JPH07169339A - Dielectric strength improvement type power cable - Google Patents

Abstract

PURPOSE: To provide a power cable having a polymer insulator of high dielectric strength and capable of conforming only locally to possibly existing impurities or cavities by forming a first dielectric layer having a specific composition on the outside of an electric core wire. CONSTITUTION: A dielectric-strength-improved DC or AC power cable has the following structure. The power cable has an electric core wire 1 and an insulating polymer first dielectric layer 3 of the core wire 1, the first dielectric layer 3 is made from an insulating polymer matrix containing at least one conducting polymer. The conducting polymer is combined with the polymer matrix in the ratio that the electric conductivity becomes 10<-14> S/cm in the case of DC, and 10<-10> S/ cm in the case of AC. In the power cable, an inner semiconductor shield 2, an outer semiconductor shield 4, and a protecting outer jacket 5 are arranged in the surroundings of the core wire 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC or AC high voltage power cable. In particular, such power cables with improved dielectric strength are of interest.

[0002]

BACKGROUND OF THE INVENTION This power cable preferably comprises an extruded polymeric insulation. The insulator generally covers the inner semiconductor shield, which itself covers the conductive core of the cable, as well as the outer semiconductor shield. This polymerized insulator has a high specific dielectric strength. However, the effective dielectric strength obtained on the cable is lower than the intrinsic strength. The reason for this difference is primarily the presence of impurities and cavities that are deposited or formed on the cable before or during installation of the insulation. The presence of such impurities and cavities causes local concentration of the electric field within the insulator, causing electrical defects through the cable insulator.

Japanese Unexamined Patent Publication (Kokai) No. 2-18811 describes a polymer insulation type electric power cable containing 0.2 to 1.5% by mass of carbon black. The insulation thus improved can be mounted directly on the conductive core of the cable. Since the content of carbon black is small,
The uniformity of the electric field distribution, that is, the reliability of the cable, is improved, and the risk of electrical defects due to irregularities on the periphery of the core wire or impurities or cavities inside the insulator is reduced. Also, since its content is a small amount but not zero,
The insulator is given a small electrical conductivity.

This conductivity is constant and is related to the intrinsic conductivity of carbon black contained in the insulator.
Typical values for the intrinsic conductivity of carbon black are 10 to 10
0 S / cm. This conductivity also promotes leakage current in the insulator, increasing its dielectric loss. In addition, the insulation thus improved has a low specific dielectric strength, which in turn reduces the effective dielectric strength on the cable. This has nothing to do with the presence or absence of internal cavities or irregularities.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to create a power cable in which the polymerized insulator has a high dielectric strength and is only locally adapted to impurities and cavities that may be present. is there.

[0006]

SUMMARY OF THE INVENTION The present invention comprises an electrical core and an insulating polymerized first dielectric layer of the core, the first dielectric layer comprising an insulating polymerized matrix containing at least one conductive polymer. And the electrically conductive polymer is incorporated into the polymeric matrix in a ratio such that the resulting electrical conductivity of the first dielectric layer is less than 10 ^-14 S / cm. Provide a DC power cable with improved dielectric strength.

The invention further comprises an electrical core and an insulating polymerized first dielectric layer of the core, the first dielectric layer comprising an insulating polymerized matrix containing at least one electrically conductive polymer, the electrically conductive matrix comprising: AC power with improved dielectric strength, characterized in that the polymer is incorporated in this polymerisation matrix in such a ratio that the resulting electrical conductivity of the first dielectric layer is less than 10 ^-10 S / cm. Provide the cable.

[0008]

EXAMPLES Please note that all conductivity values were obtained at room temperature.

The cable shown in FIG. 1 comprises a conductive core 1, which is formed of conductive strands but can also be formed of a single conductor, the circumference of which is It is surrounded by an inner semiconductor shield 2, the inner semiconductor itself is surrounded by an insulating dielectric layer 3, which in turn is surrounded by an outer semiconductor shield 4. A protective sheath 5 surrounds the outer semiconductor shield 4 and serves to protect the cable. The sheath is made of lead or lead alloy, in particular. The sheath can also be an insulator, in which case it is preferably integrated with the ground metal shield beneath it.

