Welding transformers

Welding transformer definition

A welding transformer (also known as a welding power source) is required to cover the high current requirements of a welding machine. A welding transformer mainly supplies alternating current, a rectifier is also required as soon as the welding transformer is running on direct current. As a rule, a current of 100 amps is required for welding. Modern welding machines are equipped with an inverter and therefore no longer require a conventional welding transformer.

Welding transformer Function

In a welding transformer, the alternating current of the mains with high voltage and low amperage is converted into an alternating current with low voltage and high amperage in order to use the transformer for welding. The current is regulated by tapping into the primary coil of the transformer. A welding transformer in the form of a mains transformer is used for the welding machine. A movable yoke is mounted between the primary and secondary coils of the transformer, which ensures infinitely variable 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 with changing loads. The voltage characteristic of a welding transformer is slightly decreasing, so that in the event 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 shocks for the user. Small welding transformers with a welding current of 50 to 125 A already weigh over 30 kg.
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. Aluminum, on the other hand, only has γ = 36. Aluminum therefore 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.

Welding transformer structure

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 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 input voltage is applied to the primary coil. The alternating voltage at 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.
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 mains voltages.

Use of welding transformers

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