US2160588A - Electromagnetic induction apparatus and method of making the same - Google Patents

Description

ay 30, 1939- .1. c. GRANFI E LD 2.160588 ELECTROMAGNETIC INDUCTION APPARATUS AND METHOD OF MAKING THE SAME Filed Jan. :50, 1937 3 Sheets-Sheet 1 Fig.1.

Inventor John C. Gfianfield His Attovneg.

' M J. c. GRANFIELD 2,160,588

ELECTROMAGNETIC- INDUCTIQI APPARATUS AND'METHOD OF MA KING THE SAME Filed Jan. 30, 19.37 3 Sheets-Sheet 2 I A l Inventor John C. Granf'ield b Jaw M 8 His A1313 ornea -May 30, 1939-- J. c. GRANFIELD ELECTROMAGNETIC INDUCTION APPARATUS AND METHOD OF MAKING THE SAME Filed Jan. 30, 1937 s Sheets-Sheet 3 Inventor: John C. Gvanfield,

b W I is Attovneg.

Patented May 30, 1939 UNITED STATES PATENT OFFICE ELECTROMAGNETIC INDUCTION APPARA- TUS AND METHOD OF MAKING THE SAME New York Application January 30, 1937, Serial No. 123,249

22 Claims.

This application is a continuation-in-part of my application Serial No. 77,499, filed May 2, 1936, for Transformer core, relating to the method of making electrical induction apparatus such astransformers'and reactors comprising a magnetic core and one or more conductive windings.

Most transformers except those for high frequency radio applications comprise a magnetic core on which there is at least one primary windl0 ing and one secondary winding. There maybe more than one primary winding and more than one secondary winding. A reactor ordinarily comprises a magnetic core and a windin on the core, the device providing an electromo ve force of self induction for a wide variety of applications. There may be other. windings on the core which in some cases may be supplied with direct current for saturating purposes.

My invention relates to an improved construction of such electromagnetic induction apparatus which enables the cost to be greatly reduced without sacrificing desirable operating characteristics. While the principles of my invention are applicable to practically all types and ratings of transformers including power transformers, X-

ray transformers, etc., my improvements have their greatest economical importance at present in the case of distribution transformers, especially in the range from 1 to 50 kw. capacity,

such transformers being used in enormous numbers. My improvements are also applicable with substantial savings to instrument transformers, to small transformers such as radio transformers and small transformers for general application on standard commercial frequencies. My improvements lend themselves also to economical constructions for much higher frequencies.

Distribution transformers have been developed to a very high state of perfection, particularly by reason of improvements in the quality of the magnetic core material. Hadfields invention of silicon-iron alloy made a radical improvement in transformers about thirty years ago, reducing the watt losses in the core about 30%- as compared with iron or soft steel previouslylused, the sillcon-iron alloy producing a reduction in both hysteresis'and eddy current losses. For thirty years or more the standard construction of distribution transformers has involved building up the magnetic core of thin laminatlons punched or stamped to appropriate sizes. The presence of silicon increased the diillculty of rolling and, in the early days, it was difllcult to roll a sheet with a silicon cgntent of as much as 3%, but with no experience in rolling and heat-treating, the silicon content has been gradually raised until it is now from 4 to 5% in transformer sheets, and has been of the order of 3 to l for about the last twenty years. The reduction in watt losses in silicon steel from about 1.25 (at 10,000 gausses and a frequency of cycles) at the time it was first used extensively, to about .5 watt per pound at the present time is in a measure attributed to the increase in silicon content which has increased the resistivity of the iron and so reduced its eddy current losses and, by its chemical action on the dissolved carbon the silicon also reduced the hysteresis loss. The larger part of the reduction in watt loss was, however, accomplished throughreflnements in the process of making the steel and a better understanding and control of the physical structure of the material eflected by improved rolling and annealing methods. One of the latest developments along this line of increasing the silicon content is the 6 to 6V sili-v con steel disclosed in Ruder application Serial No. 97,678, filed August 24, 1936, assigned to the-same assignee as'the present application, and also disclosed in British Patent 380,387 of. 1932 of the British Thomson-Houston Company, Ltd. Since the filing of the present application the Ruder application has resulted in United States Patent No. 2,088,440, issued July 27, 1937.

This increase in silicon content, together with improvements in the technique of hot rolling and annealing, have resulted in increased permeability, as well as reduced watt losses in the hot rolled product, permitting a constant'gain in watt losses and an improvement in magnetizing current characteristics of distribution and power transformers so long as they were designed tooperate at flux densities not exceeding 10,000 to 12,000 gausses. The increased permeability has been in the lower range of magnetic densities, and with higher densities, the amount of magnetizing current required increases so rapidly as to overbalance any gain from reduced watt losses. A flux density of 10,- 000 gausses has therefore become the standard reference point for watt losses in transformer sheet steel specifications.

The loss in transformer steel is partly a hysteresis loss and partly an eddy current loss. The ratio of these losses varies with the silicon content, the

eddy current loss increasing as the silicon content is lowered and decreasing as the silicon content is increased by reason of the fact that the resistivity of the material increases with the silicon content. At normal densities, that is densities of about 10,000 gausses, the hysteresis loss in hot rolled 455% silicon transformer steel is about and the eddy current loss about 25% of the total. The ratio is also affected by the thickness of the sheet used, the eddy current loss in the apparatus being reduced as the thickness of the sheet is reduced. With thin sheets, the eddy current loss decreases roughly in proportion to the square of the thickness; that is, by decreasing the thickness of the sheets by one-half, the eddy current loss in a device such as a transformer may be decreased to about one-fourth. In the present day developments of hot rolled sheets, however, a limit is reached in the direction that one may go in reducing thickness. Below a thickness of 10 or 11 mils, the total watt losses are increased because of the increase in hysteresis loss which is probably due to a breaking up of the grain of the material, the result being that 14 mil sheets have usually been adopted as standard in the hot rolled high grade material because of limitations in thickness tolerance necessary to avoid producing sheets below a thickness which would increase hysteresis loss.

Moreover, where the cores of electromagnetic induction apparatus such as transformers, reactors, and the like, are built up of punched or stamped pieces, as in present day standard practice, there are a number of other considerations which militate against going to a thinness below about 14 mils. The hot rolled sheets are customarily made by the pack-rollingprocess producing sheets about 10 feet long and of a width of about 30 inches, although wider, as well as narrower, sheets may be made. The thinner the sheet, the more likely the sheets are to stick together during annealing and the more diflicult it is to handle the sheets without distorting them and the thinner the materialis, the greater is the number of sheets required for any given volume of materiaL The punching of laminations from sheets as they come from the mill is expensive in handling and is wasteful because of the scrap left after the punching operation. It has therefore been customary with certain large transformer manufacturers for many years to cut the sheets intostrips of the desired width, weld them end to end to make a continuous strip, and then run such strip through the punching machine. The punched out laminations after annealing are then ready to be assembled around the windings of the transformers or reactors for which they have been punched. The thinner the material used, the greater is the tendency of the laminations to stick together when annealed and the greater the number of laminations which must be handled and stacked, all of which adds to the cost of manufacture. It has been found by experience that a reduction in the thickness of the punched out laminations with a corresponding increase in their number, causes an increase in magnetizing current which seems to correspond to increased air gap reluctance.

The present hot rolled silicon steel sheet material depends for its desirable characteristics upon relatively large crystals. Tests show that there is some difference in permeability in the hot rolled material, depending upon whether the flux flows through the sheetin one direction or another, but since there is no very pronounced favorable magnetic orientation of the grain of the material, the difference in the losses, depending upon whether the flux flows in the most favorable direction or at right angles hereto, is only of the order of 10% to 15%. It is common to punch out the laminations from the hot rolled strip in theform of L-shaped punchings, each armpf the 24, 1933, and Goss 1,965,559, July 3, 1934. The

hot rolled material at the 45 degree angle are about as good as at the most favorable angle. The use of L-shaped instead of straight punchings reduces the air gap reluctance, since each L- shaped punching eliminates one corner air gap in the built-up core. It is therefore possible by punchings of such L shape from such hot rolled material to secure an actual gain in the magnetizing current and watt loss characteristics of the complete apparatus, as well as reduce the number of punchings which have to be made and assembled. However, in any structure built up from laminations, it is impossible to take full advantage of the magnetic properties of the material because, even if the laminations be punched so as to have the most favorable orientation of the grain longitudinally of the laminations, the direction of the flux at the corners will always be at an angle varying from zero to to the direction of the grain. The punching of the laminations so as to have the favorable grain orientation longitudinally of each lamination requires that there be an air gap at each corner of the built-up core.

It is an object of my invention to provide a construction wherein full advantage is taken of the favorable magnetic orientation of the grain while at the same time air gap reluctance is enormously reduced. It is a further object of my invention to provide a method of construction which makes it possible economically to use material having a pronounced favorable orientation of the grain and greatly reduce the cost of the apparatus while obtaining very desirable opcrating characteristics from the standpoint of watt loss and magnetizing current. While my method of assembly, hereinafter described in detail, is particularly applicable 'to material such as high reduction cold rolled 3% silicon strip, and apparatus such as distribution transformers utilizing such strip and made in accordance with my invention can be produced at a saving .of from about 25 to 40% over the cost of manufacture with standard present-day constructions built up from stamped laminations; and while a saving of the order of 20% may be made in small transformers such as radio transformers for standard frequencies using such strip, it is possible by my invention to meet any given efliciency at any flux density using a given quality core material 'with less such material than required by any other construction with which I am familiar.

