BIODEGRADABLE FLUIDS FOR HIGH VOLTAGE CABLES

Abstract

The present invention relates to electrical cables, particularly high voltage cables, comprising a biodegradable fluid to act as an electrical insulating material. The electrical cables may be located overground, in subterranean environments, or under waterways.

Claims

1. An electrical cable comprising a biodegradable fluid as an electrical insulation material.

2. An electrical cable according to claim 1, wherein the biodegradable fluid comprises an ester composition comprising one or more natural or synthetic esters.

3. An electrical cable according to claim 1, wherein the ester composition comprises a plurality of esters derived from a reaction of: i) one or more polyols, wherein the one or more polyols are each independently a straight chain or branched C.sub.2-C.sub.8 polyol; and ii) two or more carboxylic acids, wherein the carboxylic acids are each independently a straight chain or branched C.sub.4-C.sub.12 carboxylic acid.

4. An electrical cable according to claim 3, wherein the one or more polyols are each independently selected from straight or branched C.sub.2 to C.sub.5 polyols; wherein the one or more polyols optionally each independently have a C.sub.2 to C.sub.3 backbone and one or more C.sub.1 or C.sub.2 hydrocarbon side groups; wherein the one or more polyols optionally each independently comprise neopentyl glycol (NPG), glycerol, butane diol, ethylene glycol or propylene glycol, or combinations of any thereof.

5. An electrical cable according to claim 3, wherein only one polyol is used, wherein the polyol optionally comprises neopentyl glycol.

6. An electrical cable according to claim 3, wherein the one or more polyols each react with first, second and third carboxylic acids.

7. An electrical cable according to claim 6, wherein the first carboxylic acid comprises a C.sub.7, C.sub.8, or C.sub.9 acid; wherein the first carboxylic acid optionally comprises a branched C.sub.8 acid, which is optionally 2-ethylhexanoic acid.

8. An electrical cable according to claim 6, wherein the second and third carboxylic acids are different to each other and are each independently selected from a straight chain or branched C.sub.8, C.sub.9, or C.sub.10 acid; wherein the second and third carboxylic acids are optionally different to each other and are optionally each independently selected from n-octanoic acid, n-decanoic acid, or isononanoic acid (3,5,5-trimethylhexanoic acid).

9. An electrical cable according to claim 3, wherein the one or more polyols comprise neopentaglycol, and the one or more polyols react with first, second and third carboxylic acids, wherein the first carboxylic acid is 2-ethylhexanoic acid, and the second and third carboxylic acids comprise a mixture of two different straight chain or branched C.sub.8, C.sub.9, or C.sub.10 carboxylic acids; optionally wherein the second and third carboxylic acids comprise a mixture of n-octanoic acid and decanoic acid.

10. An electrical cable according to claim 1, wherein the ester composition comprises a plurality of esters derived from a reaction of: i) one or more polyols, wherein the one or more polyols are each independently a straight chain or branched C.sub.2-C.sub.8 polyol; and ii) first, second and third carboxylic acids, wherein the first, second and third carboxylic acids are each independently a straight chain or branched C.sub.4-C.sub.12 carboxylic acid.

11. An electrical cable according to claim 10, wherein the one or more polyols are each independently selected from straight or branched C.sub.2 to C.sub.6 polyols; wherein the one or more polyols optionally each independently have a C.sub.2 to C.sub.3 backbone and one or more C.sub.1 or C.sub.2 hydrocarbon side groups; wherein the one or more polyols optionally comprise pentaerythritol, neopentyl glycol (NPG), glycerol, butane diol, ethylene glycol or propylene glycol, or combinations of any thereof.

12. An electrical cable according to claim 10, wherein only one polyol is used; wherein the polyol optionally comprises pentaerythritol.

13. An electrical cable according to claim 10, wherein the first carboxylic acid comprises a C.sub.7, C.sub.8, or C.sub.9 acid.

14. An electrical cable according to claim 13, wherein the first carboxylic acid comprises a branched C.sub.8 acid, which is optionally 2-ethylhexanoic acid.

15. An electrical cable according to claim 10, wherein the second carboxylic acid is selected from a straight chain or branched C.sub.6, C.sub.7, or C.sub.8 acid.

16. An electrical cable according to claim 15, wherein the second carboxylic acid is a C.sub.7 acid, which is optionally n-heptanoic acid.

17. An electrical cable according to claim 10, wherein the third carboxylic acid is selected from a straight chain or branched C.sub.8, C.sub.9, or C.sub.10 acid; wherein the third carboxylic acid is optionally a C.sub.9 acid, which is optionally n-nonanoic acid.

18. An electrical cable according to claim 10, wherein the one or more polyols comprise pentaerythritol, the first carboxylic acid comprises 2-ethylhexanoic acid, the second carboxylic acid comprises n-heptanoic acid, and the third carboxylic acid comprises n-nonanoic acid.

19. An electrical cable according to claim 1, wherein the biodegradable fluid is substantially free of additives and/or moisture.

20. An electrical cable according to claim 10, wherein the biodegradable fluid is substantially free of additives and/or moisture.

Description

EXAMPLE 1

[0076] An ester composition (I) suitable for use as a dielectric fluid was prepared by forming esters by reacting pentaerythritol with a mixture of n-heptanoic acid (C.sub.7), n-nonanoic acid (C.sub.9), and 2-ethylhexanoic acid. An ester composition was prepared according to the following method:

[0077] Pentaerythritol was combined with n-heptanoic acid, n-nonanoic acid, and 2-ethylhexanoic acid. The amounts of acids and alcohols were selected such that the acid mixture was present in a molar excess relative to the alcohol.

