Grade 7 Natural Sciences

National Electricity Supply System,

Dynamos, Conserving Electricity, and
Careers in Power Generation
 National Electricity Supply System
• Many homes in South Africa use electricity as the main source
of energy and power.
• Our government is responsible for providing electricity since
electricity is an effortless way to cook food, heat water and
provide light.
• Electricity cables carry electricity to our homes The national
Grid is The electrical system that supplies electricity to all
parts of South Africa
• Electricity in South Africa is generated from sources such as
coal, oil, gas, nuclear fuels, falling water and wind.
• Approximately 95% of all energy inSouth Africa comes from
burning coal in power stations and most power stations in SA
are in Mpumalanga.
• Electricity is produced and supplied following a specific
sequence, starting in a power station and ending in the
electrical appliances in our homes.
• In all power stations, the energy produced from the coal,
oil, gas, nuclear fuels, falling water and wind is transferred
to make large turbines rotate. Turbines look like giant fans
with large metal blades.
• The mechanical energy from the turbine is transferred to a
generator, where it is converted to electrical energy.
• The electricity produced is transferred through the cables
of the national electrical supply system to our homes and
businesses.
• The electricity produced by all the forms of power is fed
into the 27 000 km of cables in national electricity grid.
 How Electricity is made in a power station
• Most of the electricity in South Africa is generated in power
stations. These power stations burn coal to produce heat
energy. The figure below shows the steps involved
Figure 1:
The process involves:
1. Coal is burned in a boiler to heat water.
2. The water turns into steam which is passed through a
turbine
3. The steam turns the wheel of the turbine.
4. The turbine drives a generator. which the energy in
generator converts movement into electrical energy.
5. Electricity is transported through pylons and cables to
homes, schools, and businesses
6. electricity is passed through a transformer and changed to
the correct voltage Transformers are used to increase or
decrease the voltage of electricity for safe transport.
• Other sources of electricity include nuclear material, falling
water (hydro), wind, and sunlight.
 Dynamos
• A dynamo is a small generator that changes movement
energy into electrical energy. Dynamos are used in bicycle
lights, wind-up torches, and miners’ helmet lamps
Figure 2:
How a dynamo works:
• Movement energy (e.g., pedaling a bicycle) makes a magnet
inside the dynamo turn.
• The magnet turns inside a coil of wire, generating electricity.
• This electricity can power a bulb or charge a battery.

Example: In a wind-up torch, turning the handle spins a

magnet inside the dynamo, which generates electricity which
is stored in the torch battery. The torch’s battery is connected
to the bulb. The Electricity is transferred from the battery to
the bulb then changed into light energy
Figure :3
Activity 1- identify steps in making electricity
Study the diagram in Figure 2 and answer these questions.
Identify the points in the diagram where:
1.1potential energy is changed into heat energy
1.2heat energy is changed into kinetic energy
1.3 kinetic energy is changed into electrical energy
1.4 electrical energy is changed into sound and light energy.

2. Identify the points in the diagram where energy is lost or

wasted.
 Conserving electricity in the Home
• South Africa has a limited supply of electrical energy. It is
estimated that it has 53 million tons of coal reserves left,
which is enough for another 200 years.
• We use energy in so many different ways each day and we
seldom think about how we use it. But, there are many
different ways to use energy wisely and save energy in the
home.
• Electricity is expensive and most of South Africa’s
electricity is made from coal, which causes pollution. We
must save electricity to reduce costs and protect the
environment.
 Ways to save Electricity
•Switch off lights and appliances when not in use.
• Use energy-saving bulbs (LED or CFL).
• Use solar water heaters and geyser blankets.
• Do not leave devices on standby.
• wear warm clothes andInsulate homes to reduce the need
for heaters and fans.
• Use natural light during the day.
•Do not leave cell phone chargers plugged in and switched on
when not in use.
•Shower instead of bath, as less hot water is used, which
means that less electricity is used in the geyser
•Always put the lid on the pot when you are cooking to stop
the loss of heat energy.
•Only heat up the amount of water you need for a cup of tea,
so you do not waste energy.
•Do not put small pots and pans on big stove plates. This
wastes heat energy.
•Make sure the bottom of the pot is flat, so it makes good
contact with the stove plate.
•Cover the windows with curtains and put mats or carpets on
the floor to stop heat loss.
• Use a hot box or solar stove for cooking food.
• Use a hot water bottle instead of an electric blanket to keep
warm in bed.
• Use the correct size fridge for your family (see Figure 10).
•Do not put warm food in the fridge, because the fridge has to
draw more electricity to get cold again.
•Hang up clothes to dry rather than using the tumble drier,
where
possible.
Activity
1. Tabulate a list of dos and don’ts for using energy wisely

2. Draw a table titled ‘Using energy wisely’. Draw two columns

labelled as ‘Electricity Dos’ and
‘Electricity Don’ts’.
Place each of the examples given above into one of the
columns.
 Careers in Power Generation
ELECTRICAL ENGINEERS
This work involves the generation and distribution of electricity
for power, heat and light. Concerned with the design,
development, installation and testing of electrical motors,
generators, m, transformers, transmission lines, cables in power
stations.
SCIENTISTS
Scientists are involved in designing power stations and carrying
out research to find ways of improving efficiency and safety in
generating electricity. Scientists develop new ideas and then test
them to see if they work.
TECHNICIANS
Power station technicians observe, control, and keep records
of the operation of various kinds of power plant and sub-
station equipment. Technicians control boilers, turbines,
generators and other equipment at power stations that
produce electricity.
ARTISANS and ELECTRICIANS
This work involves people who have technical knowledge
and skills. They. play a significant role in the functioning of
power stations and in quick repairs and maintenance. the
skilled labour that takes the ideas of the engineers and
scientists and make them a working reality. You will need an
electrician's certificate to work as an electrician.
• These careers are important for ensuring that South Africa
has a safe and reliable electricity supply.