P1.4.2 The National Grid

Overhead power lines
1. +
  1. lower set up cost
  2. easy to access
  3. easy to set up
  4. minimal disturbance to land
2. -
  1. lots of maintenance needed
  2. looks ugly
  3. affected by weather
  4. less reliable
Underground cables
1. -
  1. higher setup cost
  2. hard to access
  3. hard to set up
  4. large disturbance to land
2. +
  1. minimal maintenance
  2. not unsightly as they are hidden
  3. not affected by weather
  4. more reliable
Is a network of cables and transformers that distributes power to our homes from distant power stations and renewable energy generators
1) Step-up transformers (used at power stations)
1. 2) High voltage (132 kV or more) transmission lines
  1. 3) Step-down transformers (at sub-stations)
    1. 4) Consumers, homes and factories- 230 V
    2. Step the grid voltage down for use in our homes
2. Power station (up to 25 kV)
3. Step up power station voltages to the grid voltage
For a given power, increasing the voltage reduces the current required and this reduces the energy losses in the cable
1. 1) a step-up transformer raises the voltage, so less current is needed to transfer the same amount of power
  1. 2) a lower current passes through the grid cables
    1. 3) so energy losses due to the heating effect of the current are reduced to almost zero
      1. 4) But we need to lower the voltage at the end of the grid cables before we can use mains electricity at home

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