US1984277A - Transformer and transformer device - Google Patents

Description

Dec. 11, 1934. M. MORRISON 1,984,277

TRANSFORMER AND TRANSFORMER DEVICE Original Filed Oct. 18, 1923 4 Sheets-Sheet 1 Dec. 11, 1934. MORRISON 1,984,277

TRANSFORMER AND TRANSFORMER DEVICE Original Filed Oct. 18, 1923 4 Sheets-Sheet 2 Dec. 11, 1934 M MORRISON 1,984,277

TRANSFORMER AND TRANSFORMER DEVICE Original Filed Oct. 18, 1923 4 Sheets-Sheet 5 Dec. ll, 1934. I ON 1,984,277

TRANSFORMER AND TRANSFORMER DEVICE Original Filed Oct. 18, 1923 4 Sheets-Sheet 4 Z 7ZUe/ZZZX1 Patented Dec. 11, 1934 TRANSFORMER AND TRANSFORMER DEVICE Montlord Morrison, Montclair, N. J assignor, by mesne assignments, to Westinghouse X-Ray Company, Inc., a corporation of Delaware Application October 18, 1923, Serial No. 669,315 Renewed December 27, 1933 4 Claims. (Cl. 250-34 My present invention relates to electrical induction apparatus, such as transformers and the like, and has for its general object an improved construction which is more permanent in opera- 5 tion, requires less attention, and and is more efficient in some respects and for some particular applications than those of the prior art.

More specifically my invention relates to high voltage transformers and in particular those in which liquid dielectric is not necessary.

Among the specific objects of my invention are: first, to provide a generally improved construction for the core and coils of high voltage transformers; second, to provide a high voltage transformer which does not require oil or other liquid insulating medium and at the same time maintain comparatively small physical dimensions; third, to provide a high voltage transformer in which the dielectric losses are substantially reduced; fourth, to provide a high voltage transformer which is comparatively light in weight and small in size for a given kilovolt rating; fifth, to provide a high voltage transformer which is substantially free from the several difiiculties encountered with the maintenance and operation of transformers employing liquid dielectrics and liquid cooling mediums; further and other objects will be in part pointed out and in part obvious to those skilled in the art to which my invention appertains, upon digesting following specifications and studying the drawings herein referred to.

I attain these objects by the construction disclosed in the accompanying drawings which illustrate one practical embodiment of my invention.

In the said drawings Fig, 1 is a view part in section and part in elevation, showing a typical internal construction and a diagram of connections of my invention, as applied to the construction of an X-ray apparatus; Fig. 2 is a view of Fig. 1, partly in section and partly in elevation drawn on a larger scale, taken at right angles to the plane of the paper, along a line through ab, with the case and holding device removed, and

' showing the windings and related parts; Fig 3 and in general how it may be used.

This invention may be considered as a developed detail of my Patent 1,466,541, issued August 28, 1923, and in part related to my applications Serial Numbers 476,155 filed June 9,

540,141 filed March 1, 1922, 559,569 filed May 9, 1922, 566,961 filed June 9, 1922, 633,712 filed April 21, 1923, and in the present case I show a novel embodiment as illustrative of a scope of my invention.

In my improvement I provide a construction which does not require liquid insulating medium, though it may be used to advantage in some cases. I employ in the construction of my core, coils and mechanical parts, not the use of improved insulation by means of internal, physical or chemical purification of the dielectric material, but surface characteristic means for not only improving its instantaneous break down strength, but also substantiallyeliminating certain deterioration thereof in some cases, as will be hereinafter referred to. My surface characteristic means equalizes and reduces the maximum dielectric stresses between the several parts, and thereby I am able to reduce the said dielectric stresses sufiiciently to not require an insulating medium with a dielectric strength greater than air in some cases, and in which cases the oil or other liquid may be eliminated. By the utilization of air as a dielectric, especially in the case of a sealed container, such as I employ in some embodiments of my invention, the deterioration of the insulating medium is substantially absent and its dielectric strength remains constant. By

the utliization of the aforesaid means for reducing dielectric field stresses in my trans former, I obviously reduce the dielectric field losses in any case, and by the elimination of solid and liquid dielectrics I further reduce these said losses, and in the substantial absence of corona during the operation of my device I practically eliminate all dielectric losses due to the high voltages. By the further extension of the aforesaid surface characteristic means for reducing the dielectric field stresses, I may so influence the said dielectric field about the high voltage coils as to greatly improve its operation. It will be appreciated that in high voltage transformers and especially in small ones employing small wire, that the said wire is subject to considerable corona discharge, even to spark over in some cases.