The high reduction cold rolled magnetic strip which I prefer to use has been available for several years. By the high reduction cold rolling process, striking improvements were achieved in the permeability of nickel-iron alloys and silicon steels. This process is disclosed, for example, in the patent to Smith et al. 1,915,766 of Jan. 27, 1933 (filed in Great Britain Oct. 31, 1930), and in the patents to Freeland 1,932,306 I-8-9, Oct.

process is a general one applicable to nickel-iron alloys and silicon steel and is, in brief, characterized by hot rolling to a thickness considerably greater than the finished size followed by annealing and a further reduction of about 60% by cold rolling to the finished size and then heat treating. The quality may if desired be improved somewhat by a further step of high reduction cold rolling and further heat treating.

In distribution and power transformers, re- (5 has a silicon content of about 3%.

actors, or the like, built in accordance with my invention, the greatest advantage is secured at the present time by using strip material having the characteristics of the high reduction cold rolled 3% silicon steel instead of the customary hot rolled material. This material can now be bought from the steel mill and while its price is at present somewhat higher than the price of ordinary hot rolled sheet material, the reductions in cost of manufacture to which I have referred can be secured in accordance with my invention even at the higher price of the material for the reasons which I shall hereinafter point out. Such sales of the material as have been made have, as far as I am aware, been principally to motor manufacturers, such as fan motor manufacturers, who have found it worth while to pay a little more for the material by reason of the fact that it comes in long strip and thereby makes possible a small saving in the cost of their finished punchings. It. may have been used to some extent in transformer cores built up of laminations punched from the strip, but I know of no such commercial use and, for reasons upon which I have touched and shall point out more in detail, its use for such purpose does not for the standard types of transformer constructions enable sufiicient advantage to be taken of the qualities of the material to make its use worth while. As far as I know there has never been any commercial use made of strip material of any quality for winding cores of transformers or reactors for any purpose in which form wound conductive coils were used. There has been some use of wound magnetic cores for instrument transformers, but not with form wound conductive windings. In all such instrument transformers with which I am familiar thev conductors have been wound on the magnetic core by threading the conductors through the opening in the core, and even in such transformers I know of no case in which the-core has been constructed and used so as to have the magnetic material in the proper physical condition to secure minimum watt losses as in the case of my invention; and all instrument transformers are characterized by the use of low flux densities to permit of operation on the straight portion well below the knee of the magnetization curve of the material so that the response of the measuring instrument supplied by the transformer shall be in accordance with changes in the quantity to be measured and not subject to error due to the magnetic material of the transformer becomingmore or less saturated.

In accordance with my invention, I eliminate entirely the step of punching a sheet or strip into laminations. In accordance with my invention, I use form wound coils for the electrical windings of transformers, reactors, and the like. and wind the magnetic strip flatwise upon the coils, following a procedure which is simple and inexpensive, which reduces air gap reluctance to a minimum, utilizes the full advantage of the favorable magnetic orientation of thegrain of the material, and in which in the completed apparatus the losses are a minimum due to the fact that .stresses in the .material which might increase its watt losses are substantially eliminated.

The high reduction, cold rolled silicon strip with which I at present obtain optimum results Silicon steel having such a content of silicon is readily rolled by the high reduction, cold rolled process. Somewhat higher' percentages may be used, but so far I have found no particular advantage in increasing the silicon content although there is a slight reduction in eddy current losses by reason of the increased resistivity. The high reduction, cold rolled silicon sheet has a very pronounced magnetic orientation of the grain in the direction of rolling. Instead of there being a comparatively small difference in the permeability and losses with the grain compared with that at right angles to the grain, as in the hot rolled sheet material, the difference is very substantial. If, the losses are 100 with the grain they will be from 140 to l60 at right angles to the grain. This great difference has probably been one of the reasons which has militated against commercial use of such cold rolled material in transformers built up of punched or stamped laminations where at the corners of the built-up cores the magnetic flux flows on the average at about 45 to the grain. If the losses are 100 with the grain, the best that can be done with L-shaped punchings from such cold rolled material cut at- 45 to the grain, is of the order of 140.

With present hot rolled transformer sheets the thickness has been limited by experience to about 14 mils, but with the cold rolled material a strip thinner than 10 mils can be produced without any impairment of hysteresis loss and with a reduction in eddy loss due to the thinner sheet, making a substantially lower total loss than can be obtained with the hot rolled material. There is, indeed, some improvement in the magnetic orientat on with the reduction in thickness of the sheet. At present I prefer to use cold rolled sheets of 10 or 11 mils in thickness and prefer in dirribution transformers to use flux densities of 13,000 to 15.000 gausses. although I may use still higher densities. Owing to the advantage which I take of the characteristics of the material and the reduction which I secure in air gap reluctance, I am able to use suchilux densities without sacrificing magnetizing current characteristics of the apparatus.

For example, with a flux density of 14,500

- gausses the magnetizing force required for the high reduction cold rolled 3% silicon material, in the most favorable direction of the grain, is about 3 oersteds (gilberts per centimeter), while for the best 4 hot rolled material it is about 15, or five times as great. A magnetizing force of 3 oersteds instead of producing a flux density of 14,500 gauses in such hot rolled material would produce only about 11,500 gausses.

For a flux density of 16,000 gausses. only about 7 oersteds are required for the cold rolled 3% silicon material, while about 100 oersteds are required for the hot rolled l material, about thirteen times as great.

In a conventional design of transformer built up from punched laminations of the hot rolled l material, the magnetizing current required for operation at a flux density of the order of 16,000 gausses becomes practically prohibitive. The magnetizing current required is made up of two components, one to produce the flux in the material and the other to force the flux through the air gaps in the built-up structure, both of which components are large. In accordance with my invention, however, operation at such high flux densities is entirely practical with material such as the 3% cold rolled silicon steel, and greatly improved operation from the standpoint of the required magnetizing current may be secured even with the hot rolled 4 /2 silicon steel because of the enormous reduction in air gap reluctance. If instead of the standard hot rolled 4 silicon steel the G silicon steel of the Ruder application, heretofore referred to, were used, the comparison would be still more favorable: that is to say, the 3% high reduction cold rolled material would show a still more striking advantage at these high densities.

My invention in its broader aspects is not limited to the use of high flux densities, however, since many of its advantages may be realized where high flux densities may not be required or desired. The 5 to 6 /2% hot rolled silicon strip of the Ruder application has high permeability and very low watt losses at low and moderate flux densities, and it is possible to apply such a strip by my winding process although such. a high silicon strip is very brittle. By heating the material and handling it very carefully during its application I have made such cores successfully. However, this material is so diflicult to wind especially into small diameters, that its commercial use for wound cores will probably have to await improvement which will somewhat reduce its brittleness. An increased silicon content is desirable where a relatively high resistivity is desired to reduce eddy current losses and hot rolled strip having less than 5% silicon content can be very readily applied by my process.

The high reduction cold rolled 3% silicon steel strip has the characteristic which is common to all magnetic materials that elastic strains in the material will impairits magnetic qualities. Moreover, if the strip is strained beyond its elastic limit; its magnetic qualities will be permanently impaired and can be restored only by further heat treatment. In accordance with my invention, such cold rolled 3% silicon strip can be applied easily and rapidly without straining the strip beyond its elastic limit and, in the completed magnetic apparatus made in accordance with my invention, the strip is free from such elastic strains as might decrease its permeability or increase its watt losses.

In accordance with my process, I have wound, heat treated and successfully applied not only cold rolled silicon steel strip having a silicon content of the order of 3%, but I have also used hot rolled material having various silicon contents. For example, I have taken hot rolled silicon sheet, cut it into strip, welded the strips end-to-end to produce along strip, and then coiled such strip into a hollow cylinder with the turns nesting tightly within one another, heat treated the coil of strip and successfully applied it to a transformer having form wound conductive windings. The completed spirally wound magnetic core was in each case of the same size as the heat treated coil of strip with the turns tightly engaging each other in the same sequence. I have done this with hot rolled sheet material having a silicon content of 2 /4% to 3%, 4 4% to 5%, and 6% to 6 without in any case bending the material beyond its elastic limit, and tests of the completed transformers have shown the absence of strains impairing the magnetic qualities of the material.

