US3678435A - Electrical resistor - Google Patents

Electrical resistor Download PDF

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Publication number
US3678435A
US3678435A US87925A US3678435DA US3678435A US 3678435 A US3678435 A US 3678435A US 87925 A US87925 A US 87925A US 3678435D A US3678435D A US 3678435DA US 3678435 A US3678435 A US 3678435A
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Prior art keywords
metal fiber
combination according
insulating material
unitary structure
electrical
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Expired - Lifetime
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US87925A
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English (en)
Inventor
Herbert M Pflanz
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Allis Chalmers Corp
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Allis Chalmers Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C10/00—Adjustable resistors
    • H01C10/50—Adjustable resistors structurally combined with switching arrangements

Definitions

  • the resistance ele- [56] References Cited ment in spirally wound ribbon form is embedded in a body in the form of solid cylindrical insulator to provide a separate re- UNITED STATES PATENTS sistor.
  • An electrical device such as a static or solid state component, can be embedded in the solid body in circuit with the 2,287,460 6/1942 Wagenhals ..338/263 resistance element
  • the resistance 2835465 5/1958 Patterso 338/269 UX element in the form of a flat sinuous member is embedded in a 3,278,279 10/1966 Kraft ..75/DIG.
  • This invention relates generally to electrical resistors. More particularly, it relates to high wattage electrical resistors which comprise a resistance element embedded in a body of insulating material and which may be employed with or built into electrical circuit interrupters or other electrical devices.
  • Some electrical devices including electrical circuit interrupters, employ high wattage resistors which perform an electrical function and are subject to rapid and intense heating when current flows therethrough.
  • some fluid (or air) blast type circuit breakers employ such resistors in circuit with separable electrical contacts for voltage grading, damping or other purposes.
  • each pair of separable contacts is enclosed in a gastight insulated housing, usually made of ceramic, and the associated resistor is mounted adjacent the housing as a separate component.
  • the prior art resistors take the form of a solid wire or ribbon which is spirally wound on a solid or hollow cylindrical ceramic body or a stack of blocks of resistance material, such as carbon, arranged in a tubular insulated housing. While such prior art resistors are generally satisfactory for their intended purpose, they are additional, large, space consuming, costly components in need of improvement.
  • circuit breakers and in some other apparatus it would be advantageous in circuit breakers and in some other apparatus to provide the necessary resistor in the form of a built-in or integrally formed device which takes advantage of existing structural features of the apparatus. Furthermore, it would be advantageous to provide such a resistor in the form of a resistance element which is actually embedded (either fully or partially) in a body of electrical insulating material.
  • prior efforts to embed or encapsulate resistance elements in electrical insulating materials have not always been completely successful. For example, thermal expansion of conventional resistance elements tends to cause breakage of the element, detachment of it from the associated insulating body, or cracking of the insulating body.
  • the present invention provides improved resistors which comprise an electrical resistance element made of resistance material having a plurality or multiplicity of voids therein, such as porous metal, fiber metal or foam metal, which is partially or fully embedded in substantially rigid, nonexpandible, noncompressible, noncombustible electrical insulating materia], such as ceramic, PYROCERAM, RE-EX or the like.
  • an electrical resistance element made of resistance material having a plurality or multiplicity of voids therein, such as porous metal, fiber metal or foam metal, which is partially or fully embedded in substantially rigid, nonexpandible, noncompressible, noncombustible electrical insulating materia], such as ceramic, PYROCERAM, RE-EX or the like.
  • Heating of the resistance element caused by electric current flow therethrough does not result in a change in the physical dimensions of that portion of the resistance element which is trapped, clamped or placed under pressure by the insulating material because the resistance material expands inwardly, so to speak, into the voids in the material and this phenomena of inward expansion results in reduced physical and mechanical stresses being imposed on the surrounding body of insulating material.
