US3598691A - Multi-ply paper for insulating high tension electric cables - Google Patents

Multi-ply paper for insulating high tension electric cables Download PDF

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Publication number
US3598691A
US3598691A US3598691DA US3598691A US 3598691 A US3598691 A US 3598691A US 3598691D A US3598691D A US 3598691DA US 3598691 A US3598691 A US 3598691A
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US
United States
Prior art keywords
paper
impermeability
layers
layer
category
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Expired - Lifetime
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English (en)
Inventor
Franco Pasini
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Pirelli and C SpA
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Pirelli SpA
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Assigned to SOCIETA' PIRELLI S.P.A., A COMPANY OF ITALY reassignment SOCIETA' PIRELLI S.P.A., A COMPANY OF ITALY ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: INDUSTRIE PIRELLI S.P.A.
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Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
    • H01B13/30—Drying; Impregnating
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/48—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances fibrous materials
    • H01B3/485—Other fibrous materials fabric
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/02—Disposition of insulation
    • H01B7/0208—Cables with several layers of insulating material
    • H01B7/0225—Three or more layers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24942—Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24942—Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree
    • Y10T428/2495—Thickness [relative or absolute]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24942—Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree
    • Y10T428/24992—Density or compression of components
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/31504—Composite [nonstructural laminate]
    • Y10T428/31971—Of carbohydrate
    • Y10T428/31993—Of paper

