FR2471031A1 - ELECTRICAL STRUCTURE WITH IMPREGNATED SYNTHETIC PAPER INSULATION - Google Patents

Abstract

ELECTRIC CABLES INSULATED BY "SYNTHETIC PAPER" TYPE PAPER IMPREGNATED WITH OIL. THEY ARE CHARACTERIZED IN THAT THE INSULATING OIL CONSISTS OF A COMPOUND HAVING A TGD DIELECTRIC LOSS OF LESS THAN 0.5.10, CONTAINING AT LEAST CARBON ATOMS AND FLUOR ATOMS, SUCH AS TRIFLUROMETHYL-PERFLUORODECALINE. THIS INSULATING OIL OCCUPANTS AXIAL CHANNEL 11 AND IMPREGNATES INSULATION 12 IN SYNTHETIC PAPER. THE SYNTHETIC PAPER SO IMPREGNATED DOES NOT SUBJECT TO DANGEROUS SWELLING FOR THE OPERATION OF THE ELECTRICAL STRUCTURE. THESE CABLES CAN BE EXPOSED TO EXTREMELY HIGH VOLTAGES, UP TO 1000KV.

Description

The present invention relates to an electrical structure comprising

metal bodies subject to

  high voltage and insulated with impregnated paper. It is

  in particular the insulation of these bodies by means of a synthetic paper impregnated with an oil having properties

high dielectrics.

  The term "electrical structure" in this specification has a very general meaning. it designates installations, devices and apparatus in which metal bodies are present in any event

  subjected to very high voltages (transformers, conden-

  electrical cables etc.) 0 However, the application

  preferred embodiment of the present invention relates to

  of the fluid oil type (HoFo cables) and in particular

  to connect cables for very high voltages (750-1000 kiv) which are expected, for a whole series of technical and economic reasons, to be more and more in demand on the market. For this reason, we will mainly refer, in

  the description and in the example, to electric cables,

  but this application is preferred, and not exclusive.

  We know that in many structures

  metal bodies subject to high voltages.

  They have insulation made of cellulosic paper wrapped around these bodies and impregnated with oils. These oils are generally hydrocarbon compounds (alkylbenzenes,

  mineral oils, polybutenes, etc.) and also hydro-

  chlorinated carbides, siliconic derivatives etc.

  In the event of operation with alternating current

  native, the insulation thus arranged is not suitable when the voltage reaches very high values. Indeed, as the losses in the dielectric increase rapidly with the voltage, the temperature of the electrical structures can increase until reaching intolerable values. This occurs for example with electrical cables for very high voltages (750-1000 kV) in which no suitable cooling system has been provided, the efficiency of which is furthermore influenced by the dissipations.

internal heat.

  In the case of electric cables of the above type, the insulation (paper impregnated with oil) must have, as an indication, at least the following characteristics dielectric loss (tg È) less than 1.103; rigidity in

  alternating current from 60 to 70 kV / mm; rigidity in current

  tinu and impulse stiffness of 150 to 160 kV / mm.

  Cellulosic paper has a rather high dielectric loss (tg) value; and even with the cleanest cellulosic papers it is not possible to obtain, for the paper and oil-formed insulator, a value of less than 1.5. It is therefore necessary, in order to be able to give the insulation the dielectric properties that are required of it, to modify suitably the combination of the

  paper with impregnation oil.

  One solution is to use "paper

  synthetic "as a replacement for cellulosic paper.

  We know that most plastics

  commonly used as insulators (polyethylene, poly-

  propylene etc.) have a dielectric loss value (tg c)

  which is usually at most 1/10 of that of cellular paper

  Losique. These materials have also, theoretically, a dielectric strength, determined on small thicknesses, very high. With these materials, mass-extruded insulators are constructed which are suitable for certainly high voltages but certainly not in the range of 750 - 1000 kV, this being due to the inevitable formation of defects in the plastic mass both at during the manufacturing process that during

the operation of the cable.

  However, we can work opportunely

  these same plastics in such a way as to modify the

  me and the physico-chemical structure, and make them

  can be used in the form of sheets, which are more

  in the form of "synthetic paper" to be wrapped around

  metal bodies of electrical structures and to

primer of insulating oils.

  These sheets consist either of a set of fibrils implemented by calendering or

of a film.

  Various types of synthetic paper are known

  tick: high density polyethylene, high crystallinity;

  stretched and biaxially oriented polyethylene, poly-

  ethylene compacted by mechanical action, thermal etc .. The isolation obtained by impregnating conventional oils synthetic paper generally has significant improvements in

  dielectric point of view, compared to the same kind of iso-

cellulosic paper.

  However, regardless of the type of synthetic paper prepared by the known techniques, it is not exempt, although to a varying extent from one case to another, of a disadvantage, namely the swelling caused by the absorption of impregnating oil in the intermolecular interstices of the plastic material, swelling which is a direct function of the temperature, and is therefore all the stronger as the operating voltage of the

  electrical structure is higher.

  The swelling of the synthetic paper, and therefore the insulation as a whole, can cause

  considerable damage to the entire electrical structure.

  Indeed, the swelling of the synthetic paper

  It generates internal mechanical tensions which can modify the geometry of the insulation and, consequently, induce irreversible deformations of this electrical structure. A suitable remedy is to swell the synthetic paper with the impregnating oil before winding it around the metal bodies of the electrical structure, but this solution is complicated by

  technical view and the preliminary treatment of syn-

  thetic often causes unwanted lowering

  mechanical properties of the synthetic paper itself.

  On the contrary, we can obtain improvements

  substantial contributions by using, as "synthetic paper"

  that ", composite insulators very thin.