In this cable according to the invention, the insulating dielectric layer 3 is composed of an insulating polymer matrix, in which the resulting electrical conductivity of the dielectric layer 3 is less than 10 ^-14 S / cm at direct current, 10 ^{-10 for} AC
At least one conductive polymer is incorporated in a ratio such that it is less than S / cm.

The electrical conductivity or the permittivity of the dielectric layer 3 in a cable according to the present invention depends on the presence of defects somewhere depending on the type of conductive polymer contained in the cable by a limited amount. , Significantly increased locally. However, depending on the location, these rates may change depending on the defect.

Therefore, it can be said that the dielectric layer 3 is locally self-adaptive in response to various existing defects. In this way, the dielectric layer 3 reduces the risk of destruction due to these defects and allows a uniform distribution of the electric field through the layer over the length of the cable.

For example, the conductive polymer may be a polymer in which impurities are injected (doping), impurities are removed (dedoping), or impurities are self-injected (autodoping).

The conductive polymer which is not implanted with impurities is
It should be noted that polyaniline obtained by polycondensation reaction of aniline and quinone, or polyacetylene whose polymerization is initiated using a Ziegler-Natta type catalyst, is a polymer whose synthesis is performed without depending on the injection of dopant.

Impurity self-implanted conductive polymers are polymers obtained by grafting of dopants during synthesis, for example polyaniline grafted with sulfone groups on the ring.

The depleted conductive polymer is a polymer such as polyaniline that has been treated with hydrochloric acid that has been impurity-implanted during synthesis and then depleted by suitable means of removal of hydrochloric acid.

When a polymer self-implanted with impurities is used to obtain the intrinsic conductivity according to the invention, its proportion in the dielectric layer 3 is large, whether it is used in direct current or in alternating current. Both are about 2% of the mass.
When using a polymer which has not been doped with impurities or has impurities removed, the proportion in the dielectric layer 3 should be at most approximately 5% of the mass, whether in direct current or in alternating current. Is desirable.

The type described in European patent application EP-A-0507676, wherein either or each of the inner semiconductor shield 2 and the outer semiconductor shield 4 is composed of an insulating polymer matrix and at least one electrically conductive polymer. It is convenient to be one of The conductive polymer is selected from a polymer in which impurities are not injected and a polymer in which impurities are removed after impurities are injected, and the conductivity of the semiconductor shield is 5 to 70% by mass so that the conductivity of the semiconductor shield is 1 S / cm or less. , Preferably 20 to 30% in the polymer matrix.

In a likewise advantageous alternative, any one or each of these semiconductor shields is made of an insulating polymer and in particular European patent application EP-A-5012926.
Of at least one electrically conductive polymer self-implanted with impurities of the type described in. This conductive polymer should account for more than 5% of the mass, and preferably of the mass.
It is incorporated in the polymerisation matrix in a proportion of 10 to 40%.

The given concentrations and conductivities for semiconductor shields are valid for both DC and AC.

The polymeric matrix of the dielectric layer 3, like the matrices of the semiconductor shields 2 and 4, comprises at least one thermoplastic polymer. This thermoplastic polymer is an acrylic resin, styrene resin, vinyl resin, cellulose resin, polyolefin, fluoropolymer, polyether, polyimide, polycarbonate, polyurethane,
It is selected from silicones, their copolymers, and also mixtures of homopolymers and mixtures of homopolymers and copolymers.

In particular, this thermoplastic polymer is polypropylene (PP), polyethylene (PE), a copolymer of ethylene and vinyl acetate (EVA), ethylene-propylene-
Diene-monomer (EPDM), polyvinylidene fluoride (PVDF), ethylene-butyl acrylate (EB
It is selected from any of A) or a mixture thereof.

Alternatively, the polymeric matrix comprises at least one thermosetting polymer selected from polyesters, epoxy resins and phenolic resins.

The one or more polymers of the dielectric layer 3 that have not been implanted or have been impurity-removed after the implantation of impurities, like polyaniline, polythiophene, polypyrrole, like the possible polymers of the semiconductor shields 2 and 4. It is selected from the group comprising polyacetylene, polyparaphenylene, polyalkylthiophenes, as well as their inductive properties and mixtures.

