Describe the role of step-up and step-down transformers in the National Grid, and explain why each is necessary.

Step‑up transformers at power stations raise the voltage of the electricity produced, which reduces the current that must travel through the high‑voltage transmission cables. Because power (P=VI) is essentially constant, a higher voltage means a lower current, and lower current results in smaller I²R losses as heat in the cables.

Step‑down transformers at substations lower the high transmission voltage to a safer, lower voltage that can be used by homes and businesses.

Both types of transformer are therefore essential: step‑ups minimise transmission losses, and step‑downs make the electricity safe and usable for consumers.