Electrical cable with self-repairing protection

• US 6,664,476 B2
• Filed: 10/09/2001
• Issued: 12/16/2003
• Est. Priority Date: 03/04/1998
• Status: Expired due to Term

• Current Assignee: Prysmian Cavi E Sistemi Italia Srl (Prysmian SPA)
• Original Assignee: Pirelli Cavi e Sistemi S.P.A. (Prysmian SPA)
• Inventors: Belli, Sergio, Balconi, Luca, Pozzati, Giovanni, Bareggi, Alberto, Bosisio, Claudio, Caimi, Luigi
• Primary Examiner(s): Mayo, III, William H.
• Application Number:
  US09/971,766
• Publication Number:
  US 20020104678A1
• Time in Patent Office: 798 Days
• Field of Search: 174/113.R, 174/120.R, 174/120.SC, 174/121.SR, 174/110.R, 174/116, 174/115, 174/36
• US Class Current: 174/120.00R
• CPC Class Codes: H01B 3/441 from alkenes
• CPC Class Codes: H01B 7/28 Protection against damage caused by moisture, corrosion, chemical attack or weather
• CPC Class Codes: Y02A 30/14 Extreme weather resilient electric power supply systems, e.g. strengthening power lines or underground power cables

Abstract

A cable for electric power transmission, electric power distribution or telecommunications, having an inner layer including a self-repairing material. The self-repairing material has properties including a predetermined cohesiveness and a controlled flowability. In the event of a discontinuity in at least one of the cable coating layers, these properties assist in reestablishing the continuity of the cable coating layers.

Claims

1. A cable, comprising from interior to exterior:

a conductor;

an inner layer of a self-repairing material, the material at a working temperature of the cable being dielectric, having sufficient cohesiveness to spontaneously re-unify after being ruptured by an external force, being capable of migrating with a controlled flowability towards a void in an adjacent layer, and having substantial physico-chemical inertness with respect to other materials in the cable; and

an outer coating layer.

2. The cable of claim 1, further comprising an insulating coating layer around the conductor, wherein the inner layer is located between the insulating coating layer and the outer coating layer.

3. The cable of claim 1, further comprising an insulating coating layer, wherein the inner layer is located between the conductor and the insulating coating layer.

4. The cable of claim 1, wherein the outer coating layer is an outer sheath.

5. The cable of claim 1, wherein the outer coating layer is an insulating layer.

6. The cable of claim 1, further comprising an expanded polymer coating.

7. The cable of claim 6, wherein the expanded polymer coating is located in direct contact with an outer protective sheath.

8. The cable of claim 1, wherein the inner layer has a thickness of not less than 0.1 mm.

9. The cable of claim 8, wherein the inner layer has a thickness between about 0.2 mm and 2 mm.

10. The cable of claim 9, wherein the inner layer has a thickness between about 0.3 mm and 1 mm.

11. The cable of claim 1, wherein the self-repairing material has a dielectric strength under alternating current greater than 15 kV/mm and a resistivity greater than about 10¹⁴ Ω

·

cm.

12. The cable of claim 11, wherein the self-repairing material has a dielectric strength under alternating current greater than about 20 kV/mm and a resistivity greater than about 10¹⁶ Ω

·

cm.

13. The cable of claim 1, wherein the self-repairing material has a cohesive force at room temperature of at least 0.05 kg/cm².

14. The cable of claim 13, wherein the self-repairing material has a cohesive force at room temperature between about 0.1 kg/cm² and 4 kg/cm².

15. The cable of claim 14, wherein the self-repairing material has a cohesive force at room temperature between about 0.2 kg/cm² and 2 kg/cm².

16. The cable of claim 13, wherein the self-repairing material has a cohesiveness in which the force of recohesion measured at room temperature has a value of not less than 80% relative to the value of the cohesive force measured on the material.

17. The cable of claim 16, wherein the force of recohesion measured at room temperature has a value of not less than about 90% relative to the value of the cohesive force measured on the material.

18. The cable of claim 1, wherein the self-repairing material has a controlled flowability in which a sample of about 3 grams of self-repairing material, placed on an aluminum plate inclined at 60°

relative to the horizontal plane and maintained at 60°

C. for 24 hours, shows a displacement of the material front along the inclined plate between 0.5 mm and 400 mm.

19. The cable of claim 18, wherein the displacement of the front of the self-repairing material sample along the inclined plate is between about 1 mm and 200 mm.

20. The cable of claim 19, wherein the displacement of the front of the self-repairing material sample along the inclined plate is between about 50 mm and 100 mm.

21. The cable of claim 1, wherein the self-repairing material has a saturation water content of less than 400 ppm.

22. The cable of claim 21, wherein the self-repairing material has a saturation water content of less than about 200 ppm.