In Fig. 1, 1 is the separated aspect of the modified form of the E-punchings of the shell-type transformer core which I employ, in the illustrated embodiment of my invention, the outline of the laminations of which core will be better understood upon reference to Fig. 2; the punchings in this view having the general form of the common E-punchings, with preferably staggered separation lines on the outer legs at 2 and 3, and some suitable lapping method for the internal leg at 4.

It will be observed that the internal leg shown herein is that of a common two-step form such as to give it a generally approximate circular cross section. Several different punching outlines are utilized to give generally rounded surfaces at 5, 6, 'Z and 8 of Fig. 2, and slightly curved or fairly straight surfaces at 9, 10, Figs. 1 and 2.

The magnetic circuit of my device comprising the material and direction represented by the 1711, the circuit being substantially closed magnetically.

With the difference of scale between Figs. 1 and 2 in mind, the several numbered parts and points of Fig. 2 will be obvious in Fig. 1 to those skilled in the art to which my invention appertains.

In Fig. 2 the rectangular cross sectioned parts 18 represent the low voltage winding, rectangular conductors being common practice for such application. The three layers {o f low voltage winding illustrated in Fig. 2 at 18 are represented by the three concentric circles indexed by the same numeral in Fig. 1.

The terminals of this said low voltage Winding are shown diagrammatically connected to leads 19 and 20, Fig. 1, which are supplied with electrical energy from potential source 21, and the circuit of which low voltage winding may be supplied with a switch 22 for practical purposes. This completes the low voltage circuit of the embodiment of my device herein shown, and with the properly engineered details my device may be thus far considered as supplied with primary energy in the form of a substantial periodically varying flux in the aforementioned magnetic circuit.

In order to obtain output energy from my device I provide secondary coil 23', Fig. 2, which is novel in construction.

Common to devices of this class I provide conductors 24, with suitable insulation between adja cent turns and'adjacent layers, such as some nonconductor material on the surface of the wire, mechanical spacing of the wire and in some cases solid insulation such as 25, between layers.

The high voltage winding thus far is not necessarily different from common practice, and in the particular embodiment shown has its first internal turn connected to the mechanical part 26, Fig. 2, and to the core of my device, which is illustrated diagrammatically in Fig; 1 by the numeral 27. The last external convolution of the said'high voltage coil is connected to the mechanical part 28 of Fig. 2, the parts 26'and 28 serving as terminals, so to speak,of the highvoltagewinding. Mechanical parts 26 and 28 are substantially devoid of points and edges and are surface'characteristic means for influencing.theelectrostatic field in and about the said high voltage winding, such as to considerably reduce the maximum di* electric stress which would otherwise be present in certain parts of my'device, and which behavior will be more fully hereinafter described.

In Fig. 1, mechanical parts 26 and 28 are recognized by identical numerals, and are split at and 76 to prevent their becoming a short-circuited turn of the windings. Over and about the high voltage winding is formed a casing 29, Fig. 1, which casing fits into the magnetic core and about the highvoltage winding of my illustrated embodiment in such a 'way' and possesses such form with particular -where the said points and surfaces might influence the electrostatic field distribution in and about the high voltage winding of the device.

Mechanically the casing 29 may be formed of two parts, parted at the line 30 and welded at 31 and 32 to combination core-clamps and casing supports 33 and 34, which by means of rivets 35 and thelike, Figs. 1 and 2, support the said casing in its fixed position and simultaneously clamp the core in its working form.

The electrical operating characteristics of my invention can bebetter understood by'reierence to Fig. 3,'in which I have eliminated substantially all parts of the described embodiment of my invention with the exception of those esssential to the understanding of the electric circuits involved. l

- In Fig. 3, parts corresponding to those in the other figures are given identical numbers. Certain parts of the electrostatic shielding have been removed for clearness as theseare fully illustratedin the other figures. In Fig. 3, the alternating current generated by alternator 21 is fed through switch 22 by leads 19 and 20 to the primary coil .18, thus completing the primary circuit. Alternator lead 20 is connected at 78 to toroid 26, which in turn is connected at 79 to the inside terminal of secondary coil 80. The outer terminal of secondary coil 80 is connected at 31 to the toroidal shell 28, which in turn is connected ate l to the anode 39 of the X-ray tube used in the present embodiment.

