A wind turbine can sit far out at sea, spinning in clean air… but your phone charger is on land.
So how does that electrical energy move across long distances without wasting huge amounts as heat?
The answer is a neat chain: generators make electricity by induction, then transformers change the voltage so transmission becomes efficient.
This is one of those IGCSE topics that feels abstract—until you realise it’s literally how modern grids are being redesigned.
Today we’ll make it intuitive, exam-ready, and connected to what’s happening in real energy projects right now.
In late January, National Grid (UK) and TenneT (Germany) announced GriffinLink—a planned link designed to connect up to 2 GW of offshore wind between the two countries. It’s part of a wider push to build a more connected North Sea power system, so offshore wind can be shared across borders rather than “trapped” behind local bottlenecks.
Projects like this only work if we can transmit power efficiently. That’s why step-up transformers and high-voltage transmission are central: higher voltage means lower current for the same power, and that slashes heating losses in cables.
Electromagnetic induction means: a changing magnetic field can induce an emf (voltage) in a conductor.
In a generator, a coil spins in a magnetic field, so the magnetic field through the coil changes continuously → an alternating emf is produced.
A transformer uses the same principle, but without moving parts:
- AC in the primary coil creates a changing magnetic field in the iron core.
- That changing field induces an AC voltage in the secondary coil.
Transformers require AC (a changing field). With steady DC, induction stops after a brief moment.
Turns ratio rule:
Intuitive analogy
Think of voltage as electrical “pressure” and current as electrical “flow rate.”
To deliver the same power, you can use high pressure with low flow, or low pressure with high flow. The grid chooses high voltage, low current because heating losses depend strongly on current.
Why high voltage reduces losses (the big exam idea)
Power lost as heat in transmission cables is:
If you step up voltage, current drops (for the same transmitted power), and because current is squared, losses fall fast.
What examiners are testing here
The question (7 marks total)
A wind farm generates electrical power which is transmitted to a city using high voltage.
(a) State what is meant by electromagnetic induction. (2)
(b) A step-up transformer increases the voltage from 11 kV to 275 kV. The primary coil has 400 turns. Calculate the number of turns on the secondary coil. (2)
(c) The power transmitted is 8.0 MW. Calculate the current in the 275 kV transmission line. (2)
(d) The total resistance of the transmission cables is 0.40 Ω. Calculate the power loss in the cables and comment on why stepping up the voltage helps. (1)
