How do transformers transform themselves

Working principle of transformers


A transformer (coll. Also: "Trafo") is a system or a tree element to increase or decrease the voltage. Transformers are used within the supply network to reduce or increase the alternating voltage as required and thus to be able to switch relatively easily between the various voltage levels (maximum, high, medium, low voltage).

Working principle

A transformer consists of an iron core around which two electrically separated coils of copper wire are wound, one with many turns, the other with a few turns. If a high voltage is applied to the coil with the higher number of turns, a lower voltage is created between the connection terminals of the coil with the few turns. If, on the other hand, you want to transform a low voltage into a higher one, the principle works exactly the other way round: you apply the low voltage to the small coil and take off the high voltage at the terminals of the larger one. Behind the transformer principle is the changing magnetic field, which is generated by the applied alternating voltage and which in turn generates an alternating voltage via the iron core in the other coil.

In the case of an ideal transformer, the ratio of input and output voltage corresponds to the ratio of the number of turns in the two coils. For example, with a turns ratio of 10 to 1 (N1: N2), an input voltage of 100 volts (U1 to U2) is transformed into an output voltage of 10 volts. Depending on the design of the transformer, the output voltage can be lower, higher or equal to the input voltage. An ideal transformer is understood to be a loss-free transformer that cannot be realized in practice. This model concept is helpful for the functional description. In practice there are more or less large deviations, the regularities only apply approximately.

The following formula therefore applies to an ideal transformer:


Structure of a transformer

Work order

On the work surface you will find various tasks in which transformers with different turns ratios are to be used to generate a certain voltage change.

  1. First calculate the turns ratio required for the conversion for each task.
  2. Now choose the right turn ratio for each task.
  3. Check your result by clicking on the evaluate button and correct it if necessary.
240 V12 V
5500 V110 kV


300 kV3000 V
400 V20,000 V