US3710187A - Electromagnetic device having a metal oxide varistor core - Google Patents

Electromagnetic device having a metal oxide varistor core Download PDF

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Publication number
US3710187A
US3710187A US00185269A US3710187DA US3710187A US 3710187 A US3710187 A US 3710187A US 00185269 A US00185269 A US 00185269A US 3710187D A US3710187D A US 3710187DA US 3710187 A US3710187 A US 3710187A
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United States
Prior art keywords
metal oxide
accordance
varistor
electromagnetic device
oxide varistor
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Expired - Lifetime
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US00185269A
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English (en)
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J Harnden
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General Electric Co
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General Electric Co
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/40—Structural association with built-in electric component, e.g. fuse
    • H01F27/402—Association of measuring or protective means
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/08—Cooling; Ventilating
    • H01F27/22—Cooling by heat conduction through solid or powdered fillings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F29/00—Variable transformers or inductances not covered by group H01F21/00
    • H01F29/02—Variable transformers or inductances not covered by group H01F21/00 with tappings on coil or winding; with provision for rearrangement or interconnection of windings
    • H01F29/025—Constructional details of transformers or reactors with tapping on coil or windings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F29/00—Variable transformers or inductances not covered by group H01F21/00
    • H01F29/06—Variable transformers or inductances not covered by group H01F21/00 with current collector gliding or rolling on or along winding
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/005—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection avoiding undesired transient conditions

