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Lecture 32

Lecture 32. Review: AC power analysis Average power, complex power, power triangles RMS values Power factor Power factor correction Related educational materials: Chapter 12.5, 12.6. AC power analysis. Average power: Average power in terms of RMS (or effective) values: Complex power:.

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Lecture 32

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  1. Lecture 32 Review: AC power analysis Average power, complex power, power triangles RMS values Power factor Power factor correction Related educational materials: Chapter 12.5, 12.6

  2. AC power analysis • Average power: • Average power in terms of RMS (or effective) values: • Complex power:

  3. Power triangles • Complex power (rectangular form): • Real (average) and reactive power: • Presented graphically:

  4. Power factor (pf) • Power factor: • Load impedance:

  5. Example 1 For the circuit below, determine: (a) the complex power delivered by the source (b) the average power delivered by the source

  6. Outline problem on previous slide: • 1. find equivalent impedance • 2. find source current • 3. complex power = VI*/2 • 4. Average power = (Vm*Im/2)*cos(thetav-thetai)

  7. (a) Determine the complex power delivered by the source

  8. (b) Determine the average power delivered by the source

  9. Effect of pf on power delivery • If v - i 0, we have some reactive power that is not consumed by the load • The current provided to the load is higher than necessary • Results in additional power dissipated during delivery • Power companies don’t like this!

  10. Power factor correction • Power companies may require that users maintain a minimum power factor • e.g. pf > 0.9 • Most large loads are inductive in nature • e.g. inductive motors • Power factor correction may be necessary • The approach must be inexpensive & simple to implement • Adding a capacitor in parallel with the inductive load will increase the power factor

  11. Power factor correction – continued • We have an inductive load with some power factor cos1: • The power triangle is shown below:

  12. Power factor correction – continued again • We can increase the power factor by adding a capacitor in parallel with the load: • The power triangle then becomes:

  13. Example 2 – power factor correction For the circuit below if (a) Determine the power factor (b) Re-design the circuit so that pf = 1

  14. Example 2 – Determine pf

  15. Example 2 – Re-design circuit so that pf = 1

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