The National Grid (AQA GCSE Physics Combined Science): Revision Notes
The National Grid
What is the national grid
The National Grid is Britain's electricity delivery system. It's a network of cables and wires that carries electricity from power stations to our homes, schools, hospitals and factories.
Think of it like a motorway system for electricity. Just as motorways connect different cities, the National Grid connects power stations to all the places that need electricity.
The grid doesn't include the actual power stations or the buildings that use electricity. It's just the transport system in between.
Why we use high voltage transmission
Electricity travels through the National Grid at very high voltage and low current. This might seem dangerous, but it's actually the most efficient way to transport electrical energy.
Here's why this works so well:
Less energy is wasted as heat When electricity flows through wires, some energy is always lost as heat. The amount of power wasted follows the equation , where is the current and is the resistance of the wires.
This equation shows us something important. If we can halve the current, the power lost as heat becomes four times smaller (¼ of the original amount).
Real Example: Power Loss with Current Changes
If the current increases by 10 times, then 100 times more energy will be lost as heat every second. That's a huge waste!
By using high voltage, we can use much lower current to transmit the same amount of power. This means much less energy is wasted during transmission.
The key insight is that power loss depends on the square of the current (), so even small reductions in current lead to significant energy savings.
How transformers work in the grid
The National Grid uses two types of transformers to change voltage levels at different points:
Step-up transformers at power stations These transformers increase the voltage from the power station to 132,000 volts (132kV) or even higher. When voltage goes up, current goes down for the same amount of power.
Fossil fuels or nuclear fuel generate electricity at power stations. The step-up transformer immediately boosts this to high voltage before it enters the transmission lines.
Step-down transformers for consumers These transformers reduce the high voltage from the National Grid down to safer levels we can use. They decrease voltage, which means current increases.
For light industry, voltage is stepped down to 11,000 volts (11kV). For our homes, it's reduced to 230 volts - the voltage of your plug sockets.
Using high voltage also means thinner wires can carry the same power, which reduces costs for building the grid.
The complete system
The National Grid system works in three main stages:
- Generation: Power stations (using fossil fuels or nuclear fuel) generate electricity
- Transmission: Step-up transformers boost voltage to 132kV or higher for efficient long-distance transport through overhead power lines
- Distribution: Step-down transformers reduce voltage to safe levels for homes (230V) and light industry (11kV)
The high-voltage transmission lines you see supported by tall pylons carry electricity across the country with minimal energy loss. This efficient system ensures electricity generated anywhere in Britain can power homes and businesses everywhere else.
Key Points to Remember:
- The National Grid transports electricity from power stations to where it's needed
- High voltage and low current transmission reduces energy waste as heat
- Step-up transformers at power stations increase voltage for efficient transmission
- Step-down transformers reduce voltage to safe levels for homes and industry
- The power equation explains why lower current means less energy loss