A welding transformer is a two-winding transformer. To adjust the arc ignition voltage, the primary winding is equipped with taps and a tap switch is used to regulate the secondary side's no-load voltage. The primary and secondary windings are mounted on two core columns, which give the transformer a significant leakage reactance, causing the secondary terminal voltage to drop sharply as the current increases. An iron-core reactor is串联 in the secondary winding circuit for adjusting the welding current. As the air gap of the reactor is lengthened, the current increases accordingly.
Welding transformers primarily come in three forms: iron-core, coil-type, and tap-type. The basic principle of welding transformers has remained largely unchanged for decades. Both domestically and internationally produced and used welding transformers are a special type of step-down transformer with a steep external characteristic. Although they can be categorized into several types based on the method of achieving the steep external characteristic, the transformer's combination with reactors, and the method of adjusting current, the fundamental principle is still that of a general transformer.
W1 is the primary winding, and W2 is the secondary winding. Both W1 and W2 are wound on the same core. The primary winding transmits electrical energy to the core, creating an alternating magnetic field within it. The core then transfers magnetic energy to the secondary winding, which induces an electromotive force. This is the basic working principle of a transformer. The ratio k, which is the ratio of the induced electromotive forces between the primary and secondary windings, is equal to the ratio of their turns.
Welding transformers are widely used in production, essentially being a special type of step-down transformer. Their operating principle is the same as that of a standard transformer, but their performance differs significantly. The characteristics of welding transformers include: before welding, the secondary winding must have sufficient arc voltage (60-75V), and during welding, as the welding current increases, the secondary voltage can quickly drop. Even if there is a short circuit on the secondary side (such as when the welding rod touches the workpiece, the secondary voltage is zero), the secondary current will not be excessively high. In other words, the relationship between the output voltage u2 and output current i2 of the welding transformer is as shown in Figure 1(b).
The welding transformer possesses the aforementioned characteristics due to its distinct structure from that of a standard transformer. The principle of the welding transformer is illustrated in Figure 1(a). Its primary and secondary windings are mounted on two separate cores, with the secondary winding connected in series with a reactor. The reactor's core has not only a certain air gap but also a rotating screw that can adjust the length of the air gap to achieve different sizes of welding current. As the air gap increases, the current increases, shifting the external characteristic curve to the right. Conversely, when the air gap decreases, the current also decreases, shifting the external characteristic curve to the left.
