The National Grid (Oxford AQA IGCSE Physics)

The National Grid

• The National Grid is the name of the transmission and distribution system for electricity across countries such as the UK

  • The National Grid monitors power usage and responds to changing demand

    • Peak usage time is around 6 pm in the UK

    • Usage is higher in the winter than the summer as people use more lighting and heating

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

• The National Grid consists of a system of transmission cables, with transformers at each end, linking power stations to consumers (houses, factories and buildings)

General structure of the national grid

• A step up transformer increases the potential difference and decreases the current of electricity

• A step down transformer decreases the potential difference and increases the current of electricity

High-Voltage Transmission

• The National Grid transmits electricity at a low current to prevent dissipation of energy in the cables

  • When current flows in a wire, there is heating in the wire due to resistance

  • Therefore, energy is dissipated to the surroundings, this energy is wasted

  • The lower the current, the more efficient the energy transfer

• For a given electrical power, increasing the potential difference decreases current, so the national grid transmits electricity at a high voltage

power = potential difference × current

• This high-voltage transmission ensures the same power transfer with a smaller current

• Voltage is increased by using a step-up transformer

• High voltage is dangerous for use in homes, so the voltage is lowered before the current reaches consumers, using a step-down transformer

Changing voltage in the national grid