Science & Technology in Action

8th Edition

The Magic of Electricity


This lesson outlines how electricity is produced and distributed. The electricity is distributed nationally at high voltage (200, 000 volts) and locally at 10,000 volts and eventually at 230 volts. An extra Poster Sheet on Eirgrid is included in the folder.

Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

The electricity that boils the water in your kettle or charges the batteries of your laptop or mobile phone started its journey at a generation station miles away from your home or school. Behind the electricity supply that we take so much for granted are hundreds of engineers, technicians, project managers and other staff. They work day and night to ensure that the network of 
high voltage power lines called the transmission grid keeps working to deliver electrical power to users all over the country. In this lesson we look at some of the features of this critical network which is managed by EirGrid. 

The electrical power system
It is useful to consider three sub-systems of the national electrical power system, namely:

  • Generation 
    This subsystem is made up of generation stations that produce electricity from an energy source. Coal and oil are common sources. These fuels are used to produce steam which spins a turbine which, in turn, drives an alternator (also called a generator). Gas is also widely used. In this case hot expanding gas spins the turbine. There are also hydro-electric and wind systems where the generator is driven by water or wind. As the generator spins it moves a magnetic field around conductors. This produces the electricity by the process known as electromagnetic induction. The electricity is produced as three phase AC (alternating current) operating at a frequency of 50 Hz. 
  • Transmission
    This consists of high voltage lines, through which electricity travels over long distances. The voltages used are 400 kV, 275 kV, 220 kV and 110 kV.
  • Distribution
    These high voltages are converted to lower voltages (38 kV, 20 kV and 10 kV) by transformers at transmission substations. The voltage is then reduced to 230 V and delivered to ordinary domestic or business users as a single phase supply. In some cases, such as industrial plants, three phase supplies and higher voltages are delivered.


Quiz questions

  1. EirGrid is responsible for the entire electricity network in Ireland. true
  2. All high voltage transmission lines operate at 220 kV. true
  3. Electrical energy consumption is measured in kilowatt hours. true
  4. The new interconnector to Wales is an AC transmission system. false
  5. Since electricity is electromagnetic energy, it travels through the cables at the speed of light. false
  6. Wind is seen as an important source of energy for the future. true
  7. The frequency of the AC supply is continually fluctuating. false
  8. DC transmission has no advantages over AC. false
  9. The transmission upgrade project is called Grid25. true
  10. No problems arise if the electricity supply does not equal demand. false
  11. Electricity is delivered to domestic customers at 10 kV. false
  12. A 100 watt light bulb, in use for ten hours uses one unit of electricity. true

Glossary of terms

East-West Interconnector,
electricity meter
electromagnetic field
electromagnetic induction,
fibre optic
HVDC (High Voltage Direct Current)
kilowatt hour (kWh),
magnetic field
non-ionising (radiation)
optical fibre
peak demand
single phase
three phase AC
transmission grid
unit (of electrical energy)
wind farm