Lead 62 connectswith terminal 61, which, by means of lead 53, supplies exciting current for the filament 52, which circuit is completed through lead 51, terminal 60, lead 63, switch 64 and lead 65, through transformer 66, the primary 82 of which is electrically connected to alternator 21' so that energysupplied by alternator 21 also supplies transformer 66, stepping the voltage down to a value suitable for filament 52.

It will be appreciated by those familiar with the art to which my invention appertains, that by the circuits just described, the high potential of the secondary 86 is impressed between the filament 52 and the anode 39 of the X-ray tube.

I have shown a small amount of the electrostatic shield 29 connected to lead 20 and grounded, though it will be appreciated that actually connecting this electrostatic ground to earth is not an essential part of my invention, the only requirementbeing that it be operated very close to ground potential. In actuality it is not always possible to operate this shield actly. at ground potential because of the various groundings met with in practice. It will be further appreciated that since the operating voltage of secondary coil 80 is .ofthe magnitude of l0,00) volts, that so long as my shielding is only a small percentage of this 40,000 volts, above ground, that my device is an operative one from a practical standpoint, so that in my claims where the expression means at substantially ground potential occurs, this expression, is used to limit the operative voltage above ground of the part, to a small fraction of that of the transformer secondary. A small fraction bearing the significance of something of the order of 1%.

The term electrpstatic ground shield is used to define an electrically conducting element in my invention interposed physically between the high voltage winding and ground, for the purpose of influencing the electrostatic field distribution included between the said high voltage winding and the said shield.

It will be appreciated by those familiar with the art that by such construction I greatly increase the dielectric strength of the air in and about the high voltage winding, greatly in excess of what would be its value in the absence of my invention. It will be borne in mind that the looped ends of mechanical parts 26 and 28 are in reality complete approximate toroids and the voltage gradient characteristic of these parts, and hence the dielectric stress between them does not follow the law of spherical electrodes, which might be suggested from an inspection of the drawing, but that of concentric cylinders which gives factors of insulation for given spacings greatly in excess of that expected by the sole familiarity with, for instance, sphere-gap sparkover characteristics. This will be apparent upon reflection and consideration of the fact that the electrostatic field between spheres or spheroids is necessarily largely concentrated between the most adjacent surface of the two spheres, whereas in the case of concentric cylinders there is no such thing. That is, all of the surface involved in the electrostatic field distribution is at equidistant points, so to speak, which has the effect of equalizing the stress instead of concentrating it. For instance, in the case of a sphere having a diameter equal to the diameter of the loop the mechanical part 26, and spaced a distance equal to the minimum spacing between parts 26 and 28, from. a second sphere of equal diameter will withstand only up to 30 kilovolts before spark over occurs, whereas two concentric cylinders one of a diameter equal to the maximum diameter of 26, and the other equal to the minimum diameter of 28, would be able to withstand kilovolts before spark over occurs, showing an insulation strength of one and one-half times as much, accomplished by the surface characteristic means employed in my device.

In general, Fig. 2 may be regarded as an operative design drawn to scale in so far as the core shape and physical outline of the high and low voltage windings are concerned, and in so far as the surface characteristic means of influencing the electrostatic field distribution is concerned. Of course the size of the conductors in the windings illustrated are greatly enlarged in size and their numbers are extensively reduced for the sake of clearness.

The external surfaces of mechanical part 28 when considered with reference to the inner surface of casing 29, Fig. 1, substantially present concentric cylinder electrostatic-field distribution-characteristics, and by properly and carefully employing the surface characteristic means of insulating a transformer, such a design as illustrated and drawn to full scale in Fig. 2, permits of the very unexpected and non-obvious result of being able to operate at 40,000 volts for some practical applications, one of which will now be described in detail.

Referring to Fig. 1, onto mechanical part 28,

is fixed a modified form of a common lamp receptacle 36, adapted to receive an X-ray tube 37.

X-ray tube 37 is novel in construction and related to several of the pending applications heretofore mentioned. It is substantially symmetrical in design about its longitudinal axis, and comprises a glass envelope 38, into which is sealed an anode stem 39, of preferably good heat conducting material, such as copper, and having a substantially spheroidal end 40, into which is set a metallic end 41, which is of preferably a highly refractory metal, such as thorium or the like, the opposite end of which anode stem being fixed at 42 to the said glass envelope 38, and the anode terminal of the said X-ray tube having a screwplug at 43, adapted to be screwed into the receptacle 36, forming the principal supporting means for fixing the position of the tube. The anode stem of the tube making contact at button 44, with the mechanical part 28, of the high opening permitting a conically divergent beam of X-rays to pass through the said focusing device covering to volumetric space represented by the solid angle 77. The said opening through which the diverging rays pass, serves simultaneously as a diaphragrning device.

