DE2600329A1 - DEVICE FOR GENERATING AND REGULATING CURRENTS OF HIGH CURRENT STRENGTH, IN PARTICULAR WELDING TROEMS - Google Patents

Description

PATENT LAWYER IN · « _Q

STUTTGART'70

ON THE HA1G3T 29

TELEPHONE 6003 06

WKS - welding technology
^! 4'illy Kalnbach
Röntgenstrasse 16

D-7O8O Basking

Device for the spontaneous generation and regulation of currents high amperage, especially welding currents.

The invention relates to a device for generating and regulating of currents of high amperage, especially welding currents, through phase control with the primary circuit and secondary circuit connected via a transformer. · *

609829/0267

In a conventional welding device, the strength of the welding current is determined by means of taps on the primary or choke coil changed by means of a step switch. The regulation of the welding currents by means of a handwheel or crank is also known are usually cumbersome to use. It is also known to regulate welding currents using transducers (DT AS 1 116 331) Such devices have the disadvantage of large components and a high expenditure of energy. They also require high inrush currents. Due to the large size of the parts, it is difficult to transport the device. The previously known measures for Regulation of welding currents also have the disadvantage that the operation is cumbersome and a remote control with mechanical Regulation is not possible.

Depending on the phase position and premagnetization of the transformer sheet When switching on the welding currents, very high magnetizing currents, the transformer, mains and fuses of the device suddenly overload.

At the beginning of the welding process, the electrodes touch the weld metal. This causes high short-circuit currents, which are the maximum rated current often exceed by 50 I. The connected load of the welding device, the nominal value of the fuses and the conductor cross-section must be designed accordingly, possibly overdimensioned in order to exclude the risk of overheating.

The invention is based on the object of a handy device to regulate currents of high amperage, which under different operating conditions (switch-on, welding and short-circuit operation) works reliably and safely and is considerably more cost-effective both in production and in operation than conventional devices. This object is achieved according to the invention in that an anti-parallel connection is made in the primary circuit of two thyristors is that a choke is parallel to this anti-parallel connection and that means are provided

'609829/0287

which shifts the phase of the ignition pulses in the event of a secondary short circuit and when switched on. The invention avoids the disadvantages of conventional devices and achieves the following advantages: faster and simpler current regulation, which can also be designed to be remotely controllable. Furthermore, only minimal inrush currents occur and no excessive short-circuit currents. The connected load of this device can be kept down. The power consumption is reduced due to lower reactive currents and no-load currents. The no-load losses and thus the heating are lower than with conventional devices. The open circuit voltage can be kept constant over the entire control range. The device according to the invention also enables easier handling by remote control, as a result of which the welder can conveniently vary the welding current in the event of changes in the weld metal, such as warping. Since the amperage can be kept down during the welding process, the risk of overheating and fire is avoided. Safe operation is possible even during long defrosting work. The device according to the invention has a particularly favorable effect that the current regulation can be carried out continuously. \

According to an advantageous embodiment of the invention, it is provided that the means for regulating the short-circuit and switching currents a semiconductor with an RC element and limiter diodes as well as a resistor in the RC circuit of the phase control part included, the semiconductor short-circuiting the resistor when the secondary voltage falls below a limit value. Included A unijunction transistor that can be programmed via a voltage divider can be provided for generating ignition pulses.

Further advantages and features of the invention are as follows Description in connection with the drawing and the subclaims.

Show it: , ·

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1 shows a schematic representation of the device according to the invention, e.g. of a welding machine, as a block diagram,

FIG. 2 is a circuit diagram of the control part of the device according to FIG. 1.

As can be seen from FIG. 1, the primary circuit consists of the mains connection terminals AS and SB, an anti-parallel connection of two thyristors T1 and T2, to which a choke Dr is parallel, and the primary winding of the S-TO welding transformer.

The secondary circuit consists of the secondary winding of the welding transformer S-TO with connections X and Y for the welding electrodes. For the continuous regulation of the welding current, the invention allows the control circuit of the thyristors T1 and T2 with connections 1,2, 3, 4 of a control part SG connected. The control part SG receives the secondary voltage at connections E, F. Above Mains connection terminals A and B are fed to the control unit SG. A potentiometer POT is arranged outside the control unit SG. A thermal switch Th closes the supply current of the control unit SG briefly in the event of excess temperature.

The thyristors T1 and T2 work according to the known type of phase control. They »act like diodes in the forward direction as soon as a current pulse ignites them. Every half cycle of the alternating current a thyristor is assigned. Depending on the time of the ignition pulse in the course of a half-wave, the thyristor is switched on for the rest of the phase conductive. Since a thyristor blocks again after every change in the direction of current, it must be re-ignited when positive voltage is applied the anode lies. The effective current values of the thyristors add up to the base current of the choke Dr. So are the curves of the phase gates rounded, the harmonics are greatly reduced and HF interference is eliminated. Steep increases in electricity with their negative effects omitted. The current strength is set via the potentiometer POT

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-S-

regulated by changing the phase of the ignition pulse. The potentiometer is advantageously built into the electrode holder, so that it can be operated by the welder during the welding process to change the strength of the welding current.

Furthermore, a thermal switch Th is provided, which the supply current of the control unit SG short-circuits in the event of excess temperature, which means that the thyristors at connections 1 to 4 do not have any control pulses get more.

