US1470214A - Alternating-current transformer - Google Patents

Description

oct. 9, 1923. 1,470,214

.L R. BR'uEcKNl-:n-

l ALTERNATING vCURRENT TRANSFORMER Fuel: Aug. 2 sheatslsieet 1 @man Patented Oct. 9, 1923.

UNITED STATES PATENT OFFICE.

JULIUS R. BRUECKNER, OF DETROIT, MICHIGAN, ASSIGNOR TO GIBBV INSTRUMENT COMPANY, OF DETROIT, MICHIGAN, A CORPORATION OF PENNSYLVANIA.

ALTERNATING-CURRENT TRANSFOBMER.

Application med August 2a, 1920. seran ita-105,466.

To ill whom it may concern.'

Be it known that I, JULIUS R. Bannon- Nnn, a citizen of the United States, residing at Detroit, county of Wayne, State of Michigan, have invented a certain new and useful Improvement in Alternating-Current Trans'- formers; and declare the following to. be a full, clear, and exact description of the same, such as will enabe others skilledin the art to which it pertains to make and use the same, reference being had to the accompanying drawingzjrs, which form a part of this specification. v

This invention relates to alternating current transformers for electric Welding systems. Electric arc Welding transformers have been devised heretofore and in such previous cases, for instance as shown in the U. S. Patent for Morton Arendt, No. 1,146,988 of July Q0, 1915, an inductance or reactance coil is used in the secondary circuit or such circuit is provided with an in terwoven or' additional secondary winding as inthe U. S. Patent' to Claude J. Holslag i\o. 1,305,362 of June 3, 1919, or an auxil- "iary secondary coil is' wound somewhere along the magnetic core which functions as a reactance or a choke coil.

All theseformer devices have a lare ohmic resistance-(since impedance may looked upon in the same light as ohmic rev sistance) and these former types of transto negative is so slow that t e gas formed at formels are therefore of 10Wv eiciency. due` to excessive consumptlon of power Whlch 1sthe arc (which is thecurrent conducting element) has time to dissipate making'such transformers unsuitable Afor arc weldingf The introduction of reactance' coils and the like as heretofore mentioned results in a distortion of current flow to cause ra id drop in voltage through the zero va ue.

The curve'of the instantaneous values durmg this vcontinuous change from positive yto negative is termed the "current or E. M. F. Wave form and for all practical purposes maybe considered a. sine wave which is usually peaked or rounded at the top: By introduction of reaetance coils in the secondary circuit as heretofore mentioned, the wave form may be changed thus flattening out the top of the sine wavewith a sudden change from maximum lpositive to maxi- ,mum negative across the neutral points.

This distortion ofthe sinewave is a direct result of the difference in phase relation of the E. M. F. and current. Ifthis distortion is caused by reactance the current lags behind the E. M. F. `An object of this invention is to provide an alternating current electric arc weldin very simple construction ispensing with or avoiding the use of' reactance coils, or ad lditional magnetic by-paths, interwoven .or

split secondaries and in which the current loss is reduced to a minimum. Further, the object is te provide a construction :produc-tive of a steadyarc and an even stable flow of current across the arc and distinguishes from the former devices above mentioned ink that the construction provides a definite means of producing a short and steady arc by magnetic flux distortion rather than by direct current distortion as transformer of in the former cases. In other Words-the object of the invention is to'provide a transformer having a core of such construction and design as vto. induce a current in theV secondary in which the change through the neutral point from maximum sitive to maximum 'negative value is sud en instead of producing a secondary current of substantially normal Wave form and introducing an Vinstrumentality in the circuit to distort such wave formi as is the usual practice. Vith my invention a current of the' desired character is primarily set up in the secondary. character With which I am acquainted the induced current is acted upon to cause the sudden drop from maximum positive to maximum negative value. These and other objects and lthe several novel features of the invention are hereinafter more fully described andclaimed and the preferred form of construction 'of a transformer embody? With all other devices of this ing my invention is shown in the accompanying drawings in which- "Fig: 1 is a side elevation ot' a transformer.

Fig. 2 is a detail of the mechanism for moving the secondary coil.

Fig. 3 is a plan view` of the transformer, taken on line 3-3 of Fig. l. Y y

I F ig. 4 is a diagram showing the wave form of the standard type of transformer.

Fig. 5 is a diagram showing the ideal 'wave form of the secondary current as approximately produced by the transformer here shown.