The said focusing device 46, is fixed by rods such as 47 and 48 into glass parts 49 and 50, such as is common practice in lamp manufacture. Into glass part 49, is pressed conductor 51, which is formed into one or more convolutions at 52, and which convolutions are of material such as will emit electrons when heated such as thorium and the like, forming a thermionic source of electrons at 52, the conductor 53 being the remaining lead in or lead out wire for the thermionic electron source. Conductors 51 and 53 are sealed into the glass at 54 and 55, and the ends of the said conductors are supplied with contact buttons 56 and 57, which by means of contacts 58 and 59 and insulated lead wires 60 and 61, serve as means for conducting low voltage electricity into the bulb of the X-ray tube 37, which supplies the heating current for the thermionic cathode 52.

Lead wire 20 is connected to conductor 62, which feeds the aforementioned lead wire 61, which in turn allows current to pass through the filament 52 and thence through the lead 60 to lead 63, thence through switch 64 is connected to the secondary 65 of a suitable heating transformer 66. The conductor 20 may serve as a common connection for the low voltage winding of the high voltage transformer, and the thermionic filament of the X-ray tube. The heating transformer 66, is not necessary to the broad aspect of my invention, but in practice it has been found advantageous to employ low voltages for thermionic filaments in X-ray tubes of the class I use, and such a voltage as would be economical practice for the thermionic cathode would not be suitable for the low voltage winding on the high voltage transformer, and because of the greater energy demand made by the high voltage transformer, I prefer to connect it directly to a power voltage source and supply a heating transformer to reduce the voltage of the said source to a value suitable for the thermionic cathode.

The focusing device 46, maybe constructed of a high atomic weight material, such as thorium and the like, and the focal spot on the anode 40 may so project into the spheroidal cavity of the said focusing device as to substantially prevent the esoapement of X-rays from the said spheroidal cavity, except through the opening represented by the solid angle '77. In this way my focusing device may serve as a shield against undesirable X-rays, though in some cases I may prefer to utilize the casing 6'7 as a shield against undesirable X-rays, and providing at the general neighborhood of 68 sufficient transparency for the desirable X-rays coming within the solid angle '77, to emerge into a useful space such as that below 68.

The casing 6'7 is of a generally cylindrical internal characteristic with a generally spheroidal end 69. The small parts 47, 50, 53 and the like are shielded electrostatically by means of the focusing device 46 and the spheroidal casing end 69, in such a way as to prevent the said small parts from substantially coming into the electrostatic field and thereby influencing it. So it may be pointed out that in. viewing the X-ray tube and its casing it will be noted that the outstanding characteristic is the substantial absence of points, surfaces and radii of small curvature in the construction of parts used in locations which influence the electrostatic field distribution of the high voltage employed in my device, and I thereby not only improve the dielectric characteristics of the insulation properties utilized in my device-in and about the high voltage winding but also in and about the load used in connection with my device as well as within the load device itself.

It will be appreciated by those familiar with theart that gaseous ionization within an X-ray tube may be dependent upon the'maximum voltage stress within the rarefied gas itself, and by 1 giving such geometric construction to the electrodes of my device as to reduce and equalize this aforesaid maximum stress I resultantly not only improve the stability of operation of the X-ray tube (which is often greatly affected by excessive gaseous ionization but further remove the necessity of utilizing such high vacuua as has been thought necessary heretofore to produce X-ray tubes which operate independent of troublesome gaseous ionization.

It will be appreciated that in all X-ray tubes,

' regardless of how much care be exercised in pumping out the residual gases, there is not only theoretically but practically in everytube, appreciable gaseous ionization. This may be made evident by taking at random any hot cathode tube of the art prior to my several inventions and with a cold filament impressing the maximum allowable potential upon the terminals of the tube and observing the phenomena which takes place within the tube. Minute pale green fluorescent spots on the glass walls of the said tubes will be found to be characteristic of all said tubes, and upon investigation these green spots will be found to be sources of X-rays produced by gaseous ions instituted by the high dielectric field stresses caused by the sharp edges of the focusing'device of the said tubes, bearing irrefutable evidence of gaseous ionization.