23. The cable of claim 1, wherein the self-repairing material has a permeability to water vapour, measured at room temperature according to ASTM E96, between 1.2×

10<sup>−

7</sup> g/(cm·

hour·

mmHg) and 8.0×

10<sup>−

6</sup> g/(cm·

hour·

mmHg).

24. The cable of claim 1, wherein the self-repairing material comprises an amorphous polymer having properties of a high-viscosity liquid or of a semi-solid.

25. The cable of claim 24, wherein the amorphous polymer comprises at least one of:

(a) polyisobutene or isobutene copolymers with minor amounts of different C₄-C₁₂ α

-olefins;

(b) atactic propylene homopolymers; and

(c) silicone rubbers, consisting of linear chains of monomer units of formula —

O—

SiR₁R₂—

, wherein R₁ and R₂ are optionally substituted aliphatic or aromatic radicals.

26. The cable of claim 25, wherein the amorphous polymer is polyisobutene having a viscosimetric (Staudinger) average molecular weight between 2,000 and 50,000.

27. The cable of claim 26, wherein the amorphous polymer is polyisobutene having a viscosimetric (Staudinger) average molecular weight between about 5,000 and 20,000.

28. The cable of claim 24, wherein the amorphous polymer is dissolved in a solvent.

29. The cable of claim 28, wherein the solvent is a mineral oil or a synthetic oil.

30. The cable of claim 29, wherein the solvent is a paraffinic oil or naphthenic oil.

31. The cable of claim 28, wherein the amorphous polymer is dissolved in a solvent which is a low molecular weight homologue of the amorphous polymer.

32. The cable of claim 31, wherein the amorphous polymer is a polyisobutene having a viscosimetric (Staudinger) average molecular weight between 2,000 and 50,000, dissolved in a polybutenic oil having an osmometric average molecular weight between 400 and 1,300.

33. The cable of claim 31, wherein the amorphous polymer is a silicone rubber, dissolved in a silicone oil having a viscosity between 100 mm²/sec and 5,000 mm²/sec at 25°

C.

34. The cable of claim 28, wherein the amount of solvent is between 5% and 95% by weight, relative to the total weight of the mixture.

35. The cable of claim 34, wherein the amount of solvent is between about 50% and 90% by weight, relative to the total weight of the mixture.

36. The cable of claim 28, wherein the self-repairing material also comprises a thickener.

37. The cable of claim 36, wherein the thickener comprises at least one of:

pyrogenic silica or bentonite.

38. The cable of claim 36, wherein the thickener is added in amounts between 1 to 20 parts by weight relative to the total weight of the mixture.

39. The cable of claim 24, wherein the self-repairing material also comprises an inorganic filler.

40. The cable of claim 39, wherein the inorganic filler comprises at least one of:

kaolin, calcium carbonate, aluminum hydroxide, magnesium hydroxide, talc, and precipitated silica.

41. The cable of claim 39, wherein the inorganic filler is present in amounts between 5 and 50 parts by weight with respect to the total weight of the mixture.

42. The cable of claim 24, wherein the self-repairing material also comprises a tackifying agent.

43. The cable of claim 42, wherein the tackifying agent comprises at least one of:

natural or synthetic rosins, or derivatives thereof, and esterified polyalcohols.

44. The cable of claim 42, wherein the tackifying agent is present in amounts between 1% and 20% by weight with respect to the total weight of the mixture.

45. The cable of claim 1, wherein the self-repairing material comprises a solid polymeric material dispersed in an oily phase.

46. The cable of claim 45, wherein the oily phase comprises at least one of:

(a) paraffinic or naphthenic oils;

(b) polybutene oils having an osmometric average molecular weight between 400 and 1,300;

(c) polypropylene oils; and

(d) low molecular weight polyesters.

47. The cable of claim 45, wherein the solid polymeric material is a high molecular weight polymer with elastomeric properties comprising at least one of:

(i) styrene block copolymers or terpolymers with different olefins and/or with dienes;

(ii) polyisobutene or copolymers of isobutene with minor amounts of different C₄-C₁₂ α

-olefins;

(iii) propylene copolymers with ethylene and/or with C₄-C₁₂ α

-olefins or with C₄-C₂₀ dienes;

(iv) polyisoprene or natural rubber;

(v) nitrile rubbers;

(vi) butyl rubbers; and

(vii) amorphous ethylene copolymers.

48. The cable of claim 45, wherein the solid polymer material is dispersed in the oily phase in a subdivided form, in an amount between 5% and 70% by weight relative to the total weight of the mixture.

49. The cable of claim 1, wherein the self-repairing material consists essentially of polyisobutene having an average molecular weight of about 64,000-81,000, an ethylene/propylene elastomeric copolymer, a polybutene oil, and an antioxidant.