  • the resistance element can take any form, for example, such as an elongated conductor, a ribbon, or a flat member, and can be arranged in the body of insulating material in any manner, for example, such as a wire passing straight through, a wire helically or spirally wound therein, or an embedded flat member.
  • the body of insulating material with which the resistance element is associated can be a solid member in which electrical components, such as solid state or static devices, in circuit with the resistance element may be embedded.
  • the body can be a hollow member in which components, such as movable circuit breaker contacts, may be housed.
  • a resistor in accordance with the present invention may be in the form of an independent unit or one which is integrally formed with insulating bodies serving other functions in electrical apparatus. Furthermore, embodiments can be provided in the form of modular resistor units which can be used individually as resistors or combined to provide resistors of higher rating.
  • the resistance element and the body of insulating material have closely matching thermal expansion characteristics. It is also preferable in some applications that the resistance material of which the resistance element is made have the highest possible resistance so as to conserve space and materials, increase thermal performance, or reduce inductive effects.
  • Another object is to provide improved resistors wherein a resistance element made of material having a multiplicity of voids therein, such as porous, fibrous or foraminous resistance metal, is embedded in a body of electrical insulating material and wherein thermal expansion of the resistance element caused by current flow therethrough is inhibited because, due to the clamping pressure of the surrounding insulating material, inward expansion of the element into its voids takes place whereby minimum physical and mechanical stresses are imposed on the insulating material.
  • a resistance element made of material having a multiplicity of voids therein such as porous, fibrous or foraminous resistance metal
  • Another object is to provide resistors of the aforesaid character wherein electrical components in circuit with the resistance element are disposed in said body of insulating material, as by direct embedding in the case of solid state components, or by being housed in a cavity in said body of insulating material.
  • Another object is to provide resistors of the aforesaid character which comprise ribbon type resistance elements fully or partially embedded in a solid or hollow insulating body.
  • Another object is to provide improved resistors of the aforesaid character which are well suited for use with electrical apparatus, such as electric circuit interrupters, especially those of the fluid (or air) blast type.
  • Another object is to provide improved resistors of the aforesaid character for use with electrical apparatus wherein the resistance element is physically mounted on or integral with an insulating body which performs other functions in the apparatus besides merely supporting the resistance element.
  • Another specific object is to provide insulators of the aforesaid character wherein the resistance element is fully or partially embedded in a tubular insulating housing of a fluid blast circuit breaker which houses separable electrical contacts.
  • a more specific object is to provide modular resistors of the aforesaid character which comprise substantially flat resistance elements embedded in insulating bodies to provide resistor modules, which modules can be used separately as resistors or stacked together to provide larger resistors.
  • FIG. 1 is a cross sectional view of one embodiment of the invention which comprises a porous resistance element fully embedded in the wall of a hollow insulating body such as a housing of an electric circuit breaker which has separable circuit breaker contacts therein;
  • FIG. 2 is a view taken along line IIII of FIG. 1;
  • FIG. 3 is a cross sectional view of another embodiment of the invention which comprises a resistance element in parallel circuit with an electrical component fully embedded in a solid insulating body;
  • FIG. 4 is a view taken along line IVIV of FIG. 3;
  • FIG. 5 is a cross sectional view of a portion of an embodiment in accordance with the invention which is applicable to the embodiments shown in FIGS. 1 and 3 and which shows a resistance element partially embedded in an insulating body;
  • FIG. 6 is a cross sectional view of another embodiment of the invention which comprises a plurality of modular units which are stacked together, each modular unit comprising an insulating body in which a resistance element is embedded;
  • FIG. 7 is a view taken along lines VII-VII of FIG. 6 showing the configuration of the resistance elements.
