1. Science A Physics – P1 Science A Physics – P1 Topic 2a : Transmission of Electricity Topic 2a : Transmission of Electricity

2. Electrical Transmission The EU domestic mains supply is notionally 230 V. However, historically the British used 240 V and mainland Europe used 220 V. The historic compromise was to allow both to call the voltage 230 V but to allow a sufficient tolerance so that both cultures could carry on with their historical values. Mains equipment for use in the EU has to be designed to accept a range of input voltages including 220-240V.

3. Electrical Transmission The United States uses 120 V, though it is often confusingly referred to as 110 V. Incandescent light bulbs which run off 120 V are generally more efficient than those at 240 V. The first main use of domestic electricity was for lighting. Edison’s light bulbs – with a carbon fibre filament – could not run on very high voltages. European bulbs were made with a metal filament and could stand high voltages. http://users.telenet.be/worldstandards/electricity.htm gives a list of virtually all countries and their voltagehttp://users.telenet.be/worldstandards/electricity.htm

4. Electricity is made in many different types of power station. It is distributed through a network called the National Grid. Electrical Generation

5. The National Grid The electricity produced at a power station is alternating current, because:  It is easier to generate  Transformers only work with alternating current.

6. In the UK, power stations produce electricity at 25,000 volts. This is passed through step-up transformers, to increase the voltage to 400,000 volts before it is distributed. Electricity Distribution

7. All types of power stations use step-up transformers to substantially increase the voltage before it is distributed. Step-up transformers

8. The National Grid Electricity is distributed from power stations all over the UK to industry, business and domestic consumers along a network called the National Grid.

9. The Super Grid Electricity is first carried around the ‘Super Grid’ at 400,000V. The Super Grid is part of the National Grid.

10. Regional Substations The electricity carried around the ‘Super Grid’ arrives at a substation, where step-down transformers are used to decrease the voltage, first to 132,000 volts and then to 33,000 volts.

11. Large factories with huge electrical consumption take the electricity at 33,000 volts.

12. The electricity is now carried to housing estates and smaller factories around the secondary distribution network. Secondary Distribution Network As the electricity approaches towns and cities, it passes through substations once again, and the voltage is stepped down to 11,000 volts.

13. Local Substations Before being passed into houses, the electricity goes through another local step-down transformer, which further decreases the voltage to 230 volts. Always be safe - never go near a substation!

14. Build your own National Grid You will be given a folder full of information cards. Each card has a tag attached to the ‘output’ and a corresponding hole for an ‘input’ Coal Cards which have no input and just an output are at the start of the grid system i.e. they are the fuels for the power stations. An example is shown opposite.

15. Build your own National Grid Cards which have no output are the final users of the electricity. In the case opposite a large hospital. You will notice that the hospital has a power input requirement of 415V, 5000A. Somewhere among all the cards will be an output of a transformer with exactly the same values. You must link the two together, and so on for every card in the pack. University Hospital. A large teaching hospital has a large demand for electricity due to all the electrical equipment being used throughout the hospital. Input Requirements: 415V 5,000A

16. Electricity Distribution Questions: 1.How many different types of Transformer are there in the distribution system. Two – Step Up and Step Down 2.Why do you think the output of the Nuclear Power Station is less than the output of the Fossil Fuel station? Nuclear Power is more dangerous than using Fossil Fuels if anything goes wrong so they are kept small to ensure they are as safe as possible.

17. Electricity Distribution Questions: 3.What does a step-up transformer do ? A Step Up transformer increases the voltage. 4.How many step-down transformers are there ? Six. 5.What does a step-down transformer do ? A Step down transformer decreases the voltage.

18. Electricity Distribution Questions: 6.The cables are carried by pylons rather than being buried underground. i.What are the advantages of this method ? Easy to see route of cables, easy to find damaged cables, no insulation needed. ii. Are there any disadvantages to using overhead cables ? Exposed to high winds, snow & ice, ugly to look at.

19. Electricity Distribution Questions: 7.By looking carefully at the Step-down transformer after the National Grid Pylon, and the transformers feeding the Steel Rolling Mill and Shopping Centre. Can you find a link between the input and output voltages and currents ? For Step Down Transformer Input = 275000V, 900A Output = 132000V, 1875A Multiplying each pair of numbers gives 275000 × 900 = 132000 × 1875 247500000 = 24750000 i.e. they are equal!

20. Electricity Distribution Questions: 7.By looking carefully at the Step-down transformer after the National Grid Pylon, and the transformers feeding the Steel Rolling Mill and Shopping Centre. Can you find a link between the input and output voltages and currents ? For Steel Rolling Mill Input = 132000V, 1875A Outputs = 33000V, 7000A and 33000V, 500A Multiplying each pair of numbers gives 132000 × 1875 = 33000 × 7000 + 33000 × 500 247500000 = 231000000 + 16500000 247500000 = 247500000 i.e. they are equal!

21. Electricity Distribution Questions: 7.By looking carefully at the Step-down transformer after the National Grid Pylon, and the transformers feeding the Steel Rolling Mill and Shopping Centre. Can you find a link between the input and output voltages and currents ? For Shopping Centre Input = 33000V, 500A Outputs = 11000V, 1300A and 11000V, 200A Multiplying each pair of numbers gives 33000 × 500 = 11000 × 1300 + 11000 × 200 16500000 = 14300000 + 2200000 16500000 = 16500000 i.e. they are equal!

22. Electricity Distribution Questions: 8.The distribution system is quite complex, and transformers are expensive to put in place. Why do you think we spend such a lot of money changing the voltage and current ? Why don’t we connect the power stations directly to our homes ? Even though transformers are expensive it is still the most efficient way of distributing electricity. We cannot connect power stations to our homes because the electricity is at too high a voltage. It is too dangerous.