The National Grid (Edexcel GCSE Physics: Combined Science)

• When electricity is transmitted over large distances, the current in the wires heats them, resulting in energy loss
  • The electrical energy is transferred at high voltages from power stations
  • It is then transferred at lower voltages in each locality for domestic uses

• To transmit the same amount of power as the input power the potential difference at which the electricity is transmitted should be increased
  • This will result in a smaller current being transmitted through the power lines
  • This is because P = IV, so if V increases, I must decrease to transmit the same power

• A smaller current flowing through the power lines results in less heat being produced in the wire
  • This will reduce the energy loss in the power lines and improves the efficiency of the energy transfer

Electricity is transmitted at high voltage, reducing the current and hence power loss in the cables

• Transformers have a number of roles:
  • They are used to increase the potential difference of electricity before it is transmitted across the national grid
  • They are used to lower the high voltage electricity used in power lines to the lower voltages used in houses
  • They are used in adapters to lower mains voltage to the lower voltages used by many electronic devices

• For the transmission of electricity in the national grid to be at high voltages, the voltage must be stepped up by a step-up transformer
  • These are placed after the power station

• For the domestic use of electricity, the voltage must be much lower
• This is done by stepping down by the voltage using a step-down transformer
  • These are placed before buildings

Electricity is transmitted at high voltage, reducing the current and hence power loss in the cables