8.7 - National Grid

• What is the national grid?

  A giant network of transformers and wires
• From where is electricity in the UK primarily generated?

  From power stations
• What do power stations do to generate electricity?

  They generate heat and convert it to electrical energy
• How does electricity generation depend on demand?

  Electricity generation varies with demand peaks
• When does electricity demand generally peak?

  In the late afternoon and evening
• Why do power stations need spare capacity?

  To cope with surges in demand
• What is the equation for power?

  Power = voltage times current
• What happens when high current flows through a wire?

  It generates lots of heat due to resistance
• Why do we need to keep the current low in power transmission?

  To minimize energy loss as heat
• What do we use to increase voltage before transmission?

  Step up transformers
• What voltage do step up transformers increase to?

  Around 400,000 volts
• What do the wires in the national grid transmit electricity between?

  Huge pylons
• What happens to the voltage before electricity reaches its destination?

  It is reduced by step down transformers
• What voltage do step down transformers lower the electricity to?

  Around 230 volts
• Why is it important to lower the voltage before use?

  High voltages are dangerous and damage appliances
• What is the process of electricity transmission through the national grid?

  • Electricity generated in power stations
  • Step up transformers increase voltage to 400,000 volts
  • Wires transmit electricity across the country
  • Step down transformers reduce voltage to 230 volts
  • Safe for use in homes
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• Fossil fuel and nuclear power stations work by generating thermal energy. This is used to turn water into steam which can then rise and turn turbines. The kinetic energy of the moving turbines can be converted to electrical energy, which is finally sent out across the national grid.
• Electricity demand varies during the day and generally peaks:

  Late in the afternoon
• The formula for electric power is:

  power=voltage×currentpower=voltage×current
• The symbol formula for electric power is:

  P=IV
• When transmitting electricity, a ________ current generates lots of wasted heat.

  • High
  • High currents cause the wire to heat up, meaning that energy is lost as heat to the surroundings. 
• Step-up transformers are used to:

  Increase the voltage and decrease the current
• Step-down transformers are used to:

  Decrease the voltage and increase the current
• • Electric power is generated at a power station.
  • Step up transformers increase the voltage and decrease the current.
  • The electric power is transmitted via the national grid at low current which minimises power loss. 
  • Step down transformers decrease the voltage and increase the current near our homes.
  • Electric power is wired into our homes at a voltage that is relatively safe to use.