US3041561A - Transformers - Google Patents

Description

June 26, 1962 's. HANNON ETAL TRANSFORMERS Filed July 29. 1958 m 0 mmvllllllit h INVENTORS STEPHEN HA/VNON WILLIAM A. BRENNAN WWW A T TORNE Y United States atent O 3,041,561 TRANSFORMERS Stephen Hannon, Weston, and William A. Brennan, N orwood, Mass., assignors to Raytheon Company, a corporation of Delaware Filed July 29, 1958, Ser. No. 751,753 8 Claims. (Cl. 336-84) This invention concerns an improvement in transformers, and more specifically, to a novel construction and disposition of the windings of a transformer capable of operation at high voltage with minimum corona.

In many instances, such as in magnetron or klystron filament transformers, a transformer is required which (1) has a low capacitance, say of the order of micromicrofarads, between the primary and secondary windings and between ground and the secondary windings and which (2) is capable of operation at peak potentials of the order of 50 to 100 kilovolts.

At such high voltages, the magnitude of the electrical field between the primary and the secondary windings or between the secondary winding and ground, is correspondingly large. With such strong electrical fields, conventional transformers are characterized by localized buildup of considerable stress which results in corona discharge between the various portions of the transformer, particularly in regions where pointed or irregular surfaces may exist. In some instances, actual breakdown by are discharge will occur, with resulting damage to the transformer.

In accordance with the invention, corona may be minimized by covering the primary and secondary windings with a smooth electrically-conductive casing or sheath which serves to distribute the potential along the entire surface of the windings. By making the outer surface of the sheath sufficiently smooth, concentration of voltage stress will be substantially reduced, with a corresponding reduction in corona loss or breakdown. The casing for either or both of the windings is made of electrically-conductive material of low surface irregularity or of a material coated with an electrically-conductive material of low surface irregularity. The casing preferably is of circular cross section, since this configuration minimizes crowding of the lines of electrical stress. Other configurations whose surface follows a smooth curve, such as an ellipse, are, of course, feasible. The secondary winding assembly preferably-is made in the form of a torus which is continuous, except for a break in the electrically-conductive casing necessary to prevent formation of a shorted turn. The primary winding assembly may .consist of a winding Wound on one leg of acore passing throughthe toroidal secondary winding assembly, as shown in FIG. 1, or it maybe a toroidal assembly linking the toroidal secondary winding assembly, as shown in FIG. 4. t

' The corona between two surfaces tends to be aggravated when separated by insulating materials which have different dielectric constants, since the electric field disvtributionvaries inversely proportional to the dielectric constant. In conventional transformers in which the secondary winding is covered with an insulated compound or dielectric-impregnated tape, there is, in addition to the air between the windings of the transformer, the dielectric of the insulating compound or tape itself. (The air space which is necessary for low capacity requirements is in effect reduced, since the air space will tend to acquire the entire electrical stress owing to the difference of the dielectric constants of the materials in the electric field. This condition is further aggravated by the irregular distribution ofthe electrical field which results from the conventional construction.) In the transformer accord- "iceing to the invention, the exposed surfaces of the winding assemblies are spaced from one another and from ground only by air, or, in the case of oil-cooled transformers, by oil only. Thus, there is only one dielectric in the path in question and only one dielectric constant is involved, namely, that of air, or oil, in the event that the transformer is submerged in oil. Consequently, corona problems are minimized in the transformer according to the invention.

Other advantages and objects of this invention will become apparent from the following description of the invention taken together with the accompanying drawings illustrating preferred embodiments thereof and wherein:

FIG. 1 is a pictorial view of a first embodiment of a transformer according to the invention;

FIG. 2 is a transverse section view of the secondary winding of the transformer of FIG. 1 taken along line 2-2 of FIG. 1;

FIG. 3 is a transverse ection view of the primary winding of the transformer of FIG. 1 taken along line 3-3 of FIG. 1; and

FIG. 4 is a pictorial view of a second embodiment of a transformer according to the invention.

Referring now to the drawing, a transformer 10 is shown which includes a primary winding assembly 12 and a secondary winding assembly 14, together with the accompanying supporting structure to be described subsequently. Details of the secondary winding assembly 14 and of the primary winding assembly 12 are shown in FIGS. 2 and 3, respectively.

