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# 12.3

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transmission of power

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### 12.3

1. 1. Topic 12: Electromagnetic induction <ul><li>12.3: Transmission of electrical power </li></ul>
2. 2. Energy losses <ul><li>Energy is lost when it is transmitted </li></ul><ul><ul><li>At the power transmission lines </li></ul></ul><ul><ul><li>transformers </li></ul></ul>
3. 3. <ul><li>Large amounts of electrical energy Are transmitted each second, from the power stations to the consumers, often over large distances. </li></ul><ul><li>Since power = current x voltage, we could use: </li></ul><ul><li>either a) a low voltage and a high current, </li></ul><ul><li>or b) a high voltage and a low current. </li></ul>
4. 4. <ul><li>Why does the National Grid always use method (b)? </li></ul><ul><li>Remember that a current always produces heat in a resistor. </li></ul><ul><li>If the cables have resistance R, and carry a current I, the energy converted to heat each second is I 2 R </li></ul><ul><li>P = I 2 R </li></ul>
5. 5. <ul><li>This means that in method (a) the high current produces a lot of heat in the cables and little of the energy from the power station gets to the consumer. </li></ul><ul><li>Method (b) is used because the low current minimises the power loss. </li></ul><ul><li>Transformers at each end of the system step the voltage up and then down. </li></ul>
6. 6. Losses in transformers <ul><li>Copper losses: the wires have some resistance </li></ul><ul><li>Hystereis loss: Magnetising and demagnetising uses power </li></ul><ul><li>Eddy currents: small currents form in the core </li></ul>
7. 7. Transmission of Power
8. 8. <ul><li>At the power station side: </li></ul><ul><li>Voltage is stepped up with a transformer to 275000 V </li></ul><ul><li>This reduces electrical loss in the transmission lines </li></ul>
9. 9. <ul><li>At the end of the line </li></ul><ul><li>Voltage is stepped-down with a transformer to </li></ul><ul><li>33000 V: heavy industry </li></ul><ul><li>11000 V: Light industry </li></ul><ul><li>230 V : Homes </li></ul>
10. 10. Health risks <ul><li>How many transformers are there in your home? </li></ul><ul><li>How many electric fields are you exposed to everyday? </li></ul><ul><li>What about wireless internet? </li></ul><ul><li>Can these pose a threat to our health? </li></ul>
11. 11. <ul><li>Electric fields from power lines and mobile phone masts are all around us </li></ul><ul><li>Electric fields are known to interact with tissues by inducing electric fields and currents in them. </li></ul><ul><li>Some studies have found a higher rate of cancer in people living close to power lines </li></ul>
12. 12. How can these fields do this? <ul><li>Results from animal studies conducted so far suggest that electric fields do not initiate or promote cancer. </li></ul><ul><li>Electric fields and magnetic fields were classified as possibly carcinogenic to humans based on epidemiological studies of childhood leukaemia </li></ul>
13. 13. <ul><li>&quot;Possibly carcinogenic to humans&quot; is a classification used to denote an agent for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence for carcinogenicity in experimental animals. </li></ul>
14. 14. What about high-voltage power lines? <ul><li>Do not touch them!! </li></ul><ul><li>Again no risk of cancer has been found </li></ul>