DIELECTRIC FLUID FOR TRANSFORMER RETROFILLING

Abstract

The present invention relates to the use, for the retrofilling of a transformer, of at least one dielectric fluid of general formula (1):

(A−X).sub.n−B  (1)

in which A and B, which are identical or different, represent, independently of each other, an optionally substituted aromatic ring, X represents a spacer group and n represents 0, 1, 2 or 3.

The invention also relates to a transformer containing at least one dielectric fluid of general formula (1) and an amount of PCBs of less than 20%.

Claims

1-10. (canceled)

11. A dielectric fluid for the retrofilling of a transformer, the fluid having a general formula (1):
(A−X).sub.n−B  (1) wherein: A and B, which are identical or different, represent, independently of each other, an aromatic ring optionally substituted by one or more saturated or partially or completely unsaturated hydrocarbon radicals comprising from 1 to 20 carbon atoms, X represents a spacer group chosen from a single bond, —O—, —S—, —(CRR′).sub.m—and —NR″—,— R and R′, which are identical or different, are chosen, independently of each other, from hydrogen and a saturated or partially or completely unsaturated hydrocarbon radical comprising from 1 to 6 carbon atoms, R″ represents a saturated or partially or completely unsaturated hydrocarbon radical comprising from 1 to 6 carbon atoms, m represents an integer of between 1 and 4, limits included, and n can be equal to 0 or represents an integer equal to 1, 2 or 3, with the restriction that, when n is equal to 0, B is substituted by one or more hydrocarbon radicals, as defined above.

12. The dielectric fluid as claimed in claim 11, wherein, in the dielectric fluid of general formula (1), n is different from 0 and B is an aromatic ring substituted by a hydrocarbon radical.

13. The dielectric fluid as claimed in claim 11, wherein, in the dielectric fluid of general formula (1), n is different from 0 and B is an aromatic ring substituted by an alkyl radical comprising from 1 to 6 carbon atoms.

14. The dielectric fluid as claimed in claim 11, wherein the dielectric fluid is selected from the group consisting of benzyltoluene, dibenzyltoluene and their mixtures in all proportions.

15. The dielectric fluid as claimed in claim 11, wherein the dielectric fluid is a benzyltoluene/dibenzyltoluene mixture comprising between 1% and 50%, limits included, by weight of dibenzyltoluene, with respect to the total amount of benzyltoluene/dibenzyltoluene.

16. The dielectric fluid as claimed in claim 11, wherein the dielectric fluid in addition contains one or more additives selected from the group consisting of antioxidants, passivators, pour point depressants, decomposition inhibitors and their mixtures.

17. The dielectric fluid as claimed in claim 11, wherein the dielectric fluid comprises at least one decomposition inhibitor selected from the group consisting of carbodiimide derivatives, phenyl glycidyl ethers, or esters, alkyl glycidyl ethers, or esters, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, compounds of the anthraquinone family, epoxy derivatives, 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylhexanecarboxylate, and epoxy resins of phenol novolak type or bisphenol A diglycidyl ether epoxys.

18. A process for the retrofilling of a transformer, said process comprising at least the following stages: a) providing a transformer comprising a first dielectric fluid, b) emptying said first dielectric fluid, c) optionally placing the transformer under vacuum, d) filling with a dielectric fluid of general formula (1) as defined in claim 11, e) optionally repeating stages b) to d), until an amount of said first dielectric fluid of less than 20%, by volume, limits included, with respect to the total volume of the dielectric fluid present in the transformer, is obtained, and f) recovering the transformer containing the dielectric fluid used in stage d), and wherein the content of first dielectric fluid is respectively less than 20%, by volume, limits included, with respect to the total volume of the dielectric fluid present in the transformer.

19. A transformer comprising at least one dielectric fluid of general formula (1) defined in claim 11 and an amount of PolyChloroBiphenyls (PCBs) of less than 20%, by volume, limits included, with respect to the total volume of dielectric fluid present in said transformer.

20. The transformer as claimed in claim 19, wherein the dielectric fluid of general formula (1) is a benzyltoluene/dibenzyltoluene mixture.

Description

EXAMPLE

Retrofilling of a Transformer Containing a PCB/Trichlorobenzene Mixture

[0072] A transformer containing a 60/40 by weight mixture of PCBs and trichlorobenzene is subjected to a retrofilling operation with a dielectric fluid which is a BT/DBT mixture sold by Arkema under the Jarylec® name.

[0073] A series of 4 retrofilling operations is carried out, each operation being carried out 3 months after the preceding one. Before each operation, the residual PCB is quantitatively determined. The results are presented in the following table 1.

TABLE-US-00001 TABLE 1 Time (months) Content of PCBs 0 .sup. 60% 3  5.5% 6 0.51% 9 0.04% 12 <<50 ppm

[0074] As indicated above, the retrofilling operations are carried out every three months, each measurement of residual contents of PCBs being carried out just before the retrofilling operation. Between the different retrofilling operations, the transformer is placed under voltage.

[0075] This example shows that the threshold of 50 ppm is reached after the 4th retrofilling operation. This threshold is reached in lasting fashion, whereas, with several retrofilling operations with a mineral oil, this threshold of 50 ppm, once reached, is not stable and it is not uncommon to observe an increase in the content of PCBs. It is then necessary to carry out one, indeed even several, additional retrofilling operation(s). It has also been found that this instability can last for very many years when the retrofilling is carried out with a mineral oil.

[0076] The great advantage of using a dielectric fluid of formula (1), as defined above, for the retrofilling operations, in particular for the retrofilling of transformers containing or having contained a PCB, is thus demonstrated.