Transformers

A transformer changes the intensity of alternating voltage and current.

Mutual Induction

Transformers A device in which two coils are placed near one another without electrical connection. The number of turns in the coils differs, causing a change in currnet in the secondary coil; this serves to either increase or decrease the voltage.

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Types of transformers

• Air core

• Open core

• Closed core

• Shell type

Air core transformer

Open core transformer

Closed core transformer

Shell type transformer

Step up vs Step-down

If you increase the number of turns on the right, the voltage coming off the transformer will increase in proportion.

Using the numbers in the example above, you can see that the right side has four times more turns. As a result, the voltage on the right has increased four times (from 100 V to 400 V). The voltage has been stepped up by a factor of four.

Because current is inversely proportional to voltage, you can see that stepping up the voltage pays a price ... the current on the right is only a quarter of what it was on the left. Step-up transformers increase the voltage, but decrease the current. In our example above, the current went from 10 A to 2.5 A, a reduction of by a factor of four

If you decrease the number of turns on the right, the voltage coming off the transformer will decrease in proportion.

Using the numbers in the example above, you can see that the right side has one fifth the number of turns. As a result, the voltage on the right is only one-fifth as large. The voltage has been stepped down by a factor of five (1000 V down to 200 V).

Because current is inversely proportional to voltage, you can see that stepping down the voltage gives a bonus ... the current on the right is five times what it was on the left. Step-down transformers decrease the voltage, but increase the current. In our example above, the current went from 2 A to 10 A, an increase by a factor of five.

Transformer law

If the turns ratio is greater than 1 the transformer is a step-up transformer.

If the turns ratio is less than 1 the transformer is a step-down transformer

Ns

Np

Autotransformer (kVp selector) self-induction