The primary winding assembly -12 includes a central core 16 made of magnetic material, such as iron. The core 16 may be of square cross section, as indicated in FIGS. 1 and 3, and is formed in a closed loop having four mutually perpendicular straight legs. Other configurations of the core, however, are within the scope of the invention. The portion of the core forming the upper transverse leg is surrounded with an electricallyinsulating material 17, such as one or more layers of insulating tape.

A primary winding 18 consists, for example, of several turns of enamel-coated wire wound about the insulator core in the usual manner. Surrounding the primary winding 18 is a mass of electrically-insulating compound which may be of plastic, such as an epoxy resin. The outer surface of the insulating compound 19 preferably is made of circular form, either by molding or by inserting the wound core into a tubular form (not shown in the drawing) and filling the region within the form not occupied with the wound core with an electrically insulating compound. The form either may be removed after the insulating compound hardens or the form may be permitted to remain integral with the insulating compounds. (For example, the form may be of the same material as the insulating compound so that there is no dielectric constant discontinuity between the insulating material 19 and the tubular form.) An electricallyconductive casing 21 is positioned about the insulating material 19 to form an electrostatic shield which serves to equalize the potential along the surface of the primary winding assembly 12. This casing may, for example, be of metal tubing, or may be a thin layer of metal foil. Alternatively, the molded dielectric material 19 may be coated with a thin layer of metal as by painting, spraying, or the like. The surface of the casing 21 preferably is polished or otherwise made as smooth as possible in order to minimize stress concentration resulting from surface irregularities. The transformer primary winding 13 is provided'with two leads 22 and 23.

The secondary winding assembly 14 includes a coil whose individual turns 25 are inserted within a tubular toroidal casing or sheath 27. The ends of the casing are separated by a small amount to permit access of the coil and the electrically-insulating material 28 which is inserted into the space within the tubular casing 27 not occupied by coil turns 25. A cup-shaped member, not shown, of inner diameter equal to that of casing 27, may be inserted between the ends of the casing to facilitate insertion of the insulating compound 28. When the compound has hardened, the cup-shaped member may be removed, leaving a portion 29 of insulating compound between the ends of the casing 27 whose outer diameter coincides with the outer diameter of the casing and Whose surface is comparable in smoothness with that of the casing. 1 In the absence of a break 29 in the case 27, the latter would constitute an obviously undesirable singleshorted turn.

The core frame 31 for the primary winding assembly 12 consists of brackets 33 to 38 inclusive. Bracket 33 is a unitary electrically-conductive member which is made up of a vertically arranged portion including vertical arms 41 and 42 and a transverse arm 43, together with a horizontally-arranged portion including horizontal arms 44 and 45. The vertical arms 41 and 42 are L-shaped. Bracket 33 may be stamped out of a single sheet of metal, such as steel, and bent into the configuration shown in FIG. 1. One face of each vertical section 41 and 42 of bracket 33 engages the core 16 adjacent to the ends. The frame 31 further consists of brackets 34 and 35, each of which is brazed or otherwise secured to the vertical and horizontal portions of bracket 33. The bracket 36, similar in all respects to bracket 33, is positioned on the other side of core 16, as shown in FIG. 1 of the drawing. Bracket 36 includes L-shaped vertical arms 46 and 47, a transverse arm which is not visible in FIG. 1, and horizontal arms 48 and 49. Brackets 37 and 38 are connected to the vertical and horizontal portions of bracket 36.

Electrically- conductive shields 51, 52, and 53, which may be made of sheet copper, are provided for presenting a substantially circular continuous electrically-conductive surface to the secondary winding assembly. These shields are of generally U-shaped configuration having straight sides and a curved central portion. The straight portions of shield 51 are at least partially inserted within the space between portions 41 and 46 of brackets 33 and 36 and the core 16; shield 52 is similarly inserted between portions of 42 and 46 of brackets 33 and 36 and the core 16. Shield 53 is inserted between the transverse arm 43 of bracket 33 and the un-numbered transverse arms of bracket '36 and the core 16. Filler pieces 55, which may be made of maple wood or any electricallyinsulating material, are inserted between the arcuate portions of the shields 51 to 53 and the core 16 for lending mechanical support to the shields.