  • the numeral 10 designates a portion of electrical apparatus such as a fluid (gas or air) blast type electrical circuit interrupter of the type in which the present invention is advantageously employed.
  • Portion 10 which is a combined resistor and contact housing, comprises a contact housing 12 in which are disposed electrical devices, such as a pair of spaced apart stationary interrupter contacts 14 and 16 which are bridgeable by a movable bridging contact 18.
  • a resistance element is embedded in housing 12 and is in parallel circuit with or shunts contacts 14 and 16.
  • resistance element 20 may reach temperatures on the order of 400 to 500 C, rising to their level from ambient in about 40 msec.
  • Housing 12 is a body of substantially inelastic non-combustible electrical insulating material such as ceramic, glass, PYROCERAM, Re-X or the like and takes the form of a hollow open ended cylinder having exterior skirts 22 and grooves 24. Housing 12 protects, supports and insulates the contacts 14, 16 and 18 and channels or contains the insulating and are extinguishing gas which also effects contact operation.
  • the stationary contacts 14 and 16 are hollow cylindrical electrically conductive members having flanged ends 26 and 28, respectively, which close off the ends of housing 12.
  • Contact 16 is further provided with a cylinder 30 which cooperates with the piston-like end 32 of bridging contact 18.
  • Contact 18 is understood to be reciprocably movable leftward and rightward in response to pressure changes to contact closed and contact open positions, respectively, but the exact details of the contact construction and operation do not form part of the present invention.
  • Resistance element 20 is in the form of an elongated conductor or ribbon which is spirally wound and completely embedded in the wall of housing 12, as by being cast therein, and is electrically connected at its opposite ends to contacts 14 and 16 by suitable connectors 34 and 36, respectively. If preferred, element 20 may be provided with convolutions 38 to increase its effective length without undue usage of space.
  • resistance element 20 comprises resistance material which has a multiplicity of voids therein, such as porous metal, fiber metal or foam metal.
  • Metals of this type are commercially available from many sources. Fiber metals, for example, are commercially available as F ELTMETAL from the Huyck Metals Company, 45 Woodmont Road, Milford, Conn.
  • these forces can be further reduced by selection of resistance material in accordance with the invention which is closely compatible from a coefficient of thermal expansion standpoint to the insulating material being selected for use.
  • Kovar metal about 42 percent nickel and 58 percent iron
  • the resistance material have high electrical resistance, high density, and high specific heat (or, at least, that the product of these factors be as high as possible) to provide the shortest possible conductive path thereby conserving space and reducing inductive effects.
  • a good interface increases artificially the product of resistivity, density and specific heat of the resistance material, because of the apparent increase of the specific heat or ability to absorb heat of the resistance material which is in contact with a higher specific heat material such as ceramic.
  • a porous resistance material is in close contact with the insulating material. Since the pores are not filled, the resistance element can still expand inwardly under the influence of heat while maintaining the heat absorbing boundary with the ceramic. Such a design is therefore suitable for thermal transients.
  • FIG. 5 shows a modification which may be employed with the embodiment shown in FIGS. 1 and 2.
  • a resistance element 40 identical to resistance element 20 hereinbefore described is shown partially embedded in a body of insulating material 41.
  • the advantage of this construction is that part of element 40 is exposed to atmosphere and more rapidly dissipates heat than one which is fully embedded.
  • element 40 is partially exposed and may not be suitable for use where shock hazards or electrical clearances are factors.
  • FIGS. 1 and 2 with or without the modification of FIG. 5, is well suited to effect conservation of space and materials in electrical apparatus such as an air blast circuit breaker which would otherwise require a separate resistor.
  • electrical apparatus such as an air blast circuit breaker which would otherwise require a separate resistor.
  • other applications are suitable and other electrical devices besides circuit breaker contacts could be disposed within the hollow cavity in housing 12 and other electrical connections besides the parallel connection shown could be employed.
  • the numeral 42 designates an independently usable resistor which comprises a body 44 of insulating material in the form of a solid cylinder having electrically conductive end caps 45 and 46 which provide a means of mechanical support and electrical connection.
