USE OF A MIXTURE AS DIELECTRIC FLUID

Abstract

The use of a mixture as dielectric fluid comprising a composition A comprising dibenzyltoluene and benzyltoluene for improving the service life of a transformer is described, in addition to a mixture comprising said composition A with at least one ester and optionally at least one additive, and a transformer comprising said composition A or a mixture comprising said composition A with at least one ester and optionally at least one additive.

Claims

1. A method of using a mixture as a dielectric fluid, the mixture comprising a composition A comprising dibenzyltoluene and benzyltoluene, for improving the service life of a transformer.

2. The method as claimed in claim 1, wherein the composition A comprises: from 2% to 30% by weight of dibenzyltoluene, relative to the total weight of composition A; and from 70% to 98% by weight of benzyltoluene, relative to the total weight of composition A.

3. The method as claimed in claim 1, wherein the composition A comprises from 10% to 30% by weight of dibenzyltoluene, relative to the total weight of composition A.

4. The method as claimed in claim 1, wherein the composition A comprises from 70% to 90% by weight of benzyltoluene, relative to the total weight of composition A.

5. The method as claimed in claim 1, wherein the mixture also comprises at least one ester.

6. The method as claimed in claim 5, wherein the ester is chosen from the group consisting of the esters of formulae (I) and (II) below:
R.sup.1C(O)OR.sup.2(I)
R.sup.3C(O)OCH.sub.2CH(OC(O)R.sup.4)CH.sub.2OC(O)R.sup.5(II), in which: R.sup.1 denotes a saturated or unsaturated, linear or branched carbon-based chain comprising from 5 to 30 carbon atoms; R.sup.2 denotes a saturated or unsaturated, linear or branched carbon-based chain comprising from 1 to 10 carbon atoms, R.sup.3, R.sup.4 and R.sup.5 denote, independently of each other, a saturated or unsaturated, linear or branched carbon-based chain comprising from 5 to 20 carbon atoms.

7. The method as claimed in claim 5, wherein the mixture comprises from 72% to 96% by weight of composition A, relative to the total weight of the mixture.

8. The method as claimed in claim 5, wherein the weight content of ester ranges from 2% to 26% by weight, relative to the total weight of the mixture.

9. The method as claimed in claim 5, wherein the mixture comprises at least one additive chosen from the group consisting of an antioxidant, a passivating agent, a flow point reducer, a decomposition inhibitor and mixtures thereof.

10. The method as claimed in claim 9, wherein the weight content of the additive ranges from 0.0001% to 2% by weight, relative to the total weight of the mixture.

11. A mixture comprising: the composition A as defined in claim 1; at least one organic acid ester; and optionally at least one additive.

12. The mixture as claimed in claim 11, comprising: a composition A as defined, said composition A comprising: from 2% to 30% by weight of dibenzyltoluene, relative to the total weight of composition A; and from 70% to 98% by weight of benzyltoluene, relative to the total weight of composition A; at least one organic acid ester preferably chosen from natural, artificial or synthetic fatty esters obtained by reaction between at least one monocarboxylic or dicarboxylic fatty acid including from 5 to 30 carbon atoms with a linear or branched alcohol, diol, triol or tetrol; and optionally at least one additive.

13. The mixture as claimed in claim 11, comprising: from 72% to 96% by weight of composition A as defined, relative to the total weight of the mixture; from 2% to 26% by weight, relative to the total weight of the mixture, of at least one organic acid ester; and optionally at least one additive, the total content of additives (when present) ranging from 0.0001% to 2% by weight, relative to the total weight of the mixture.

14. The mixture as claimed in at claim 11, comprising: from 72% to 96% by weight of composition A as defined, relative to the total weight of the mixture, said composition A comprising: from 2% to 30% by weight of dibenzyltoluene, relative to the total weight of composition A; and from 70% to 98% by weight of benzyltoluene, relative to the total weight of composition A; from 2% to 26% by weight, relative to the total weight of the mixture, of at least one organic acid ester obtained by reaction between at least one monocarboxylic or dicarboxylic fatty acid including from 5 to 30 carbon atoms with a linear or branched alcohol, diol, triol or tetrol; and optionally at least one additive chosen from the group consisting of antioxidants, passivating agents, flow point reducers, decomposition inhibitors and mixtures thereof, the total content of additives (when present) ranging from 0.0001% to 2% by weight, relative to the total weight of the mixture.

