US3287625A

US3287625A - Magnetic amplifier circuits, especially for arc-welding equipments

Info

Publication number: US3287625A
Application number: US311127A
Authority: US
Inventors: Malatier Robert; Theuret Richard
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-09-24
Filing date: 1963-09-24
Publication date: 1966-11-22
Anticipated expiration: 1983-11-22

Description

Nov. 22, 1966 R. MALATIER ETAL 3,287,625

MAGNETIC AMPLIFIER CIRCUITS, ESPECIALLY FOR ARC-WELDING EQUIPMENTS Filed Sept. 24. 1963 2 Sheets-Sheet l INVENTORS ROBERT MALAT/ER RlfiHARD THEURET MAW/4 ATTORNEYS Nov. 22, 1966 R. MALATIER ETAL 3,237,625 MAGNETIC AMPLIFIER CIRCUITS, ESPECIALLY FOR ARC-WELDING EQUIPMENTS Filed Sept. 24, 1963 2 Sheets-Sheet 2 mvswroras ROBERT MAL-A TIER RICHARD THEUKET 'ATTORN EYS United States Patent 3,287,625 MAGNETIC AMPLIFIER CIRCUITS, ESPECIALLY FOR ARC-WELDING EQUIPMENTS Robert Malatier and Richard Thenret, both of 33 Place du 1er Mai, Dijon, France Filed Sept. 24, 1963, Ser. No. 311,127 Claims priority, application France, Sept. 24, 1962, 910,258; Sept. 17, 1963, 947,776 6 Claims. (Cl. 32389) The present invention relates to magnetic amplifier circuits and in particular but not exclusively to those which are employed in arc-welding equipments.

It is well known that a magnetic amplifier comprises a load winding, a control win-ding and a polarizing winding. In certain applications such as arc welding, it should be possible to vary the intensity of the output current of the magnetic amplifiers supplied from the rectified output of a transformer. This intensity can be varied by modifying the number of ampere-turns of the control winding. In the known systems, a rheostat is employed for that purpose. However, this involves a certain number of disadvantages.

It is in fact necessary to add an auxiliary rectifier which is capable of delivering a high current and which is therefore relatively costly. The regulating rheostat is of delicate mechanical design and has a fairly considerable overall size; more especially, it develops a high temperature as a result of theJoule effect in the resistance wire.

In addition, the welding current is subjected to the voltage variations of the supply network, since the voltage drop is reflected back in cascade by the presence of the magnetic amplifier.

Finally, it is desirable to provide vigorous cooling for the whole of the rectifiers and the rheostat, which involves the utilization of a relatively powerful fan.

Apart from the fairly considerable risk of breakdown, mention may also be made of the ageing of the components, and more particularly of the rheostat, large overall size together with considerable weight, and the necessity for periodical maintenance.

The present invention makes it possible especially to overcome these drawbacks.

To this end, according to the invention, the control ampere-turns of the magnetic amplifiers are varied by supplying their control windings with a rectified current of variable intensity obtained from a grid-type. rectifier controlled by a phaseshifting network.

The controlled-grid rectifier is preferably a silicon thyratron.

The phase-shift network provides a horizontal phase displacement along the time axis which enables the output current of the controlled grid rectifier to be varied from zero up to almost the maximum value.

According to a first form of embodiment, the network which effects the phase displacement comprises a winding having a central tapping in which the current is in phase with the anode current of the rectifier, this Winding forming part of a group comprising a phase-shifting capacity, a supplementary rheostat, and a transformer supplying the grid of the thyratron. The phase-shift angle is determined by a set of resistances, with which is associated a second set of resistances which shunt the rheostat and permit the range of regulation to be corrected in dependence on the selected intensity.

According to a particular feature of the invention, the transformer which serves to supply the grid of the thyratron supplies a voltage greater than the striking voltage of the thyratron, so as to take account of the voltage variations of the supply network. This too high voltage supplied by the transformer is peak-clipped by a suitable circuit, comprising a resistance and a Zener diode, so as to give a votlage with a square-top wave-form corresponding to the average voltage required for striking the thyratron. In this way, there is obtained a well-defined point of intersection, and the variation of the voltage of the supply system has no longer practically any effect on the striking angle of the thyratron.

