Correction http://www.allaboutcircuits.com/vol_2/chpt_11/4.html

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