Definitions

  • Electromagnetic devices such as inductors and autotransformers having improved suppression to sparking or high voltage peaks at the terminals and between coil windings are provided using certain sintered metal oxide insulators having varistor characteristics.
  • the metal oxide can be employed in conjunction with magnetic core material, as a composite core in such electromagnetic devices.
  • electromagnetic devices such as inductors and autotransformers were often subject to severe arcing problems resulting from sudden surges of voltages which reduced the service life and performance of such devices.
  • electrical devices often suffered from over heating due to the poor thermal conductivity of the core structure.
  • the present invention is based on the discovery that sintered metal oxide material or varistor can be used for minimizing voltage flash-over and sparking, and as a useful thermal conductor to reduce excessive heating in inductors and autotransformers.
  • the valuable results achieved by using such metal oxide varistors is based on the fact that the metal oxide material exhibits nonlinear resistance characteristics which can be described by the following relationship:
  • V is the voltage between two points across the metal oxide material
  • I is the current flowing between the two points
  • C is a constant and a is an exponent greater than 1.
  • C and a are functions of the shape of the body and the composition of the body, where C is principally a function of the material grain size, and a is primarily a function of the grain boundry. Although materials such as silicon carbide also exhibit non-linear resistance, these materials when employed as commercial varistors do not provide exponents greater than 6.
  • the metal oxide varistor employed in the present invention can provide a in excess of 10, such as 30, within a current density range of to 10 amperes per square centimeter.
  • the metal oxide material can be more particularly described as a polycrystalline ceramic material of a particular metal oxide, utilized in combination with small quantities of one or more other metal oxides.
  • Some of the metal oxides materials which can be employed in the present invention are shown by Matsuoka US. Pat. No. 3,503,029.
  • the metal oxide found to be most effective is zinc oxide with small quantities of bismuth oxide, while other metal oxides, such as aluminum oxide, iron oxide, magnesium oxide, and calcium oxide can be added in combination with bismuth oxide.
  • the various metal oxides are sintered after being shaped in a particular manner from the metal oxide powder or mixture.
  • the characteristics of the metal oxide as shown by the above equation are defined by the grain crystal size, grain composition, grain boundry composition, the grain boundry thickness, all of which can be controlled in the ceramic fabrication process.
  • the sintered metal oxide varistor can be readily fabricated into a variety of shapes and sizes. As a result it can be precision machined to produce composites by pressure contact between conventional magnetic core material and varistor when properly fashioned to size.
  • FIG. 1 shows a composite electromagnetic core of sintered metal oxide and magnetic material. As decore when used as the outer sheath.
  • FIG. 2 (a) and (b) shows views of the electromagnetic core composite of sintered metal oxide and magnetic material wired to produce inductors in accordance with the invention.
  • FIG. 3 (a) is a view in section of a self-adjusting autotransformer having a sintered metal oxide layer between the conductor windings and the magnetic core.
  • FIG. 3 (b) is a sectional view of an autotransformer having sintered metal oxide layers between the conductor windings and exterior to both sides of the magnetic core.
  • FIG. 4 is a top view of a transformer showing electrodes between conductor coil windings in ohmic contact with a metal oxide varistor as an outer layer of a sintered metal oxide magnetic core composite.
  • a composite core for an electromagnetic device such as an inductor which can have an inner portion at 11 disposed within an outer sheath at 12.
  • the composite core can consist of sintered metal oxide, as defined above, which can constitute either the inner portion or outer sheath, and a magnetic material constituting the remaining mass of the composite core which can be conducting, such as Mo-Permalloy metal, or non-conducting, such as ferrite.
  • wire insulation can be required depending upon the degree of volts per turn and volts per mil.
  • An inductor having a composite core of FIG. 1, for example, with an inner mass of metal oxide varistor, which is electroded at both ends to provide ohmic contact between the varistor and soldered terminals, can suppress sparking during sudden voltage surges.
  • Conduction through the varistor can be readily achieved as defined by the above relation where a can be 10 or more.
  • Electroding of the varistor can be effected with a silver-frit which can be silver screened on the surface of the varistor by firing.
  • the metal oxide in instances where the metal oxide is not electroded it can serve as a thermal conducting means to an external heat sink, as it can be readily fabricated to a variety of shapes.
  • the metal oxide varistor can again serve as a spark suppressor between coil windings, or if properly electroded, between the terminals. Electromagnetic devices having the composite core of FIG. 1, are more particularly shown in FIGS. 2 (a) and 2 (b).
  • FIG. 2 (a) shows an inductor 20 having at 21 an inner mass of sintered metal oxide as part of the composite core, a sheath of magnetic material at 22, coil windings at 23, and electrodes 24 and 25 at the ends of the sintered metal oxide.
  • the electrodes provide ohmic contact between the varistor and the conductor and can be applied as a slurry of glass and silver by firing at temperatures of 500 to 850C in an oxidizing atmosphere such as oxygen or air. Contact between the silver electrodes and the conductor can be achieved by conventional soldering techniques.
  • the sintered metal oxide can be initially molded or extruded in the form of a milled metal oxide mixture comprising on the average of from about 96.5 to 97.5 mole percent of zinc oxide and from about 2.5 to about 3.5 mole percent of a mixture of anyone or more of the aforementioned oxides as described above.
  • Sintering of the metal oxide core can be achieved in air at l250 to l450C for l-3 hours.
  • Spark suppression can be achieved between electrodes 24 and 25, when during a sudden voltage surge for example, if the varistor characteristics of the inner sintered metal oxide mass are exceeded conduction will occur in accordance with the previously described relationship where a can exceed 10.
  • FIG. 2 (b) shows another modification of an inductor, where the sintered metal oxide constitutes the outer sheath and again serves as a spark suppressor. Electrodes are shown at 28 and 29.
  • FIG. 3 (a) shows more particularly how the sintered metal oxide varistor can be employed as a spark suppressor in a self-adjusting autotransformer, which is shown in toriodal form.
  • a sintered metal oxide varistor layer which can be of uniform thickness or tapered in accordance with voltage requirements.
  • a magnetic core is shown at 32 and coil windings at 33.
  • a sweep arm at 34 contacts exposed coil windings insulated on the side on contact with the varistor.
  • spark suppression can be achieved by providing a current path across the varistor during voltage surges originating between the sweep arm and an electrode on the varistor not shown.
  • FIG. 3 (b) shows more particularly an autotransformer at 35, in toroidal form, or which can be rectangular in shape if desired, having an inner magnetic core at 36, which can be conducting or non-conducting, varistor layers at 37 and 38 and coil windings at 39.
  • the electromagnetic device at 35 provides for spark suppression between coil windings in contact with the sintered metal oxide and in instances where the magnetic core is conducting, across both varistor layers.
  • FIG. 4 the top view of a transformer in toroidal form is shown, having a metal oxide varistor layer at 41, six electrodes typified by 42 in ohmic contact with such varistor, conductor coils at 43, and terminal leads typified by 44-47 soldered to such electrodes. If desired, a rectangular shaped composite core connecting path to an external heat sink to urt er dissipate heat generated by such electromagnetic device.
  • An electromagnetic device comprising,
  • a composite core said core comprising a composite of a metal oxide varistor and magnetic material
  • An electromagnetic device in accordance with claim 1 having electrodes in ohmic contact with metal oxide varistor and terminals soldered to such electrodes.
  • An autotransformer in accordance with claim 1 having a varistor layer between the coil windings on magnetic core, where said varistor layer provides an a greater than l0 and has electrodes in ohmic contact with conducting leads soldered thereto to provide improved spark suppression between said electrodes during high voltage surges.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Regulation Of General Use Transformers (AREA)
  • Thermistors And Varistors (AREA)
US00185269A 1971-09-30 1971-09-30 Electromagnetic device having a metal oxide varistor core Expired - Lifetime US3710187A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US18526971A 1971-09-30 1971-09-30

