Electricity Transmission And Distribution
Visão Geral
The cables slung between pylons across open country are thinner than most people expect, and they are carrying the output of an entire power station. They manage it because the potential difference across them is enormous and the current in them is small, and that trade is the single decision on which the whole national supply rests. Get it wrong and a useful fraction of everything a station produces would be wasted warming up the countryside before it reached a single house.
This lesson follows the energy along that route, from the station to the socket, and asks you to be able to name every part of it in order. You will meet the two kinds of transformer that sit at the ends of the transmission line, one raising the voltage for the journey and one lowering it again so that what arrives in a street is safe to bring indoors. Then you will do the arithmetic that shows exactly how much is saved by sending the energy at hundreds of thousands of volts, using two equations you already have on the sheet at the back of your paper.
Objetivos
- Electricity is distributed from power stations to consumers along transmission cables with transformers at both ends. Students should be able to identify and label the essential parts of an electric power transmission and distribution system.
- For a given power rating, a high distribution voltage reduces the current flowing, therefore reducing energy losses due to heating and making the system more efficient.
- Step-up and step-down transformers are used to increase the voltage before the distribution lines and reduce it at the end to produce a safer voltage for local consumers.
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- Which transformer is placed between a power station and the transmission cables, and what is the effect on the current in those cables? A. A step-up transformer, which increases the current B. A step-up transformer, which decreases the current C. A step-down transformer, which increases the current D. A step-down transformer, which decreases the current Answer: B
- A fixed amount of electrical power is transmitted along an unchanged line. The transmission voltage is doubled. What happens to the power wasted heating the cables? A. It doubles B. It halves C. It falls to one quarter D. It is unchanged Answer: C
- A transmission line carries a current of 50 A and its cables have a total resistance of 4.0 ohms. What is the power wasted heating the cables? A. 200 W B. 2.0 kW C. 10 kW D. 200 kW Answer: C
- Why is the voltage reduced by a transformer before the supply reaches houses in a street? A. To increase the amount of energy delivered each second B. To produce a voltage that is safe for local consumers C. To reduce the resistance of the transmission cables D. To change the alternating supply into a direct one Answer: B
- Which list gives the essential parts of a transmission and distribution system in the order that energy passes through them? A. Power station, step-down transformer, transmission cables, step-up transformer, consumers B. Power station, step-up transformer, transmission cables, step-down transformer, consumers C. Power station, transmission cables, step-up transformer, step-down transformer, consumers D. Step-up transformer, power station, transmission cables, consumers, step-down transformer Answer: B
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