Definitions

  • the present invention relates to an improved type of paper suitable for insulating high tension electric cables. More particularly, it relates to paper tape which is helically wrapped about a conductor and thereafter impregnated, and to the cable so insulated.
  • a good cable insulator must primarily posses: (a) a high dielectric strength (in order to withstand high electric gradients and, therefore, enable cables to be fabricated with reasonable radial dimensions); and -(b) a low dielectric loss factor (in order to maintain within tolerable limits the power losses in the dielectric which, the loss factor being constant, increase proportionally with the square of the voltage).
  • the paper In the case of paper which is to be impregnated, the paper must possess certain additional physical character istics. For instance, the impermeability of the papers must not be so great as to prevent its becoming completely impregnated by the usual impregnating fluids, such as mineral oils, synthetic fluids or their mixtures.
  • the expression impermeability of the paper refers to the papers resistance to the passage of liquid or gaseous fluids. It is a quantity that can be measured and repre sented in terms of Emanueli units (E.U.). In addition to its impermeability the paper must possess sufiicient me chanical strength and the like to permit its application to the conductor by modern wrapping machinery.
  • An object of the present invention is to provide insulating papers for use in very high voltage electric cables having considerable dielectric strength, equal to or higher than that of paper normally used for the insulation of electric cables, and a substantially lower dielectric loss factor.
  • a paper for insulating high tension electric cables comprising a plurality of layers whose individual physical characteristics fall into one or the other of two categories, there being at least one layer in each category, the first category being distinguished by an apparent density less than that of the second with a maximum value of 0.7 gram per cubic centimeter, the second category being dis tinguished by an impermeability greater than that of the first and equal to at least l0 l0 Emanueli units, the ratio of the total thickness of the layers in the second category to the total thickness of the layers in the first category being no higher than 1:1.
  • the low density of the first category not exceed 0.6 gram per cubic centimeter, that the impermeability of the second category be no lower than 50 10 EU, and that the mentioned ratio be no higher than 1:2.
  • the term density as it applies to the paper means the apparent density, namely, that obtained by dividing the mass of a given paper volume by the volume itself, thereby taking into account the air gaps between the cellulose fibres.
  • the paper according to the present invention is admirably suited to this purpose since it can be produced with very high values of dielectric strength without exceeding the dielectric loss factor values of conventional papers used for the insulation of very high voltage electric cables. This result is obtained by imparting to the high impermeability layers extremely high impermeability values, over 200 X 10 EU. and preferably over 500 10 EU.
  • the paper according to the invention can be easily impregnated when it is tightly wrapped on the conductor.
  • it is sutficient to impart to the low density layers int he first category an impermeability value lower than l EU. and preferably lower than 0.5 X 10 EU.
  • the papers according to the invention may be constituted by two layers, namely, one impermeability layer in the second category and one low density layer in the first category. Alternatively, it may have three layers, namely, one low density layer sandwiched between two high impermeability layers.
  • the two-layer type it is advantageous to dispose the paper in such a way that the layer having high dielectric strength is directed towards the conductor.
  • the use of paper constituted by three layers is advantageous when still better performance is required with respect to the electric gradient which can be withstood whent he papers are wrapped on the cable. In the latter case, the sum of the thickness of the two high impermeability layers is equal or approximately equal to the thickness of the single high impermeability layer used in the paper constituted by two layers.
  • a further advantage of the three-layer paper is it symmetry which facilit-ates the wrapping operations.
  • FIG. 1 is a sectional view through a paper constructed in accordance with the invention
  • FIG. 2 is a view similar to FIG. 1 showing a modification of the paper therein;
  • FIG. 3 is a view in longitudinal half section of a conductor wrapped with the paper of FIG. 1;
  • FIG. 4 is a view in longitudinal half section of a conductor wrapped with the paper of FIG. 2.
  • FIG. 1 A two layer paper is shown in FIG. 1.
  • the high impermeability layer is designated 10 and the low density layer is designated 11.
  • the letters t and T indicate the thickness of the layers 10 and 11, respectively.
  • FIG. 2 a three layer paper is illustrated in FIG. 2 having a high impermeability layer 10 on each face of the low density layer 11.
  • the paper in accordance with the invention has: (a) a dielectric strength very near to that of a homogeneous paper having an equal total thickness and an impermeability equal to that of the high impermeability layer; (b) dielectric losses practically equal to those of a homogeneous paper having an equal thickness and a density equal to that of the low density layer; and (c) an impregnation capacity equal to what it would have if it were constituted by the low density layer only. It is believed that the impregnation capacity is affected by the disposition of the paper layers in the winding on the conductor. In particular, referred to the arrangement of FIG.
  • the path of the impregnant during the impregnating process is that indicated by the arrows 14.
  • This path in the low density layers 11, follows in part a longitudinal direction and in part a perpendicular direction with respect to said layers.
  • the paper which can be easily impregnated per se, offers very little resistance to the passage of the impregnant. This is due to the fact that the cellulose fibres constituting the paper lie for the most part parallel to the cable conductor and create, therefor, longitudinal ducts within which the oil may flow.
  • the impregnating agent can reach in a very short time the layers nearest to the conductor, even admitting that the layers 10 are quite impermeable.
  • This arrangement is easier to handle since the paper tapes are symmetrical on both sides and it is not necessary to be concerned with the position of the high impermeability layer.
  • the best feature of this arrangement is, however, its ability to withstand very high electric gradients when the cable is in service.
  • the weak points in cables having a stratified and impregnated dielectric are the butt spaces 13 between the turns of the insulation. These spaces are also called oil gaps, since they are totally filled with the impregnating fluid.
  • the maximum electric gradient which can be withstood by the stratified and impregnated dielectric of an electric cable decreases.
  • the presence of a high impermeability layer on both sides (in the radial direction) of the oil gaps 13 gives rise to a better definition of the radial extent of the latter and, therefore, increases the maximum electric gradient which can be withstood by said dielectric.
  • the oil gaps 13 are bounded on one side by the low density layer 11 (low impermeability layer) which can be considered as an effective extension in the radial direction of the oil
  • the papers according to the invention have a value of dielectric strength practically equal to that of the material constituting the high impermeability layers and virtually independent of the value of the dielectric strength of the low density layers.
  • the papers according to the invention have a value of dielectric strength practically equal to that of the material constituting the high impermeability layers and virtually independent of the value of the dielectric strength of the low density layers.
  • K is a constant depending on the size of the dielectric V is the applied voltage 6 is the dielectric loss angle of the dielectric
  • e is the dielectric constant
  • the papers according to the invention have: (a) a dielectric strength very near to that of a very high impermeability paper; and (b) a dielectric power factor equal to that of a low density paper. No paper among those at present in use shows a combination of values of high dielectric strength and low power factor comparable with that of paper constructed in accordance with present invention.
  • the papers described herein can be made in any suitable way.
  • they can be manufactured by employing the technology already in use for conventional multi-ply papers. That is, use can be made of conventional paper machines of the multi-wire type, either equipped with Fourdrinier or cylinder forming devices. These machines, with the simultaneous manufacture of the individual layers, also provide for the uniting of said layers which, joining spontaneously to one another, results in a perfectly compact finished product.
  • each wire is to be supplied with different pulp stocks intended to provide the desired characteristics of impermeability and/ or density in the individual layers and consequently in the final product.
  • a multi-ply paper for insulating high tension electric cables said paper being divided internally into a plurality of adjacent layers extending generally parallel to the surfaces of the paper and each layer being united with the adjacent layer throughout the extent thereof, said layers having diflerent physical characteristics which fall into one or the other of two categories, there being at least one layer in each category, the first category being distinguished by an apparent density less than that of the second with a maximum value of 0.7 gram per cubic centimeter, the second category being distinguished by an impermeability greater than that of the first and equal to at least 10 10 Emanueli units, the ratio of the total thickness of the layers in the first category being no higher than 1:1.
  • a paper according to claim 2, wherein said impermeability which distinguishes the second category is equal to at least 50 10 Emanueli units.
  • a paper according to claim 5 consisting essentially of one layer in said first category sandwiched between two layers in said second category.
  • a paper according to claim 1 consisting essentially of one layer in said first category sandwiched between two layers in said second category.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Insulating Bodies (AREA)
  • Paper (AREA)
  • Organic Insulating Materials (AREA)
US3598691D 1967-03-25 1968-03-08 Multi-ply paper for insulating high tension electric cables Expired - Lifetime US3598691A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
IT1418967 1967-03-25

