1 / 28

11.2-11.3 Electric Power Distribution, Generators and Motors

11.2-11.3 Electric Power Distribution, Generators and Motors. New ideas for today Magnetic induction Lenz’s law Transformers and power transmission Motors and Generators. Why such high voltage?. Transformers!. Observations about Power Distribution.

Download Presentation

11.2-11.3 Electric Power Distribution, Generators and Motors

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. 11.2-11.3 Electric Power Distribution, Generators and Motors

  2. New ideas for today • Magnetic induction • Lenz’s law • Transformers and power transmission • Motors and Generators

  3. Why such high voltage?

  4. Transformers!

  5. Observations about Power Distribution • Household power is AC (alternating current) • Power comes in voltages like 120V & 240V • Power is transmitted at “high voltage” • Power transformers are everywhere

  6. Power Consumption in wires • Reminder: power consumption = current × voltage drop voltage = resistance × current power consumption = resistance × current2 • So what? • Wires waste power as heat • Doubling current quadruples wasted power • Better not transmit high current!

  7. AC DC vs. Edison Tesla Westinghouse

  8. AC = alternating current Current switches direction 60 times per second (in N. America) DC= “direct current” AC

  9. Power Transmission • Power delivered to a city is: power delivered = current × voltage drop • Power wasted in transmission wires is: power wasted = resistance × current2 • For efficient power transmission: • Use low-resistance wires (thick, short copper) • Use low current and high voltage drop • Can accomplish this with AC (alternating current) power transmission.

  10. 160-800 kV 7000 V 120 / 240 V neutral hot ground

  11. Voltage Hierarchy • High voltage is dangerous • High current is wasteful • Use the following scheme: • low voltage circuits in neighborhoods (120/240 V) • medium voltage circuits in cities (7000 V) • high voltage circuits across the countryside (155,000-765,000 V) • Use transformers to change voltage

  12. Click me

  13. Electromagnetic Induction • Changing magnetic field  electric field • Electric field in conductor  current • Current  magnetic field • Induced magnetic field opposes the original magnetic field change (Lenz’s law)

  14. inductive charging B

  15. Lenz’s Law

  16. That “emf” can be useful…

  17. Transformer • Alternating current in one circuit induces an alternating current in a second circuit • Transfers power between the two circuits • Doesn’t transfer charge between the two circuits

  18. Click me

  19. Current and Voltage • Power arriving in the primary circuit must equal power leaving the secondary circuit • Power = current × voltage • A transformer can change the voltage and current while keeping the power unchanged! Secondary turns Secondary voltage = Primary voltage Primary turns

  20. Step Down Transformer • Fewer turns in secondary circuit so charge is pushed a shorter distance • Smaller voltage rise • A larger current at low voltage flows in thesecondary circuit

  21. Step Up Transformer • More turns in secondary circuit so charge is pushed a longer distance • Larger voltage rise • A smaller current at high voltage flows in the secondary circuit

  22. Transformers are often filled with nasty stuff

  23. Clicker question You decide to use a transformer to increase the voltage from a battery, and hook it up in the circuit shown below. When you close the switch, 1.5 the voltage across the lightbulb is: (A) bigger than 1.5 V (B) smaller than 1.5 V (C) zero

  24. Electric Generators and Motors • A generator provides electric power • A generator requires a mechanical power • A motor provides mechanical power • A motor requires electric power Alternator

  25. Click me

  26. Electric Generator Rotating magnet • makes changing magnetic field • induces AC current in the loop Converts mechanical power into electrical power

  27. Electric Motor Input AC power • AC current makes changing magnetic field • causes magnet to turn Converts electrical power into mechanical power A motor is a generator run backwards !

More Related