A system of this kind has numerous advantages, especially when it is utilized in an arc-welding equipment. In fact it enables a very steady welding current to be maintained in the case of variations of voltage of the supply system, since the number of ampere-turns of the magnetic amplifier practically does not vary.

In addition, it is presented in the form of an extremely robust shielded electronic unit which does not include any component necessitating periodical maintenance and developing no appreciable heat. In consequence, it is not necessary to-provide any cooling system which represents an economy in electric power, the risks of breakdown are almost non-existent, there is no maintenance, the overall size is very small and the weight is negligible. The unit does not comprise any fan, is silent and is extremely simple and easy to handle.

According to a second form of embodiment of the invention, the phase-shift network only comprises a fixed capacity and a resistance variable bet-ween very wide limits, in the form of a rheostat mounted on the electrode holder within easy reach of the operator. This arrangement permits a continuou regulation of the phase of the voltage applied to the transformer which supplies the thyratrons of the control circuit of the self-saturating inductances, that is to say it definitely permits continuous regulation of the welding current by the operator during the actual operation of welding.

In this second form of embodiment, there is provided a fixed polarization of these inductances, and also a safety circuit having essentially the function of protecting the operator in the event of accidental contact with the two poles of the apparatus and the rectifier diodes together ample and without limitation, in its application to the construction of a direct-current genenator for electric arc welding.

FIG. 1 is a basic diagram of a first form of embodiment of the invention.

FIG. 2 is a basic diagram of a second form of embodiment of the invention.

Finally, FIGS. 3a and 311 show diagrammatically an electrode holder designed for use with this second form of embodiment.

In the diagram of FIG. 1, there is shown at T a main three-phase transformer, for example of 10 k-va., which does not have a falling characteristic. The secondary windings of this transformer supply rectifier systems constituted by the silicon rectifiers D D D to the terminals of which are connected condensers C C C serving as a protection against reverse voltage surges.

One the output of each rectifier is connected at self-saturable inductance constituted by a load winding and a control-polarization winding.

The self-satura'ble inductances have been designated by S S S the load windings by f f f and the controlpolarizati-on windings by e e e The control-polarization winding '(e e e is traversed by a half-wave rectified current, making it possible to obtain a number of polarization or control ampereturns which adjust the minimum or maximum value of the output current.

. According to the invention, the control winding (e e a is traversed by a half-wave rectified current having an intensity variable in accordance with the value of the control angle of the grid of a thyratron Thy acting as a controlled grid rectifier. There is thus obtained a variation of the number of control ampere-turns which enables the output of the rectifier unit to be varied. To this end, the control windings of the magnetic amplifiers are connected in a network supplied from the output of the thyratron Thy.

The thyratron is supplied in turn by an auxiliary transformer T having an output of two watts for example. The alternating voltage of this transformer is substantially greater than that which is necessary at the control electrode of the thyratron for the excitation of all the elements; for example, it is about six times greater than this minimum voltage. A voltage of this amplitude cannot be applied directly to the grid of the thyratron, since it exceeds the maximum value of the direct-current voltage applicable between the control electrode and the cathode, and which is for example volts.

It is quite clear that a lower alternating voltage, for example of 3 volts, which has not been peak-clipped, causes the striking of the thyratron. However, it has been found in this case that a variation of voltage of the supply system results in a variation of the striking angle as a result of variation of the point of intersection. This too high voltage is therefore peak-clipped by means of a system comprising for example a resistance R and a Zener diode Z. There is thus obtained a voltage of square-top wave-form, slightly trapezoidal, which corresponds to the average voltage required for striking the thyratron. By this means, a well-defined point of intersection is obtained and the variation of the voltage of the supply system causes practically no variation in the striking angle of the thyratron.

The output of the thyratron is controlled by a horizontal phase displacement along the time axis. This phase displacement is obtained by a phase-shift unit comprising a winding g with a central tapping i connected in the circuit of the transformer T Between the winding g and the transformer T is connected a phase-shift condenser C The winding with a central tapping in which the current is in phase with the anode current of the thyratron forms part of a group which comprises, in addition to the capacity C, and the transformer T a set of resistances and a supplementary rheostat Rh.

