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The National Grid
The National Grid Revision
The National Grid
The National Grid supplies electricity to homes and businesses all over Great Britain. It is made up of a system of cables and transformers that link power stations to consumers.
Efficiency of the National Grid
The National Grid transfers electricity using a high potential difference and a low current.
This is because the National Grid needs to transfer a very large amount of energy. A high current cannot be used because the wires would get very hot and a lot of energy would be lost to the surroundings as heat energy.
It is cheaper and more efficient to use a very high potential difference (approximately 400 \, 000\text{ V}) and to keep the current very low.
Transformers
Transformers are used throughout the National Grid to increase and decrease the potential difference when it is needed.
Transformers are made up of two coils: the primary and secondary coil. These coils are wrapped around an iron core.
If the transformer increases the potential difference, there are more turns on the secondary coil. This is called a step-up transformer and it is used to increase the potential difference of electricity for transportation via cables. If the transformer decreases the potential difference, there will be fewer turns on the secondary coil. This is called a step-down transformer and is used to reduce the potential difference electricity reaches homes.
Transformers are nearly 100\% efficient.
Transformer Calculations
Because transformers are nearly 100\% efficient, almost no power (\text{P}=\text{VI}) is lost when energy moves across a transformer and so we can write:
\text{V}_2\times \text{I}_2=\text{V}_1 \times \text{I}_1
- V_2 = the potential difference in the secondary coil in volts \text{(V)}
- I_2 = the current in the secondary coil in amps \text{(A)}
- V_1 = the potential difference in the primary coil in volts \text{(V)}
- I_1 = the current in the primary coil in amps \text{(A)}
Example: Transformer Calculation
The diagram on the right shows the current and potential difference going into and coming out of a transformer. Calculate the missing value of current.
[2 marks]
The National Grid Example Questions
Question 1: What is the National Grid?
[2 marks]
The National Grid is a system of cables and transformers that link power stations to consumers and hence supply Great Britain with electricity.
Question 2: Why does the National Grid use a high potential difference and a low current?
[2 marks]
The National Grid is required to transfer a large amount of energy.
The current needs to be kept low to reduce heat loss and therefore make the National Grid more efficient.
Question 3: What is the purpose of transformers in the National Grid?
[1 mark]
To increase or decrease the potential difference of the electricity supply.
Question 4: A transformer on the national grid receives a primary current of 12\text{ A} and a primary potential difference of 5\,000\text{ V}. The secondary current is 6\text{ A}. What is the secondary potential difference?
[2 marks]
Rearrange for \text{V}_2:
\text{V}_2 = \dfrac{\text{V}_1\times \text{I}_1}{\text{I}_2}=\dfrac{5 000\text{ V} \times 12\text{ A}}{6\text{ A}} = \bold{10\,000\text{ V}}The National Grid Worksheet and Example Questions
Domestic Uses and Safety Questions 1
GCSEOfficial MME
Domestic Uses and Safety Questions 2
GCSEOfficial MME
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