Transformers and the National Grid

An alternating curren in the primary coil causes a changing magnetice field in the soft iron core.

The changing magnetic filed through the secondary coil causes an alternating potential difference across the ends of the secondary coil.

potential difference across the primary coil   =  number of turns on primary coil

potential difference across secondary coil        number of turns on secondary coil

Switch mode transformers transform high voltage A.C current to low voltage D.C current using electronic circuitry. By operating at high frequencies ( often between 50 kHz and 200 kHz) they can be made much lighter and smaller than traditional transformers and are therefore used in devices such as mobile phone chargers. They use very little power when switched on but no load is applied.

To transfer energy from the power station to my home, we could use either: 1) A low voltage and a high current OR 2) a high voltage and a low current.

The first method is not efficient because the high current heats the power lines and wastes energy.Method 2 is used. To get the high voltage a step-up transformer is used. At the other end of the grid near my home, a step-down transformer is used. A.C current has to be used, because the transformers do not work with D.C current.

1) Gas or coal is burned in air in the power station.

2) Water is heated to make steam.

3) The steam makes a turbine turn.

4) The turbine turns a generator.

5) The generator produces electricity (A.C).

6) The voltage is stepped-up to 132 kV or more by a transformers.

7) The energy is transferred through the National grid at this high voltage.

8) The high voltage is stepped-down to 230 V by a transformers.

9) The electricity is supplied at 230 V to my home.