1. Steady State Power Calculation Section 10.1-10.4

2. Instantaneous Power

3. Use current as point of reference

4. Apply Some Trig Identities

5. Power for Purely Resistive Circuits (θ v = θ i ) For purely resistive circuits, θ v = θ i θ v = θ i (all the electric energy is dissipated in the form of thermal energy)

6. Power for Purely Inductive Circuits (θ v = θ i +90 deg) For purely inductive circuits, θ v = θ i +90 deg θ v = θ i +90 deg (Voltage leads current by 90 deg) (Q is 1 VAR) V olt- A mp R eactive (No transformation of energy from electric energy to nonelectric form)

7. Power for Purely Capacitive Circuits (θ i = θ v +90 deg) For purely inductive circuits, θ i = θ v +90 deg θ i = θ v +90 deg (Current leads voltage by 90 deg) (Q is -1 VAR) V olt- A mp R eactive (No transformation of energy from electric energy to nonelectric form)

8. Power Factor Knowing the power factor does not tell you the value of power factor angle. We need to use descriptive language: 1.Lagging power factor: current lags voltage. (most appliances such as lighting fixtures and washing machine…etc operate at a lagging power factor. We usually want to operate a power factor of 1. 2. Leading power factor: current leads voltage. (power factor angel)

9. Average Power (P) A 120 V, 100W lamp has a resistance of 120 2 /100=144 Ohms

10. Power Factor Correction Example We can use a capacitor in parallel of L1 and L2 to correct Power. We would ideally like to have a power factor of 1.