A transformer consists of a magnetic circuit, called the core. The core has two windings through which current flows, the primary winding and the secondary winding. When an alternating 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 consists essentially of two or more coils and a shared 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. That 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 inductance. The magnetic flux passes through the secondary coil with the help of the iron core. Thus, the output voltage can be taken from the secondary side of the transformer. Corresponding to the primary side, the coil on secondary side, is called secondary coil. The winding ratio of the primary and secondary coils defines whether the output voltage is smaller or larger 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 less, then the output voltage is less than the input voltage. If both coils have the same number of turns with wire wrapped around them, then the output voltage is equal to the input voltage. A transformer works mainly with AC voltage. The ratio of the number of turns is decisive for the change in power or voltage or current. It is important to note that the transformer can either increase or decrease the voltage or the amperage. 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 is often made of iron powder, ferrite or silicon steel alloys. Coils are wound on the iron core with wire to create a magnetic connection between them. Many transformers are also cooled. 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. In addition, additional cooling systems can be installed for very high power ratings and or line voltages.
The manufacturing technique for the core and the quality of the transformer core used has an effect on the magnetic circuit. The magnetic circuit of a transformer (magnetic field) should ideally produce low eddy current losses and have low remagnetization losses (hysteresis losses). Another aspect is the resistances in the winding of a transformer. Only with layered and ordered windings on the primary coil and the secondary coil and the best winding metal can the winding losses be reduced. The voltage is controlled with the number of turns on the coil. The current determines the diameter of the winding metal.
The construction power of a transformer is expressed in VA or kVA (VA is the term for voltampère and stands for the unit of measurement of apparent electrical power, kVA for kilovoltampère).
Except for silver, copper has the best conductance with γ = 56. Aluminum, on the other hand, has only γ = 36. Aluminum thus follows with a gap of about 35 percent. Thus, copper is 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 of electricity, and alloys generally have considerably lower conductivity than pure metals. Silver or gold are ruled out altogether because of their high price.