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12.3
 

12.3

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transmission of power

transmission of power

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    12.3 12.3 Presentation Transcript

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