Electricity is distributed via the Nation Grid

The national grid is a giant system of cables and transformers that covers the UK and connects power stations to consumers
The national grid transfers electrical power from power stations anywhere on the grid to anywhere else on the grid where it’s needed

Electricity production has to meet demand

Throughout the day, electricity usage changes. Power stations have to produce enough electricity for everyone to have it when they need it
They can predict the most electricity will be used through. Demand increases when people get up in the morning and when it starts to get dark. Popular events on TV also cause peak in demand
Power stations often run at well below their maximum power output, so there’s spare capacity to cope with high demand, even if there’s an unexpected shut down of other stations
Lots of smaller power stations that can start up quickly are also kept in standby just incase

To transmit the huge amount of power needed, you need either a high potential difference or a high current
The problem with a high current is that you lose loads of energy as the wires heat up and is transferred into thermal energy of the surroundings
It’s much cheaper to boost the pd really high, 400,000V, and keep the current as low as possible
For a given power, increasing the pd decreases the current, which decreases the energy lost by heating the wires and the surroundings. This makes the national grid an efficient way of transferring energy

To get the voltage up for efficient transmission we use transformers
Transformers all have two coils, a primary coil and a secondary coil joined with an iron coil
Potential difference is increased using a step-up transformer. They have more turns on the secondary coil than the primary coil. As the pd is increased by the transformer, the current is decreased
The pd then reduced again at the local consumer end using a step-down transformer. They have more turns on the primary coil than the secondary
The power of a primary coil is given by power=pd x current. Transformers are nearly 100% efficient, so the power in primary coil = power in secondary coil. This means that:
P.d. across secondary coil x current in secondary coil = p.d across primary coil x current in primary coil

The national grid is a giant system of cables and transformers that covers the UK and connects power stations to consumers
The national grid transfers electrical power from power stations anywhere on the grid to anywhere else on the grid where it’s needed

Throughout the day, electricity usage changes. Power stations have to produce enough electricity for everyone to have it when they need it
They can predict the most electricity will be used through. Demand increases when people get up in the morning and when it starts to get dark. Popular events on TV also cause peak in demand
Power stations often run at well below their maximum power output, so there’s spare capacity to cope with high demand, even if there’s an unexpected shut down of other stations
Lots of smaller power stations that can start up quickly are also kept in standby just incase

To transmit the huge amount of power needed, you need either a high potential difference or a high current
The problem with a high current is that you lose loads of energy as the wires heat up and is transferred into thermal energy of the surroundings
It’s much cheaper to boost the pd really high, 400,000V, and keep the current as low as possible
For a given power, increasing the pd decreases the current, which decreases the energy lost by heating the wires and the surroundings. This makes the national grid an efficient way of transferring energy

To get the voltage up for efficient transmission we use transformers
Transformers all have two coils, a primary coil and a secondary coil joined with an iron coil
Potential difference is increased using a step-up transformer. They have more turns on the secondary coil than the primary coil. As the pd is increased by the transformer, the current is decreased
The pd then reduced again at the local consumer end using a step-down transformer. They have more turns on the primary coil than the secondary
The power of a primary coil is given by power=pd x current. Transformers are nearly 100% efficient, so the power in primary coil = power in secondary coil. This means that:
P.d. across secondary coil x current in secondary coil = p.d across primary coil x current in primary coil