  • a resistance element 48 identical to resistance element 20, is fully embedded in body 44 and has its opposite ends connected to end caps 45 and 46. If preferred, element 48 may be partially embedded, as FIG. 5 shows, if its application so warrants.
  • an electrical device or component 50 such as a static state or solid state device, i.e., a capacitor or diode or the like, may be embedded by casting in body 44 and connected in circuit with resistance element 48, as by conductors or wires 52 and 54 which are connected to the device and to the end caps 45 and 46, respectively.
  • the numeral 56 designates another independently usable resistor which comprises a plurality of modular resistor units 58 which are stacked end-to-end and physically secured together by suitable means such as adhesive 60 between adjacent units.
  • Each modular unit 58 comprises a solid body 62 of insulating material, cylindrical in fonn and having flat end faces, in which is embedded a resistance element 64 having a substantially flat, sinuous shape to increase its resistance path.
  • Each element 64 has integrally formed connectors 66 and 68 at each end which extend from the sides of body 62 and enable electrical connections to be made to the element. As FIG. 6 shows, adjacent connectors 66 in resistor 56 are electrically connected by means of jumpers 70.
  • each element 64 is made of resistance material of the same type as used in resistance element 20, hereinbefore described. lf preferred, each element 64 can be fabricated by stamping or punching from sheet stock and each is provided with integrally formed ears or tabs 72 which project from at least one surface of the element and serve as a supporting and positioning means whereby the element is held in place in a suitable casting mold while the insulating material is poured around it during manufacture of each modular unit.
  • each end module in resistor 56 has one of its connectors 66 or 68 electrically connected to end caps 74 or 76 which are secured to the ends of the stack of modules and provide a mounting means and electrical connection means for resistor 56.
  • Resistor 56 can comprise as many modular units 58 as are necessary to provide a suitable resistor for any given application. Or, an individual modular unit 58 can be used as a complete resistor.
  • a continuous electrical resistance element at least partially embedded, in said body and comprising a plurality of intact metal fibers defining a unitary structure having a multiplicity of voids therein, said metal fiber structure being in intimate contact with said insulating body but the voids not being impregnated with the insulating material,
  • the metal fiber structure can expand inwardly when heated by electrical current passing therethrough.
  • a continuous metal fiber electrical resistance element of high resistivity having a multiplicity of intact metal fibers forming an integral structure having a multiplicity of voids and a density per unit volume of less than 100 percent, said resistance element being at least partially embedded on a body of electrical insulating material but not being impregnated with the insulating material,
  • integral metal fiber structure can expand inwardly when heated by electrical current passing therethrough so that mechanical stresses are not imparted to the body of electrical insulating material.
  • a combination according to claim 2 wherein the density per unit volume of said intact metal fiber integral structure is at least 20 percent.
  • a combination according to claim 1 wherein the intact metal fiber unitary structure has a coefi'icient of thermal expansion which is substantially similar to the coefficient of thermal expansion of said body of electrical insulating material.
  • a combination according to claim 11 wherein said helix arranged intact metal fiber unitary structure is also corrugated.
  • a combination according to claim 1 wherein said intact metal fiber unitary structure is foraminous.
  • said intact metal fiber unitary structure presents a configuration which in cross section has substantially greater width than depth so as to be relatively flat and being completely embedded in said body of electrical insulating material, said unitary structure having its ends extending externally of said body and having connector means thereon, said body and said intact metal fiber unitary structure cooperating to form a modular resistor unit.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Details Of Resistors (AREA)
  • Arc-Extinguishing Devices That Are Switches (AREA)
  • Thermistors And Varistors (AREA)
US87925A 1970-11-09 1970-11-09 Electrical resistor Expired - Lifetime US3678435A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US8792570A 1970-11-09 1970-11-09

