Powering Earth — generation and distribution

How power stations generate electricity

Most large-scale power generation uses the same chain:

energy source → boiler → steam → turbine → generator → electricity.

A generator works by electromagnetic induction — when a coil rotates in a magnetic field, an alternating current is induced.

Sources of energy

The National Grid

power station → step-up transformer (to 400 kV) → pylons / underground cables → step-down transformer → consumers.

Domestic supply in the UK: 230 V, 50 Hz alternating current.

Why transformers matter

Transformers change p.d. for AC only:

• Step-up at power station: raises V → lowers I → less heat loss in cables.
• Step-down near homes: drops V to safe ~230 V.

A transformer has primary and secondary coils on a soft-iron core. Voltage ratio = turns ratio: V₁ / V₂ = N₁ / N₂.

Efficiency

efficiency = (useful energy out / total energy in) × 100%

A coal power station is ~35–45% efficient overall — most input energy is lost as heat through cooling towers and as heat in transmission cables.

Reducing energy losses

• High-voltage transmission (low I → low I²R losses).
• Insulation of homes (loft, walls, double glazing).
• LED lights instead of filament (80–90% efficient vs ~5–15%).
• Heat pumps and condensing boilers replace traditional boilers.

OCR exam tip

When asked "evaluate" two energy sources, give a positive for each, a negative for each, and a comparative conclusion. Stand-alone facts max at 2/4.