The phase-shift angle is determined by the position of a contact member on one of the resistances R to R or R to R and at the same time on one of the resistances R to R or R to R which shunt the rheostat Rh. These latter resistances R to R are intended to correct the range of regulation as a function of the intensity selected. As indicated above, the output of the transformer T is connected on the one hand to the cathode of the thyratron and on the other to the peak-clipping assembly constituted bythe Zener diode mounted in shunt across the terminals of the thyratron and by the resistance R The diagram is completed by a reversing switch I which enables the control winding of the inductances of the magnetic amplifiers to be reversed and the positioning of the intensity to be communicated by variation of the phaseshift angle by means of the resistances R to R the fine adjustment being obtained by the balancing resistances R to R3.

The circuit is of course completed .by the usual protection systems. Thus, there is provided a condenser C for filtering the control-polarization current, a condenser C for protecting the windings, a condenser C connected to the output terminals for raising the striking voltage, a leakage resistance R for the grid of the thyratron, and a discharge resistance R 0 for the condenser C The device according to the invention thus eliminates the control rheostat, which is a costly and fragile apparatus, necessarily amply dimensioned in order to dissipate the Joule effect produced in the resistance wire. The silicon thyratron and the phase-shift system have no mechanical parts to require any maintenance, do not give rise to any Joule heating and are absolutely invariable with time.

The utilization of a silicon thyratron for varying the control ampere-turns of the inductances enables a flexible and reliable assembly to be produced, since the thyratron has properties of strength, hermetic sealing, invariability and good performance under temperature, and its life is unlimited if the rules of use provided by the manufacturers are observed.

In the diagram of FIG. 2, the transformer T comprises a three-phase primary and :a six-phase secondary which, by means of two groups of rectifiers D to D and D' to D' Each group rectifying the same halfwave, supplies two separate channels K and K connected through shunting resistance RSH. Channel K supplies welding voltage and channel K supplies striking voltage.- The inductances S' to 8' comprise, between the main current winding Ch to Ch a control winding e to e and a fixed polarizing winding P to P which are separate and independent. The windings P to P are supplied through the resistance R by two diodes D and D mounted in push-pull and by one of the windings of a single-phase auxiliary transformer T having three secondary windings. In addition, this transformer supplies on the one hand the control circuit of the main circuit through the intermediary of the phase-shift network C-D-Rh, the transformer T .and the thyratrons Thy; and Thy on the other hand, it supplies a safety circuit which comprises an electro-rnagnetic contactor CE, a condenser C a transformer TP which supplies, through the intermediary of the diodes D and D the fixed polarization voltage, limited by the Zener diode Z and which, through the intermediary of the diode D and the resistance R supplies the grid voltage of the thyratrons Thy and Thy,

The operation of this system is as follows:

The protection of the operator is based on the fact that, by construction, the voltage at no-load on the electrode- .earth terminals T+ and T is 6 volts. For putting the generator into operation, it is necessary for the shunting resistance (R in the diagram of FIG. 2) to be less than 10 ohms. On no-load, with the contactor CE open, no welding voltage is available on the electrode. If the welder happens to touch simultaneously the twowelding terminals he only receives a current less than 0.005 ampere, which means that he is completely protected. This current will be supplied by the winding F in series with the polarization voltage transformer T1? and the capacity C the resistance of the operators body (greater than 1,000 ohms) does not permit of obtaining a secondary voltage sutficient to cause the release of the thyratrons- Thya and Thy At the moment when the operator begins to strike the are, he causes 'a dead short-circuit between the welding outputs; in consequence, the transformer TP is supplied by an alternating current since it is then in series with the condenser C and this combination is coupled in parallel to the terminals of the winding P The diodes D and D connected as push-pull rectifiers, rectify the two halfwaves of the voltage supplied by the secondary of the transformer TP; there will therefore appear a direct-current voltage limited to the peak value of the Zener diode Z this voltage is applied to the respective grids of the thyratrons Thy and Thy through the resistances R R and R and causes the release of the thyratrons Thy and Thy The rectified direct current passes through the excitation coil of the electromagnetic contactor CE and causes the closure of the welding circuit. The are is established and its very low resistance does not permit the de-excitation of the thyratrons Thy and Thy This will take place when the arc is broken. At that moment, the transformer TP is no longer traversed by an alternating current but only by the peak ripples of the rectified current which is definitely insufficient to overcome the effect of the polarization applied to the grids of Thy and Thy This polarization is obtained by a potential divider R -R connected to the terminals of the polarization current rectifiers, the polarization voltage being stabilized by the Zener diode Z and the resistance R which prevents any accident to the thyratrons as a result of an accidental shortcircuit or of a break in the resistance R This polarization is continuously applied to the grids of the thyratrons through the resistances R R and R A time constant obtained by means of one of the condenscrs C to C and its resistances R to R enables the generator to continue to maintain its voltage for one, two or three seconds after the welder has broken the arc, this having the purpose of preventing the operation of the contactor CE at each interruption of the arc. The diode D permits the condensers C to C to be rapidly charged in the case where the arc is broken close to the beginning of the striking.