My improved transformer is ofthe usual shell type having three legs, 1, 2 and 3. The primary coil i and the secondary coil 5 are two distinct units each surrounding the center coreand the primary winding is ,securely fastened at the lower end of the core 2. This fastening may be of any approved type as by bolts G passing through a frame 7 and base member 8 of the trans'- former. The secondary winding 5 is movable on the core 2 and by movement of the secondary coil the secondary current may be varied as heretofore described. lVhen the secondary is nearest/the primary the maximum secondary current is obtained and when furthest from the primary the minimum current is available. This move ment of the secondary coil isaccomplished by meansof a rack 9 which extends upward through the closed casing of the trans former and engages a pinion 11 shown more particularly in Fig Z on the shaft of the operating wheel 10. This movable secondary is essential for different classes ot' work requiring a greater or less degree of heat at the are. As the transformer is preferably enclosed within a casing 12 some means should be provided to enable the operator to determine the relative position of the secondary coil as for instance by placing graduation lines (not here shown) on the rack end 9.

The primary coil is provided with leads 13 and 14 while the secondary coil is provided with the leads'll and'lG the lead 15 providing the ground line and the line 16 being provided with an electrode holder 17. These several leads are connected with the respective tcoils in the usual manner being supported on the upper end of the trans former by insulating block 18. The closed casing is lled with oil preferably to about the upper end of the transformer so that both coils are immersed in the oil. I have found by a series of carefully conducted eX- periments that, by maintaining the core portions in certain .relation to the winding of the primary and secondary and the length of the core in definite proportion to the width of the windows of the transformer onder;7 windings or intermingling the pri mary and secondary or the addition of a reactance coil or the like in the secondary circuit. Therefore, by the construction stated the impedance or ohinic resistance of the windings is reduced to a minimum.

The relative proportions of the core parts that I have found most effective is in providing a window of three and one-half inches width and fifteen inches in length with a two inch width of each outside legv and four inch width ot central leg. The capacity of transformers may be varied by adding metal to the side thereof to increase the cross sectional area and cubical content of the core parts. This structure permits the usel of a comparatively low voltage open circuit for t-he striking of the arc greatly reducing the shock hazard and providing a core of sufficient capacity to permit the magnetic iux to surge without leakage when the transformer is on open circuit. The comparatively narrow windows also provide a ready means for magnetic leakage when the transformer is under load (that is when an arc is maintained). By reducing the ohmic resista-nce to a minimuml (as by elimination of choke coils etc.,) the current losses are reduced and at the Same time a steady and an even fiow of ciu-rent across the arc is secured. These beneficial results are obtained through distortion of magnetic tiux rather than by directly distorting the current as formerly and the theory of operation is as follows: Vhen the secondary circuit is open and current passing through the primary, the magnetic field is unobstructed throughout the several parts of the core. Upon closing of. the secondary circuit, as in the striking of the arc, and with the secondary spaced to some extent from the primary, there is what is termed a magnetic leakage between the central leg and outside legs of the core between lthe two coils, the extent of which is determined by the spacing of the coils. Vhen t-he secondary circuit is closed, the magnetic flux may not take its normal path'due to the counteracting influence of that set up by the secondary coil at the upper end of the core. The greater the distance between the secondary coil and the primary coil the less will be the amperage and the greater the voltage of the secondary current and decreasing the distance between the coils increases the amperage and decreases the voltage.

It is well known in the art that a short arc is essential in the production of a good weld and that, due to oxidation, the weld is brittle when a long arc is maintained. Vith the construction of apparatus according to my invention the arc will extinguish upon lengthening to a dangerous point due to the comparatively low voltage of the secondary circuit and thus the length of the struction and design of ni Iao - velo are ossible to be drawn is automatically regu ated and maintained within the necessa limits for the production of a good we d. For the usual arc welding operation, the secondary coil should be positioned about midway between the'primary coil and up` vper end of the core in the .design herein wave form isy secured and heretofore` deemed-necessary in securing the desired wave form. By the particularity of contransformer, especially the narrow win ows having va Width practically onefourth of the height, a ready leakage of magnetic flux is ermitte-:l when the coils are separated, an I avoid the detrimental features of the former oonstruction mentioned and secure the following desired results--namely, low current consumption due to the current impedance being reduced to a minimum, a comparatively low voltage on striking the yarc and, simply varying the position of the secondary, automatically varies the extent of magnetic leakage and varies the character of the current to correspondingly vary the heat ded at the arc. e'benefits obtained by the construction heretofore set forthl results principally from the use vof an excessive massA of iron in relation to the mass of copperwith a comparatively very shortf'iiiagnetic'air gap se- ,ciired by the narrow window construction.`

