Boardworks Electricity Distribution

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Electricity Distribution


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.


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.


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


Why use high voltages for distribution?


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.


Transformers and the supply chain


The electricity supply chain


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