Transformer structure

A transformer consists of a magnetic circuit, which is referred to as the core. The core has two windings through which current flows, the so-called primary winding and the secondary winding. If an alternating electrical voltage is applied to the primary winding, an alternating current begins to flow through the primary winding. This alternating current generates a magnetic field in the winding, which changes its strength and frequency with the alternating current source. The magnetic flux of the transformer changes with the frequency of the AC voltage.

A real transformer essentially consists of two or more coils and a common iron core. The windings of a transformer are usually made of insulated copper wire and are wound on the iron core.

The input voltage is applied to the primary winding of the transformer. This is why the coil on the primary side is often called the primary coil. The alternating voltage on the primary coil creates an alternating magnetic field due to inductivity. The magnetic flux passes through the secondary coil with the help of the iron core. The output voltage can therefore be taken from the secondary side of the transformer. Corresponding to the primary side, the coil on the secondary side is called the secondary coil. The winding ratio of the primary and secondary coils defines whether the output voltage is lower or higher than the input voltage. If the number of turns of the secondary coil is greater than that of the primary coil, the output voltage is greater than the input voltage. However, if the number of turns of the secondary coil is lower, the output voltage is lower than the input voltage. If both coils have the same number of turns of wire wound around them, the output voltage is equal to the input voltage. A transformer works mainly with alternating voltage. The ratio of the number of windings is decisive for the change in power, voltage or current. It is important to note that the transformer can either increase or decrease the voltage or current. The respective counterpart will then decrease or increase to the same extent.

In addition to the coils, the iron core is an important component of a transformer. An iron core often consists of iron powder, ferrite or silicon-steel alloys. The coils are wound onto the iron core with wire to create a magnetic connection between them. Many transformers are also subject to cooling. Transformers are cooled in and by an oil bath. In addition to cooling, the oil also acts as an insulator and insulates better than air. Additional cooling systems can also be installed for very high outputs and/or mains voltages.

The manufacturing technology for the core and the quality of the transformer core used have an effect on the magnetic circuit. Ideally, the magnetic circuit of a transformer (magnetic field) should generate low eddy current losses and have low remagnetization losses (hysteresis losses). Another aspect is the resistances in the winding of a transformer. Winding losses can only be reduced with layered and ordered windings on the primary and secondary coils and the best winding metal. The voltage is regulated by the number of turns on the coil. The current strength determines the diameter of the winding metal.
The power rating of a transformer is expressed in VA or kVA (VA stands for volt-ampere and is the unit of measurement for apparent electrical power, kVA for kilovolt-ampere).

With the exception of silver, copper has the best conductivity value with γ = 56, while aluminum only has γ = 36. Aluminum follows with a gap of around 35 percent. Copper is therefore the best metal and aluminum “only” the second best of the technically and economically usable conductor materials for electrical energy. All other metals cannot be considered as conductors, and alloys generally have a considerably lower conductivity than pure metals. Silver or gold are ruled out completely due to their high price.