It is essential to observe that since the arc is always interrupted as a result of the electrode being moved away, the contactor CE always breaks the circuit while the latter is open, which prevents any deterioration of its contacts.

FIG. 3a completes the diagram of FIG. 2 in the sense that it represents diagrammatically the rheostat Rh and the line Q which connects it to the points X and Y of the control circuit comprising the phase-shift condenser CD, while FIG. 3b represents the practical circuit of this rheostat. The rheostat is mounted in a protection casing and is fixed on the insulating sleeve Q of the cable V which leads the welding current to the moving electrode EL, by means of a clamping collar M. It comprises a knurled knob N, the rotation of which enables the resistance to be varied from 0.1 to SOKQ for example, starting from a reference point P corresponding to a well-defined and known value.

What we claim is:

1. In an arc welding system supplying a direct current output through load terminals to form a welding arc; an alternative current source; a first transformer having a three-phase primary, secondary windings and rectifying device thereon to supply a rectified output; a magnetic amplifier supplying said direct current welding output from said rectified output, said magnetic amplifier having load windings, control windings and polarization windings; the improvement comprising a circuit, comprising, in combination, at least one grid-controlled solid state thyratron with an anode therein supplying said control windings of said magnetic amplifier, and a phase shifting network having a winding with a central tapping in which the current is in phase with said anode of said solid state thyratron, said winding of said phase shifting network forming part of a group comprising an auxiliary transformer and at least one variable resistor for varying the phase angle of the current supplying said grid of said solid state thyratron through said auxiliary transformer to provide a rectified control current to said control windings of said magnetic amplifier, means for electrically connecting said winding and central tapping with said auxiliary transformer and means for electrically connecting the other end of said winding through said at least one variable resistor to said auxiliary transformer whereby the number of ampere-turns of said control windings may be modified to vary the intensity of said direct current welding output.

2. In an arc welding system supplying a direct current output through load terminals to form a welding arc; and alternate current source; a first transformer having a three-phase primary, secondary windings and rectifying device thereon to supply a rectified output; a magnetic amplifier supplying said direct current welding output from said rectified output, said magnetic amplifier having load windings, control windings and polarization windings; the improvement comprising a circuit, comprising, in combination, at least one grid-controlled solid state thyratron with an anode therein supplying said control windings of said magnetic amplifier, and a phaseshifting network having a winding with a central tapping in which the current is in phase with said anode of said solid state thyratron, said winding of said phase-shifting network forming part of a group comprising an auxiliary transformer, a supplementary rheostat, a first set of resistors and a second set of resistors for varying the phase angle of the current supplied by said phase-shifting network, by adjusting said first set of resistors, said second set of resistors shunting said supplementary rheostat for correcting the range of adjustment, said current supplying said grid of said solid state thyratron through said auxiliary transformer to provide a rectified control current to said control windings of said magnetic amplifier, means for electrically connecting said winding and central tapping with said auxiliary transformer and means for electrically connecting the other end of said winding through said supplementary rheostat and said first and second resistors to said auxiliary transformer, whereby the number of ampere-turns of said control windings may be modified to vary the intensity of said direct current Welding output.