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US3678435A true US3678435A (en) 1972-07-18

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Application Number Title Priority Date Filing Date
US87925A Expired - Lifetime US3678435A (en) 1970-11-09 1970-11-09 Electrical resistor

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US (1) US3678435A (xx)
CA (1) CA934838A (xx)
CH (1) CH549859A (xx)
DE (1) DE2155698A1 (xx)
FR (1) FR2113683A5 (xx)
IT (1) IT944805B (xx)
NO (1) NO129486B (xx)
SE (1) SE367506B (xx)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3724226A (en) * 1971-04-20 1973-04-03 Gulf Research Development Co Lng expander cycle process employing integrated cryogenic purification
US3813631A (en) * 1972-08-09 1974-05-28 Hitachi Ltd High resistance resistor device for dc high voltage circuits
US5940958A (en) * 1995-05-10 1999-08-24 Littlefuse, Inc. Method of manufacturing a PTC circuit protection device

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2287460A (en) * 1940-11-29 1942-06-23 Rca Corp Insulated heater and method of manufacture
US2835465A (en) * 1953-12-01 1958-05-20 Roger W Patterson Resistor mounting brackets
US3278279A (en) * 1962-10-25 1966-10-11 Wmf Wuerttemberg Metallwaren Uniformly porous product consisting basically of metal fibers and process of making it
US3285825A (en) * 1964-09-16 1966-11-15 Atomic Power Dev Ass Inc Reinforced ceramic fuel elements
US3287166A (en) * 1965-01-27 1966-11-22 Douglas Aircraft Co Inc Battery electrode and battery, and process for preparing said electrode
US3344385A (en) * 1965-01-04 1967-09-26 Dow Corning Flexible resistance element with flexible and stretchable terminal electrodes
US3398233A (en) * 1965-04-20 1968-08-20 Dennis G Wyman Electrical conductor of fibers embedded in an insulator
US3400356A (en) * 1965-11-16 1968-09-03 Bayard C. Davis Screen heater with an outer metallic sheath
US3477058A (en) * 1968-02-01 1969-11-04 Gen Electric Magnesia insulated heating elements and methods of production

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2287460A (en) * 1940-11-29 1942-06-23 Rca Corp Insulated heater and method of manufacture
US2835465A (en) * 1953-12-01 1958-05-20 Roger W Patterson Resistor mounting brackets
US3278279A (en) * 1962-10-25 1966-10-11 Wmf Wuerttemberg Metallwaren Uniformly porous product consisting basically of metal fibers and process of making it
US3285825A (en) * 1964-09-16 1966-11-15 Atomic Power Dev Ass Inc Reinforced ceramic fuel elements
US3344385A (en) * 1965-01-04 1967-09-26 Dow Corning Flexible resistance element with flexible and stretchable terminal electrodes
US3287166A (en) * 1965-01-27 1966-11-22 Douglas Aircraft Co Inc Battery electrode and battery, and process for preparing said electrode
US3398233A (en) * 1965-04-20 1968-08-20 Dennis G Wyman Electrical conductor of fibers embedded in an insulator
US3400356A (en) * 1965-11-16 1968-09-03 Bayard C. Davis Screen heater with an outer metallic sheath
US3477058A (en) * 1968-02-01 1969-11-04 Gen Electric Magnesia insulated heating elements and methods of production

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3724226A (en) * 1971-04-20 1973-04-03 Gulf Research Development Co Lng expander cycle process employing integrated cryogenic purification
US3813631A (en) * 1972-08-09 1974-05-28 Hitachi Ltd High resistance resistor device for dc high voltage circuits
US5940958A (en) * 1995-05-10 1999-08-24 Littlefuse, Inc. Method of manufacturing a PTC circuit protection device
US5955936A (en) * 1995-05-10 1999-09-21 Littlefuse, Inc. PTC circuit protection device and manufacturing process for same

Also Published As

Publication number Publication date
FR2113683A5 (xx) 1972-06-23
SE367506B (xx) 1974-05-27
IT944805B (it) 1973-04-20
CA934838A (en) 1973-10-02
NO129486B (xx) 1974-04-16
DE2155698A1 (de) 1972-05-10
CH549859A (fr) 1974-05-31

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