Physics - The National Grid (AQA)
In GCSE Science students will look at electrical energy. This is the last of six quizzes on that subject and it looks at how electricity is transported via the National Grid.
The National Grid is the name given to the network of cables and transformers that transport electricity from the power stations in Britain to homes, factories, offices, shops and the other places that require it. It was created during the 1920s and 1930s in order to give the country a more reliable supply of electricity. Before the National Grid, power stations were owned by private electricity generating companies who had their own local electricity grids. These ran on different voltages so a kettle bought in Birmingham might not work in Lichfield, just 20 miles away!
Generators at the power stations produce electricity at 25,000 volts. Electricity transported, or transmitted, at that voltage over the distances covered by the National Grid would create high currents. The electricity would lose a lot of its energy as heat which would be very wasteful. To get round this, the electricity generated by the power station is passed through a 'step up' transformer, increasing the voltage to as much as 400,000 volts. This means that the current will be a lot lower. To understand how this works, think about the relationship P = V x I where P is power, V is volts and I is current. If you increase the voltage, the current must decrease. With a lower current, there is less of a heating effect and so less energy is wasted.
The high voltage electricity is transmitted along overhead lines on pylons and through underground cables - the supergrid. But this high voltage is no good to consumers so it is reduced by step down transformers to an appropriate level for the end user - higher voltages for factories, car garages etc. than for homes and offices.
________ transformers are used at power stations to produce the very high ____________ needed to ensure that electricity is transmitted efficiently through the National Grid. Such high voltages are dangerous to use in the home, so _________ transformers are used in substations near to homes to reduce the voltage to safe levels. The voltage of ________ electricity is about 230 V.
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