Casing 21 of the primary winding assembly 12 is grounded by means of a lead 58 connected between the core and a lug 59 inserted between bolt 65 and washer 66 in electrical contact with bolt 65.

The frame for the secondary winding assembly 14 includes two sets of mounting panels 61 and 62 made of an electrically-insulating material, such as Lucite or polystyrene. As shown in FIG. 1, these panels are made of optically transparent material; however, any type of plastic or electrically-insulating material may be used. The two upper mounting panels 61 are generally U-shaped, having vertical portions apertured in the ends to receive through bolts 65. Bolts 65 also pass through washers 71, brackets 33 and 36, and core 16. Bolts 65 serve to support the core 16 relative to core frame 31 and also to support the secondary winding assembly 14. The

horizontal portion of the mounting panel 61 contains arcuate recesses into which the toroidal secondary winding assembly 12 seats to prevent lateral movement there of. The proper spacing between mounting panel 61 is maintained by a spacer block 66 which is secured in spacing between the upper and lower mounting panels a 61 and 62 is such that the toroidal secondary winding assembly 14 i firmly held in position.

Alternate embodiment of the invention is shown in FIG. 4, wherein the primary winding assembly 112, like the secondary winding assembly 114, is of toroidal construction with it diametric axis perpendicular to the diametric axis of the secondary winding assembly. The cross section of the primary winding assembly 112 may be identical to that indicated in the device of FIG. 1, that is, as shown in FIG. 3. The secondary winding assembly 114 of PEG. 4 may be identical to that of the device shown in FIG. 1, that is, its cross Section may be as shown in FIG. 2. The casings 121 and 127 of the toroidal Winding assemblies 112 and 114, like casing 21 of the device of FIG. 1, must contain a break which may be filled by electrically-insulating sleeves and 128 for the primary and secondary winding assemblies, respectively, and whose peripheries correspond in configuration and surface smoothness to that of portion 29 of the secondary winding assembly 14 of FIG. 1. V

The secondary winding assembly 114 may be supported from the primary winding assembly 112 by means of spokes 13b of ceramic or other electrically-insulating material which can be bonded to the casings 121 and 127 of the toroidal winding assemblies, as by conventional ceramic-to-metal sealing techniques. The primary winding assembly 112 may be located within a groove in a base 140, said groove being of sufficient depth to prevent lateral movement within the groove. Further support for the primary winding assembly 112 may be achieved by means of an electrically-insulating clamp 142 surrounding the primary winding assembly and attached to the base by screws 143. Brackets 148 and 150, which are attached to base 140 and are provided with curved grooves for contact with the toroidal assemblies 112 and 114, respectively, are used to support these assemblies. In some cases, the primary winding assembly 112 may, like the asemblies 12 of FIG. 1, include a third lead connected to ground, such as base 140.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It'is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

l. A transformer comprising a primary winding assembly and a toroidal secondary winding assembly, said primary winding assembly including a magnetic core covered with a layer of insulating material and surrounded by a primary winding which is continuously contiguous with said first insulating material and a mass of electrically-insulating material in the order named, said toroidal secondary winding assembly including a secondary winding disposed within a body of electrically insulating material, each of said winding assemblies having a major portion thereof surrounded by a separate electrically-conductive sheath having a circular periphery and a minor portion surrounded by an electrically insulating sheath whose periphery is of substantially the same configuration as said electrically conductive sheath.

2. A transformer comprising a primary winding assembly and a toroidal secondary winding assembly, said primary winding assembly including a magnetic core covered with a layer of insulating material and surrounded by a primary winding which is continuously contiguous with said first insulating material and a mass of electrically-insulating material in the order named, said toroidal secondary winding assembly including a sec ondary winding disposed within a body of electrically insulating material, each of said winding assemblies having a major portion thereof surrounded by a separate electrically-conductive sheath having a smooth periphery and a minor portion surrounded by an electrically insulating sheath whose periphery is of substantially the same configuration and smoothness as said electrically conductive sheath.

