Welding Transformer

Core functions and features

Voltage reduction: This is its most basic function. It utilizes the principle of electromagnetic induction to reduce the input AC voltage (usually 220V or 380V) to the no-load voltage required for welding (usually in the range of 50V-90V, relatively safe).

High current output: While reducing voltage, in order to provide sufficient welding heat, it will significantly increase the output current (up to tens of amperes to hundreds or even thousands of amperes). Transformers follow the principle of power conservation (input power ≈ output power), so when the voltage decreases, the current must increase.

Adjusting welding current: This is a key performance of welding transformers. By changing its internal structure or circuit parameters, the output current can be easily adjusted to meet the requirements of different workpiece thicknesses, electrode diameters, and welding processes.

Provide necessary reactance/impedance: Welding transformers are typically designed with specific leakage flux or external reactors (inductive coils). This part of the reactance limits the growth rate of short-circuit current, which helps stabilize the arc, maintain a constant welding current, and limit the damage of short-circuit surge current (during arc initiation or droplet short circuit) to the transformer.

Simple and reliable, low cost: Compared to more complex welding power sources such as inverter welding machines, traditional power frequency welding transformers have a simple structure, relatively low failure rate, and usually lower manufacturing and maintenance costs.

Output AC power: Traditional welding transformers output AC power with the same frequency as the grid (usually 50Hz or 60Hz).

Main structural components (taking the common moving iron core or moving coil type as an example)

Iron core: usually composed of stacked silicon steel sheets to form a magnetic circuit. Designed with a main magnetic circuit and movable parts (moving iron core or moving coil) to regulate leakage flux and current.

Primary winding: connected to high voltage of the power grid, with multiple turns.

Secondary winding: Output welding low voltage high current with few turns. The winding is thick and robust to withstand high currents.

Current regulation mechanism:

Dynamic iron core type: By moving a movable iron core inserted or removed from the iron core window, the size of the leakage magnetic flux is changed, thereby changing the output current (the larger the leakage magnetic flux, the greater the inductance, and the smaller the output current).

Dynamic coil type: By mechanically moving the distance between the primary or secondary windings, the degree of magnetic coupling (leakage flux) is changed, and current regulation is also achieved.

Other methods include tap type (changing the turns ratio by switching taps), but they are relatively rare now.

External reactor (sometimes required): For certain types of welding transformers, especially large welding machines or situations that require a larger current regulation range and better arc stability, an independent reactor (inductor) will be connected in series in the secondary circuit.

Application scenarios

Mainly used for AC arc welding, especially manual arc welding (SMAW or MMAW) using acidic or alkaline electrodes.

It is also used for other welding methods that require AC power, but it is not as popular as manual welding.

Due to the output being AC power, the arc during welding is not as stable as DC power, resulting in relatively larger spatter.

Advantages and limitations

Advantages:

Simple structure and mature manufacturing process.

High reliability and relatively easy maintenance.

Lower cost compared to inverter welding machines.

Not easily affected by electromagnetic interference.

limitations:

Large volume and heavy weight: The inherent characteristics of power frequency transformers result in bulky welding machines.

Relatively high energy consumption: The efficiency is usually lower than modern inverter welding machines (about 70-80%), and the no-load loss is relatively large.

Adjustment accuracy and response speed: The precision and dynamic response of current regulation are not as good as electronic controlled welding machines.

Low power factor: During operation, the power factor (cos φ) is low (0.3-0.6), which increases grid losses and usually requires a capacitor compensator.

Output AC power: It is not as good as DC welding machines in situations where welding of certain materials and high arc stability are required.

Arc noise: The noise of AC arc is usually greater than that of DC arc.

Adaptability: Not suitable for modern welding processes that require direct current or specific waveforms (such as gas shielded welding, pulse welding, etc.).

summary

Welding transformer is the core component of traditional arc welding power source, which provides basic electrical energy support for AC arc welding by reducing voltage, providing high current and necessary reactance. Although inverter welding machines with smaller size, higher efficiency, and more precise control are gradually replacing them in the modern welding field, they still have important application value in basic welding, maintenance, and situations with limited budget or low requirements for volume and weight due to their sturdy, durable, and economical characteristics.

Safety reminder: Welding transformers can generate high current and high temperature during operation. It is necessary to follow the welding safety operating procedures, wear protective equipment (face mask, gloves, protective clothing), ensure good ventilation, and pay attention to electrical safety (to prevent electric shock).