The choke DR is made with regard to the number of turns, air gap and iron core dimensioned so that it is optimally adapted to the S-TO welding transformer. During the switch-on process, the inventive Choke Dr that only low magnetizing currents due to the ohmic resistance of the thin-wire choke winding and can arise as a result of the reactance of the choke. In no-load operation, the throttle Dr reduces the no-load current of the Transformer to about a third of the nominal value. The choke must have the smallest possible inductive resistance in order to achieve a to ensure that the open circuit voltage is as constant as possible. The energy consumption for the magnetization of the iron core is reduced and the heating during idling is lower. During the welding process, the Dimensioning of the throttle Dr decisive for the minimum welding current, if the thyristors are not yet effective. As a result of their versatile functions under the operating conditions mentioned above Together with the thyristors, the choke forms an essential part Part of the device according to the invention.

Fig. 2 shows an embodiment of the control part SG, with which the solutions described above (phase control method, Short circuit monitoring, temperature monitoring). The potentiometer POT is included. But it can be Increasing the ease of use can be arranged separately from the control part SG, as indicated in FIG. 1 and is preferred. For phase angle control, the control pulses are supplied with an RC element and a, preferably programmable, unijunctions

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transistor PUT generated. From the connections A and B comes the Current from the network via resistors RI and R2 to a rectifier G1 in Graetz circuit. A Zener diode Z1 stabilizes the voltage to a desired value, for example to approx. 22 V, in order to ensure an ignition voltage sufficient for the device. The level of the charging voltage across the capacitor C1 is determined by a voltage divider R3, R4. The level of the charging voltage at the capacitor C1, in which the unijunction transistor PUT switches through, is determined by the voltage divider R3, R4. If current flows from the positive pole through the potentiometer POT, through a resistor R8 and a trimming resistor R7, C1 is charged. If the specified charging voltage is reached, so the unijunction transistor PUT switches through suddenly and the capacitor C1 discharges via the primary coil of an ignition transformer Z-TO .. The ignition pulses control the thyristors T1 and T2 via resistors R5, R6. The timing of the start of the ignition is determined by the potentiometer POT is set. As a result, the effective welding current also changes. The trim resistor R7 is used to Factory adjustment of the value formed by the resistors R7, R8, and the potentiometer POT as well as the capacitor C1 RC element and is set once according to the requirements of the user.

If the welding voltage falls below one due to the Zener diodes Z2 and Z3 defined limit value, a transformer T02 is fed. The current is rectified in a Graetz rectifier G2 and fed to an RC element R1O / C2. When the device is switched on the transistor T therefore remains in the blocking phase for a short time; the resistor R8 is fully effective and provides the gate pulses back in time. The high inrush currents can practically not pass the thyristors. The high inrush current flows through it consequently the throttle Dr and is limited by this. The resistor R8 also remains fully functional if as a result of a Short circuit in the welding electrodes, e.g. by touching the electrodes * with the weld metal, the secondary voltage falls below the limit value sinks. In this case the resistor R8 determines the level

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the maximum short-circuit current by timing the ignition pulses' resets.

In contrast, when idling or welding, the base of transistor T receives current through resistor R9; the resistor R8 is bridged and remains ineffective. The potentiometer POT is only decisive for the welding current control.

The following is used to clarify the short-circuit current limitation Table showing the characteristic values of a welding device according to the invention with a limitation of the secondary Short-circuit current of 100 A and a welding machine of conventional design with mechanical control without such limitation, assuming a control range of 30 to 250 A with a mains voltage of 380 V (all data in A)

Welding current Mains power
at the
welding primary short circuit
• current
convent Jerf.gem. 12th
21 , 7
xi sec short circuit
current
convent.; req. according to 38
100 30th
100 8.5
21.5 12.7
28.8 '21 Λ 38
122 100 · 150 27.2. 36.3 21 Λ 177 100 250 34.8 48.1 286

The underlined values show the superiority of those according to the invention Contraption.

In the foregoing, a welding device was described as an embodiment of the device according to the invention. But it is straightforward possible to use the invention profitably with all its advantages wherever under different operating conditions high currents are to be regulated. Use as an example in electric motors, e.g. fan motors, or in rectifier stations such as devices for stepless regulation for rectification and called AC drives. It is irrelevant whether it is a single or multi-phase system.

. 609829/0267

Claims (8)

Claims f 1.! Device for generating and regulating currents of high amperage, in particular welding currents, by phase control with a primary circuit and a secondary circuit connected via a transformer, characterized, that in the primary circuit there is an anti-parallel connection of two thyristors (T1, T2), that of this anti-parallel connection a throttle (Dr) lies in parallel and that means are provided, which at a secondary side Short circuit and shift the phase of the ignition pulses when switching on. 2. Device according to claim 1, characterized in that the means for shifting the phase of the ignition pulses a semiconductor (T) with RC element (R1O, C2) and limiter diodes (Z2, Z3) and a resistor (R8) contained in the RC circuit of the phase control part, where the semiconductor (T) has the resistor (R8) short-circuits when the secondary voltage reaches a limit falls below. 3. Device according to claim 1, characterized in that that for the spontaneous generation of the ignition pulses a Voltage divider programmable unijunction transi- disturbance (PUT) is provided. 4. Apparatus according to claim 1, characterized in that a thermal switch (Th) is inadmissible in places Heat generation is provided. 609829/0267 5. The device according to claim 4, characterized in that the thermal switch (Th) is installed on the transformer, preferably on its windings. 6. The device according to claim I _1, characterized in that a potentiometer (POT) is provided for phase control, which is on the electrode holder is appropriate. 7. The device according to claim 1, characterized by its use with electric motors. 8. The device according to claim 1, characterized by its use with rectifier systems. 609829/0267