DE1094895B - Welding rectifier with chokes pre-magnetized by direct current - Google Patents

Description

Welding rectifier with chokes pre-magnetized by direct current The invention relates to a welding rectifier with pre-magnetized by direct current Chokes such as those used to regulate the welding current.

It is known to have such a welding rectifier via a transformer (Transformer) to be fed from a three-phase network. The transformer is on the secondary side a three-phase choke in a bridge circuit with a downstream rectifier connected.

To pre-magnetize the chokes, the chokes have direct current windings equipped, which is from an auxiliary winding of the transformer via a rectifier be fed.

A controller is used to set the premagnetization of the chokes, which is firmly dependent on the required welding current.

The direct current received at the output terminals of the welding rectifier and the associated DC voltage are good for welding purposes according to their characteristics suitable. In particular, the steady-state short-circuit current is due to the characteristic curve practically equal to the working current and approximately proportional to that of the premagnetization the direct current used for the chokes.

In many cases, however, it is disadvantageous when the welding electrode is ignited Occurring surge short-circuit current noticeable, which is far greater than the stationary one Short circuit current.

This is the result of the fact that the throttles essentially one through represent the pre-magnetization adjustable inductive resistance. That is, that Ignition puts the sudden switching on of an alternating current on an inductance represents, which is known to result in a surge short-circuit current which is of its maximum value on the steady working current given by the premagnetization of the chokes falls off.

In order to reduce this surge short-circuit current, it is known to use the pre-magnetization to control the chokes automatically by the welding current in such a way that the chokes have the highest resistance value during ignition and thus the short-circuit current limit.

The invention is concerned with an arrangement for influencing the Surge short-circuit current in welding rectifiers that are pre-magnetized with direct current Control throttle for setting the welding current as a function of the welding current be operated that in idle a lower bias than in operation is achieved. It is characterized in that to adapt to different Operating conditions of the ignition current surge by influencing the premagnetization optionally presettable from its complete suppression to its full utilization is. An advantageous embodiment of the invention is characterized in that for the optional pre-setting of the bias current in a special one A changeover switch is provided for switching to a constant rectifier circuit Voltage source or a combined voltage source, consisting of at least two voltage sources connected in series and delivering alternating voltages of different magnitudes, one of which is a constant voltage and the other is a voltage drop supplies voltage proportional to the operating current.

The regulation of the ignition current impulse down to the complete elimination and the option of using the full ignition current surge has the advantage of to be able to adapt the ignition conditions to all operating conditions. So it is from Advantage of working with thin sheets with thin electrodes without the ignition current surge, otherwise there is a risk of undesirable burns. With thicker material the ignition current surge in an adapted strength can be advantageous, since it produces a rapid Warming up of the still cold material and thus an immediate deep penetration of the Moment of ignition.

In a further embodiment of the invention, this is the bias current generating combined voltage through an additional winding on the input transformer into a constant and through additional windings on the chokes into one to the voltage drop of the working current at the chokes is divided into proportional voltage, both of which serve to feed the auxiliary rectifier. the direct current for the premagnetization generated. Because the voltage generating the bias current is derived from composed of two partial voltages, of which one partial voltage (from the transformer) is constant and the second partial voltage (across the reactors) is proportional addicted from the voltage drop of the working current at the chokes, the premagnetization higher during welding than when idling, so that when correctly selected Ratio of the two partial voltages of the ignition current surge can be completely avoided can. With an intermediate rectifier for the magnetizing current upstream of the auxiliary rectifier Changeover switch can optionally combine the voltage with the variable partial voltage switched off and on the known circuit described at the beginning with constant Voltage can be switched.

In a special embodiment of the invention, instead of the additional windings on the chokes a relay can be provided, which after insertion of the welding current, the voltage effective in the premagnetization circuit by switching on elevated.

In the drawing, as Fig. 1, is the circuit diagram of a welding rectifier shown as an exemplary embodiment.

