US2197254A

US2197254A - Arc welding system

Info

Publication number: US2197254A
Application number: US275140A
Authority: US
Inventors: Thomas M Hunter
Original assignee: AMERICAN TRANSFORMER Co
Current assignee: AMERICAN TRANSFORMER Co
Priority date: 1939-05-23
Filing date: 1939-05-23
Publication date: 1940-04-16
Anticipated expiration: 1957-04-16

Description

' 16, 1940. T. M. HUNTER ARC WELDING SYSTEW Filed May 23, 1939 N E] a I v INVENTOR mama .9 Ma: 0) BY a firfii ATTORNE Patented Apr. 16, 1940 UNITED STATES PATENT OFFICE ARC WELDING SYSTEM Application May 23, 1939, Serial No. 275,140

7 Claims.

This invention relates to an alternating current arc welding system and is an improvement on the system set forth in my Patent 2,097,327, issued October 26, 1937, as well as on my appli' cation Serial No. 174,331, filed November 13, 1937.

Since the introduction of alternating current arc welding, many improvements have been made. The early machines had a high open circuit voltage, poor power factor and delivered an are more or less unstable. Today, an alternating current arc welding transformer, to meet the competition of direct current arc welding machines and the general requirements of the trade, must have a good power factor, low open circuit terminal voltage and be able to deliver a stable arc. Good arc stability will result if the voltage across the arc rises, should the arc tend to go out. If this is accomplished by using a high voltage source and merely a series impedance, the power factor and efiiciency are poor.

In my patent and application previously referred to, I have indicated certain ways and means by which many of the difliculties or objections to alternating current transformer Welders may be overcome. However, after further intensive study of the various problems involved, and experiments, I have evolved a much improved system of alternating current arc welding.

In my pending application previously referred to, I have set forth several advantages of the same over my prior patent. My present invention, while attaining all the objects and advantages set forth in the said prior application, has the additional and primary object of greatly reducing the size, weight and cost of the units making up the system, while at the same time increasing the overall efllciency of the system.

Other objects will be discerned from a reading of the following specification, taken in connection with the annexed drawing, wherein M is a main supply transformer having one or more primary windings such as PI and P2 which may be connected in series by throwing a switch I into the position 2; or in parallel by throwing the switch I into the position 3, the series arrangement being used when the voltage supply is, for example, 440 volts; and in parallel when the supply voltage is 220 volts. The main transformer M has a suitable laminated iron core 4 and a secondary winding S arranged thereon so as to provide a step-down transformer of low reactance between the primary and secondary windings thereof. A low impedance transformer of this type is much smaller since it takes much less copper and other materials throughout than a high-reactance transformer such as disclosed in my pending application heretofore referred to. In addition, the eddy current losses are much less with a low reactance transformer and the efliciency is materially higher, and the weight and cost lower.

One end of the secondary S is connected by the lead 5 to the electrode E for cooperation with the other electrode W which is the work-piece. The other end of the winding S is connected by a lead 6 to a winding 7 on an auto-transformer 10 AT, the other end of the winding 1 being connected to a ground point G which is also connected to the electrode W.

Connected'across a part of the secondary portion 8 of the transformer AT, through the me dium of a switch member 9 having contacts l0 and II which are connected to the winding 8, is a voltage regulator R such as shown and described in Schermerhorn Patent 2,089,434, issued August 10, 1937. The regulator R is so constructed as to have a difference of only about one-half volt between the commutator bars. The movable brush or contact of the voltage regulator R is connected to the common ground point G. By this connection the safety factor to an operator is vastly improved as the movable contact on the regulator R is the part which the operator has to move to adjust the arc current to the desired value. As will be noted,

the movable arm of the switch 9 is connected to one end of the regulator R, while the other end of the regulator is connected to the point 12 on the secondary winding of the auto-transformer AT. The contact I l is connected to another point on the winding 8 of the auto-transformer AT. It will be apparent that by the use of the switch 9, the regulator R may be switched to d fferent portions of the winding 8 and its range of operation multiplied.

Connected to one extremity of the winding of the auto-transformer AT, is an inductive reactor Z which takes the place of the reactance removed from the transformer M. Connected in series with the reactor Z is a capacity C. The other side of the capacity C is connected to the extremity of the secondary winding of the auto-transformer AT.

By way of illustration but not of limitation, the voltage across the capacity C must be on the order of about 880 volts in order to have a charg- 5o ing current of a definite value sufficient to get the required welding current through the circuit. The open circuit voltage on the secondary winding S of the transformer M may be taken at approximately 65 volts, which is materially below preferably 20 the present-day standard of arc welding machines. Assuming that the voltage drop across the primary I of the auto-transformer is 50 volts and with a ratio of approximately 8 -to-1 between the primary and secondary portions of the auto-transformer AT, this provides a voltage of approximately 425 across the secondary of the auto-transformer. This gives a voltage across the reactance Z of 455, so the voltage transformed by the auto-transformer is 425 volts; whereas, in the circuit of my prior application, the actual voltage necessary to be transformed is 880 volts. Since the charging current of the capacity is the same in my present arrangement as in my prior application, the kva. rating of the auto-transformer in my present arrangement is 25 kva. whereas in the circuit of my pending application it is 52.8 kva., which means that the size of the auto-transformer in my present arrangement is approximately one-half that of my prior arrangement, although I still get a stored energy of 52.8 kva. in the capacity C, which is an important point, because it is this stored energy that acts to maintain the arc should it tend to go out. Furthermore, the regulator R is about one-half of what it was in the said prior circuit. The reactor Z is of the low-current type instead of the high-current type, which means that the gaps in the core can be concentrated on the center leg, shielding the leakage from all external apparatus. This makes a much simpler reactance to build and gives less loss than is the case with a highcurrent reactor.

