Transformers (double)

A transformer is an electrical device that changes the voltage of an ac supply.

A transformer changes a high-voltage supply into a low-voltage one, or vice versa.

A transformer that increases the voltage is called a step-up transformer.

A transformer that decreases the voltage is called a step-down transformer. Step-down transformers are used in mains adapters and rechargers for mobile phones and CD players.

Transformers do not work with dc (direct current) supplies.

Transformers are used within The National Grid

 When a current flows through a wire some energy is lost as heat. The higher the current, the more heat is lost. To reduce these losses, the National Grid transmits electricity at a low current.

This needs a high voltage. Power stations produce electricity at 25,000V. Electricity is sent through the National Grid cables at 400,000V, 275,000V and 132,000V.

Step-up transformers are used at power stations to produce the very high voltages needed to transmit electricity through the National Grid power lines. These high voltages are too dangerous to use in the home, so step-down transformers are used locally to reduce the voltage to safe levels.