1. The average ac power (P av ) is the power dissipated on the load resistor. 0  cos  1, dependent on the complex load. ideal power factor: cos  =1, Z=R, pure resistive load Exam II Review: AC Power rms value Average power

2. Review cont.: Complex Power real power P av : power absorbed by the load resistance. Q (volt-amperes reactive, VAR): exchange of energy between the source and the reactive part of the load. No net power is gained or lost during the process.  S  : compute by measuring the rms load voltage and currents without regard for the phase angle. if Q 0, the load is inductive Instantaneous power p(t) Pay attention to complex conjugate

3. Example 7.8, P345: power factor correction

4. Transformer Transformation of Voltage: Transformation of Resistance:

5. Residential Wiring GFCI

6. An electrical engineering major has designed and constructed a motor for your sophomore design project. It has been wound with an inductance of 16 mH and a resistance of 3.0 ohm. You had specified that it be optimized for the best possible power factor at 60 Hz; consequently, a 354 microFarad capacitor was added in parallel with the motor, as shown below. a. Operated at 120 V, what is the current through the motor when operated at 60 Hz? b. What power is delivered by the voltage source? c. What power is dissipated by the motor? Your complete project was so innovative that your engineering professor entered it in an international competition. You arrive in Germany for the competition before remembering that the line frequency there is 50 Hz. d. What is the power factor of this circuit at 50 Hz? e. What capacitance do you need to correct the power factor back to unity? Example: Midterm 1998

7. Example Cont. a. Operated at 120 V, what is the current through the motor when operated at 60 Hz? b. What power is delivered by the voltage source? d. What is the power factor of this circuit at 50 Hz? e. What capacitance do you need to correct the power factor back to unity? Note: you calculate S only on the motor part! Negative just means Capacitor

8. Example 3: 1 st Fall 199 An electrical engineering firm has designed a motor for your sophomore design project. You specified that it should be wound with an inductance of 16 mH and a resistance of 3.0 ohm. You had specified that it be optimized for the best possible power factor at 60 Hz; consequently, a 354  F capacitor was added in parallel with the motor. Unfortunately the motor was actually wound with an inductance of 61 mH and a resistance of 30 ohm because of typographical errors in the FAX to the motor manufacturer. a.What power is delivered by the voltage source? b.What power is dissipated by the motor? c.What capacitance do you need to correct the power factor back to unity?

9. Example Cont. a. What power is delivered by the voltage source? b. What power is dissipated by the motor? d. What capacitance do you need to correct the power factor back to unity?