These polymers which are not impurity-implanted or impurity-removed do not contain ionic groups. Their intrinsic conductivity, measured at direct current, is very low, approximately 10 ⁻¹⁰ to 10 ⁻⁹ S / cm. The conductivity of the dielectric layer 3 containing at most 5% of the unimplanted or depleted polymer may be less than about 10 ^-14 S / cm for direct and low field applications. 10 ^-10 S for use in AC and low electric field
/ Cm or less. In other words, it does not impair the high dielectric strength of this layer if it is free of defects or if the existing defects are insignificant. Also, this conductivity is locally about 10 ^-9 S / in a high electric field due to the presence of defects.
It may be cm. As a result, the dielectric strength is impaired only locally and in a form adapted to the defect,
It allows the distribution of high electric fields to the defective location while avoiding the risk of resulting destruction.

The one or more self-implanted polymers of the dielectric layer 3 are, like the possible polymers of the semiconductor shields 2 and 4, self-implanted polyaniline having benzene nuclei or benzene and quinone nuclei. To be selected from. Polyaniline has a side chain consisting of a hydrocarbon radical having 2 to 8 carbon atoms interrupted by at least one heteroatom and a strongly acidic radical or one of its salts. The heteroatoms are themselves selected from O and S, and the strongly acidic groups are selected from sulfonic acid, phosphonic acid and phosphoric acid residues or salts thereof.

The intrinsic electrical conductivity, measured at direct current, of these polymers self-implanted with impurities, averages around 10 ^-3.
Or 10 ^-2 S / cm. Furthermore, this intrinsic conductivity is
By changing the molecular ratio of the two types of side chains, 10
^-Can be adjusted freely from ^-5 to 1 S / cm. The electrical conductivity of the dielectric layer 3 composed of the above polymer matrix, to which at most 2% of the mass of this polymer self-implanted with impurities has been added, is itself tunable and at low DC electric fields. Approximately 10 ^-14 S / cm or less for use, and approximately 10 for use in low AC electric fields.
^-10 S / cm or less. This dielectric strength decreases as the electric field increases. On the contrary, the electrical conductivity and the permittivity of such a dielectric layer rise significantly with electric field, so that it is possible to withstand important local concentrations of space charges without difficulty and to distribute those charges.

In a variant of FIG. 1, which is not shown in the accompanying drawings, the above-mentioned dielectric layer 3 directly surrounds the cable core and is directly covered by a protective sheath 5.
The two inner and outer semiconductor shields are removed.

In a variant of the embodiment according to FIG.
The same reference numerals as in FIG.

The cable shown in FIG. 2 comprises an inner dielectric layer 7 between the conductive core 1 and the dielectric layer 3 and an outer dielectric layer 8 between the dielectric layer 3 and the protective sheath 5. ing.

Each of these two dielectric layers 7 and 8 is
It is comprised of at least one polymer of any of the above insulating polymerized matrices and at least one electrically conductive polymer incorporated into the matrix at a rate of 5 to 20% by weight. The conductive polymer is at least one of the three types of conductive polymers described above, but is preferably selected from a single polymer that has not been impurity-implanted or has impurities removed. The conductive polymer is added to the polymerized matrix of the dielectric layer in a proportion of not more than 20% and not less than 5% by weight.

The resulting electrical conductivity of the dielectric layers 7 and 8 is 10 ^-14 to 1 S / cm for direct current use and 10 ^-10 to 1 S / cm for alternating current use.
Is.

The electrical conductivity of these inner and outer dielectric layers 7 and 8 with the doped or undoped polymer can reach several siemens / cm in high electric fields.

In this variant of FIG. 2, the cable is provided with two semiconductor shields as in FIG. 1, the inner shield being covered by the inner dielectric layer 7 and the outer shield being the outer dielectric layer 8. Covers.

Similarly, in one variation, shown in phantom in FIG. 2, either or each of the inner dielectric layer 7 and the outer dielectric layer 8 has several basic elements, such as 7A, 7B, 8A, 8B. It is divided into layers. The proportion of conductive polymer in these base layers varies from 5 to 20%, but varies from layer to layer. The conductive polymer ratio of the base layer of the inner layer 7 is the innermost base layer 7A in contact with the core wire.
It decreases in order from. On the contrary, in the outer layer 8,
From the innermost base layer 8A in contact with the dielectric layer 3 to the outermost base layer 8 in contact with the protective sheath 5.
It increases to B.

