1. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 1 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu Engineering 43 Chp 9 [8-9] House Power

2. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 2 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Outline – AC Steady State Power  Instantaneous Power Concept For The Special Case Of Steady State Sinusoidal Signals  Average Power Concept Power Absorbed Or Supplied During in Integer Number of Complete Cycles  Maximum Average Power Transfer When The Circuit Is In Sinusoidal Steady State

3. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 3 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Outline – AC SS Power cont.  Effective or RMS Values Heating Value for Sinusoidal Signals  Power Factor A Measure Of The Angle Between Current And Voltage Phasors  Power Factor Correction Improve Power Transfer To A Load By “Aligning” Phasors  Single Phase Three-Wire Circuits Typical HouseHold Power Distribution

4. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 4 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Single Phase, 3Wire Circuits  Power Supplied to Most Houses And Other Residences Takes This form  For residential Electrical Power Service  115V → Lights and convenience (3-prong) Outlets Powered from “Line” to Neutral  230V → Large Appliances, e.g; Electric Ovens, Air Cond, Dryers Run “Line-to-Line” Neutral Wire

5. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 5 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Residential Electrical Service PG&E Electrical Service Utility Connection 110/115/120 Vac Circuits Run Line → Neutral 220/230/240 Vac Circuits Run Line → Line

6. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 6 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Actual Residential Wiring  WattHour Meter  Main Service Disconnect CB 200 Arms Service  Circuit Breaker Power Distribution Panel Two, 100 Amp CBs

7. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 7 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Distribution Panel 115Vrms 15Arms GFICB –BathRooms 230Vrms 30A/2Pole CBs –Clothes Dryer –Oven 115Vrms 20Arms CBs –Appliances 115Vrms 15Arms CBs –Convenience OutLets

8. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 8 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Single- , 3W Electrical Power  In A “Balanced” Condition, The Loads across the two Sources are EQUAL  In the N-n Branch for Equal Loads by KCL  Thus the Current in the Neutral Wire is ZERO This is the Ideal Condition And the Neutral Wire is (theoretically) NOT NEEDED  Next, Account for Line Impedances Line-to-Line Loads

9. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 9 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis 1- , 3W Pwr cont  A more Realistic 230Vac, 1  Ckt Model  Analyze Ckt by Superposition +  If Any Line or Load Z’s are Unequal, Then I neutral  0

10. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 10 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Example – Unbalanced Load  Given a 1 , 3Wire Household Power Load  By KCL at A, B, N  Assuming Resistive Loads

11. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 11 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Example – Unbalanced Load cont  Then The ENERGY use  For Each Load, Daily  The Total Daily Energy Usage  Then The Total Cost at 15¢/kWh

12. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 12 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Electrical Safety  Globally, Electrical Power Systems Run at Frequencies of either 60 Hz –USA, Most Asia 50 Hz –Most of Europe  The Danger From Electricity is not the Voltage, but the CURRENT Thru the Human body

13. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 13 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Grounded Neutral  Typical 1 , 110/115/120 Vrms Household Power Wiring  Note The Neutral Wire is Tied To the Ground Wire The Neutral and GND wire are Run in Tandem to all Loads  But, The GROUND conductor Does NOT Carry any Working Current; so Why is it there? As a Safety PreCaution; Illustrate Function by Way of Example

14. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 14 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Example – Grounded Case When switched-on the tool-case is energized without the ground connector the user can be exposed to the full supply voltage! Conducting due to wet floor If the case is grounded then “Joe” is at the Case, i.e. GND, Potential, and Cannot Receive A Shock. Essentially the supply is shorted Around Joe, and the Circuit Breaker Trips to open the circuit. The Tripped CB Alerts Joe that Something is Wrong Somewhere. CB Drill Case

15. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 15 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Numerical Example  Another Shorted Drill; Ground Prong Removed Ground prong REMOVED Suggested resistances for human body Wet skin Limbs trunk Can cause ventricular fibrillation

16. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 16 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Numerical Example  A 7.2 kV Power-Line Falls on Car. The Driver can Get Out or Stay in. Which is better? Wet Road Option 1. Driver opens door and steps down. Conduction Path = ARM + TRUNK + LEG Option 2: Driver stays inside the car No Path to GND  7200V Car body is good conductor Tires are insulators Suggested resistances for human body 

17. BMayer@ChabotCollege.edu ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt 17 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis WhiteBoard Work  Let’s Work Text Problems 9.79 9.80 9.78 9.32