[0078] Esters were then prepared by refluxing pentaerythritol with the acid mixture at a temperature of over 220 C. under a nitrogen atmosphere for a number of hours to produce an ester composition. Water was removed as it was formed using a Dean-Stark apparatus.

[0079] Following completion of the reflux stage, excess acid was removed by vacuum distillation, and the acid value, hydroxyl value and colour of the ester composition were determined. The results are presented in Table 3 below.

[0080] The ester composition was then processed further to prepare a dielectric fluid composition.

[0081] The ester composition was then stirred under heating for one hour in the presence of Alumina in such an amount as was required to neutralise the reaction mixture to remove any residual acid, as well as Fullers' earth powders to clean the sample, and sterically hindered phenolic antioxidant. The composition was then filtered.

[0082] A tolutriazole derivative metal deactivator was added to the composition.

[0083] Electrical and physical testing was performed on the composition according to the test methods given in Table 1 below. The results are presented in Table 2.

TABLE-US-00001 TABLE 1 Property Test Method Water content IEC 60814 Acid Value Modified IEC 62021-2 Hydroxyl value IR spectrometer Colour ISO 2211 Tan delta at 90 C. IEC 60247 VR at 90 C. IEC 60247 Breakdown IEC 60156 Viscosity at 40 C. Brookfield DV-I Prime Viscometer Density at 20 C. ISO 3675 COC fire point ISO 2592 PMCC flash point ISO 2719 Pour point Modified ISO 3016

TABLE-US-00002 TABLE 2 Physical and electrical Value Water content (ppm) 50 Acid Value (mgKOH/g) 0.022 Hydroxyl (mgKOH/g) 0.5 Colour (HU) 57 Tan delta at 90 C. 0.008 VR at 90 C. (Gm) 32.6 Breakdown (kV) 93.5 Viscosity at 40 C. (cP) 26.4 Density at 20 C. (g/cm.sup.3) 0.973 COC Fire point ( C.) 312 PMCC Flash point ( C.) 268 Pour point ( C.) 56

[0084] As can be seen from the above, the dielectric composition of Example 1 has physical and electrical properties rendering it entirely suitable for use as a dielectric fluid.

EXAMPLE 2

[0085] This example shows the preparation of an ester composition (II). Neopentyl glycol, 2-Ethylhexanoic acid, and n-nonanoic acid blend were added to a 2-Litre round bottom flask fitted with Dean-Stark apparatus and a condenser. The reaction mixture was stirred under heating for one hour in the presence of alumina to neutralise the reaction mixture, subjected to a purifying powder treatment, and an antioxidant was added. The ester was filtered twice, a metal deactivator was added, and the ester was degassed until the moisture content of the ester was about 50 ppm.

[0086] The properties of the ester composition (II) are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Property Units Example 2 Test Method Water content ppm 50 IEC 60814 Acid Value mgKOH/g <0.03 IEC 62021-2 Colour HU 100 ISO 2211 Tan delta at 90 C. <0.03 IEC 60247 and 50 Hz Volume resistivity Gcm >10 IEC 60247 DC at 90 C. Breakdown voltage kV >75 IEC 60156 Viscosity at 100 C. cP ISO 3104 Viscosity at 40 C. cP Viscosity at 0 C. cP 42.1 Viscosity at 10 C. cP 79.4 Viscosity at 20 C. cP 172 Viscosity at 30 C. cP 434 Viscosity at 40 C. mm.sup.2 s.sup.1 1330 Viscosity at 50 C. mm.sup.2 s.sup.1 5060 Density at 20 C. kg dm.sup.3 0.92 ISO 3675 PMCC flash point C. 190 ISO 2719 COC fire point C. 220 ISO 2592 Pour point C. 72 ISO 3016 (modified)/ ISO 3016

EXAMPLE 3

[0087] An ester composition (I) suitable for use as a dielectric fluid was prepared by forming esters by reacting pentaerythritol with a mixture of n-heptanoic acid (C.sub.7), n-nonanoic acid (C.sub.9), and 2-ethylhexanoic acid. An ester composition was prepared according to the following method:

[0088] Pentaerythritol was combined with n-heptanoic acid, n-nonanoic acid, and 2-ethylhexanoic acid. The amounts of acids and alcohols were selected such that the acid mixture was present in a molar excess relative to the alcohol.

[0089] Esters were then prepared by refluxing pentaerythritol with the acid mixture at a temperature of over 220 C. under a nitrogen atmosphere for a number of hours to produce an ester composition. Water was removed as it was formed using a Dean-Stark apparatus.

[0090] Following completion of the reflux stage, excess acid was removed by vacuum distillation

[0091] The ester composition was then processed further to prepare a dielectric fluid composition.

[0092] The ester composition was then stirred under heating for one hour in the presence of Alumina in such an amount as was required to neutralise the reaction mixture to remove any residual acid, as well as Fullers' earth powders to clean the sample. The composition was then filtered.

[0093] The composition of Example 3 is essentially the same as that of Example 1, but not including any additives.

[0094] As can be seen from the above, the dielectric fluid composition of Example 2 has physical and electrical properties which render it particularly suitable for use and successful operation as a dielectric fluid in electrical apparatuses in extreme low temperatures.

[0095] The fluids of Examples 1-3 are all considered to be readily biodegradable according to the OECD 301 tests.

[0096] It is of course to be understood that the present invention is not intended to be restricted to the foregoing specific embodiments, which are described by way of example only. The invention extends to any novel feature, or combination of features, disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.