Fig. 2 shows a vector diagram.

Fig.3 shows another circuit diagram as an exemplary embodiment.

In this diagram, PT is the primary side of the transformer with the phase supply lines R, S and T. ST is the secondary side of the transformer with the connected reactors D. H is the usual auxiliary winding for supplying the auxiliary rectifier G2 for generating the direct current for the premagnetisation the throttles D is used. This direct current flows through the direct current windings G of the chokes D. The regulator RE or the remote regulator FR is used to regulate the premagnetization. The working current is drawn as direct current from the outer terminals KI of the rectifier G1, which is connected to the chokes D. In this respect, the circuit diagram corresponds to the known circuit diagrams.

In the arrangement according to the invention is now on the input transformer an additional winding Z1, a second additional winding Z2 is on 'the chokes D.

A changeover switch Sch can be used optionally to preset the bias current with this new or the known type of circuit.

With the new switching method, the premagnetization is obtained a constant partial voltage at Z1, which is responsible for the low initial value of the premagnetization is decisive. At Z2 one receives the inductive voltage drop of the working current Variable voltage proportional to the chokes, with the help of which the premagnetization can increase to the value corresponding to the required working current.

Due to the type of circuit specified, a phase shift can occur reached between the two partial voltages UT at the transformer and UD at the choke as shown on the vector diagram (Fig.2), with both voltages in the event of a short circuit, enclose an angle of 90 °. The pointer for UD moves to different load on a circle, with decreasing load shows that the sum voltage UT -I- UD initially changes little vectorially, which is desirable in the interest of favorable operating conditions.

According to the circuit diagram Fig. 3, instead of an additional winding Z1 z. B. two additional windings Z1 and Z11 arranged, there can also be arranged more which generate a constant voltage that differs from one another. they lay in series with different winding parts of the additional windings Z., on the chokes D and are so coordinated with the variable voltages generated by them that at Welding the total voltage is roughly the same in each case while idling the voltage for generating the premagnetization is adjustable depending on the choice.

A multi-stage switch is used to set the premagnetization Ski.

It is irrelevant for the subject matter of the invention whether the production the auxiliary voltages for the premagnetization takes place in one or more phases.

Claims (6)

PATENT CLAIMS: 1. Arrangement for influencing the surge short-circuit current in the case of welding rectifiers that are equipped with a DC-biased control choke Welding current setting can be operated depending on the welding current, that a lower pre-magnetization is achieved in idle than in operation, thereby characterized in that the ignition current surge to adapt to different operating conditions by influencing the premagnetization ", sometimes from its complete suppression can be preset until it is fully utilized. 2. Arrangement according to claim 1, characterized in that for the optional presetting of the bias current A changeover switch (.Sch) is provided in a special rectifier circuit for Switching to a constant voltage source (H) or to a combined voltage source, consisting of at least two series-connected, differently sized alternating voltages supplying voltage sources (Z1, Z11, Z2), one of which (Z1 or Z1, Z ") one constant voltage and the other (windings Z2) one the voltage drop of the working current supplies proportional voltage. 3. Arrangement according to claims 1 and 2, characterized characterized in that the combined voltage producing the bias current through an additional winding (Z1) on the input transformer into a constant and through Additional windings (Z2) on the chokes (D) in one for the voltage drop of the working current at the chokes (D) proportional voltage is divided. 4. Arrangement according to the Claims 1 to 3, characterized in that the input transformer (PT) is second or has further additional windings (Z "). 5. Arrangement according to claims 1 to 4, characterized characterized in that the additional windings (Z1, Z ") of the input transformer (PT) with the Additional windings (Z2) of the choke (D) are connected in series. 6. Arrangement according to claim 1, characterized in that instead of the additional windings (Z2) on the chokes, a relay is provided which increases the voltage effective in the bias circuit by switching on after the welding current has started. Documents considered: German Patent No. 718032.