High reduction cold rolled nickel-iron alloy strip is characterized by a high permeability, as pointed out in the patent to Smith et al. 1,915,766, heretofore referred to, but this high permeability is obtainable only at low magnetic densities. This nickel-iron alloy material is extremely. dimcult to handle without impairing its magnetic characteristics. Merely dropping a piece of the material so as to give it a sudden jar is very likely to impair its permeabiiity and increase its watt losses so that in handling stampings of this material it has been customary to pick them up and lay them down carefully: The material is very soft and very easily bent or stretched, and it takes but a very slight distortion after heat treatment to impair its magnetic characteristics seriously. One of the best known of the nickeliron alloys for electrical purposes is sold under the trade name Mumetal which contains about 74% nickel, 20% iron, 4% copper, 1 chromium, and a small amount of manganese and silicon. When a tightly coiled hollow cylinder of this nickel-iron alloy material isheat treated, there is a very severe adhesion between the turns. I have wound up a coil of such material into a core with an inside diameter of 4 inches and an outside diameter of 6% inches of a strip 3 inches wide and 14 mils thick. This core comprised about turns and in winding the strip in order to insulate the turns from each other I applied a thin alkyd resin varnish in which magnesium oxide powder has been ground in a ball mill. After winding, the core was heat treated at 1100 C. in pure dry hydrogen. The watt losses of the core after the heat treatment were very high, indicating excessive adhesions between turns. I carefully separated the turns from each other by using a hack-saw blade which had been narrowed down to less than A; inch and the narrowed portion ground to a knife edge on both the front and back sides and working this small blade around the spiral. After the adhesions had thus been removed the coil was tested. At a flux density of 3,100 gausses the exciting current required was .0405 ampere and the watt losses were .3897 watt. I then applied the strip to a transformer following out the process of my invention with the greatest possible care. After application of the core to the transformer a test showed that an exciting current of .0810 ampere was required for a flux density of 3,100 gausses. That is, the permeability of the strip had been decreased so that the magnetizing current required had increased 100%. The test also showed that the watt losses had increased from the former value of .3897 watt to .5832 watt, or 50%. In other words the magnetic permeability of the material had been decreased by one-half and the watt losses increased by one-half due to distortions unavoidably introduced by the process of application. For a flux density of 6,200 gausses, the exciting current was increased well over 400% and the watt losses by over 60%, showing that for this higher but still relatively low flux density, the permeability had been decreased to 'less than one-quarter of that of the strip before its application to the conductive winding. This serious impairment of the magnetic qualities of nickel-iron alloy strip caused by the operation of transferring the coil to its position in the windows of the electrical winding, even in accordance with my present invention, makes it undesirable to use this material, as it'now exists, for my present purposes except in certain special applications, such as,- for example, instrument transformers, which are to be operated at low flux densities.

As heretofore pointed out, the high reduction cold rolled 3% silicon steel strip presents no such serious difliculties as are encountered with strip such as nickel-iron alloy strip, and the permeability and watt loss characteristics of the completed transformer core are as good as those obtained with Epstein samples of the material within the limits of the error of measurement. In

greases "making Epstein samples, the magnetic material sufllcient to make 10- kilograms of the strip material, and the strips are divided into four piles of equal weight and these four piles are assembled into each of the four coils of an Epstein frame, the piles of strip being carefully assembled into a rectangle with butt joints and being held in place by suitable holding means. The current, in making the Epstein test, is adjusted to give the desired flux density and the watt loss is read on a wattmeter in the same way as .watt losses are read when testing any transformer.

In accordance with my process, the strip is first wound -flatwlse on a roll or mandrel so'that the inside diameter of the spiral coil of strip materlal is of the exact size it is to have in the completed apparatus. The strip is tightly coiled so that the spiral turns of the strip nest within each other and closely engage each other, the exact 1 amount of material desired for the completed coiled core element of the transformer or reactor being wound upon the roll or mandrel. The coiled strip is then bound or tack welded to prevent the turns from loosening up, and is then heat treated as a unit to remove all strains and to set the core to size and shape. Preferably, the

width of the strip is but slightly less than the width of the window in the form wound electric coil or winding to which the strip is to be applied, although it will be understood that my invention is not in its broader aspects limited to a construction in which there is only a single strip wound core element, but embraces constructions in which there are two or more such core elements wound on the same or different legs of the conductive winding, and in large transformers it may be desirable to provide spaces between the tightly wound core elements for circulation of the cooling medium between the core elements. After the heat treatment the strip is then simultaneously unwound from the heat treated coil and applied to the form wound electric winding without bending or straining the strip material sufficiently to impair its permeability and watt loss characteristics in the finished product. After the strip core has been applied it is tightened'to the same diameter as it had in the heat treated coil. In accordance with my process,

when the winding of the strip material into the window of the form wound winding has been completed, the spirals of the strip will be in the exact condition, with the turns closely engaging each other and in the same sequence, that they were when the coiled'strip was heat treated, and the inside and outside diameters will be unchanged. This is of importance if the best. results are to be secured. I have found, for example, from tests of several particular designs of transformers'having cores of about 4 inches inside diameter that when the inside diameter of the core after application to the transformer was but one-sixteenth of an inch larger than it was when the coil of strip was heat treated, the watt loss (at 14,000 gausses and 60 cycles) was increased from 5 to and the exciting current about above the values obtained when the cores were applied with the exact diameter they had when heat treated.

If a high value of magnetic flux is to be used in the apparatus and high efficiencies with low magnetizingcurrents are to be secured, the mag- These strips are asnetic strip core material should substantially fill the window in the insulated form wound conductive coil and the inside turn of the magnetic spiral should closely embrace the leg of'the insulated conductive coil to which it is applied in order to provide a high space factor, or ratio of net copper section to the cross section of the space available for the winding. The window of the form wound conductive coil maybe substantially rows in the longitudinal direction of the strip and entirely with the grain. No such difliculty is present as occurs at the corners of the conventional core construction built up of punched laminations. Air gap reluctance is reduced to a minimum because the turns of the spirally wound magnetic strip closely engage each other, and the area of the air gap between adjacent turns is very large, being the product of the width of the strip by the length of one turn. The length of the magnetic circuit is somewhat reduced, and air gap reluctance is enormously reducedfrom the values inherent in the conventional construction in which the coreis built up of punched laminations.

I am able greatly to reduce the amount of magnetic material as well as the amount of copper over'that required in conventional designs. For example, I have built distribution transformers from 1 to 5 kw'., according to my invention, with approximately one-half of the amount of magnetic material and approximately threequarters the amount of the copper of the conventional punched and laminated construction with the same full load efilciencies and substantially the same magnetizing current.

The following tabulation shows, for example,

results I have obtained in three samples of distribution transformers as compared with corresponding sizes of conventional transformers of standard construction:

5 kva.

My method of assembling the magnetic core on the conductive coils or windings permits form wound coils to be used with the advantages of the simplicity in structure, low cost of manufacture and the reliability incident to form wound coils. Such coils are capable of being wound so as to provide a high space factor. By using a primary coil or coils having a width nearly equal to the inside diameter of the spirally wound magnetic core, and placing two secondary windings of narrower width, one inside and one outside or one on either side of the primary winding or windings, as hereinafter described, so as to give a stepped or cruciform section to the winding structure, I have provided a construction for transformers which has a relatively high space factor, and which lends itself to conventional methods of manufacture, insulation and impregnation.

My method of applying the coiled strip to the should be.

form wound conductive coil is particularly desirable where thin magnetic material is to be used, although it is applicable with many advantages to strip 25 mils in thickness or even thicker strip. A given amount of magnetic material in the form of a very thin strip requires a larger number of turns in the magnetic core than does the same amount of material with a thicker strip, but by my method of winding, the magnetic strip may be so rapidly applied that the increase in the number of turns to be applied causes little difference in the cost of manufacture, whereas if such thin strip were to be used with the conventional punchings it would be difiicult to heat treat and handle them without introducing too great strains in them from serious distortion, and the additional number of pieces to be handled would considerably increase the cost of manufacture. The punching operation introduces strains in all magnetic materials which strains must beremoved by heat treating. When the laminations are very thin they tend to stick together and are very apt to be seriously distorted when separating them after the heat treating operation. By my process, the heat treating operation is carried out as simply with thin strip as with-thick strip, and I have found that the unwinding of the heat treated magnetic coil, and the rewinding it upon the conductive winding actually reduces the losses of the magnetic coil in the completed transformer compared to the tested lossesof the heat treated coil before it has been unwound. This is probably in large part due to the fact that during the heat treating process, the turns stick together more or less at various points and cause short circuiting paths for eddy currents. These adhesions are pulled apart in the unwinding process. It is evident that the completed core is substantially free from strains which would increase losses because tests I have made show that the losses are as good as, and in some cases even better than, those obtained on small Epstein samples which are free from strain.

While I have discussed the application of my invent.on to distribution and other transformers for standard commercial frequencies, it will be apparent to those skilled in the art that it is also applicable to frequencies much higher than standard commercial frequencies. In high frequency transformers and the like using magnetic cores, it is important to use very thin strip material to avoid excessive eddy current losses. The higher the frequency, the thinner the material If, for example, for frequencies from several hundred to several thousand cycles per second a strip of the order of 7 mils in thickness should be desired, such thickness of strip can be very easily used in accordance with my invention. I apprehend no difiiculty in using strip much thinner than 7 mils of exceedingly thin strip is desired. Low magnetic densities are desirable for high frequency applications and in such work it may be desirable to use strip material having a higher resistivity than that of 3% silicon cold rolled strip.

From the foregoing discussion it is believed to be apparent that my invention involves a radical change in the transformer art where for twenty years or more it' has been exceedingly worth while to adopt improvements which have made even small gains. Briefly summarizing the objects and advantages of my invention as applied to distribution transformers, the transformer has a high all-day efiiciency based on present loading practice, the total losses being either equal to or less than those of the present design, resulting in a lower operating cost to the public utilities. The transformers can be made smaller at very appreciable savings, resulting in lower initial investment, and greater return on the investment to the public utilities. The reduction in the weight of the transformer makes it easier to handle in the warehouses and in the field and reduces transportation costs. Better production methods at lower cost are available to the manufacturer and a more uniform product can be made.

