P1.4.2 The National Grid

P1.4.2 The National Grid

1. Overhead power lines

   • +
     • lower set up cost
     • easy to access
     • easy to set up
     • minimal disturbance to land
   • -
     • lots of maintenance needed
     • looks ugly
     • affected by weather
     • less reliable

2. Underground cables

   • -
     • higher setup cost
     • hard to access
     • hard to set up
     • large disturbance to land
   • +
     • minimal maintenance
     • not unsightly as they are hidden
     • not affected by weather
     • more reliable

3. Is a network of cables and transformers that distributes power to our homes from distant power stations and renewable energy generators

4. 1) Step-up transformers (used at power stations)

   • 2) High voltage (132 kV or more) transmission lines
     • 3) Step-down transformers (at sub-stations)
       • 4) Consumers, homes and factories- 230 V
       • Step the grid voltage down for use in our homes
   • Power station (up to 25 kV)
   • Step up power station voltages to the grid voltage

5. For a given power, increasing the voltage reduces the current required and this reduces the energy losses in the cable

   • 1) a step-up transformer raises the voltage, so less current is needed to transfer the same amount of power
     • 2) a lower current passes through the grid cables
       • 3) so energy losses due to the heating effect of the current are reduced to almost zero
         • 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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