Page 530 - Basic Electrical Engineering

changing the frequency. The block diagramatic representation of a
transformer has been shown in Fig. 6.1.

6.2 APPLICATIONS OF TRANSFORMERS

Volt–ampere rating of the transformer is the same whether calculated on the
low-voltage side or at the high-voltage side. It must be noted that a

transformer does not generate any electricity. It only transforms and transfers
electrical power from one circuit to the other at different voltage levels.

Depending upon the requirement, transformers are made for various voltage
and current ratings. Transformers used to raise the voltage level at the
sending end of the transmission lines, and to lower the voltage level at the

receiving end are called power transformers. These are very big transformers
rated at, say, 11 kV/220 kV and several MVAs (mega volt ampers) as their

power ratings.
Smaller transformers are used in lowering the voltage level for the purpose

of distribution of electricity to consumers. The transformer which feeds
electricity to your house will have specifications like 11 kV/400 V, 50 Hz,

500 kVA. Here, the voltage is being reduced to 400 V or 230 V at the user
end for safe supply to residences. These are called distribution transformers.
Supply of power at high voltage to residences may lead to chances of fatal

accidents and other problems. Equipment to be used also have to be
manufactured for higher voltage ratings. Insulation of wires used in house

wiring will have to be sustaining for higher voltages. Therefore, electricity is
supplied at residences at 230 V for single-phase appliances and at 400 V for
three-phase equipment. Very small transformers are used in many electrical

and electronic equipment, and gadgets to lower the voltage level from 230 V
on one side to, say, 6 V or 3 V, on the other side. For example, if you are to

construct a battery eliminator for your transistor radio, or your tape recorder,
you need to get 6 V dc supply from the available 230 V ac supply. A

transformer is required to step down the voltage and then a diode rectifier and
filter are required to get the steady 6 V dc output. Fig. 6.2 shows the use of

transformers of different voltage ratings.