Publications (1)

Publication Number Publication Date
US3598691A true US3598691A (en) 1971-08-10

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Family Applications (1)

Application Number Title Priority Date Filing Date
US3598691D Expired - Lifetime US3598691A (en) 1967-03-25 1968-03-08 Multi-ply paper for insulating high tension electric cables

Country Status (10)

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US (1) US3598691A (US08177716-20120515-C00003.png)
AT (1) AT276521B (US08177716-20120515-C00003.png)
BE (1) BE710750A (US08177716-20120515-C00003.png)
CH (1) CH500562A (US08177716-20120515-C00003.png)
DE (1) DE1765011A1 (US08177716-20120515-C00003.png)
ES (1) ES352284A1 (US08177716-20120515-C00003.png)
FR (1) FR1554336A (US08177716-20120515-C00003.png)
GB (1) GB1190962A (US08177716-20120515-C00003.png)
NO (1) NO122079B (US08177716-20120515-C00003.png)
SE (1) SE339840B (US08177716-20120515-C00003.png)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3959549A (en) * 1973-08-08 1976-05-25 Siemens Aktiengesellschaft Multi-layer insulation for deep-cooled cables
US4556756A (en) * 1981-01-16 1985-12-03 Societa' Cavi Pirelli S.P.A. Electric power cable impregnated with insulating fluid

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3959549A (en) * 1973-08-08 1976-05-25 Siemens Aktiengesellschaft Multi-layer insulation for deep-cooled cables
US4556756A (en) * 1981-01-16 1985-12-03 Societa' Cavi Pirelli S.P.A. Electric power cable impregnated with insulating fluid

Also Published As

Publication number Publication date
ES352284A1 (es) 1969-07-01
GB1190962A (en) 1970-05-06
CH500562A (it) 1970-12-15
DE1765011A1 (de) 1971-07-01
FR1554336A (US08177716-20120515-C00003.png) 1969-01-17
SE339840B (US08177716-20120515-C00003.png) 1971-10-25
AT276521B (de) 1969-11-25
NO122079B (US08177716-20120515-C00003.png) 1971-05-18
BE710750A (US08177716-20120515-C00003.png) 1968-06-17

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Legal Events

Date Code Title Description
AS Assignment

Owner name: SOCIETA PIRELLI S.P.A., PIAZZALE CADORNA 5, 20123

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:INDUSTRIE PIRELLI S.P.A.;REEL/FRAME:003847/0084

Effective date: 19810101