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The National Grid

20 April 2023

Objectives

Be able to explain the use of the National Grid.HSW: AF2: Make balanced judgments about scientific developments by

evaluating the economic, moral, social or cultural implications. Used before in: Will use again in:

PLTS: Independent enquirers: support conclusions, using reasoned arguments and evidence.

Used before in: Will use again in:

KeywordsTransformers, Power, Voltage, Current, Energy,

National Grid, Megawatt, Kilowatt, Joule, Energy.

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Outcomes

All students should be able to: • Draw and label a diagram of the National

Grid.

Most students should be able to: • Describe why electricity is transferred at

very high voltages .

Some students should be able to: • Use power calculations to explain the use

of transformers in the National Grid.

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What is the National Grid?

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Demo Time!!

• Watch the demo of the National Grid.• Can you answer these questions?• When the transformers were not

connected what happened to the bulb at the far end of the model?

• What do the transformers do?• Why does the voltage have to be so

big in the wires?

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The National Grid takes …………… from power stations to businesses and homes at extremely large voltages.

It does this to limit the ………….. lost by heat from the wires.

The bigger the electric ………… in a wire, the more heat is lost.

To make the voltages bigger, step up ……………….. are used. To make voltages…………, step down transformers are used.

transformers smaller electricity energy current

2 Copy Figure 2 on Page 260 – label the parts and voltages.

1 Copy and complete using the key words below:

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The voltage of an alternating current can be changed using a device called a transformer.

The alternating current in the primary (input) coil produces an alternating magnetic field.

This alternating magnetic field induces an alternating current in the secondary (output) coil.

What is a transformer?

A transformer contains two coils that are wound around a soft iron core.

iron core

primarycoil

secondarycoil

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Where are transformers used?

This outdoor transformer decreases the voltage of the electricity carried by the national grid. It is an example of a step-downtransformer.

A television needs a very high voltage to operate. It contains a step-up transformer, which increases the voltage of the electricity supplied to the television.

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Power is measured in watts (W) or kilowatts (kW).

Current is measured in amps (A).

Voltage is measured in volts (V).

What are the units of power, current and voltage?

What is the formula for electrical power?

power = current x voltage

P = I x V

In electrical devices, power can be calculated using the formula:

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A formula triangle helps you to rearrange a formula. The formula triangle for P = IV is shown below.

Cover up whatever quantity you are trying to find to leave the calculation required.

So to find current (I), cover up I…

…which gives the formula…

I =P V

Can I use a formula triangle?

x

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A power station produces electricity of 2.5 kV 20, 000 A.

How is power calculated?

What is the Power of the Power station?

= 500 MW

= 20 000 A x 2500 V

P = IV

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Power Calculations

• What is the current running in the wires of the National Grid?

• I = P/V• I = 500 000 000 W/ 400 000V• I = 1250 A (A lot less than the 20 000A from the

Power Station.)

500 MWPower of 500 MW remains constant but Voltage increases to 400 000V.

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Power – The Big Q: Why have a National Grid?

All

Finish Figure 2 on Page 260 – label the parts and voltages.

Most

Explain why the National Grid uses high voltages in the overhead cables.

Some

Given the power output of the power station you have drawn is 500MW, what current does it produce? And therefore, from the Voltage that you have labelled in the diagram what is the current through the National Grid? Describe what the transformer has done and why this is useful.

SO: from today’s lesson and previous lessons on Electricity Generation answer this: Why have a National Grid?

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Plenary

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Plenary