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Electric welding. Features of specialized welding transformers. Encyclopedia of radio electronics and electrical engineering

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The main element of the AC welding source is specialized welding transformer. Let's get acquainted with the design features of these devices.

According to the shape of the core distinguish between transformers armored и pivotal types (Fig. 18.3). To reduce eddy current losses, the transformer core is made of sheet transformer steel with a thickness of 0,27-0,5 mm.

Rice. 18.3. Types of magnetic cores: a - armor; b - rod

Rod Type Transformers, compared to armored transformers, have a higher efficiency and allow higher current densities in the windings. Therefore, welding transformers are usually, with rare exceptions, of the rod type.

By the nature of the winding device, transformers with cylindrical and disk windings are distinguished (Fig. 18.4).

Rice. 18.4. Types of transformer windings: a - cylindrical; b - disk

To consider the features of a transformer of one type or another, it is convenient to use the equivalent circuit of a transformer (Fig. 18.5), where: U₁, SHE IS₂ - voltage on the primary and secondary windings of the transformer; r_1, r₂ - ohmic resistance of the primary and secondary windings of the transformer; L_1s, L_2s - leakage inductance of the primary and secondary windings of the transformer; L_μ - magnetization inductance of the transformer; G_c - resistance, characterizing the losses in the core of the transformer; n is the transformation ratio of the transformer.

In this case, all parameters of the transformer are given to its secondary winding. Therefore, in the equivalent circuit, there is no ideal transformer necessary to simulate the transformation ratio.

Rice. 18.5. Transformer equivalent circuit

Leakage inductance L_s winding is caused by the presence of its own magnetic flux Ф_snot interlocked with another winding. The farther the transformer windings are from each other, the greater the value of F_s and L_s.

In transformers with cylindrical windings one winding is wound on top of the other. Since the windings are at a minimum distance from each other, almost the entire magnetic flux of the primary winding is linked to the turns of the secondary winding. Only a very small part of the magnetic flux of the primary winding, called the leakage flux, flows in the gap between the windings and is therefore not connected to the secondary winding.

Current I₁ limited practically only by active (ohmic) resistance and g₂ windings, so the transformer has a rigid characteristic, and the short-circuit current on the secondary winding is more than 10 times the operating current of the transformer.

To obtain a steeply falling external characteristic, an AC choke is used, which was present in early welding sources as an independent structural element, which additionally increases the mass and dimensions of the welding source.

Later they began to use transformer leakage inductance. To obtain the required value of leakage inductance, the transformer windings began to be made in the form of disks (Fig. 18.4, b).

In transformers with disc windings, one winding is separated from the other. Since the windings are separated from each other, a significant part of the magnetic flux of the primary winding is not connected with the secondary winding. They also say that these transformers have developed electromagnetic scattering. Leakage inductance L_1s and L_2s have a significant value, and their reactance affects the current of the transformer to a greater extent than in the case of a transformer with cylindrical windings.

Using a transformer with disk windings, we can easily obtain the required falling external characteristic, where the operating current is ~ 80% of the short circuit current.

Welding current adjustment usually achieved by changing the distance between the windings, which are movable.

In domestic conditions, it is difficult to manufacture a transformer with movable windings. The solution to the problem in this case will be a transformer for several fixed values ​​​​of welding current. For a finer adjustment of the welding current (of course, in the direction of decrease), you can use the inductance of the welding cable, laying it in rings.

Author: Koryakin-Chernyak S.L.

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