3. A transformer comprising a primary winding assembly and a toroidal secondary winding assembly, said primary winding assembly including a magnetic core covered with a layer of insulating material and surrounded by a primary winding which is continuously contiguous with said first insulating material and a mass of electrically-insulating material in the order named, said toroidal secondary winding assembly including a secondary winding disposed Within a body of electrically insulating material, each of said winding assemblies having a major portion thereof surrounded by a separate electrically-conductive sheath having a smooth, circular periphery and a minor portion surrounded by an electrically insulating sheath whose periphery is of substantially the same configuration and smoothness as said electrically conductive sheath.

4. A transformer comprising a primary winding assembly and a toroidal secondary winding assembly, said primary winding assembly including a magnetic core covered with a layer of insulating material and surrounded by a primary Winding which is continuously contiguous with said first insulating material and a body of electrically-insulating material in the order named, and a first smooth arcuate electrically-conductive sheath surrounding said body, said toroidal secondary Winding assembly including a secondary winding disposed within a mass of electrically insulating material, and a second smooth arcuate electrically-conductive sheath surrounding said mass, each of said sheaths having a smooth surface and having a minor portion thereof constructed of electrically insulating material whose periphery is of substantially the same configuration as the remaining portion.

5. A transformer comprising a primary winding assembly and a secondary Winding assembly, said primary Winding assembly including a substantially rectangular multilegged core covered with a layer of insulating material and one of which legs is surrounded by a primary winding which is continuously contiguous with said first insulating material, a core frame assembly for mechanically supporting said core, and a first electrically-conductive sheath positioned about said primary winding and electrically insulated therefrom, said secondary winding assem bly including a secondary winding surrounded by a second electrically-conductive sheath and electrically insulated from said second sheath, the remaining legs of said core being provided with electrically-conductive shields having arcuate portions attached to said frames for presenting a smooth curved surface to said secondary winding assembly.

6. A transformer comprising a primary winding assembly and a secondary winding assembly, said primary winding assembly including a substantially rectangular multi-legged core covered with a layer of insulating mate! rial and one of which legs is surrounded by a primary winding which is continuously contiguous with said first insulating material, a core frame assembly for mechanically supporting said core, a first electrically-conductive sheath positioned about said primary winding and electrically insulated therefrom, said secondary winding assem: bly including a secondary winding surrounded by a sec ond electrically-conductive sheath and electrically insulated from said second sheath, the remaining legs of said core being provided with electrically-conductive shields having arcuate portions attached to said frames for presenting a smooth curved surface to said secondary winding assembly, and means secured to said core frame assembly for insulatedly mounting said secondary winding assembly with respect to other portions of said trans former.

7. A transformer comprising a primary winding assembly and a toroidal secondary winding assembly, said primary winding assembly including a magnetic core covered with a layer of insulating material and surrounded by a primary winding which is continuously contiguous with said first insulating material and a body of electrically-insulating material in the order named, a first smooth circular sheath surrounding said body of electrically insulating material, said toroidal secondary winding assembly including a secondary winding disposed within a mass of electrically insulating material, a second smooth circular sheath surrounding said mass of electrically insulatin g material, each of said sheaths having a minor portion constructed of electrically insulating material whose outer periphery is of substantially the same configuration and smoothness as the remaining portion, and an electricallyconductive base for mechanically supporting said primary winding assembly, said primary winding assembly being electrically connected to said base, said secondary winding assembly being mounted in electrically insulating relation relative to said primary winding assembly and to said base.

8. A transformer comprising a toroidal primary winding assembly and a toroidal secondary winding assembly interlinked with said primary winding assembly, said secondary winding assembly being insulatedly mounted from said primary winding assembly with the axes of said assemblies being perpendicular to one another, an electrically-conductive base, and means for mounting said primary and secondary winding assemblies from said base, opposing parts of said winding assemblies each being shielded by a separate continuous electrically-conductive sheath having a curvilinear periphery and a minor POI-I tion surrounded by an electrically insulating sheath.

References Cited in the file of this patent UNITED STATES PATENTS 1,586,078 Fischer May 25, 1926 2,214,915 Wehrlin Sept. 17, 1940 2,241,914 Koschmieder May 1 3, 1941 2,451,324 Dunton Oct. 12, 1948 2,462,106 Kram Feb. 22, 1949 2,519,133 Hartmann Aug. 15, 1950 2,549,426 Clark Apr. 17, 1951 2,601,042 Marks June 17, 1952

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