Three-phase transformers or transformers in general are needed to increase or decrease AC voltages. To change a three-phase AC voltage a three-phase transformer is needed.
A transformer consists of a magnetic circuit, this is called a core, and has at least two windings through which current flows. The winding facing the electrical voltage (line voltage) is called the primary side, and the side with the load (separate winding) and the electrical load is called the secondary side. The manufacturing technique for the core and the quality of transformer core material used affects the magnetic circuit. Ideally, the magnetic circuit should produce low eddy current losses and low re-magnetization losses (hysteresis losses). Another aspect is the resistances in the winding. Only with a layered and ordered winding on the primary side and the secondary side of the coil and the best winding material can the winding losses be reduced.
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 γ = 36). Aluminum thus follows with a gap of about 35 percent. Thus, copper is the best precious metal and aluminum “only” the second best of the technically and economically usable conductor materials. All other metals cannot be considered as current conductors, and alloys generally have considerably lower conductivity than pure metals. Silver or gold are ruled out altogether because of their high price.
In principle, a three-phase transformer consists of three single-phase transformers. It combines three individual transformers, which are needed for a three-phase system, into one transformer. The structure of a normal single-phase transformer therefore remains largely the same.
A 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 onto 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. According 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 windings 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 windings of the secondary coil is less, then the output voltage is less than the input voltage. If both coils have the same number of windings with wire wrapped around them, then the output voltage is equal to the input voltage. A transformer works mainly with alternating voltage. The decisive factor for the change in power or voltage or current is the ratio of the number of turns. N1/N2. It is important to note that the transformer can either increase or decrease the voltage or the current. The respective counterpart will then decrease or increase to the same extent.
The difference between single-phase and three-phase transformers is that the primary and secondary sides each consist of separate windings. In addition, the differences lie in the reduced design. If the terminals of the primary windings and those of the secondary windings of three single-phase transformers are permanently connected, these transformers can be used in the three-phase network. The advantage of a three-phase transformer is the reduced size and the associated cost advantages in purchasing as well as the reduced power loss during operation.
Three-phase transformers are the basis of power supply and are used for electrical distribution and transmission of current and voltage and are used in every industrial plant worldwide.