My invention will be better understood when considered in connection with the following detailed description and accompanying drawings.

In the drawings, Fig. 1 shows a conductive form wound winding structure such as the winding of a reactor to one leg of which a magnetic core is to be applied; Fig. 2 shows a cylindrical coil of magnetic strip suitable for application to the winding structure shown in Fig. 1; Figs. 3 to 7 inclusive show various stages in the method of applying the magnetic core to the winding structure; Fig. 8 shows the magnetic core completely applied; Fig. 9 shows the first stage in the application of a magnetic core to one leg of a form wound winding structure of a transformer and illustrates one arrangement of the primary and secondary transformer windings; Fig. 10 is a similar view showing a modification of the arrangement of the primary and secondary windings; Fig. 11 is a fragmentary view in perspective illustrating one phase of the operation of applying the magnetic core to a transformer winding structure; Fig. 12 is a view of a similar transformer winding structure with two magnetic cores completely assembled thereon; Fig. 13 is a view in perspective showing suitable mounting means applied to a transformer such as shown in Fig. 12; Fig. 14 is a view of a transformer in which the magnetic core is applied to but one leg of the winding structure; Fig. 15 is a view in perspective with parts broken away showing a machine for automatically applying magnetic cores to a transformer; Fig. 16 is a view taken generally from the left of Fig. 15 indicating means for raising and lowering the means for holding the transformer during the core winding operation; Fig. 17 is a perspective showing of part of the mechanism shown in Fig. 15; Fig, 18 is a view showing a detail of the machine of Fig. 15 and Fig. 19 shows another detail.

Referring to Fig. 1, a form wound conductive winding l0 having a substantially rectangular window II is shown. The right-hand straight leg of this conductive winding is indicated as having been surrounded by cylindrical insulating means l2. Fig. 2 shows a cylinder l3 of thin magnetic strip material spirally wound flatwise with the turns tightly engaging each other, the end of the outside turn being secured to the next underlying turn in any suitable manner as, for example, by being tacked or welded in spots as indicated at H. The cylinder or coil of magnetic strip is represented in the condition that it comes from the heat treating oven. The inside diameter of the cylinder of magnetic strip is the same as the outside diameter of the insulating cylinder. l2 to which it is to be applied.

Fig. 3shows a section of the winding structure of Fig. 1 taken on line 3-3 of Fig. 1, and it shows more clearly one suitable construction of the insulating cylinder 12 in which the cylinder is made up of two semi-circular insulating pieces l5 and I6 held together by a suitable wrapping of tape. The first step in applying the core of Fig. .2 to the winding structure of Fig. l is also shown in Fig. 3. The core I3 is placed over a suitable post or roller I1". The tack welds I4 are loosened up as, for example, by a screw driver, and the end of the strip is carried in a clockwise direction through the window 4 and brought around to form a' fairly large .loop I8, the end of the strip being suitably secured to the next underlying turn by tying or tack weldingit at I9. The loop I8 should be small enough so that the strip may be turned freely without touching the far side of the window, and it should be large enough so that when all of the materialof the coil I3 is wound into the larger loop, the loop may be turned freely without having the inside turn of strip touch the inner side of the window. Ordinarily the number of turns in the large loop will be about half the number of turns in the coil I1. and, in such case, the first turn oi the loop I8 needs to clear the insulating cylinder I2 by a distance only about half the thickness of the layer of turns of the coil I3 shown in Fig. 2. The coil I3 is then rotated together with the large loop I8 which causes the strip to be unwoundfmm the coil I3 and simultaneously rewound into the loop I8, the turns building up successively from the outside in. It will be observed that the direction of curvature of the strip in the large loop I8 is the same as in the coil I3.

Fig. 4 shows a stage in the operation where about half the material of the coil I3 has been wound into the larger loop, and Fig. 5 shows the stage in the operation where all but a fraction of a turn of the coil I3 has been wound into the larger loop I8. It will be observed that by reason of the fact that the loop I8 has a larger diameter than the outside diameter of the coil I3, the number of layers in the large loop is so much less than the number in coil I3 that the large loop may be freely rotated through the window II in the winding structure I without scraping or in any way damaging the insulation on the conductive winding ID, or scraping or 'damaging the insulating cylinder I2. Further rotation of the loop I8 beyond the position shown in Fig. permits the inside turn of the strip to coil about the insulating cylinder I2 which it does by reason of the permanent set which wasimparted to the strip by the heat treatment. The post or roller I1 is then lifted out of the way and the tack weld I9 broken, whereupon the strip collapses to the general shape shown in Fig. '7. By reason of the permanent set imparted by the heat treatment, the coil of strip tends to collapse to the exact physical condition it was in when heat treated, but the friction of the edge of thestrip on the table tends to cause the spiral turns to assume the shape shown in Fig. '7. The operator will then secure the inside turn of the strip to the insulating cylinder I2 and then work the turns of the strip around by hand to close the turns of the strip down into the completed form I3 shown in Fig. 8. Each turn of the magnetic strip in the cylindrical coil now occupies exactly the same position it did when the coil I3 was heat treated. The inside and outside diam- ,eters are the same as they were in the heat treated coil, and the turns are in the same sequence that they were in the heat treated coil.

. The inside turn closely embraces the cylinder I2.

from freely turning through the window II.

along the end of the strip of the heat treated coil and then tightening the turns upon the completion or the winding operation until the end of thestrip lines up with that mark.

High reduction cold rolled silicon steel strip having a silicon content of the order of 3% takes a definite permanent set when heat treated to remove elastic strains, and the elastic character of such strip permits it to be very readily applied by my method oi' winding without bending it beyond the elastic limit. While the strip is in the larger loop II it, of course, contains strains but when the coil is flnally collapsed to its final position in the completed apparatus, such strains are absent. During the winding operation the strip is not distorted in any respect so as to impair its magnetic qualities, and tests made'oi the core in the completed apparatus show that the permeability and watt loss characteristics are as good as those obtained from strain-tree Epstein samples.

The unwinding and rewinding oi. the coil of strip greatly improve the watt loss characteristics over those 01 the coil as it comes from the heat treating oven. This is probably due to the fact that the heat treatment for at least an hour at a temperature oi! about 800 C. to about 900 C. in the heat treating oven produces slight adhesions between the turns of the strip providing short circuiting paths for eddy currents- The unwinding operation separates these adhesions without the slightest difllculty.

The elasticity of high reduction cold rolled 3% silicon strip is such that the large loop ll can be considerably more elliptical than that illustrated in Figs. 3 to 6 without straining the material of the stripbeyond the elastic limit. This quality of the strip may be availed of advantageously where the room available for the loop is limited by the presence of several winding structures around the adjacent legs of which the strip is to be wound simultaneously. For example, if there are three such winding structures spaced 120 degrees apart with their adjacent legs nested together so as substantially to fill the opening in the cylindrical core when applied, it may be necessary to make the large loop somewhat elliptical to prevent its rubbing against the outside portions of the adjacent winding structures. The length of the loop can be varied by adjusting the position 01 the post or roller H to vary the distance between the post and the leg of the conductive winding structure upon which the strip is to be wound. With more brittle strip such as strip containing a high percentage of silicon or with softer strip which cannot be bent so much without exceeding the elastic limit, the loop I8 should be substantially circular and not large enough in diameter to straighten out the strip too much when its curvature changes from that of the original coil to the larger loop. The loop should, however, always be large enough so that the winding operation may be completed without having the number of layers of strip in the loop I8 sufliciently great to prevent the loop By reason of the fact that a greater amount of material may be accommodated in the larger loop with a smaller number of layers, it is possible in accordance with my invention to wind enough strip through the window in the conductive winding so that the strip is collapsed to its final form the number of layers will be sufllcient to flll the window in the winding structure irrespective of whether the cross section of the leg of the winding structure upon which the strip is wound, and the corresponding, inside diameter of the coil of the strip in its heat treated form, is large or small. It is thus possible, in accordance with my invention, to have the conductive winding structure fill the opening in the cylindrical coil and have the core fill the opening in the winding structure permitting an arrangement which gives the minimum length of turn of the conductive winding and the minimum length of path for the magnetic flux produced in the core by the winding and, as heretofore pointed out, the air gap reluctance between turns of the strip is reduced to a minimum, and by having the most favorable magnetic orientation of the grain of the strip in the longitudinal direction of the strip, the exciting current required for any given flux density is kept down by reason of the high permeability of the material and the efiective use of both copper and magnetic material. The economy in the core of magnetic material reduces the total watt loss.

I have referred in the foregoing description to adhesions between turns of the magnetic strip produced in the heat treating oven. The amount of insulation required between turns of the strip is very small. Heat treated coils of strip will ordinarily have, without any special provisions for such insulation, suflicient insulation between turns to keep the'eddy current loss from becoming appreciable if the slight adhesions between the turns referred to are separated during the winding operation. If, however, the magnetic qualities of the strip have been improved by resort to special expedients such as pickling in acid in conjunction with an annealing treatment under deoxidizing or purifying conditions, as pointed out for example in the patent to Ruder 1,648,697, Nov. 7, 1927, it may in some cases be desirable to apply an insulating surface to the strip. A solution such as a chrome silicate solution which will survive the heat treatment can be used. However, with my process of winding it is a simple matter to spray on a very thin insulating coat while the core is being unwound and applied to the winding structure in which case the insulating material does not need to be of a character to survive the heat treatment.

