It starts at the power stations where the electricity is generated. The power stations then feed the electric current into large power lines called transmission lines.
There is a massive network of transmission lines that extends throughout the entire country. The transmission lines are supported by pylons. The national power lines transmit electricity across the country from the power stations. The following diagram illustrates a coal-powered power station connected to the national electricity grid.
Very high currents are generated at the power stations. The transmission lines have some resistance. If the power stations transferred electricity at high currents, what do you think would happen in the transmission lines? Remember what we learned about the effects of resistance. Transferring electricity at very high currents through wires that have resistance would cause the wires to become hot and so a lot of energy would be wasted in the form of heat to the surroundings. To prevent the waste of energy, the electric current is rather sent through the transmission lines at very high voltages and low current.
However, these voltages are too high for use in both private homes and commercial buildings. In our homes and buildings we need a low voltage and high current again. Transformers are used to change the voltages at different points in the grid.
As you can see in the previous diagram, the electricity first goes through a transformer before entering the national transmission lines. This is a step-up transformer as it increases the voltage and lowers the current. When the electricity reaches the substation to be distributed locally, there is a step-down transformer which decreases the voltage again and increases the current.
All the systems in the national electricity grid are connected and this means that a power surge or a grid overload can cause blackouts and disruptions throughout the network. What is a power surge? A power surge is a sudden increase in the voltage somewhere in an electric circuit. The power surge causes an increase in the current strength. This sudden increase in the current strength can damage sensitive circuits. Lightning strikes near a transmission line can cause a power surge.
Other causes of power surges or a grid overload include faulty wiring, or appliances or equipment that require a lot of energy when they are switched on and off. These sudden demands or excesses of energy cause brief changes in voltage that can cause a surge.
There are several points in the national grid which can detect a power surge or grid overload. If these are detected then the power supply to that area is cut off. The national grid is a network of interacting parts. If one part of the system is damaged, it will affect the entire network. Electricity in South Africa is mainly produced using coal-fired power stations.
In a coal station, coal is burned to heat water to produce steam. The steam turns a turbine, which turns a generator to produce electricity. There are alternative sources of energy besides coal, to drive turbines, such as wind, hydropower, sun-heated steam, nuclear power and tidal energy. Koeberg is the only nuclear power station in South Africa. Nuclear power stations use nuclear fuels, such as uranium, to generate heat and radiation by nuclear fission.
This heats the water to produce steam to turn the turbine. Nuclear fuels are very energy-efficient as a large amount of energy is obtained from a very small mass of nuclear fuel. There is no emission of greenhouse gases in the use of nuclear fuels. Nuclear power stations generate radioactive waste materials which need to be properly disposed of.
There is much debate around the use of nuclear fuels. The national electricity grid is a system to deliver electricity around the country.
Electricity is carried at high voltages and low current through the national transmission lines to reduce the heating effect of the wires and minimize the energy wasted. Transformers are needed to step-up the voltage as the electricity leaves the power station and enters the national grid, and to step-down the voltage for local distributors and consumers.
Concept Map Complete the concept map on the following page to summarise this chapter on electricity production and delivery. Teacher's version Revision questions Why do you think we can refer to the national electricity supply as a grid? It is a system. What is the main source of energy for power stations in South Africa? Why are renewable sources of energy referred to as alternative forms of energy? Any other form of energy is an alternative to the main form of coal.
Look at the diagram of a power station. Write a paragraph to describe the process by which electricity is produced in a coal power station. The energy released by the burning coal is used to heat the water. The water particles have enough energy to change from liquid to vapour.
The steam rises and the kinetic energy of the steam particles is transferred to the blades of the turbine. The turbine blades gain kinetic energy and turn. What is nuclear power? Where is South Africa's nuclear power station?
What is the difference between nuclear fission and nuclear fusion? Write a paragraph to explain the differences and similarities between a coal-fired power station and a nuclear power station.
Coal-fired power station burns coal to produce heat needed to boil water to produce the steam that turns the turbine. Nuclear power stations use nuclear fuel to generate heat by nuclear fission to heat the water to produce steam to push the blades of the turbine.
Both stations turn a turbine which turns a generator. Write a paragraph to compare how the use of coal impacts on the environment when compared to how the use of nuclear fuels impacts the environment.
They must also discuss the fact that the burning of fossil fuels generates an increase in the amount of greenhouse gases in the atmosphere which contributes to climate change. Learners can discuss the fact that nuclear fuels do not generate greenhouse gases. However, the spent nuclear fuel is still radioactive and therefore needs to be stored safely for very long periods of time so that it does not damage the environment or any organisms.
Study the following diagram and answer the questions that follow. The proportion of electricity generated using nuclear fuels in each country in Which country has the highest percentage of its electricity being produced using nuclear fuels? Not all countries have nuclear power stations, so only those with nuclear power are shown here.
Learners must draw a bar graph with the bars which do not touch [1 mark]. They must provide a heading [1 mark], labels for each of the axes [2 marks], and plot the correct percentages for each country listed [3 marks]. Why can we consider the national electricity grid as a system? A change in one part of the grid will affect other parts. We can divide the national electricity grid up into 4 main stages.
Generation this is where electricity is generated B: Transmission the electricity enters the power lines of the national grids and is transmitted C: Distribution the electricity is distributed from substations to various towns and areas D: Consumers this is where the electricity is transferred to useful energy outputs Use this information to write the letters A, B, C and D on the diagram of the national electricity grid to label these stages.
If the current is very high then a lot of energy is lost to the lines in the form of heat. If the current is low then less energy is wasted in the lines. Most household appliances need a voltage of - V.
If the electricity in the transmission lines is very high then how are we able to use it? Why should you protect your computer from power surges? A power surge puts a large current into the circuit.
This can damage the wiring in the circuit and stop it from working.