The inner dielectric layer 7 and the outer dielectric layer 8 or, if appropriate, their basic layers, in the case of high electric fields due to internal defects and also to the peripheral irregularities of the conductive core or defects of the protective sheath, Acts as an inner and outer semiconductor shield. It also plays the role of a dielectric layer in a low electric field.

For direct current use, the electrical conductivity of layer 7A is 10 ^-9 to 1 S / cm and that of layer 7B is
10 ^-14 to 10 ^-9 S / cm, the conductivity of the layer 8A is 10 ^-14 to 10 ^-9 S / cm, and the conductivity of the layer 8B is 10 ^-9 to 1 S / cm.
cm.

For use in alternating current, the electrical conductivity of layer 7A is 10 ^-5 to 1 S / cm and the conductivity of layer 7B is
10 ^-10 to 10 ^-5 S / cm, the conductivity of the layer 8A is 10 ^-10 to 10 ^-5 S / cm, and the conductivity of the layer 8B is 10 ^-5 to 1 S / cm
cm.

In addition to the main advantages of making the power cable according to the invention more reliable, the following can be mentioned in particular:

The overall dielectric strength of the cable increases. This, on the one hand, is due to the fact that the dielectric strength of one or more of the dielectric layers of this cable remains high,
On the other hand, the resulting effective dielectric strength is
This is because this eigenvalue is continuously maintained in every defect-free zone, and when a defect is present, it changes only locally depending on the defect.

The maximum locally allowed electric field is large. A typical value of about 10 kv / mm for a certain type of power cable according to conventional construction is 20 to 30 kv / mm for the same type of cable according to the invention.
Can be raised to the value.

-Increasing the working voltage of the cable allows an increase in the power delivered by the cable.

The thickness of the insulating dielectric layer can be reduced while maintaining the performance of the cable.

Of course, the invention is not limited to the embodiments described above.

In particular, if the cable according to the invention is provided with a corresponding semiconductor shield, these shields can be formed from the materials mentioned above or the conventional materials used for semiconductor shields in existing construction cables. It can also be configured with.

Furthermore, the cable according to the invention can also be produced using the conventional process of manufacturing this type of cable.

Finally, in the embodiment shown in FIG. 2, it is possible to create more than one base layer for each of layers 7 and 8.

[Brief description of drawings]

1 shows a cross-sectional view of a power cable according to the invention.

2 shows a cross-sectional view of an alternative embodiment of the cable of FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jijan Bequer, France, 62610 Otung, Riu D'Ardre, 263 (72) Inventor Jijan-Claude Asier, France, 91860 Epine Suh Senar , Vila de 3 Cayeu 13 (72) Inventor Bernard Aradourneys France, 91360 Epinee Siul Orgyu, Liu d'Ateis, 7 (72) Inventor Alain Le Muoutou France, 91190. Ziff Sieur Ibet, Are Do La Vanier Do Moperte Yui 90

Claims (5)

[Claims] 1. A DC power cable with improved dielectric strength, comprising an electric core wire and an insulating polymerized first dielectric layer of the core wire, the first dielectric layer comprising at least one conductive polymer. An electric power, characterized in that it is composed of an insulating polymer matrix which comprises a conductive polymer incorporated into this polymer matrix in such a ratio that the resulting electrical conductivity of the first layer is 10 ^-14 S / cm. cable. 2. An AC power cable with improved dielectric strength, comprising an electrical core wire and an insulating polymerized first dielectric layer of the core wire, wherein the first dielectric layer comprises at least one conductive polymer. An electric power, characterized in that it is composed of an insulating polymer matrix which comprises a conductive polymer incorporated into this polymer matrix in such a ratio that the resulting electrical conductivity of the first layer is 10 ^-10 S / cm. cable. 3. A conductive polymer as claimed in claim 1 or claim 2, which is an unimplanted or impurity-removed polymer whose proportion in the polymerization matrix is at most approximately 5%. The cable described in 2. 4. Cable according to claim 1 or 2, characterized in that the electrically conductive polymer is an impurity self-implanted polymer with a proportion in the polymerisation matrix of at most approximately 2%. . 5. Further, an inner semiconductor shield is provided between the core wire and the first dielectric layer, and an outer semiconductor shield is provided between the first dielectric layer and the protective sheath, and each of the shields has an electric conductivity. The cable according to any one of claims 1 to 4, which is composed of an insulating polymer matrix containing a polymerized semiconductor at a ratio of 1 S / cm or less.