boardworks electricity distribution
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Electricity Distribution
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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.
What is a transformer?
A transformer contains two coils that are wound around a soft iron core.
iron core
primarycoil
secondarycoil
This alternating magnetic field induces an alternating current in the secondary (output) coil.
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The voltage induced in the secondary (output) coil depends on the number of turns on the primary and secondary coils.
How does a transformer change voltage?
A step-up transformer has more turns on the secondary coil and so increases voltage.
A step-down transformer has fewer turns on the secondary coil and so decreases voltage.
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Transformer power
Transformers not only change voltage; they also change current.
If the voltage increases, such as in a step-up transformer, the current decreases. This is because for any transformer:
If the voltage increases, the current must decrease to ensure that power out remains the same as power in.
power in = power out
And because:
power = voltage × current
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Why use high voltages for distribution?
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Example uses for transformers
Step-up transformers are mainly used in power transmission to increase voltage to reduce energy loss. Some household appliances (such as older style CRT TVs) also increase voltages using step-up transformers.
Step-down transformers are used in electricity substations to reduce the voltage to 230 V for domestic use.
Appliances generally reduce this again, as most electronic circuits use 5–12 V.
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Transformers and the supply chain
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The electricity supply chain
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