  These composite insulators consist of a plastic laminate

  tick (polypropylene, fluorinated ethylene-propylene copolymer

  etc.) coupled to a layer of cellulosic or

  sere between two layers of cellulosic paper (as is or reinforced with synthetic materials).

  The use of composite elements

  The use of conventional impregnating oils greatly improves, as can easily be expected, the swelling behavior. But there are still disadvantages related to the dielectric characteristics and to the realization of these

composite insulators.

  Indeed, the presence of one or two cou-

  cellulosic paper does not allow for complete enjoyment

  the dielectric characteristics of the material

plastic.

  Moreover, as one can easily

  take and as can be verified in practice it

  is not at all simple from the technical point of view of com-

  Perfectly multiply several layers of different materials to form a thin film (and this has consequences not negligible economically too).

  In any case, it seems quite

  both from a technical and economic point of view, of

  the "synthetic paper" (in the form of a set of calendered fibrils or a film or composite) in the dielectric structures by impregnating it with insulating oils which do not compromise the dielectric properties of synthetic paper and, unlike the usual insulating oils, do not cause the swelling of synthetic paper; or at least cause it to a small enough extent not to jeopardize

  the electrical structure in operation.

  This is the purpose of the present invention,

  which makes it possible to overcome all the disadvantages of

as known.

  In particular, the object of the invention is an electrical structure, in particular an electric fluid-type electric cable, comprising at least one metal body

  maintained under high voltage, isolated with synthetic paper

  tick around this metal body and impregnated with a

  insulating oil, this insulating oil having a dielectric loss

-3

  (tgt) less than O05olO310 electrical structure

  characterized in that said insulating oil is composed of an organic-type compound containing at least carbon atoms and fluoro atoms

  In addition, this insulating oil may also contain

  The present invention will be better understood by the

  description of a particular e-example relating to an application

  preferable non-recirculating cation an electrical cable of the

  fluid oil type (cSble H0Fo) o On the other hand, there is

  as already pointed out, that the present invention

  advantageously applies to all cases of elec-

  which comprise at least one metal body maintained under high electrical voltage and which is insulated by oil-impregnated paper (transformers, capacitors, etc.) The single figure of the attached drawing represents the

  fluid oil cable C, which comprises: the driver 10 par-

  run longitudinally through channel 11; an insulator 12 cons

  characterized by a winding of synthetic paper (in the form of a set of fibrils used in the shell, or a film or a composite) on the conductor 10; a

  metal sheath 13 serving as a sleeve disposed on this insulation

  lant 12o An insulating oil occupies this longitudinal channel 11 and impregnates the synthetic paper insulation 12o. In accordance with the present invention, this oil,

  which has a "dielectric loss" (tg) of at least

-3

  less than 0.5.10 3, consists of a compound of the type

  containing at least carbon atoms and atoms

  of fluorine. This oil may also contain oxygen atoms.

  Two compounds have been shown to be

  this particular in the invention: trifluoromethyl-

  perfluorodecalin and a perfluorinated polyether having a weight

  molecular.pris between 200 and 5000.

  The first is a compound containing exclusively

  carbon atoms and fluorine atoms and corresponding to the formula

F2F F CF

F2 f + 3

F2O F2

F2F F2

  The second is a polymer containing carbon atoms, fluorine atoms and oxygen atoms, with a molecular weight between 200 and 5000, and having the following formula:

CF CF3

- - SF - CF - CF2 - CF 2 0 - CF2-

  The chemical structure is basically the one

  of a hexafluoropropylene polyether.

  The advantages offered by the compounds of the in-

  used as impregnating oils for syn-

  theories, compared to the compounds of the prior art

  of the results in Table 1,

  relating to swelling tests carried out at various times

  tures. In these tests a sample of

  synthetic stone (high density polyethylene film of high crystallinity) immersed in the oil at the desired temperature for 72 consecutive hours and then measured

  the percentage volume change resulting from this

  ment. From the values given in Table I, it is deduced that the swelling of the synthetic paper is, at equal temperature, much less in the oils of the invention (example N 1 with trifluoromethyl-perfluorodecalin and

  Example N 2 with a perfluorinated polyether having a molecular weight of

  between 200 and 5000) than in an oil of the

  prior art (example N 3 with decylbenzene).

  In practice, the swelling recorded with

  the oils of the invention are not dangerous under the conditions

  usual operating procedures for electrical structures

  and temperatures close to

  melting synthetic papers.

BOARD

  I Swelling tests of a high density polyethylene film of high crystallinity in various

  oils and at various temperatures.

  Volume variation in% Example NO Oil after 72 hours

1000C 1100C 1200C 130C

1 Trifluoromethyl

  perfluoro-decalin + 3.8 + 4.5 + 5.2 +35 2 Perfluorinated polyether (average molar weight =

1000) + 0.5 + 1.8 + 3.7 +28

  3 Decylbenzene + 5.5 + 21.0 early diss.

of com

dissol. plete

Claims (4)

  1. Electrical structure, in particular an electric cable of the fluid oil type, comprising at least one metal body maintained under high tension, isolated with a synthetic paper disposed around this metal body and impregnated with an insulating oil, this insulating oil. having a dielectric loss (t g) of less than 0.5 · 10 3, characterized in that said insulating oil consists of an organic-type compound containing at least carbon and fluorine atoms.   2. Electrical structure according to claim 1, characterized in that the insulating oil also contains oxygen atoms.   3.- Electrical structure according to the claim   1, characterized in that the insulating oil is trifluoro-   methyl-perfluorodecalin. 4. Electrical structure according to claim 2, characterized in that the insulating oil is a perfluorinated polyether having a molecular weight between 200 and 5000.