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

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?

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

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

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

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

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

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, at high voltages, therefore low power loss and transformed to low voltages, closer to the user Easier to convert from AC to DC when needed than vice versa (stuff that runs on batteries can be plugged in to an outlet)

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)

Electrical Power Transmission When transmitting electric power over long distances, it is most economical to use high voltage and low current Minimizes I2R 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

Follow the flow!

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

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

How do you get 240v?

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

Breaker panel Your house?

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