The application of wound strip magnetic cores to transformers may be carried out in accordance with my invention just as simply as the application of such cores to reactors. The form wound winding structure In shown in Fig. 1 may indeed represent either the conductive winding or windings of a reactor or the conductive windings of a transformer. In Fig. 9 I have shown the first step in the application of such a core to a transformer having a conductive winding structure comprising a primary winding 20 and two secondary windings 2-1 and 22, the winding 2| lying outside of the winding 20 and the winding 22 lying inside of the winding 20. The arrangement of these windings more clearly appears from the fragmentary perspective view shown in Fig. 11. The windings 20, 2!, and22 are form wound coils which may be wound, insulated, and, if desired, impregnated, simply, effectively, and inexpensively.

Referring further to Fig. 9, the first stepof applying the coil of magnetic strip 23 to the conductive winding structure of the transformer is illustrated, the stage of the winding operation corresponding to the stage shown in Fig. 3 of applying such a coil of strip to a reactor.- The end of the coil 23 has been brought through the window 24, a large Ioop 25 has been formed and the end of the strip has been secured as by tack welding at 28 to the next underlying turn of the coil 23. This tack welding may be done in various ways, one simple way being to press a carbon; electrode of a welding circuit momentarily against. the strip, preferably holding a small piece of wood or the like under the strip to which the end is to be tacked to facilitate the operation,'the other terminal of the welding circuit leading to the coil of strip. The coil 23 and large loop 25 are then. rotated in the direction shown by the arrow to unwind the coil 23 and rewind the strip into the inside of the larger loop 25 with the large loop passing freely through the window 24. This operation may be carried out manually, as heretofore described in connection with Figs. 3 to 8 inclusive. It may be also carried out automatically, and Fig. 9 illustrates how this may be simply and rapidly done. The roll 21 corresponds to the post or roller ll of Fig. 3, and a similar roll 28 is mounted against the outside surface of the coil 23. By driving the rolls 21 and 28 simultaneously in opposite directions as indicated by the arrows while the roll 21 is pressed toward the roll 28 by a suitable spring mechanism which keeps the rolls 21 ,and 28 in engagement with the inside and outside surfaces of the coil 23, the coil may be unwound forming the loop 25 rests upon a suitable table,

not shown in Fig. 9. To prevent any tendency of the strip to climb up the rollers. 21 and 28 during the winding operation, a roller 3| may be provided which bears on the top edge of the coil of strip 23 and the top edge of the loop of strip 25.

When the coil of strip 23 has all been unwound into the larger loop 25 and the inside end of the coil of strip 23 has curved around the insulating cylinder 32, as heretofore described'in connection with Figs. 5 and 6, the roller 21 is removed and the tack weld 26 broken, whereupon the strip of the large loop 25 assumes the general shape shown in Fig. 7. The inside end of the strip is then clamped to the insulating cylinder 32 as, for example, by the clamp 33 shown in Fig. 11. The strip is then collapsed .to the completed form, as heretofore described in connection with Figs. 7 and 8, and the outside end of thestrip is secured to the next underlying layer of strip in any suitable way, as for example, by tack welding. The clamp 33 is then removed. The conductive winding structure may then be turned around and a similar coil of strip wound on the other leg of the winding structure. Fig. 9 represents a stage of the operation in which a cylindrical coil of strip 34 has already been applied to the other winding leg. It will be observed from Figs. 9 and 11 that the conductive winding structure has a cruciform cross section, the primary winding 20 extending diametrically of the opening in the hollow cylindrical magnetic core while the secondary windings 2| and 22 are narrower than the primary winding 20 andoccupy the spaces left in the opening in the core.

The periphery of the conductive winding structure has a step shaped periphery which generally approximates the circular periphery of the inside of the hollow core. The arrangement, in which the opening in the core is substantially fllled by the conductive windings, provides a high space factor or ratio of net copper cross section to the cross section of the space available forthe conductive wingings, 'only such space being left as is requisite for insulation and circulation of the cooling medium where spaces are desired for such circulation; My invention is not limited to form wound coils of rectangular cross section, as shown in Fig. 11, but such coils are more simply and inexpensively wound than coils of a cross section which would still more completely flll the space available for the conductive windings.

Instead of having the primary and secondary windings located concentrically, as shown in Figs. 9 and 11, they may be located side-by-side, as shown at 20', 2|, and 22', in Fig. 10. This arrangement also provides the desired cruciform or stepped cross section substantially'fllling the opening in the strip wound cylindrical core.

Fig. 12 shows a completed transformer with the primary windings 20, 2i, and 22 arranged as in Fig. 9 and two completed strip wound cores 34 and 35 applied thereto. The tack welds for the outside end of the strip of the core 35 are indicated at 36 in Fig. 12. The width of the magnetic strip may be substantially as great as the length of the window 24 in the winding structure, and the number of turns passing through the window may be sufiicient substantially to hi] the window with magnetic strip.

While a single thin strip of the magnetic material is fairly delicate and subject to injury by distortion, the completed cylindrical cores with the turns tightly engaging each other are rugged.

The completed transformer of Fig. 12 may be very simply provided with mounting means. Fig. 13 shows one form of mounting applied to the transformer of Fig. 12. The mounting shown comprises a pair of channel-shaped members 38 and 39 secured together by strap members 40, M, 42. and 43. These strap members may be welded to the channel member 38 and bolted to the channel member 39, as indicated by the'bolts 44, suitable spacers I! being provided. The upper ends of the strap members 40, ll, 42, and 43 may be provided with lugs and bolt holes for securing the transformer in a tank filled with insulating fluid. Inthe construction shown in Fig.

13, the strap members 40 and 43 are shown as provided with bent-over lugs 46 and 41 provided with oblong holes for securing them in place, and the strap members 4| and 42 are indicated as straight withsuitable circular holes, but it will be understood that the particular arrangement used may be changed as desired.

The transformer of Figs. 12 and 13 is preferably mounted horizontally as shown in Fig. 13 so that the insulating fluid may circulate freely through the spaces between the windings. The channel members 38 and 33 are provided with openings permitting a free circulation of the insulating fluid, two of such. openings being indicated in the channel member 38 at 48 and. Suitable terminal mounting means may be provided. In Fig. 13, an insulating member I is shown forv mounting the high voltage terminals II and I2 of'the primary winding. An insulating member '3 is shown for leading out the con-.

ductors I connected to the-secondary windings.

The secondary windings may be connected in series or parallel, as may be desired.

While I have shown the secondary winding 2| surrounding the primary winding 20 with the winding 20, in turn, surrounding the secondary winding 22 in Figs. 9 and 11 and have shown the secondary windings 2i and 22 located one each side of the primary winding 20 in Fig. 10, it will be understood that my invention in its broader aspects is not limited to any particular arrangement of such windings or to the number ofsuch windings. In some cases, it may be desirable further to divide up the windings. For example, the primary winding 20 may be divided into two windings with a space between to facilitate circulation of the cooling medium, and such an arrangement of windings is shown in Fig. hereinafter described. Where the secondary windings are located alongside the primary winding, as shown in Fig. 10, the best circulation of the cooling medium will ordinarily be attained where the transformer is mounted vertically instead of horizontally as in Fig. 13.

Instead of dividing the magnetic core of the transformer into two cylinders, one wound rm each leg of the transformerras shown in Fig. 12, a single magnetic core wound on only one leg may be provided. Such an arrangement is shown in Fig. 14, wherein the core 55 is mounted on one leg of the winding structure, as in the case of the reactor.- shown in Fig. 1. It will be understood, however, that my invention is not limited to a construction in which the magnetic strip is applied to only one or two of the legs of a conductive winding structure.

In Fig. 15, I have shown one form of machine which I have found very effective for applying strip-wound magnetic cores to winding structures. This machine is disclosed and claimed in my application Serial No. 123,250, filed concurrently herewith, but it is shown and described here in order to show how the transformer and reactors embodying my invention can be made by carrying out the process of my invention automatically.

Fig. 15 shows a transformer comprising two primary windings 50 and two secondary windings 51 and 58 located respectively outside and inside of the primary windings to provide winding legs having a cruciform cross-section, as heretofore described. The completed transformer is shown having two strip-wound magnetic cores 59 and 60 applied thereto. Fla 15 shows that phase in the operation of manufacturing the transformer at which the transformer has been completed and is ready to be lifted out of the machine preparatory to inserting another winding structure to which magnetic cores are to be applied.

