The power supply classification features. The potential distribution in the arc. The welding arc properties (Part 1).

The arc power supply is classified according to the following characteristics:

1. by the current type: a) alternate current: transformers, elevated-frequencies generators; b) direct current: generators, rectifiers.
2. by the design features:

The transformers are divided into 3 groups:

• With the normal magnetic scattering:

1. a) with the separate throttle;
2. b) with the combined throttle.

• With the increased magnetic scattering:

а) with the moving coils;

1. b) with the moving magnetic shunt;
2. c) with the magnetizing magnetic shunt.

3) The special welding transformers:

а) for the electroslag welding;  б) three-phase.

3. The welding generator can be:

а) with the independent magnetizing and sequential demagnetizing windings;

1. b) with the parallel magnetizing and sequential demagnetizing windings;
2. c) universal and others.
3. The welding rectifiers can be:

а) by the nature of the material used in the valves: selenium, silicon;

1. b) by the number of external characteristics: universal (2 characteristics).
2. By the number of simultaneous connected operators: single-operator, multi-operator.
3. By the form of the external characteristic: with the hard (gently dripping), with the falling external characteristic.
4. By installation method: mobile and stationary.

The welding arc is a powerful electric discharge in the ionized mixture of gases, electrode vapors and substances that protect the welding arc.

The arc gap has 3 areas: anodic, cathodic and arc column. The potential distribution (Fig. 1) in the arc is abrupt (Fig. 2).

The fact that the arc consists of the three regions (sections), the data were obtained after the experiment (test), the scheme of which is shown in Fig. Between the electrode (tungsten, item 1 in Fig. 1, so that the arc gap does not disturb the electrode drops, if the electrode were to be melted) and the product (2) the arc was ignited, the length of which did not change during the experiment (l_д = const). The short-term probe (5) was inserted into the arc column (3), and the voltage drop between electrode 1 and probe 5 was measured with the voltmeter 4. The probe 5 is made of thin tungsten (refractory) wire (0.1 … 0.2 mm in diameter).

In the experiment, the distance between the end of the electrode (1) and the probe (5), the distance Z, was changed. Then, according to the experimental data, the voltage drop between the electrode (1) and the probe (5) was plotted. The typical graph obtained in the experiments is shown in Fig. 2. It was typical that at the minimum distance Z from the end of the electrode (1), the probe (5) recorded the voltage «jump» (Uк). The region of this voltage jump was of the length l_к – the cathode region. The similar voltage «jump» was observed when the probe (5) touched the product (2). This voltage jump is U_a on the length l_a (Fig. 2). This is the anode region of the arc. Between these regions is the  arc column (l_с,U_c), in which the voltage along the axis OZ has changed practically linearly.

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