The National Grid: Electrical power is transferred from power stations to consumers using the National Grid.

The idea

The National Grid is a nationwide network of cables and transformers that links power stations to homes, schools, hospitals and factories. Electrical power is generated at power stations, often at around 25 kV, and must travel long distances to consumers. Because the cables have resistance, some energy is transferred to the thermal store of the surroundings, reducing efficiency. To reduce this waste, the potential difference is increased using step-up transformers before transmission, so that a smaller current transfers the same power. The grid therefore transfers electrical power continuously from generators to consumers, matching supply to demand.

What earns the marks

• The National Grid is a system of cables and transformers connecting power stations to consumers.
• Electrical power is generated at power stations and transferred through the grid to homes, industry and other consumers.
• The grid operates at high potential difference during transmission to reduce energy losses in the cables.
• Step-up transformers increase potential difference from the power station to the transmission cables.
• Step-down transformers reduce potential difference to safe domestic levels for consumers.
• Energy losses in transmission cables are reduced because a lower current is used for the same power transfer.

Common mistakes and how to put them right

• Thinking the National Grid stores electricity.

  Put it right: It transfers electrical power continuously; energy is not stored in the cables.

• Confusing power stations with the grid.

  Put it right: Power stations generate electricity, while the grid is the network that distributes it.

• Assuming electricity travels instantly with no energy loss.

  Put it right: Cables have resistance, so some energy is transferred thermally to the surroundings.

Exam tips

• Define the National Grid clearly as a network of cables and transformers linking power stations to consumers.
• When explaining efficiency, link high potential difference to low current and reduced heating in the cables.
• Use the correct terms: step-up transformer, step-down transformer, transmission cables and consumers.