DE1300614B - Short-circuit current limitation for a welding rectifier - Google Patents

Description

The invention relates to a short-circuit current limiter for welding rectifiers, which are fed from a single-phase alternating current network for gas-shielded arc welding with consumable electrode, especially for short arc technology.

When gas-shielded arc welding with a consumable electrode (MIG- and C02 welding) are now predominantly power sources with almost horizontal load characteristics applied in the field of welding values. These power sources are known to have the advantage of a good self-regulating effect when disturbance variables affect the wire feed act. Due to the self-regulating effect, changes in length are made in the arc section largely balanced. Furthermore, the material transfer takes place specifically for CO # inert gas welding or for welding with mixed gases in the area of wire thicknesses <1.2 mm in diameter and currents <200Ä - with short-circuit formation. If the power source is not correctly dimensioned, this results in high short-circuit current peaks, which lead to increased splatter formation.

A number of measures and facilities are therefore known which serve to limit the surge short-circuit current. In these institutions, the Short-circuit current z. B. limited by a greater slope of the characteristic curve. With this Measure, however, the self-regulating effect already described is worsened. the The inclination of the characteristic curve should therefore be <4 V / 100 A, so that there is sufficient short-circuit current limitation not possible.

It is also known to switch on inductances in the welding walls, which limit the current peaks, with the rate of current rise as well is decreased. These inductances can be used in a known manner as simple air chokes, Iron chokes or as direct current pre-magnetized chokes with constant or adjustable inductance.

There are current limiting circuits using DC bias Chokes in connection with semiconductor components (transistors, Zener diodes) are known. All known additional devices relate primarily to welding rectifiers with three-phase rectification and low output voltage ripple.

The influence of the ripple of the output voltage on the inner and outer seam shape in CO, welding is known, but a limitation of the waviness has not yet taken place. ; It has now been found in studies on the influence of the waviness on the welds, that even then still good results can be achieved if there is a match between the number of maxima of the ripple the output voltage and the number of short circuits in the arc section.

Accordingly, the invention is based on the object of limiting the short-circuit current for welding rectifiers fed from a single-phase alternating current network for gas-shielded arc welding to create with a melting electrode, especially for short arc technology, which at the same time the influence of the ripple of the welding current and the rate of current rise considered.

According to the invention, the object is achieved by the combination of the following features solved: A transformer designed as a two-leg type carries on both legs evenly divided primary and secondary windings, with the primary windings connected in series and connected to a single-phase alternating current network.

The secondary windings, which are also divided, are connected to a center tap connected to one weld joint, while the other weld joint of the is tapped via rectifier coil ends connected in parallel. In the welding circle there is also an adjustable throttle, preferably with a closed one Iron circle without air gap.

The short-circuit current limitation results from the special arrangement the transformer windings in connection with the rectifier arrangement required for this in mid-point connection and the inductance (choke) that is also arranged in the welding circuit.

With such a rectifier arrangement, each valve is only alternately charged during a half-wave. Accordingly, only each one becomes Secondary winding of the transformer located on one leg alternately claimed. However, since there is a series connection, the primary current flows through both partial windings. If short circuits occur in the arc section, the secondary current increases suddenly in the partial winding, and a higher primary current inevitably flows. the Current peaks are dampened by the second primary winding that is connected in series or limited.

If the time constant of the welding circuit is correctly adjusted to the Welding parameters will be a correspondence between the maxima of the output voltage and the number of short circuits per unit of time. When voting the The time constant of the welding circuit must besides influencing the short-circuit current the ripple and the rate of current rise are also taken into account at the same time will. For a welding rectifier with a single-phase AC connection for MIG or CO., welding it is necessary, absolutely the entire structure the rectifier circuit with regard to the short-circuit current limitation and the To interpret coordination of the short-circuit frequency in relation to the ripple.

The advantages of the short-circuit current limitation according to the invention are in that only through the combination of a known two-leg transformer in the described winding circuit with a likewise known rectifier arrangement in mid-point circuit and a well-known choke, in particular with one closed iron circle without air gap, the correct coordination of the time constant is achieved. In addition, the short circuit limitation according to the invention makes it possible to with only two rectifier units (silicon diodes) compared to four with a single-phase bridge circuit get along.

The invention is to be described in more detail below using an exemplary embodiment explained. In the drawings, F i g. 1 the circuit diagram of the short-circuit current limitation, F i g. 2 the arrangement of the windings on a two-limb transformer of Short-circuit current limitation.

The short-circuit current limitation for a welding rectifier fed from a single-phase AC circuit is achieved by combining a known two-leg transformer 1 with primary windings 2, 3 and secondary windings 4, 5 evenly divided on both legs and a rectifier arrangement 7, 8 in a mid-point connection with one in the Welding circuit switched choke 10 reached. Here, the primary windings 2, 3 of the transformer 1 are connected in series to a single-phase alternating current network 6 and the series-connected secondary windings 4, 5 are connected to the rectifier arrangement 7, 8 in a mid-point connection. A coil connection 9 serves as a center tap. The throttle 10 located in the welding circuit preferably has a closed iron circuit without an air gap.

Claims (1)

Claim: short-circuit current limitation for welding rectifiers, which are fed from a single-phase alternating current network for gas-shielded arc welding marked with a melting electrode, especially for short-arc technology by combining the following known features: a) the transformer (1) carries evenly divided primary windings (2, 3) and on both legs Secondary windings (4, 5); b) the primary windings are connected in series, same the secondary windings, but with a center tap as the one welding connection and with external taps connected in parallel via rectifiers as the other welding connection and with an adjustable throttle in one of the welding connections.