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Energy & Forces - Conversion & transfer of energy - Electric circuits - G20
This is the Teacher's Guide for this targetThis is the Teacher's Guide for this targetTeacher's Guide


1. Electrical energy is carried from power stations by a network of cables called the National Grid. Since electrical energy of this amount cannot be stored it has to be made on demand. Often one area or another may not have sufficient supply locally and so via the grid they can get what they need from elsewhere around the country. For example about 30% of the electricity produced in Scotland is exported south to England and Wales.

As the demand increases during the day - for example there is often a surge of power being used when there is an advert break on a favourite TV programme as people go and put on the kettle for a cup of tea - the power stations increase their output accordingly.

Massive Power Surge After England Win
( June 08, 2002 )

The National Grid experienced one of its biggest ever daytime power surges during the half-time interval of England's epic 1-0 win against Argentina.

The 1,500 megawatt power surge experienced just seconds after skipper David Beckham scored that penalty was the equivalent of 600,000 kettles being switched on at the same time.

National Grid spokesman Ross Hayman said: "The biggest surge was at half-time of 1,500 mega watts, which is the equivalent of 600,000 kettles all being switched on at the same time.

At full time the surge was of 800 megawatts, which is the same as about 300,000 kettles being switched on.

The half-time power surge is one of the biggest we have ever recorded in the daytime as normally the big televised matches are played in the evening UK time."


Power leaving a power station is at a very high voltage. Voltage is the amount of ‘push’ the electricity has. It is maybe easier to compare electricity to water -if you have several thousand gallons of water stored in a tank it is of little danger. If the tank burst and comes flooding through your living room you are likely to drown. The amount of electricity is not so dangerous it is the amount of push or voltage it has which is dangerous. Transformers increase the voltage and the electricity leaves the power station at either 400,000 volts or 275,000 volts.

Thick cables carried on tall pylons carry the power across the countryside. Near to the towns and cities, the power is taken through another set of transformers where some of the voltage is reduced to 132,000 volts.

More cables and pylons carry the power into towns and cities where again it enters transformers.

Heavy industries are supplied with power at 33,000 volts, light industries at 11,000 volts. By the time the power reaches us in our homes it has been stepped down to 240 volts.

Many children will be familiar with small local transformers which have danger signs on them warning them to keep out.

The reason for these high voltages is to reduce losses as the power is carried through the cables. At low voltages too much is lost.

To show this as a diagram you should have something like this :-

This is probably a good time to mention the dangers of high powered cables, transformers and pylons to the children. High power cables are obviously lethal to humans.

The reason why birds can sit on the wires without being electrocuted is that they are not touching anything else. You are safe if you are only touching the one cable. If in any way you have contact with a second cable, the ground or anything which is linked to the earth you will be electrocuted. That is why sometimes parachutists land on cables but are not injured so long as no-one gets a ladder to rescue them while the power is still on!

If such an accident occurs, you must not go near the stranded person until the power has been turned off - telephone number given at the bottom of the pylon.

Transformers are often found in estates and housing areas - they are highly dangerous and should not be entered for any reason.

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