The winding structure is clamped in a winding head, In the arrangement illustrated, the winding structure is shown clamped between a lower set of four rollers 6i and four upper rollers 62, which rollers are preferably provided with surfaces of rubber or the like so as not to damage the transformer windings when clamped against them. The rollers 6i are mounted on a member 63 near the bottom of the winding head and the upper rollers 81 are mounted 'on a member 64 near the top of the winding headi. Both of the members 6 3 and 64 are mounted so that they may been wound on one leg of the winding structure,

the winding structure may be turned through 180 degrees to put the other winding leg in position to have the core applied thereto. The winding head comprises a back member 65 having a lower forwardly projecting member 66. for supporting the pivoted member 63 and an upper forwardly projecting member 81 through which a threaded rod 88 operated by a hand-wheel 69 projects for raising and lowering the member 64 pivoted at the lower end of the rod 88. By turning the hand-wheel 69, the member 64 may be moved downwardly to cause the winding structure to be clamped between the lower rollers 6| and the upper rollers 62. A rod I0 biased downwardly by a spring or gravity is provided with a. projection adapted to fit into openings II, one of which openings is provided in each end of the member 04. When the Winding structure has been clamped between the rollers 6| and 62, it is turned about its axis until the projection on the rod I0 fits into one of the openings "II in the member 64, thus holding the winding structure in the position shown in the drawing. Upon'raising the rod 10 slightly, the winding structure can be turned through 180 degrees, whereupon the projection on the rod 10 will enter the opening 'II in the other end of the member 84 and hold the winding structure in its new position.

To remove the transformer from the winding head, it is merely necessary to turn the hand wheel 69 to back off the threaded rod 68 and raise the upper clamping member 64, whereupon the transformer can be lifted out and a new winding structure put in and clamped in place by lowering the clamping member 64. v

The winding structure should then be lowered into the table I2 so that the top surface of the table will be even with the point on the winding structure where the bottom of the cylindrical magnetic core to be applied will come.

To permit of raising and lowering the winding head bodily with the transformer clamped therein, the member 65 is arranged to be moved vertically on the standard I3, as shown more clearly in Fig. 16. In order to guide the member 65 during its movement, rollers I4 and I5, mounted on themember 65, engage the side edges of the standard 13, and rollers 16 mounted on the forwardly projecting member 81 of the member 65 bear on the back of the standard I3. To raise and lower the winding head, means is provided comprising a rack 11 welded to the edge of the plate 65, a pinion I8 engaging the rack and a hand wheel I9 for operating the pinion. The shaft of the pinion 18 and hand wheel 19 is mounted in a bearing on a supporting member 80.

The member is secured to a member I58 hereinafter referred to which is secured to the table 12 but adapted to be adjusted to move the winding head longitudinally of the table as hereinafter described. To hold the member 65 in any position to which it has been adjusted vertically, a dog 8i is arranged to engage the rack TI, and a clamping screw 82 is provided passing through a slot 83 in the standard 13 to clamp the members- 'a pulley 0.

support 81 which may be clamped in any adjusted position by the wing nut 88. The roller 89 for bearing on the top edge of the strip during winding corresponds to the roller 3| of Figs. 9 and 10, this roller being mounted on a shaft 90 which may be clamped in any adjusted position in the member 9| by the set screw 92.

The 21 of Figs. 9 and 10 is shown in Fig. 17, and this roller is removably mounted in a member 94 which is rotatably mounted in a member and driven by suitable gearing, as hereinafter described. The roller 93 is shown with a projecting shaft 96 and a collar 91 provided with a cross pin 98 which fits in slots 99 in the member 94 so that when the roller is placed in position in the member 94 it is rotated by the member 94 through the pin and slot connection.

Assuming that the winding head has been lowered to bring the winding structure into proper position with reference to the table I2 for applicaroller 93 which corresponds to the roller I tion of the magnetic strip core, the coil of strip, as

it comes from the heat treating oven as shown in Fig. 2 for example, is placed on the table I2 and the roller 93 put into place inside the coil so that the rollers 93 and 84 occupy the positions of the rollers 21 and 28 shown in Figs. 9 and 10. In order to bias the roller 93 toward the roller 84 and clamp the coil of strip between these two rollers, the member 95 in which the member 94 is rotatably mounted is supported on rods I00 and IOI sliding through openings which constitute hearings in the table I2. The outer ends of the rods I00, IOI are bolted to a cross piece I02 which slides on guide pin I03 supported in the frame I 04 which is fixed to the table I2. Springs I05 and I06 bearing against the table I2 and the cross piece I02 bias the roller 93 toward the roller 84.

Preliminary to placing the coil of magnetic strip on the table, the operator moves the member 95 against the bias of the springs I05 and I06 by lifting up on the lever I01, which liftin movement moves the crank I08 downwardly the end of this crank being secured to the cross piece I02 by a flexible rope or chain I09 passing over The pawl II I engaging teeth on the member II2 mounted on the shaft carrying the lever I01 and crank I08 holds the cross piece 95 against the bias of the springs. Theroller 93 may then be readily mounted in the member 94, and the coil of magnetic strip placed on the table over the roller 93. The operator then lifts up slightly on the lever I01 and releases the pawl I II and permits the springs I05 and I08 to press the roller 93 against the inside of the coil of magnetic strip, the outside of which is pressed against the roller 84. The end of the coil of magnetic strip is then loosened up and carried through the window of the' winding structure and brought around in the relatively large loop and tack welded to the next underlying turn 01' the coil of magnetic strip, as described in connection with Fig. 3 and also in connection with Figs. 9 and 10.

As heretofore described, the rollers 88 and 84 are driven to unwind the strip from the heat treated coil and rewind it into the larger loop, winding from the outside in as described in connection with Figs. 3 to 6. To drive the rollers 98 and 84, amotor II3 is provided operating through'suitable pulleys and a belt H4 to drive the shaft II5 shown in Figs. 15 and 17. As shown in Fig. 15, the drive is through beveled gears II! 76 and a shifting clutch IIl controlled by a foot lever "I I0.

As shown more clearly in Fig. 1'7, a gear H0 is secured to the upper end of shaft H0 and this gear drives a pinion I20 which turns the roller 04. The pinion I20 also drives the gears I2I and I22 which in turn drive the pinion I20 which turns the member 94 and roller 90. The rollers 04 and 00 turn in opposite directions. The shaft of the gear I2I is fixed, but the gear I22 is floatingly mounted between members pivoted about the axes of the gear I2I and pinion I20, the two upper members being shown at I24 and I20. These members or links, two of which are shown at I24 and I20, are pivoted to each other and support the gear I22. This arrangement permits the gearing to remain in mesh notwithstanding the horizontal movement of the member 90 heretofore described.

In order to permit the winding structure of the transformer to be lowered into the table 12 and raised-therefrom, an opening is provided in the table, and to prevent any difficulty from the coil of strip or any part of it going into this opening, a removable member I20 may be set into the opening with its top surface level with the top of the table 12. The position of this member I20 in the opening may be adjusted and its proper position in the opening may be determined by the position of a 'stud screwed into the member I20 and locked in the desired position by the nut The step of collapsing the turns from the position shown in Fig. '1 to the position shown in Fig. 8 has been heretofore described as carried out manually. In Fig. 15, however, I show mechanism for carrying out this step automatically which I have found operates very successfully.

This is accomplished in the machine shown in Fig. 15 by rotating rollers I29 and I29 havingfriction surfaces of rubber or the like, which rollers are moved manually to bear against the sides of the large loop when it is in the stage of operation shown in Fig. 7. The rotation of these rollers rapidly collapses the loop and as the size of the loop decreases, the rollers are moved inwardly until the coil assumes its completed shape, after which the rollers are moved out of the way and the outer end of the magnetic strip tackwelded in place, as heretofore described. The rollers I20 and I29 are respectively mounted at the ends of pivoted supporting arms I00 and IOI, the pivot for the arm I00 being shown at I02. To drive the rollers I20 and I29, belts I00 and I04 are provided opera ng on suitable pulleys. The pulleys at the pivo (1 ends of the arms I00 and IOI are mounted on vertical shafts, one of which is shown at I00, and driven through bevel gears, one set of which is shown at I04. These bevel gears are located at theends of shafts I00 and I00. The shaft 100 is driven through bevel gears I01 from the shaft.i00 which is operated by a bevel pinion I09 engaging the bevel gear I40 on the shaft IIO, shown in Fig. 17. The-shaft I00, also shown in Fig. 17, is driven by the bevel gear I40 through the bevel pinion I. The rollers I20 and I29 are driven with the same direction of r'oitation. In consequence, the points of tangency th the coil of magnetic strip have opposite directions of linear motion and cause the layers of magnetic strip to be wrapped around the winding-structure in much the same manner as occurs when an operator twists the coil manually by the aid of the friction between his hands and 10 theouterlayergfthecoil. Theeflectistoclose does not ?ppear in Fig. 15, turns the member I44 about ts pivot I40. One end of the member I44 is connected through means I40, which will be more clearly described hereinafter in connection with Fig. 19, to a member I" rigidly secured to the supporting arm for the roller I20 so that upon moving the lever I42 and turning the member I44, the member I40 moves the roller I20 about the pivot I02. A member I40, like the member I40, moves the support for the roller I29 about its pivot. It will be apparent that the rollers I29 and I20 may be moved toward each other to close up the loop of strip while still being driven rotatably. In order to ensure that the rollers I20 and I20 engage the loop gently and to assist the operator in keeping the rollers in engagement with the loop while it is being collapsed, the members I40 and I40 are constructed as shown in Fig. 19. The member I40 for example comprises an outer cylinder I40 and. a plunger I40. The plunger I40 is pivotally secured to the member I44 and the cylinder I40 is pivotally secured to the member I41, which in turn is attached rigidly to the under portion (not visible in the drawing) of the roller-supporting arm I00. A spring I00 located in the cylinder provides a yielding pressure on the roller I20 on the loop of strip. In order to limit the movement of the plunger I49 in the cylinder I40, a slot IOI is provided in thecylinder and a pin I02 engaging the slot extends through the plunger I49. The result is a kind of springpr'essed yielding dash-pot connection in which the movement of the plunger in the cylinder is limited by the length of the slot. The member I40 likewise provides a yielding pressure on the roller I29. be used for applying the strip wound core to a winding structure in which the core is applied to either one or both legs of the winding structure. If it is used for applying such cores to both legs, after one core has been applied the winding structure is raised out of the opening in the table 12 by operating the hand wheel 19. The rod 10 is slightly raised lifting the projection out of the hole in the end of the member 04, and the winding structure is turned through 180 as heretofore described, whereupon the projection on the rod I0 will engage the other opening 'II of the member 04 after which the winding structure is moved to the lower position and the other magnetic core applied.