3. A circuit as claimed in claim 2 including a peakclipping device comprising a resistance and a Zener diode electrically connected from said auxiliary transformer to the terminals of said solid state thyratron whereby any excess voltage, provided by said auxiliary transformer, greater than the striking voltage of said solid-state thyratron is limited.

4. A circuit as claimed in claim 1 further comprising a second group of rectifying devices connected in pushpull and means for electrically connecting said rectifying devices to one of said secondary windings of said first transformer and to said polarization windings of said magnetic amplifier whereby said rectifying devices supply said polarization windings With .a fixed polarization.

5. A circuit as claimed in claim 1 in which a striking voltage is superimposed on the welding voltage.

6. A circuit as claimed in claim 1 further including a safety network comprising an electromagnetic contactor in series with said load windings of said magnetic amplifier, a safety transformer having primary and secondary windings, a first circuit connected to the load terminals comprising, in series, said secondary winding of said first transformer supplying said magnetic amplifier said primary windings of said safety transformer and a capacitor; a second circuit comprising said secondary windings of said safety transformer, a rectifier, at least one storage capacitor, at least one solid-state thyratron, a fixed polarization circuit for said thyratron and a control winding for controlling said contactor, whereby said secondary winding of said safety transformer supplies said rectifier to provide said thyratron through said storage capacitor with a polarization voltage opposed to said fixed polarization voltage; and whereby said thyratron supplies said control winding of said contactor only for small load impedance, said storage capacitor keeping said thyraof said welding arc.

8 Lobosco et a1. 219-131 Miller 323-89 Greene 321-25 Brown 321-25 X Davis 323-60 JOHN F. COUCH, Primary Examiner. RICHARD M. WOOD, LLOYD MCCOLLUM,

7 tron in conductive state for a short time after extinction 3,041,445 3,092,769 3,123,761 References Cited by the Examiner 3,128,422 UNITED STATES PATENTS 5 3,128,440

3/1928 Churchward 219-135 8/1947 Hall 219-132 X 11/1953 Welch 219-132 10/1957 Huge 321-25 X 1/1962 Rebuffoni 219 131 10 W 3/1962 Bergmann 219-131 Examiners.

. E. RAY, Assistant Examiner.

Claims

1. IN AN ARC WELDING SYSTEM SUPPLYING A DIRECT CURRENT OUTPUT THROUGH LOAD TERMINALS TO FORM A WELDING ARC; AN ALTERNATIVE CURRENT SOURCE; A FIRST TRANSFORMER HAVING A THREE-PHASE PRIMARY, SECONDARY WINDINGS AND RECTIFYING DEVICE THEREON TO SUPPLY A RECTIFIED OUTPUT; A MAGNETIC AMPLIFIER SUPPLYING SAID DIRECT CURRENT WELDING OUTPUT FROM SAID RECTIFIED OUTPUT, SAID MAGNETIC AMPLIFIER HAVING LOAD WINDINGS, CONTROL WINDINGS AND POLARIZATION WINDINGS; THE IMPROVEMENT COMPRISING A CIRCUIT, COMPRISING, IN COMBINATION, AT LEAST ONE GRID-CONTROLLED SOLID STATE THYRATRON WITH AN ANODE THEREIN SUPPLYING SAID CONTROL WINDINGS OF SAID MAGNETIC AMPLIFIER, AND A PHASE SHIFTING NETWORK HAVING A WINDING WITH A CENTRAL TAPING IN WHICH THE CURRENT IS IN PHASE WITH SAID ANODE OF SAID SOLID STATE THYRATRON, SAID WINDING OF SAID PHASE SHIFTING NETWORK FORMING PART OF A GROUP COMPRISING AN AUXILIARY TRANSFORMER AND AT LEAST ONE VARIABLE RESISTOR FOR VARYING THE PHASE ANGLE OF THE CURRENT SUPPLYING SAID GRID OF SAID SOLID STATE THYRATRON THROUGH AUXILIARY TRANSFORMER TO PROVIDE A RECTIFIED CONTROL CURRENT TO SAID CONTROL WINDINGS OF SAID MAG-