1. AC DC Not the awesome, long-may-they- reign, Australian kings of the power chord ……..

2. Technology Wars  Why is alternating current used to supply electricity virtually everywhere in the world??? And not direct current?  Why iPod vs. Rio vs. Zune?  Why PC vs. Mac?

3. Typical reasons why one ‘wins’ over a competitor…  Possess key ‘enabling’ technologies  Better reliability, safety, ease of use, ability to meets customers’ long term needs  Public perception about reliability, ‘image’, safety, ease of use  More funding available or stronger backing from scientific community

4. The War of the Currents  Thomas Edison (proponent of direct current) and Nicolai Tesla funded by Westinghouse (of alternating current)  Addressed these issues through extensive research, public demonstrations and lectures, ‘news’ reports via newspapers

5. Direct current  Thought of as supplied by batteries  Can also have DC powerplants  Always flows in one direction

6. Alternating current  Electrons move back and forth  Net motion is zero  BUT the transport of energy between the electrons is the important thing  Because it’s cyclic, there is another issue  Can be transmitted at various frequencies  In US, 120V and 60Hz for homes

7. Your requirements, needs, expectations for electricity?  Does voltage, current matter to you?  Does it matter where the powerplant is?

8. Residential and commercial customer requirements  electricity of various voltages  Smooth delivery of power for running motors  People would prefer not to live close to powerplants, so electricity should be able to be transmitted over relatively long distances  Transmission should be efficient, not a lot of power loss from powerplant to customer  Might need both DC and AC

9. View the Tesla video  http://www.youtube.com/watch?v=ViS4t8j ye4c http://www.youtube.com/watch?v=ViS4t8j ye4c http://www.youtube.com/watch?v=ViS4t8j ye4c

10. Tesla’s contribution  Didn’t invent DC nor AC BUT….  Did design  better AC generators  An AC transformer (a key technology)  An AC motor (also key technology)  The whole AC system would not have worked without his inventions

11. Transformer is just wire coiled around metal  Magnetic field is generated by current in primary coil  Iron core channels magnetic field through secondary coil  Secondary Voltage is V 2 = (N 2 /N 1 ) V 1  Secondary Current is I 2 = (N 1 /N 2 ) I 1  But Power in = Power out  negligible power lost in transformer  Works only for AC, not DC

12. AC’s not perfect but it ‘won’ because….  AC can be transformed from higher to lower voltage and vice versa  Enabling technology: the transformer  AC provides ‘smoother’ flow  AC can be transmitted over long distances efficiently  Easier to convert from AC to DC when needed than vice versa (stuff that runs on batteries can be plugged in to an outlet)

13. Could you still use DC to power your house?

14. Let’s look at how it’s done today….

15. Electrical Power Transmission  When transmitting electric power over long distances, it is most economical to use high voltage and low current  Minimizes I 2 R power losses  In practice, voltage is stepped up to about 230 000 V at the generating station and stepped down to 20 000 V at the distribution station and finally to 120 V at the customer’s utility pole

16. three-phase “live” wires 500,000 230,000 138,000 69,000 7–13,000 long-distance neighborhood to house

17. How does it get to my house? Right outside your house, Voltage is transformed to 120V

18.  Lower (rounded) hole is earth ground  connected to pipes, usu.  green wire  Larger slot is “neutral”  for current “return”  never far from ground  white wire  if wired correctly  Smaller slot is “hot”  swings to +170 and  170  black wire  dangerous one 120 volt AC outlet

19. Household Circuits  The utility company distributes electric power to individual houses with a pair of wires  Electrical devices in the house are connected in parallel with those wires  The potential difference between the wires is about 120V

20. So, why the different types of plugs on different appliances?  Safety for appliances and wiring  A way to match the appliance with its required voltage and frequency  No way you can mix up a square peg (120 V plug) into a round hole (240 V)

21. How do you get 240v?

22. Breaker panel  Your house?

23. Household Circuits, cont.  A meter and a circuit breaker are connected in series with the wire entering the house  Wires and circuit breakers are selected to meet the demands of the circuit  If the current exceeds the rating of the circuit breaker, the breaker acts as a switch and opens the circuit  Household circuits actually use alternating current and voltage

24. What’s with that third prong? Ground Wire  Electrical equipment manufacturers use electrical cords that have a third wire, called a case ground  Prevents shocks

25. Generators vs motors  Generator converts (chemical or wind, etc.) energy to mechanical energy and then to electrical energy  Motor converts electrical energy to mechanical energy