To accommodate various types and sizes of winding structures it is desirable to have the winding head movable longitudinally of the table to vary the distance between the leg to be wound and the roller 90. To accomplish this longitudinal movement a hand wheel I00 is provided tuming a pinion I04 which engages the rack I00 secured to the member I00 which slides on the top of the table 12. Another member I0! is provided which slides on the bottom surface of the table 12. A clamping screw I00 is provided which is loosened up when it is desired to adjust the longitudinal position of the winding head and which is tightened up to clamp the table I2 between the members I00 and I01 in the adiusted position. Since the transformer is heavy and its weight is all in front" of the plate 00.'

forwardly causing the parts I56 and I5I to bind on the table I2. To prevent this binding which would interfere with ready longitudinal movement, a member I59 is bolted or otherwise secured to the standard I3 and member I56, which member I59 has a pair of forward projections I60, one of which is shown in Fig. 15. On the forward ends of these projections rollers are mounted, one of which is shown at I6I in Fig. 15. These rollers bear on track members, one of which is shown at I62 in Fig. 15, which are in turn mounted on the supporting plate I63 which also supports the table I2 and various parts of the machine heretofore described.

' As I have pointed out in the foregoing description, the form wound conductive winding structures may be impregnated with suitable insulating compound and. the magnetic cores wound thereon after such impregnation. If this practice is followed, it is relatively easy to remove such cores if it becomes necessary to do so. While the magnetic strip material preferably substantially fills the window in the conductive winding structure in transformers such as distribution transformers, a space of about inch will usually be left, and this is sufficient to permit loosening up the coil of magnetic strip sufficiently to permit its turning about the leg of the winding structure to which it has been applied. It is merely necessary to loosen up the tack welds holding the outer end of the strip and loosen up the turns by pressing on the sides of the strip and imparting a turning movement in a direction to unwind the strip. In this way, a slight clearance may be produced between the inside turn and the insulation on the winding leg, after which the end of the inside turn is tack welded to the next adjacent outer turn at the edge of the strip. The outside end of the strip may then be placed around a mandrel and unwound from the winding structure about which the cylinderof magnetic strip turns, the tack welding of the inside turn preventing the closing up of the coil of strip to grip the leg upon which it turns. The winding of the strip onto the mandrel will produce a coil of strip, the turns of which will have a sequence opposite to that which existed in the coil of strip on the apparatus. This permanent- 1y impairs the magnetic qualities of the strip which must be again heat treated if its original condition is to be restored. If the impregnation of transformers, reactors, and the like, is carried out after they have been completely wound, it is much more diificult to remove the magnetic strip, and after it has been removed it is likely to have no value above its scrap value.

While I have shown particular forms of electromagnetic induction apparatus embodying my invention and have illustrated a particular mechanism for practicing my process, it will be apparent to those skilled it the art that many changes and modifications may be made without departing from the spirit and scope of my invention and I aim in the appended claims to cover such changes and modifications.

I use the expression form-wound, as applied to electrical coils, to denote the type of coil which is wound on a former or winding-form, taped or otherwise insulated, and usually impregnated, and which, usually assembled with other such coils in the form of a coil assembly, is thereafter combined with a magnetic core, as distinguished, for example, from the type of coils,

75- known as -core woundf coils, produced by winding electrical conductors on a previously assembled part (or whole) of a magnetic core.

The term unwinding as used herein does not refer to a mere progressive separation of the turns of the coil, such as occurs, for example, when one passes a needle between the turns of the hair spring of a watch. Such an operation does not destroy the identity of the coil. I use the terms unwinding and rewinding to refer to true unwinding and rewinding operations, in which during the unwinding the turns are progressively removed from a coil, and in which during the rewinding the turns are formed into a new and different coil. Such an operation necessarily and inherently involves that the new coil has either an axis or a diameter different from that of the original coil.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. Electromagnetic induction apparatus comprising a conductive winding of the form wound type and having a leg which is straight for substantially the length of the window of the conductive winding, and a magnetic core substantially filling said window and composed of thin magnetic strip material including a length 01' strip wound flatwise spirally many times around said leg, the inside surface of said magnetic core closely embracing said leg so that the cross section of the conductive winding in said leg bears a high ratio to the cross sectional area of the opening in said core, the turns of said length of strip nesting tightly within one another, said strip having the most favorable magnetic orientation of the grain of the material in the longitudinal direction of the strip and said core being characterized by substantial freedom from elastic strains which would impair the magnetic characteristics of the material.

- 2. Electromagnetic induction apparatus comprising a conductive winding of the form wound type, a magnetic core for said conductive winding comprising a cylindrical core element passing through the window of said conductive winding and composed of thin magnetic strip material tation or the grain of the material, the spiral turns of said cylindrical core element tightly engaging each other to reduce air gap reluctance, the permeability and watt loss characteristics of said completed cylindrical core element at any given magnetic density and frequency being substantially as good within the limits of error as those of strain-free Epstein samples of the same material cut in the direction of the most favorable magnetic orientation of the grain of the material and tested by present standard methods of measurement of such samples.

3. Electromagnetic induction apparatus comprising a conductive winding of the form wound type, and core means comprising magnetic strip material substantially filling the window in said conductive winding so that the cross section of said core means is substantially the same as the opening in said cylindrical core and arranged cross section of the space available for said core means, said core means comprising spirally wound thin flat strip the spiral turns of said strip nesting within each other and closely engaging each other to reduce air gap reluctance between the turns, the most favorable magnetic orientation of the grain of the material being in the longitudinal direction of the strip so that the magnetic flux will be in the direction of the most favorable magnetic orientation of the grain, said material having at least substantially as high permeability and substantially as low watt loss characteristics as high reduction cold rolled 14 mil steel strip containing.3% silicon, and the inside turn of the spiral closely embracing the side of the insulated conductive coil so that in the completed apparatus the side of the conductive winding located in the opening through which it passes in the spirally wound core substantially fllls such opening to provide a high space factor, the material of said strip in the completed apparatus being substantially free from elastic strains, whereby for any given emclency and any given magnetiflng current and at any desired flux density less magnetic material and copper are required than for constructions of the same kva and voltage rating built up'of laminations punched from either high reduction cold rolled 3 to 3 silicon strip or hot rolled 3 to ti /2% silicon sheet and whereby with a substantial reduction in the amount of magnetic material and copper and at flux densities of the order of 15,000 gausses an efllciency substantially the same as that obtainable in such built-up constructions of such cold rolled or such hot rolled material may be obtained with little or no increase in magnetizing current over that required in such built-up constructions for the same kva and voltage rating at flux densities therein of the order of 12,000 to 13,000 gausses.

4. Electromagnetic induction apparatus comprising a conductive winding and a magnetic core of thin magnetic strip material wound flatwise spirally into. the form of a hollow cylinder with the turns of the spiral tightly engaging each other, said core being free from adhesions between turns which would provide short circuiting paths for eddy currents, the material of said strip being characterized by a permanent set due to heat treatment, said completed core being characterlzed by the same permeability and watt loss characteristics as would characterize a cylinder of the same strip material which had been made by winding said strip material into a cylinder having the same size and same sequence oi turns and heat treating it to give it a permanent set and then unwinding said cylinder and rewinding it into a cylinder of the same size having the same sequence of turns withoutdistorting it beyond the elastic limit, said strip material being characterized by the fact that it has an elasticity when set by heat treatment sufllcient to permit such unwinding after heat treatment into a loop of sufliciently larger diameter than the outside diameter of said cylinder when heat treated to accommodate all of the strip material with about hali the number of turns nesting within each other in such larger loop without introducing strains sufhcient to impair the permanent set or the magnetic qualities of the strip material, the turns in said core .r. the completed apparatus being in the position which they tend to assume by reason of the permanent set due to the heat treatment, the turns of said conductive winding passing through and substantially filling. the

when excited to produce a magnetic flux in the longitudinal direction of the magnetic strip.