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US3710187A true US3710187A (en) 1973-01-09

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Country Status (8)

Country Link
US (1) US3710187A (de)
JP (1) JPS559820B2 (de)
DE (1) DE2247410A1 (de)
FR (1) FR2154724B1 (de)
GB (1) GB1384079A (de)
IT (1) IT967759B (de)
NL (1) NL7213179A (de)
SE (1) SE373976B (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4396970A (en) * 1981-01-12 1983-08-02 Tii Industries Inc. Overvoltage surge arrester with predetermined creepage path
EP0831499A2 (de) * 1996-09-12 1998-03-25 SIEMENS MATSUSHITA COMPONENTS GmbH & CO. KG Einrichtung zur Abführung von Wärme von Ferritkernen induktiver Bauelemente
US6547596B1 (en) * 2000-05-30 2003-04-15 Amphenol-Tuchel Electronics Gmbh Filtered electrical connector with ferrite member and coil
US20030078005A1 (en) * 2001-10-18 2003-04-24 Airnet Ltd. Apparatus and methods for noise suppression in communications systems
US20070128822A1 (en) * 2005-10-19 2007-06-07 Littlefuse, Inc. Varistor and production method
US20100189882A1 (en) * 2006-09-19 2010-07-29 Littelfuse Ireland Development Company Limited Manufacture of varistors with a passivation layer

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6152307B2 (ja) * 2013-06-19 2017-06-21 パイオニア株式会社 コイルユニット

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2803570A (en) * 1952-08-05 1957-08-20 Michigan Bumper Corp Method of making magnetic core layers
US3307074A (en) * 1964-11-05 1967-02-28 Westinghouse Electric Corp Transformer structure with built-in overvoltage protection

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2803570A (en) * 1952-08-05 1957-08-20 Michigan Bumper Corp Method of making magnetic core layers
US3307074A (en) * 1964-11-05 1967-02-28 Westinghouse Electric Corp Transformer structure with built-in overvoltage protection

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4396970A (en) * 1981-01-12 1983-08-02 Tii Industries Inc. Overvoltage surge arrester with predetermined creepage path
EP0831499A2 (de) * 1996-09-12 1998-03-25 SIEMENS MATSUSHITA COMPONENTS GmbH & CO. KG Einrichtung zur Abführung von Wärme von Ferritkernen induktiver Bauelemente
EP0831499A3 (de) * 1996-09-12 1998-07-29 SIEMENS MATSUSHITA COMPONENTS GmbH & CO. KG Einrichtung zur Abführung von Wärme von Ferritkernen induktiver Bauelemente
US6002318A (en) * 1996-09-12 1999-12-14 Siemens Aktiengesellschaft Device for dissipating heat from ferrite cores of inductive components
US6547596B1 (en) * 2000-05-30 2003-04-15 Amphenol-Tuchel Electronics Gmbh Filtered electrical connector with ferrite member and coil
US20030078005A1 (en) * 2001-10-18 2003-04-24 Airnet Ltd. Apparatus and methods for noise suppression in communications systems
US20070128822A1 (en) * 2005-10-19 2007-06-07 Littlefuse, Inc. Varistor and production method
US20100189882A1 (en) * 2006-09-19 2010-07-29 Littelfuse Ireland Development Company Limited Manufacture of varistors with a passivation layer

Also Published As

Publication number Publication date
SE373976B (de) 1975-02-17
IT967759B (it) 1974-03-11
GB1384079A (en) 1975-02-19
JPS4842322A (de) 1973-06-20
DE2247410A1 (de) 1973-04-12
FR2154724A1 (de) 1973-05-11
NL7213179A (de) 1973-04-03
JPS559820B2 (de) 1980-03-12
FR2154724B1 (de) 1977-08-26

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