Welding Transformer

Definition of a Welding Transformer

A welding transformer (also called welding power sources) is needed to cover the high current demand of a welding machine. A welding transformer mainly supplies alternating current, a rectifier is additionally needed as soon as the welding transformer runs on direct current. Generally, a current of 100 amperes is required for welding. Modern welding equipment is equipped with an inverter and therefore no longer requires a conventional welding transformer.

Function of a Welding Transformer

In a welding transformer, the alternating current of the mains with high voltage and low amperage is converted into alternating current with low voltage and high amperage to use the transformer for welding. The current is regulated by tapping the primary coil of the transformer. A welding transformer in form of a power transformer is used for the welding equipment. A movable yoke is mounted between the primary and secondary coils of the transformer, which allows stepless regulation (adjustable welding current). The current output of the transformer is similar to a constant current source, which keeps the set welding current almost constant under changing load. The voltage characteristic of a welding transformer is slightly decreasing, so that in the case of a short circuit slightly more than the set current flows. The open-circuit voltage is 50 V, so there is no risk of dangerous electric shock to the user. Small welding transformers with a welding current of 50 to 125 A power already weigh more than 30 kg.

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.

Construction of a Welding Transformer

A 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 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 input voltage is applied to 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.

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 wire-wound onto the iron core 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 be installed for very high power ratings and line voltages.

Application Areas of a Welding Transformer

A welding transformer is used in a welding machine to meet the high power demand during welding. In addition to welding transformers, similar devices can be used in welding to achieve the same result. These are welding rectifiers, welding converters or welding inverters. All these electronic devices are ways to power a welding machine.