The National Grid (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note

The National Grid

• The National Grid distributes electricity across the UK

  • It consists of a system of cables and transformers linking power stations to consumers (houses, factories and buildings)

• Electrical power is transferred from power stations to consumers using the National Grid

• The transformers include:

  • Step-up transformers which increase the voltage (and reduces the current) through the wires

  • Step-down transformers which decrease the voltage (and increases the current) through the wires

Benefits of The National Grid

• The National Grid system is an efficient way to transfer energy due to the use of step-up and step-down transformers

• The current generated by power stations is greater than that which is required for homes and other buildings, and so it must be transmitted through a network of wires that travel across the country

• When electricity is transmitted over large distances, the resistance in the wires causes heating, which results in wasted energy transfers

• By increasing the potential difference at which the current is transmitted, the same amount of power can be transferred using a much smaller current (due to the equation P = IV)

  • This results in less heating in the wire and hence less wasted energy

• Therefore:

  • High potential difference means low current (less energy dissipated) for the same power

  • Low potential difference means high current (more energy dissipated) for the same power

• The potential difference is increased using the step-up transformers and decreased using the step-down transformers

Transformer equation

Higher Tier Only

• The type of current produced in power stations is alternating current (AC) which is transferred to homes via the National Grid

• Transformers are used to increase and decreases the potential difference of the current before and after transmission across the National Grid

• They are made up of two coils of wire, called the primary and secondary coils, around a magnetic iron core

  • A step-up transformer has more turns on the secondary coil than the primary

  • A step-down transformer has more turns on the primary coil than the secondary

• Step-up transformers are used to increase the potential difference from the power station to the transmission cables

• Step-down transformers are used to decrease the potential difference, to a much lower value, from transmission cables for domestic use (houses, offices, shops)

Transformer calculations

• The relationship between potential difference and current in a transformer is given by:

V_p × I_p = V_s × I_s

• Where:

  • V_p = potential difference across the primary coil, in volts (V)

  • V_s = potential difference across the secondary coil, in volts (V)

  • I_p = current in the primary coil, in amperes (A)

  • I_s= current in the secondary coil, in amperes (A)