GLOSSARY

Mains Transformer

Definition of a Mains Transformer

A mains transformer consists mainly 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. Generally, mains transformers are used in similar situations as autotransformers. They are mainly used when the neutral point of the high voltage and low voltage systems need to be separated. In addition, power transformers are larger than autotransformers, according to the physical size as well as in terms of power (rated power).

Function of a Mains Transformer

A mains transformer consists of a magnetic circuit, this is called the core. The core has two windings through which current flows, called the primary winding and the secondary winding. When an AC voltage is applied to the primary winding, an AC 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. Power transformers are usually wound according to galvanic isolation.

Copper has the best conductance except for silver with γ = 56. Aluminum, on the other hand, has only γ = 36. So aluminum follows with about 35 percent gap. 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.

Construction of a Mains Transformer

 

A transformer consists essentially 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 at the primary winding is often called the primary coil. The input voltage is applied to the primary coil. The alternating voltage at 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 the secondary side, is called secondary coil. The winding ratio of the primary and secondary coil 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 power 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 windings. N1/N2. 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.

The manufacturing technique for the core and the quality of the transformer core (iron core) used will affect 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 name for voltampère and stands for the unit of measurement of apparent electric power, kVA for kilovoltampère).

Application Areas of a Mains Transformer

Mains transformers are used in situations similar to autotransformers. In addition, mains transformers are installed in power distribution, in various industrial plants and in railroads.