As before stated, the central leg of the transformer has a width equal4 to the two outside ylegs with the air space therebetween about one-fourth the height. The transformer is made of a series of plates so that the length of the transformer may be increased or diminished readily by addition' or removal of one or more plates. In-the specific-transformer heretofore mentioned having windows-of about three and onehalf inches by fifteen inches I use approximately ninety-two turns in the primary coil, using a at wire ..125 thick and .375 wide. The second coil is made of forty-four turns of two wires each of .125 by 1440; With the construction I secure ninety volta in the secondary circuit with 22() volts in the primary circuit. Thel'mass of iron weighs approximatel 200 pounds, and the 'mass of copper Weig is approximately pounds. 4With this construction the voltage in the secondary on open circuit is ninety irrespective of the position of the secondary. laminated core' formed of three legs of mag- There is no variation in the voltage that may be detected by any of the usual instruments whether the secondary is positioned adjacent the primar coil or at a point most remote there rom. Thisl indicates positively that there is no magnetic leakage whatever when the secondary is on open Vcircuit although, by reasonof the short air gap a very ready magnetic leakage occurs` on closed circuit-as themagnetic flux of the primary is counteracted by that of the secondary. The essential characteristic of my' invention consists in the provision of en excessive mass of iron relative to the copper as compared with that of the standardalternatingcurrent type of transformer and in so constructing thetransformer .to permit a high degree of magnetic leakage to readil shorten the path of the magnetic circuit o the primary coil. In this manner,

when the secondary circuit is closed, as upon striking an arc, a distortion of the magnetic fiux of the primary coil is occasioned and,

as this is out of phase with that set up by the secondary on closed circuit, a prolonga- .tion of the maximum, positive and max- 'imi'im negative value sof the secondary current is occasioned together with a sudden Adrop therebetween through the neutral fpoint. This is a desired wave form of secondary current as heretofore stated and by the construction described, a current of the desired wave form is primarily effected in the secondar circuit rather than secondarily eiecte through the introduction in the secondary circuit of a reactaiice coil or the 'like as has been the practice. The specific proportions of the transformer parts herein specified are iven `solely as an example and it is to e understood various changes may be within the limitations of the appended claims without departing from the spirit of the invention. Having thus fully described my invention, whatfI claim and desire to secure by Letters Patent of the United States is- 1. Air alternating'v current transformer for use in electric are weldin comprising a core formed with three legsI 0% magnetic'ma-A terial connected together at the top and bottom, the windows'between the legs being of a -widthvsubstantially one fourth their length roviding a short air gap, a primary circuit aving a coil at the bottom of the ycentral leg, a secondaryhcircuit, -a movable `-coil therein on the central .leg above the primary coil, means for holding the secondary coil at any of its possible distances from the primary, the secondary coil and circuit bein yfree' from ohmicresistance other than that inherentin the wire forming the same andthe resistance of the arc.-

2. An alternating current transformer for use in electric arc welding comprising a liao netic material connected together at the top and bottom and having narrow window-S between the legs providing a short magnetic air gap permitting ready magnetic leakage, a prima'ry circuit having a. coil at the bottom ot the central leg, the mass ot iron being sutiicient to permit surge of magnetic flux without leakage, a secondary circuit having a coil on the central leg adapted to be adjusted to various delinite positions relative to the primary, the secondary coil and circuit being unimpeded except by the inherent resistance of the wire and the resistance of the arc.

3. An alternating ciiirent transformer for use in electric are welding comprising a core formed of three legs of magnetic material connected together at the top and bottom, the width of the central leg being substantially equal to that of both the other legs and the three legs being connected together at the top and bottom, the windows between the legs being comparatively narrow and of the same Width throughout their length and providing a comparatively short magnetic air gap permitting ready magnetic leakage,'a primary circuit having a coil on .the core, a secondary circuit also having a coil on the core, means whereby one of the coils may be positioned and held, the iow of current through either of the circuits and respective coils being impeded only by the natural resistance of the Wire form-v ing said circuits and the resistance of the arc in the secondary circuit.

4. An alternating current for use in electric arc Welding which comprises a core formed of three legs of magnetic material connected together at the top and between and providing windows7 between the legs of a uniform width of about one-fourth their length providing a short magnetic air gap and whereby the extent of magnetic leakage 1s proportioned to a distance the coils are positioned apart. a primary circuit having a coil fixed at the bottom ct the central leg, a secondary circuit free from impedance except that natural to the wire of the circuit and the resistance of the arc and having a coil about the central leg and movable thereon relative to the primary, and means for positioning the secondary and holding the saine at various predetermined distances from the primary, coil whereby the an'iperage of the secondary circuit is determinable.

5. An alternating current transformer for use in electric arc welding comprising a core having a cross sectional area sullcient to normally permit unrestricted magnetic linx, said core further having a form permitting a high degree of magnetic leakage, a primary coil and circuit therefor of a character permitting practically unimpeded flow of current, a secondary circuit free from impedance except that natural to the wire and the resistance of the arc and having a coil niovablerrtoward Vor from the primary coil to effect magnetic leakage by distorting the magnetic flux of the primary coil to a desired extent, the said secondary coil and circuit therefor, by reason of the freedom of magnetic leakage and ,unrestricted magnetic flux having current primarily induced therein of a wave form having prolonged maximum positive and maximum negative values with a sudden drop through the neutral point therebetween.

In testimony whereof, I sign this specification.

JULIUS R. BRUECKNER.

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