15. A transformer comprising a composition A as defined in claim 1.

Description

EXAMPLES

1. Preparation of Dielectric Fluids

[0103] A comparative dielectric fluid (B) and two dielectric fluids that may be used in the context of the invention (C and D) are prepared according to the compositions as indicated in Table 1 below:

TABLE-US-00001 TABLE 1 Fluid B (comp.) C (inv.) D (inv.) Mineral oil.sup.1 (weight %) 100 Composition A.sup.2 (weight %) qs 100 qs 100 CEL2021P.sup.3 (weight %) 0.2 0.2 Esterol F (weight %) 14.9 .sup.1Nytro Libra mineral oil (non-inhibited mineral oil sold by Nynas) .sup.2Composition A: Jarytherm BT06, sold by the company Arkema, and consisting of 25% by weight of dibenzyltoluene, relative to the total weight of composition A, and 75% by weight of benzyltoluene, relative to the total weight of composition A .sup.3Decomposition inhibitor, available from the company Whyte Chemical

2. Evaluation and Results

[0104] a. Study of the Aging of Paper

[0105] The water content of fluids B and C was measured before impregnation of paper in each of these fluids. It is, respectively, 20.8 ppm for fluid B and 81.4 ppm for fluid C. Paper was then impregnated with fluid B and fluid C. The aging of the paper in each of these fluids was studied at various temperatures and times.

[0106] Thus, fluids B and C are tested at 70 C., 100 C. and 130 C. for times of 250 hours and 500 hours, respectively. The water content was measured at room temperature. The degree of polymerization was measured for the experiments conducted at 100 C. and 130 C. The results are collated in Table 2 below.

TABLE-US-00002 TABLE 2 Water content Temperature Time of the fluids Degree of Fluid ( C.) (h) (ppm) polymerization B (comp.) 70 250 3.0 C (inv.) 70 250 38.8 B (comp.) 70 500 3.8 C (inv.) 70 500 22.1 B (comp.) 100 250 0.1 640 C (inv.) 100 250 22.0 920 B (comp.) 100 500 0.5 490 C (inv.) 100 500 21.2 1000 B (comp.) 130 250 0 350 C (inv.) 130 250 14.4 780 B (comp.) 130 500 0.5 410 C (inv.) 130 500 18.4 790

[0107] Before impregnation of the paper, the water content in the fluids is high. The water, being more soluble in the paper, migrates into the paper in the course of the impregnation at room temperature.

[0108] In comparison with fluid B (comparative), the water content in fluid C (according to the invention) is always higher, irrespective of the temperature and time of the tests. This indicates that the water migrates faster into fluid C, which keeps the paper drier than fluid B, by means of the greater solubility of water in fluid C, at a given temperature, relative to fluid B.

[0109] Comparison of the degrees of polymerization clearly shows that the degradation of the paper is approximately twice as pronounced with fluid B, irrespective of the duration of the aging relative to fluid C.

[0110] b. Evaluation of the Thermal Performance

[0111] The thermal performance of fluids B, C and D is evaluated. In a 400 KV transformer with an oil capacity of 400 L and functioning in free convection, the temperature difference of the fluid between the inlet (or outlet) of the transformer and the outlet of the condenser was measured. The results are indicated in Table 3 below:

TABLE-US-00003 TABLE 3 Fluid B (comp.) C (inv.) D (inv.) Transformer outlet temperature ( C.) 90 84 87 Condenser outlet temperature ( C.) 40 30 35 Temperature ( C.) 50 54 52

[0112] Table 3 clearly shows a greater temperature difference between the outlet of the transformer and the outlet of the condenser when fluids C and D are used relative to fluid B.

[0113] Thus, better heat evacuation may be observed when the dielectric fluids C and D are used. The use of the dielectric fluids C or D thus enables more efficient heat exchange.

[0114] More efficient heat exchange contributes toward slowing down the aging of the paper in which the dielectric fluids are impregnated, and consequently toward improving the service life of a transformer.