1. Natural Sciences Grade 7
Term 3: Energy and Change
The national electricity supply system

2. Topic 6 The national electricity supply system
Energy transfers in the national grid
Natural Sciences - Grade 7

3. Two forms of energy generation
Wind turbines on a windfarm
Coal fired power station
Natural Sciences - Grade 7

4. How electrical energy is generated at power stations
Energy Sources
Coal/Oil/Gas
Nuclear
Hydro
Wind
Heating of water to produce steam
to turn the blades of the turbine.
Generator turns. Mechanical energy change into electrical energy.
Non-renewable
Turbine
Generator
Electrical energy transported through power lines across the grid to where it is needed.
Renewable
Falling water (gravity) and wind
turns the blades of the turbine.
Natural Sciences - Grade 7

5. The national electricity grid.
The national electricity grid is one large system.
It is like one giant electrical circuit with many components connected by conducting wires.
Once electrical energy is generated at the power stations, it is transported to our homes, schools, factories etc. through power lines.
Power lines are called transmissions lines that transmit (move) the electrical energy to where it is needed.
Natural Sciences - Grade 7

6. The national electricity grid
We can divide the national electricity grid up into 4 main stages.
These are:
Generation (this is where electricity is generated)
Transmission (the electricity enters the power lines of the national grids and is transmitted)
Distribution (the electricity is distributed at substations to various towns and areas)
Consumers (this is where the electricity is transferred to useful energy outputs)
Natural Sciences - Grade 7

7. The dynamo – a mini power generator
A dynamo can be regarded as a small power station. It is uses to generate small currents.
The dynamo on a bicycle can provide enough electricity for use in its lamp.
Electricity is generated when a magnet spins around a coil made from conducting wire. We call this process electromagnetic induction.
On a bicycle, the cog of the dynamo, which touches the tyre, turns the magnet when the bicycle moves.
Dynamos are also used by miners and is used to power their headlamps in the dark underground. Wind-up torches and radios also use dynamos.
Natural Sciences - Grade 7

8. Replace incandescent bulbs with energy saving bulbs
Natural Sciences - Grade 7