1. Chapter 11 – Power AC Circuits
Resistor:
Assume: vR(t) = Vm cos(ωt)
Instantaneous Power:
Average Power:

2. Inductor:
Assume: iL(t) = Im cos(ωt)
Instantaneous Power:
Capacitor:
Assume: vc(t) = Vm cos(ωt)
Instantaneous Power:

4. If you apply a V=100cos(wt) to a Capacitor and an Inductor…

5. In General
i(t) = Im cos(ωt- θ)
v(t) = Vm cos(ωt)
Instantaneous Power:

7. Complex Power

8. Example1. Find
Power factor
Real (ave.), reactive, and apparent power

9. Maximum Average Power Transfer
What value of ZL will receive maximum average power?

11. Example 2. Find the impedance, ZL, of the load that will receive maximum power from the circuit. What is the maximum power?

12. Example 3. Find the resistance, RL, of the load resistor that will receive maximum power from the circuit. What is the maximum power?

13. Power Factor Correction
Low power factor means high apparent power for same P.
To increase pf, add a capacitor parallel to the inductive load.
What value of C is needed to change pf from cosθ1 to cosθ2?

15. Example 2. When connected to a 120-V (rms), 60-Hz line, a load absorbs 4 kW at a lagging power factor of 0.8. Find the value of capacitance necessary to raise the power factor to 0.95