By the employment of surface characteristic means for reducing the dielectric field stresses about my electrodes, I find that I can produce a more dependable X-ray tube, with less gaseous ionization present than in the prior art tubes, and with higher gas pressures than possible without my improved electrodes, and further, with such pressures as have been common prior to the general use of thermionic X-ray tubes.

Further, it will be appreciated that X-ray tubes which are dependent upon gaseous attenuation to reduce the gaseous ionization within the tube, are subject to instability and erratic behavior, due to minute gas pressure changes within the envelope of the said tubes. These devices, like all pointed or edged electrodes, do not have very pronounced critical working characteristics, and work more or less good or bad, depending upon the instantaneous value of the gas pressure within the tube. However, in my device this characteristic is not pronouncedly present, as more sharply defined critical points are found present in the behavior of its operation, and phenomena due to gaseous ionization may be almost non-existent up to critical values, where it becomes more pronounced with greater rapidity. 7

It will be appreciated that with such a char.- acteristic, so long as the critical point has not been overstepped, gaseous ionization is conspicuously absent, and the X-ray tube may operate with constantly changing and fluctuating gas pressures without these-changes or fluctuations being apparent in the operation, or interfering with the stability of the X-ray tube.

The principal and essential elements of my invention have been described and their operation recited except for minor details which are common knowledge and immediatelyobvious to those skilled in the art and which would directly follow from the disclosure.

Fig. 4 shows a side elevationof a complete X- ray apparatus involving the embodiment of my invention, said device being provided with a support 70, which may turn about an axis 71, giving angular positions by virtue of rotation about the axis '72 and '71 in joint operation.

The shaft '73 may be attached so as to rotate within any suitable holder and generally I prefer to attach this to an extendable arm, such as used by dentists for their drilling motors, as the illus trated embodiment is intended primarily for dental X-ray work. The device thus hangs in the air, so to speak, from its axis '71, which axis is supplied with suflicient friction to hold the device in any desired position into which it may rotate about the said axis.

The casing 67 is made removable by a common slot-and-screw construction '74. The casing may be removed by turning it first counterclockwise and then pulling it in a direction from the axis 71 along the imaginary axis of the cylindrical surface 6'7. The X-ray tube may then be removed like any common incandescent bulb by unscrewing it from the receptacle 36, as obvious from inspection of Fig. 1. The active field of the X-rays is that below the X-ray translucent surface 68. The novel removable feature of the X-ray bulb is of great practical importance in the X-ray art and in the application of my invention.

In the claims for my invention where the term magnetic circuit is used and its electrostatic potential with reference to the other elements involved is implied the meaning to be construed in the claim is the highly permeable material of the magnetic circuit proper and, or such other mechanical parts connected thereto as may be at substantially the same electrostatic potential.

What I claim is:

1. In an X-ray apparatus, a transformer having a high voltage coil, an X-ray tube, means electrically connected with said coil and supporting the anode end of the X-ray tube in juxtaposition with said coil, said X-ray tube comprising a thermionic cathode, means to be connected to ground for conducting electric current to said cathode, and an electrostatic ground shield surrounding said coil.

2. In an X-ray apparatus, a transformer comprising a high voltage coil having the intersection of its cylindrical and plane surfaces provided with a toroidal surface having a radius of curvature in a plane coincident with the longitudinal axis of the coil of at least several percent of the diameter of the said coil, and X-ray tube, means electrically connected with said coil and supporting the anode end of said X-ray tube in juxtaposition with said coil, said X-ray tube comprising a thermionic cathode, means to be connected to ground for conducting electric current to said cathode, and an electrostatic ground shield surrounding said coil.

3. In an X-ray apparatus, means for supporting an X-ray tube at its anode end, an X-ray tube affixed thereto and mounted to emit X-rays along the axis of said tube, said X-ray tube having a cathode to be connected to ground and said cathode being supplied with electric current through two butt-j oint contacts under pressure.

4. In an X-ray apparatus, a transformer comprising a high voltage coil having the intersection of its cylindrical and plane surfaces provided with a toroidal surface having a radius of curvature in a plane coincident with the axis of said coil of at least several percent of the diameter of said coil, an X-ray tube, means electrically associated with said coil for supporting the X-ray tube in juxtaposition with said coil, said tube being adapted to emit X-rays along the axis of said tube and an electrostatic ground shield surrounding said coil.

MONTFORD MORRISQN.

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