My present arrangement is such that a constant load impedance is provided on the secondary of the auto-transformer AT, since the inductance Z and capacity C are of a constant value, and consequently their difference is a constant value. Also, since the impedance in the welding circuit varies as the inverse ratio of the auto-transformer, the impedances at low current values increase as the square of the ratio reduces, which means that I can get a very high impedance on low welding currents, which is highly desirable for maintaining a good arc.

In the operation of this welding circuit, I have noticed a marked increase in the high frequency currents across the arc, although it is to be understood that the inductance Z and capacity C are so chosen that they will never get into complete resonance, and this adds greatly to the smoothness of the arc. Another advantage of my present welding system is that I am able to get all the control that is necessary by reason of the regulatofR, without the use of any taps on the secondary of the main transformer or on the primary of the auto-transformer, thereby eliminating heavy current switches. The efficiency of the welding system herein shown and described is materially higher, being on the order of from 15% to 20% more than the system shown and described in my pending application, or patent.

The welding system shown and described herein differs from my prior patent and pending ap-- plication in that all impedance including, both the inductance and capacity is in the secondary circuit of the auto-transformer and the resulting voltage as heretofore pointed out is controlled by the regulator R which, in my pending application, controls only the voltage on the capacity. This means that a constant impedance is always in the resonant part of the circuit which operates at the same point on the resonance curve. Therefore, the impedance can be initially set for the most ideal condition, as described, and maintained throughout the entire range of welding; whereas, if the impedance is incorporated in the transformer M or as a series device in the main line from the secondary of the transformer M, this impedance will not be in the resonant part of the circuit wherein the capacity is located. Furthermore, as heretofore pointed out, the resultant impedance which actually does the maintaining of the arc varies as the square of the ratio of the auto-transformer, and increases as the current is reduced in such a manner that the same characteristic is maintained at all cur rent values, and the capacity discharge is greater in effect at smaller currents than it is at the larger current values, which is exactly what is needed to maintain the arc. This method of operation is therefore materially different from my patent and pending application.

While I have shown an auto-transformer as the interconnecting means between the main source of current supply and the welding electrodes, I may use instead a low impedance, double-wound transformer in which the primary corresponds to the winding 1 and its secondary to the balance of the winding on the auto-transformer AT. Therefore, in the claims, where I refer to a supplemental transformer, this term is used to include either type, but in general I prefer to use an auto-transformer which has low Q impedance. Further, while I much prefer to use the voltage regulator as set forth herein, I do not wish to be limited to this particular form.

What I claim is:

1. In an alternating current arc welding cirhaving a movable brush electrically grounded and contacting with turns of the inductive winding of the regulator, a switch for connecting said inductive winding of the regulator across different portions of the secondary of the supplemental transformer, and an inductance and capacity connected in series and across the entire winding of the supplemental transformer.

2. In an alternating current arc welding circuit, a main supply transformer having a low reactance between its primary and secondary windings, the arc circuit being supplied with current from said secondary, a supplemental transformer as described having a portion of its wind ing connected between the secondary of the main transformer and a point common to the ground electrode in the arc circuit, a voltage regulator of the type herein described having a movable brush electrically connected to said common ground point and contacting with turns of its inductive winding, means for connecting said inductive winding of the regulator across portions of the supplemental transformer secondary winding, and a reactor and capacity permanently connected in series and across the entire winding of the supplemental transformer.

3. In an alternating current arc welding circuit, a main supply transformer having a low reactance between its primary and secondary windings, the arc circuit being supplied with ourrent from said secondary, a supplemental transformer as described having the primary end of its winding in series with the arc circuit and that end of its primary winding which is connected to an arc electrode being grounded, a

voltage regulator of the type herein described having a movable brush electrically grounded and contacting with turns of the inductive winding of the regulator, a switch for connecting said inductive winding of the regulator across different portions of the secondary of the supplemental transformer, and means for securing a substantially constant load impedance in the supplemental transformer and also for obtaining a relatively high impedance in the arc circuit, especially with low current values, said'means including a fixed inductance and capacity connected in series and across the supplemental transformer. windi 4. In an alternati current arc welding system, a main'supply t nsformer for the are current, an auto-transi rmer having a winding in series with an elect de 01' the arc, a voltage regulator having a movable brushmaking electrical contact with the turns of an inductive winding excited from a winding on the auto-transformer, means for reducing the size and cost of the main and auto-transformers as well as the regulator, while at the same time increasing the emciency of the system, said means including; an inductive reactance separate from'the main supply transformer, thereby allowing this to be of low reactance, and a capacity in series with said inductive reactance and connected across the autotransformer, whereby the voltage to be transformed is only the difference between the voltage across the capacity and the inductive reactance.

5. An alternating current arc welding system as set forth in claim 4, further characterizedin that means are provided for increasing the safety factor to an operator, said means comprising a ground point for the movable brush on the regulator, and for that end of the auto-transformer winding which is connected to the work electrode in the arc circuit.

6. An alternating current arc welding system including a main source of current comprising a transformer having an open circuit voltage below that of the present-day standard for arc welding, a terminal of said source being connected to one of the arc electrodes, a supplemental transformer having a primary winding in series with another terminal of said source of current and the other are electrode, a voltage regulator connected across some portion of the secondary of the supplemental transformer, and an inductive reactance and capacity connected in series and across the secondary winding of the supplemental transformer.

'7. An alternating current arc welding system including a main supply transformer of low impedance having its secondary winding connected to the arc electrodes through the primary of a supplemental transformer, a fixed inductance and capacity comprising substantially all the impedance in the weldingcircuit, connected across the secondary of the supplemental transformer and means for regulating the resultant voltage between the inductance and capacity.

THOMAS M. HUN'I'ER.