50. The cable of claim 1, wherein the self-repairing material consists essentially of an ethylene/propylene elastomeric copolymer, paraffinic oil, and an antioxidant.

51. The cable of claim 1, wherein the self-repairing material consists essentially of polyisobutene having an average molecular weight of about 2,000-50,000 and an antioxidant.

52. A method for imparting to a cable comprising a cable core and at least one coating layer a capacity of self-repairing the at least one coating layer, comprising:

providing directly on the cable core a dielectric material, the material at a working temperature of the cable having a controlled flowability, having sufficient cohesiveness to spontaneously re-unify after being ruptured by an external force, having a capacity, upon creation of a discontinuity in the at least one coating layer, of migrating to the discontinuity and reestablishing a continuity in the at least one coating layer in a reversible manner, and having substantial physico-chemical inertness with respect to other materials in the cable.

53. The method of claim 52, wherein the material is capable of at least partially filling the discontinuity without leaking from the cable in an uncontrolled manner.

54. The method of claim 52, wherein the at least one coating layer is an outer sheath.

55. The method of claim 52, wherein the at least one coating layer is an insulating layer.

56. The method of claim 52, wherein the material consists essentially of polyisobutene having an average molecular weight of about 2,000-50,000 and an antioxidant.

57. The method of claim 52, wherein the material consists essentially of an ethylene/propylene elastomeric copolymer, paraffinic oil, and an antioxidant.

58. The method of claim 52, wherein the material consists essentially of polyisobutene having an average molecular weight of about 64,000-81,000, an ethylene/propylene elastomeric copolymer, a polybutene oil, and an antioxidant.

59. A process for manufacturing a cable having a layer of self-repairing material, comprising the steps of:

extruding a cable core including a flexible conductor;

depositing a dielectric self-repairing material, maintained in a fluid state, directly on the cable core, the material at a working temperature of the cable being dielectric, having sufficient cohesiveness to spontaneously re-unify after being ruptured by an external force, being capable of migrating with a controlled flowability towards a void in an adjacent layer, and having substantial physico-chemical inertness with respect to other materials in the cable; and

forming the layer of self-repairing material so as to obtain a uniform layer of a predetermined thickness.

60. The process of claim 59, further comprising the steps of:

introducing an initial section of the cable core inside an application head through an inlet hole with a diameter which is slightly larger than the diameter of the cable core, and an outlet hole having a diameter which is predetermined according to the desired thickness of the layer of self-repairing material;

feeding the application head with the self-repairing material maintained in a fluid state by pre-heating; and

passing the cable core through the application head so as to perform the deposition of the self-repairing material and the simultaneous forming of the layer of self-repairing material.

61. A cable, comprising:

a conductor;

a first insulating layer;

a self-repairing layer in contact with the first insulating layer, the self-repairing layer being a dielectric material, having sufficient cohesiveness to spontaneously re-unify after being ruptured by an external force, and being capable of migrating with a controlled flowability towards a void in an adjacent layer at a working temperature of the cable; and

an outer layer located substantially around the self-repairing layer.

62. The cable of claim 61, further comprising:

a second insulating layer in contact with the self-repairing layer.

63. A cable, comprising:

a conductor;

a dielectric self-repairing layer in contact with the conductor;

a first insulating layer in contact with the self-repairing layer, the self-repairing layer having a controlled flowability at a working temperature of the cable, having sufficient cohesiveness to spontaneously re-unify after being ruptured by an external force, and having a capacity, upon creation of a discontinuity in the first insulating layer, of migrating to the discontinuity and reestablishing a continuity in the first insulating layer in a reversible manner; and

an outer layer located around the first insulating layer.

64. The cable of claim 63, further comprising:

a second insulating layer in contact with the first insulating layer.

65. A method for imparting to a cable comprising a conductor and at least one coating layer a capacity of self-repairing the at least one coating layer, comprising:

providing the cable with an inner layer comprising a dielectric material substantially surrounding and in contact with the at least one coating layer, the dielectric material at a working temperature of the cable having a controlled flowability, having sufficient cohesiveness to spontaneously re-unify after being ruptured by an external force, having a capacity, upon creation of a discontinuity in the at least one coating layer, of migrating to the discontinuity and reestablishing a continuity in the at least one coating layer in a reversible manner, and having substantial physico-chemical inertness with respect to other materials in the cable.

66. The method of claim 65, further comprising a second coating layer, wherein the second coating layer is an outer sheath.

67. The method of claim 65, wherein the at least one coating layer is an insulating layer.

68. A cable, comprising:

a cable core including at least a conductor;

an inner layer of a dielectric self-repairing material, the material at a working temperature of the cable having sufficient cohesiveness to spontaneously re-unify after being ruptured by an external force, being capable of migrating with a controlled flowability towards a void in an adjacent layer, and being positioned in contact with the cable core; and

an outer layer.