• Like
  • Save
12.3
Upcoming SlideShare
Loading in...5
×
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
No Downloads

Views

Total Views
291
On Slideshare
0
From Embeds
0
Number of Embeds
0

Actions

Shares
Downloads
0
Comments
0
Likes
1

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide

Transcript

  • 1. Topic 12: Electromagnetic induction
    • 12.3: Transmission of electrical power
  • 2. Energy losses
    • Energy is lost when it is transmitted
      • At the power transmission lines
      • transformers
  • 3.
    • 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.
  • 4.
    • 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
  • 5.
    • 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.
  • 6. 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
  • 7. Transmission of Power
  • 8.
    • At the power station side:
    • Voltage is stepped up with a transformer to 275000 V
    • This reduces electrical loss in the transmission lines
  • 9.
    • 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
  • 10. 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?
  • 11.
    • 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
  • 12. 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
  • 13.
    • "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.
  • 14. What about high-voltage power lines?
    • Do not touch them!!
    • Again no risk of cancer has been found