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Power in the National Grid

New GCSE spec...
by

Carl Bater

on 8 January 2018

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Transcript of Power in the National Grid

Power in the National Grid
If I gave you £150000, but took back £10, how would you feel?
What about if I gave you £100, and took back £10?
A typical Nuclear plant produces 350,000,000 Watts of electrical power at a voltage of 35,000 volts.
Use P = I x V to calculate the current this plant produces.

10,000 Amps...
A 350 km long power line will have a resistance of 275 Ohms.
Use P = I R to find how many Watts of energy would be wasted in this power line if we fed our 10,000 Amps into it.
2
27,500,000,000 Watts of wasted energy.
This is where transformers come in...
To reduce the wasted energy, we reduce the current and increase the voltage using a STEP UP transformer.
First, use P = I x V to find the current that would need to flow to move our 350,000,000 Watts of electrical energy at 437,500,000 Volts.


Then, use P = I R to find out how much energy would be wasted in sending this smaller current along our 275 Ohm power line.
0.8 Amps
2
176 Watts
This is quite obviously a HUGE energy saving.
Before some of this energy is used in the domestic supply, this huge voltage needs to be reduced by a STEP DOWN transformer.
Use P = V x I to find what current would flow out of a step down transformer that supplies 165,600 Watts of electrical energy to homes at 230 Volts.
720 Amps
Note in your books:

"Transformers allow us to transmit electrical energy long distances with an efficiency of above 90%. Step up transformers are used to increase the voltage and reduce the current flowing in the grid. This small current does not waste much energy as heat. Step down transformers are used to reduce this voltage (and increase the current) before it is used in homes."
To Do: Choice of exam question...
Full transcript