11) The National Grid

The National Grid is a large system of cables and transformers that spans the UK, connecting power stations to consumers (those using electricity).

Electricity usage varies throughout the day, requiring power stations to produce enough electricity to meet demand.
Demand increases during peak times, such as morning wake-ups, after school or work, and when it gets dark or cold.
Major events (e.g., sporting finals on TV) can also lead to spikes in electricity demand.
Power stations usually operate below maximum capacity to have spare capacity for unexpected demand or station shutdowns.
Smaller power stations are kept on standby to quickly meet high demand.

To transmit large amounts of power, either high potential difference or high current is needed (P=VI)
High current leads to significant energy loss due to heating of wires.
Increasing the potential difference to 400,000 V while keeping the current low reduces energy loss, making transmission more efficient.

Transformers are used to step up the voltage to 400,000 V for efficient transmission.
A transformer consists of two coils (primary and secondary) and an iron core. A step-up transformer has more turns on the secondary coil than the primary.
As potential difference increases in a transformer, the current decreases.

At the consumer end, a step-down transformer reduces the voltage to safer levels.
The power relationship in transformers can be described as:
Power = Potential Difference × Current
Transformers are nearly 100% efficient, meaning:
Primary Coil Power=Secondary Coil Power
V_primary × I_primary= V_secondary × I_secondary