5. A transformer having a magnetic core composed of high reduction cold rolled silicon steel strip having a silicon content of about 3% and of a thickness not exceeding 14 mils, said core being in the form of a hollow cylinder the length of which is equal to the width of the strip, the strip being coiled spirally flatwise with the turns closely engaging each other, and a winding structure comprising primary and secondary windings passing through the opening in said cylinder and substantially filling the same to produce a magnetic flux flowing longitudinally of saidstrip, the most favorable magnetic orientation of the grain of said strip being in the direction of the length of the strip, the permeability and watt loss characteristics of said core being substantially the same as in a cylindrical core of the same strip material which has been wound tightly to the same inside and outside diameter and heat treated to eliminate elastic strains and then unwound and rewound into a cylinder of the same inside and outside diameter with the turns in the same sequence without introducing strains sufllcient to impair either the permeability or the watt loss characteristics of the material.

6. An electromagnetic induction apparatus comprising a conductive winding structure of the form-wound type and a strip of magnetic material passing flatwise in closely superposed turns many times around and closely embracing and interlinking said winding structure, said strip having the most favorable magnetic orientation of its grain substantially in the longitudinal direction of the strip, and being characterized by substantial freedom from adhesions between turns to minimize eddy current loss, and by substantial freedom from eflects of strain beyond the elastic limit, and also from elastic strain sufllcient substantiallyto impair the magnetic characteristics of the material.

'7. An electromagnetic induction apparatus having a ccnductive'winding structure and a core element consisting of 'a coil of thin highreduction, cold-rolled magnetic strip free from strains below the elastic limit, wound many times flatwise around and closely embracing and interlinking the winding structure and having the most favorable magnetic orientation of its grain substantially in the direction in which it is wound, the magnetic qualities of which strip have been improved by heat treatment prior to the winding operation, and which .has been wound in place after the last heat treatment in such manner as not to produce such bending or distortion as substantially to injure its magnetic qualities by strains above the elastic limit.

8. A transformer having a magnetic core element composed of high-reduction cold-rolled silicon steel strip having a silicon content of about, 3% and of a thickness not exceeding about 14 mils, said core element being in the form of a hollow cylinder the length of which is equal to the width of the strip, the strip being coiled spirally flatwise with the turns radially supersaid strip being in the direction of the length of the strip, the permeability and watt loss characterlstics of said core element being substantially the same as in a cylindrical core element of the same strip material which has been wound tightly to the same inside and outside diameter and heat treated to eliminate elastic strains and then unwound and rewound into a cylinder of the same inside and outside diameter with the turns in the same sequence without introducing strains sufficient to impair the permeability and watt loss characteristics of the material.

9. Electromagnetic induction apparatus comprising, a magnetic core of thin magnetic strip material wound flatwise spirally into the form of a hollow cylinder with the turns radially superposed and a conductive winding having turns passing through the opening in said core and arranged, when excited, to produce a magnetic flux in the longitudinal direction of the magnetic strip, the material of said strip being characterized by a permanent set due to heat treatment and having its most favorable magnetic properties with a direction of magnetic flux along the length of the strip, said core being substantially free of adhesions between turns which would provide short-circuiting paths for eddy currents and being substantially strain free, having its turns occupying the positions which they tend to assume by virtue of the permanent set of the material due to said heat treatment.

10. Electromagnetic induction apparatus comprising, a magnetic core of thin magnetic strip material wound flatwise spirally into the form of a hollow cylinder with the turns closely engaging each other and a conductive winding having turns passing through the opening in said core and arranged, when excited, to produce a magnetic flux in the longitudinal direction of the magnetic strip, said strip being composed of high-reduction cold-rolled silicon steel characterized by a permanent set due to heat treat ment and having its most favorable magnetic properties in the longitudinal direction of the strip, said core being substantially free of elastic strain and having its turns occupying the positions which they tend to assume by virtue of the permanent set of the material.

11. The method of producing an assembled magnetic core and winding, said method including the steps of winding a strip of magnetic sheet material into a coil, passing the outer end of said coil through the winding and securing it to the outer surface of the coil to form a loop around one side of the winding, and rotating the coil to unwind it and simultaneously rewind it around one side of the winding.

12. The method of producing an assembled magnetic core and winding, said method including the steps of winding a strip of magnetic sheet mate ial into a coil, passing the outer end of said coil through the winding and securing it to the outer surface of the coil to form a loop around one side of the winding, rotating the coil to unwind it and simultaneously rewind it around one side of the winding, detaching the outer end of the coil from the outer surface thereof, and tightening the rewound strip into a compact cylinder.

13. The method of assembling a wound core on a form wound winding structure comprising the steps of heat treating a flatwise spirally wound coil of magnetic strip material, the turns of which tightly engage each other and the inside diameter of which is equal to the maximum diameter of the portion of the winding structure to which it is to be applied, to improve the magnetic qualities of the strip and give it a permanent set, threading the outer end of said magnetic strip through the window of the winding structure and forming a loop larger in diameter than the outside diameter of said heat treated coil and then rotating the coil and 1001) while maintaining the end of the strip in substantially fixed relation to the next underlying strip to unwind the coil into the inside of the loop, said loop being of such size that the material of said strip is not strained beyond the elastic limit and large enough to permit it to move freely through the window in the winding structure when all of the material has been wound into the larger loop, and then collapsing said loop upon the winding structure so that the completed core will have the same dimensions as the coil had during heat treatment and the turns in the completed core will have the same sequence as in the heat treated coil.

14. The method of producing an assembled magnetic core and winding, said method comprising the steps of unwinding a flatwise spirally wound coil of radially superposed turns of magnetic strip material, simultaneously rewinding said strip around one side of said winding into a loop large enough to avoid binding on the winding sufficient to damage the winding or the strip and then collapsing said loop upon the winding so that the completed core thus formed will have substantially the same size as the origi nal coil and will have the turns in the same sequence.

15. The method of producing an assembled magnetic core and winding, said method comprising the steps of winding a strip of magnetic sheet material flatwise into a coil of radially superposed turns, winding said coil around one side of said winding into a coil large enough to avoid binding on the winding suflicient to damage the winding or the strip and tightening said coil to its original diameter.

16. The method of applying a flatwise spirally wound heat treated coil of magnetic material to a winding structure which comprises passing the outer end of said coil through the winding structure and back to the coil to form a loop around one side of the winding structure, rotating the coil to unwind it and simultaneously rewind it around one side of the winding structure, securing the inner end of the rewound coil to the winding structure and collapsing the turns of said rewound coil to form a compact magnetic core tightly surrounding the side of the winding structure to which it has been applied, the turns of the completed core being in the same sequence as in the heat treated coil and the inside and outside diameters of the core being substantially the same as in the heat treated coil.

17. The method of producing an assembled magnetic core and winding structure comprising the steps of winding a strip of magnetic sheet material flatwise into a coil, passing the outer end of said coil through the winding structure and back to the'coil to form a loop around one side of the winding structure, rotating the coil to rewind it around one side of the winding structure, securing the end of the rewound strip againstgmotion relatively to the winding structure, and tightening said coil to form a compact magnetic core tightly surrounding the side of the winding structure.

18. The method of applying a coil of flatwise spirally wound magnetic strip material to a leg of a conductive winding structure which comprises relatively moving the coil and winding structure so as progressively to link the convolutions of said coil around said leg and transfer said leg from the outside to the inside ofsaid coil while maintaining sufllcient space between said leg and said strip to permit of free movement of said leg from the exterior to the interior of said coil without contact between said strip and said leg.

19. The method oi producing an assembled magnetic core and winding, said method including the steps of winding a strip of magnetic sheet material into a coil of many superposed turns one outside the other, unwinding the strip from said coil and simultaneously rewinding it around one side of the winding with the turns in the same sequence as in the coil, maintaining during the operation a clearance between the strip and the winding.

20. Themethod of producing an assembled magnetic core and winding, said method including the steps of winding a strip of magnetic sheet material into a coil of many superposed turns one outside the other, unwinding the strip from said coil and simultaneously rewinding it about one side of the winding and the axis of the coil, maintaining during the operation a clearance between the strip and the winding and tightening the rewound strip into a compact cylinder.

21. The method 01 iorming a core for an electromagnetic induction apparatus comprising an electrical coil assembly and a core of thin strip material'having a pronounced favorable magnetic orientation longitudinally of the strip, which method comprises winding the strip flatwise into a coil of many turns, one above the other, heat treating the resulting coil to produce high permeability and a permanent set, unwinding the strip to break up adhesions and rewinding the strip so as to interlink it with the eiectrical coil assembly, keeping the bending action during unwinding and rewindlng always below that valuewhich would strain the strip beyond the elastic limit of the material, and so conducting the rewinding operation that the resulting final coil will be of the same size which it had when it was heat treated, whereby elastic strains in the rewound coil of strip are eliminated.

22. A transformer comprising a conductive winding including primary and secondary coils of the form-wound type and a magnetic core substantially filling the opening in the conductive winding, said core comprising a magnetic core element in the form of a spirally wound roll containing many turns of strip material characterized by a permanent set due to heat treatment, said turns nesting flatwise tightly within one another, each turn being of substantially the size which it tends to assume because of the permanent set of the material due to heat treatment, said turns passing many times through the opening in the conductive winding, said conductive winding substantially filling the opening in said roll and adapted to produce a magnetic flux flowing longitudinally of said strip.

Joan c. GRANFIELD.

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