The National Grid Revision Notes for AQA GCSE Physics

The National Grid

What is the National Grid?

The National Grid is a network of wires that carries electricity from power stations to places where we need it. This includes homes, hospitals, factories, and schools across the country.

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The National Grid does not include the actual power stations or the people using the electricity. It's just the transmission system in between.

Why use high voltage and low current?

Electricity travels much more efficiently when it uses high voltage and low current. Here's why:

When current flows through wires, some energy is always lost as heat
The amount of energy wasted depends on the equation: $P = I^2R$
This means power wasted is proportional to the square of the current
If we halve the current, we reduce energy losses by four times
If current increases by 10 times, energy losses increase by 100 times

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Worked Example: Current and Power Loss Relationship

Doubling the size of current means the power wasted increases by $2^2 = 4$ times as much.

If the original current is $I$ , the new current is $2I$ . Using $P = I^2R$ :

Original power loss: $P_1 = I^2R$
New power loss: $P_2 = (2I)^2R = 4I^2R$
Therefore: $P_2 = 4P_1$

How transformers work in the National Grid

The National Grid uses two types of transformers to change voltage levels:

Step-up transformers

Located near power stations
Increase the voltage to 132kV or higher
This reduces the current for efficient transmission
Allow thinner wires to be used, which saves money

Step-down transformers

Located near homes and industry
Decrease the voltage to safer levels
Provide 230V for homes
Provide 11kV for light industry
Higher current is now acceptable since distances are short

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The positioning of transformers is crucial - step-up transformers must be close to power stations to immediately convert electricity to high voltage for efficient long-distance transmission, while step-down transformers are placed near end users to convert back to safe, usable voltages.

How the National Grid system works

Power station generates electricity using fossil fuels or nuclear fuel
Step-up transformer increases voltage to 132kV or more for transmission
High voltage cables carry electricity across long distances efficiently
Step-down transformers reduce voltage to safe levels
Local distribution delivers 230V to homes and 11kV to industry

Key voltage levels to remember

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Reference Voltage Levels:

132kV or higher: transmission across the country
230V: voltage supplied to homes
11kV: voltage supplied to light industry

Remember!

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Key Points to Remember:

The National Grid transmits electricity efficiently using high voltage and low current
Step-up transformers increase voltage near power stations to reduce energy losses
Step-down transformers decrease voltage to safe levels for homes (230V) and industry (11kV)
Energy losses as heat are proportional to $I^2$ , so reducing current dramatically cuts waste
The system allows electricity to travel long distances with minimal energy loss

The National Grid (AQA GCSE Physics): Revision Notes