Science & Technology in Action

9th Edition

Keeping the Lights on


This lesson describes the function some of the main components of the national power grid. The conductivity of materials constituting a multi-core power cable is described. The lesson then describes how these cables are supported on the steel pylons and discussed the function of insulators.

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

Lesson excerpt

A little history
The first electricity distribution system was set up in part of New York by Thomas Edison in 1882. His was a direct current (DC) system, which had some advantages. An alternating current (AC) distribution system was set up in Cerchi, Italy in 1886 and within a few years many other cities did the same.

Electricity suppliers do not charge for current or voltage; what they sell is electrical energy. The rate at which the energy is used is called power. The transmitted power is equal to the voltage multiplied by the current (VxI). However the energy lost in transmission
is proportional to the square of the current ( I 2). Clearly then, a higher voltage with a lower current will deliver power more efficiently. The big advantage of AC is that it can be easily stepped up (for transmission) and stepped down again (for local distribution).

The conductors
Metals are generally good conductors of electricity, silver and copper being the best. Because silver is expensive, copper is commonly used for local distribution systems. For the longer transmission lines aluminium cables are more commonly used; for added tensile strength they are reinforced with steel and can be used for spans of more than a kilometre. Although the conductivity of aluminium is only about 63% of that of copper, it ismuch cheaper and lighter.

In ACSR cables (aluminium conductors steel reinforced cables) the steel is...

To read the full lesson, download the pdf above.

Quiz questions

  1. The National Grid is a DC transmission system. false
  2. The Grid carries three phase electricity. true
  3. The high tension lines in the Grid are insulated by a plastic sheath. false
  4. The high tension lines are suspended from the pylons by insulators. true
  5. Insulators are made from materials with high conductance. false
  6. A transformer operates on the principle of electromagnetic induction. true
  7. The function of a circuit breaker is to change the voltage levels. false
  8. The core of a transformer is made from materials with high magnetic permeability. true
  9. In transmission, energy is lost as heat from the conductors. true
  10. Eirgrid is responsible for setting the price of electricity. false
  11. The resistance of a conductor is inversely proportional to its diameter. true

Glossary of terms

electromagnetic induction