DISTRIBUTION OF A DIELECTRIC GASEOUS MIXTURE TO A HIGH-VOLTAGE APPARATUS

Abstract

A method of distributing an electrically insulating liquefied gas mixture to high-voltage electrical equipment from a storage means containing an insulating gas mixture, including: heating the insulating gas mixture to a temperature such that the contents of the storage means are a homogeneous fluid; and withdrawing the insulating mixture resulting from step a) to fill high-voltage electrical equipment by raising the temperature of the mixture resulting from step a), wherein, during step b), a set value for regulation is applied at variable pressure, calculated in real time based on weighing the storage means, when the change in the set value of pressure is less than 0.2 bar per 1 kg/m.sup.3 of change in density, and then a set value for regulation is applied at constant temperature until the storage means is emptied of its content.

Claims

1.-12. (canceled)

13. A method of distributing an electrically insulating liquefied gas mixture to high-voltage electrical equipment from a storage means containing an insulating gas mixture, the method comprising the following steps: Step a): heating the insulating gas mixture to a temperature such that the contents of the storage means are a homogeneous fluid; Step b): withdrawing the insulating mixture resulting from step a) to fill high-voltage electrical equipment by raising the temperature of the mixture resulting from step a); wherein, during step b), a set value for regulation is applied at variable pressure, calculated in real time based on weighing the storage means, when the change in the set value of pressure is less than 0.2 bar per 1 kg/m.sup.3 of change in density, and then a set value for regulation is applied at constant temperature until the storage means is emptied of its content.

14. The method of claim 13, wherein step a) comprises heating the insulating gas mixture to a temperature greater than or equal to a critical temperature in order to obtain a homogeneous supercritical fluid inside the storage means.

15. The method of claim 13, wherein, during step b), the insulating mixture undergoes expansion to a pressure between 0 bar and 12 bar relative.

16. The method of claim 15, wherein the temperature of the insulating mixture resulting from step a) is raised to a temperature between 65 C. and 90 C. during withdrawal in step b).

17. The method of claim 13, wherein the pressure inside the storage means between step a) and step b) is between 15 bar and 90 bar relative.

18. The method of claim 13, wherein the temperature of the insulating mixture inside the storage means between step a) and step b) is between 40 C. and 65 C.

19. The method of claim 13, wherein said storage means comprises heating means consisting of electromagnetic induction means capable of heating the insulating mixture inside the storage means.

20. The method of claim 13, wherein the insulating gas mixture comprises at least 80 mol % of CO.sub.2 in the case of a two-component mixture and comprises at least 50 mol % in the case of mixtures comprising at least three components.

21. The method of claim 20, wherein that the insulating mixture comprises at least one component selected from the fluoronitriles having at least four carbon atoms.

22. The method of claim 21, wherein the insulating mixture comprises between 2 and 20 mol % of said component selected from the fluoronitriles having at least four carbon atoms.

23. The method of claim 13, wherein said storage means has a capacity for storage of the insulating mixture between 30 L and 700 L.

24. The method of claim 13, wherein, in step b), the rate of withdrawal of the insulating mixture resulting from step a) is between 10 Nm.sup.3/h and 50 Nm.sup.3/h.

Description

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] One of the problems solved by the method according to the invention is to homogenize the mixture in the storage means and then transfer it into the high-voltage equipment without any loss of homogeneity.

[0034] The present inventors have elaborated a solution allowing the aforementioned problems to be solved.

[0035] The present invention relates to a method of distributing an electrically insulating liquefied gas mixture to high-voltage electrical equipment from a storage means containing an insulating gas mixture, said method comprising the following steps:

[0036] Step a): heating said insulating gas mixture to a temperature such that the contents of the storage means are a homogeneous fluid;

[0037] Step b): withdrawing the insulating mixture resulting from step a) to fill high-voltage electrical equipment by raising the temperature of said mixture resulting from step a);

characterized in that, during step b), a set value for regulation is applied at variable pressure, calculated in real time based on weighing the storage means, when the change in the set value of pressure is less than 0.2 bar per 1 kg/m.sup.3 of change in density, and then a set value for regulation is applied at constant temperature until the storage means is emptied of its contents.

[0038] According to other embodiments, the invention also relates to:

[0039] A method as defined above, characterized in that step a) consists of heating said insulating gas mixture to a temperature greater than or equal to its critical temperature in order to obtain a homogeneous supercritical fluid inside said storage means.

[0040] A method as defined above, characterized in that, during step b), the insulating mixture undergoes expansion to a pressure between 0 bar and 12 bar relative, preferably from 5 bar to 10 bar relative.

[0041] A method as defined above, characterized in that the temperature of the insulating mixture resulting from step a) is raised to a temperature between 65 C. and 90 C. during withdrawal in step b).

[0042] A method as defined above, characterized in that the pressure inside the storage means between step a) and step b) is between 15 bar and 90 bar relative.

[0043] A method as defined above, characterized in that the temperature of the insulating mixture inside the storage means between step a) and step b) is between 40 C. and 65 C.

[0044] A method as defined above, characterized in that said storage means comprises heating means consisting of electromagnetic induction means capable of heating the insulating mixture inside said storage means.

[0045] A method as defined above, characterized in that the insulating gas mixture comprises at least 80 mol % of CO.sub.2 in the case of a two-component mixture and in that it comprises at least 50 mol % in the case of mixtures comprising at least three components.

[0046] A method as defined above, characterized in that the insulating mixture comprises at least one component selected from the fluoronitriles having at least four carbon atoms.

[0047] A method as defined above, characterized in that the insulating mixture comprises between 2 and 20 mol % of said component selected from the fluoronitriles having at least four carbon atoms.

[0048] A method as defined above, characterized in that said storage means has a capacity for storage of said insulating mixture between 30 L and 700 L.

[0049] A method as defined above, characterized in that, in step b), the rate of withdrawal of the insulating mixture resulting from step a) is between 10 Nm.sup.3/h and 50 Nm.sup.3/h, and preferably between 15 and 30.

[0050] The normal cubic meter, with the symbol Nm.sup.3 or sometimes m.sup.3(n), is a unit of measurement of the amount of gas that corresponds to the contents of a volume of one cubic meter, for a gas in normal conditions of temperature and pressure (0 or 15 or less often 20 C. depending on the frames of reference and 1 atm, or 101 325 Pa). For a pure gas, a normal cubic meter corresponds to about 44.6 moles of gas.

[0051] It is therefore a method of regulating the heating of means of storage of liquefied mixtures in order to make these mixtures homogeneous before and during transfer. This method of regulating heating is useful and effective throughout transfer, i.e. from the storage means full state to the storage means empty state.

[0052] Heating the storage means makes it possible to exceed the critical temperature of the mixture and obtain a homogeneous dielectric mixture in situ.

[0053] When the density of the mixture inside the storage means no longer allows the state of supercritical fluid to be maintained, the present invention makes it possible to maintain the fluid in the gas phase, which makes it intrinsically homogeneous.

[0054] The invention allows high-voltage equipment to be filled from a storage means of liquefied dielectric gas mixture without changing the initial proportions of the mixture, in conditions of temperature and pressure suitable for filling (10 C. to 30 C. and 0 to 12 bar relative), at values of flow rates that are sufficient for the final use (greater than 15 Nm.sup.3/h).

[0055] The solution for making the mixture homogeneous consists of heating the storage means.

[0056] For this purpose, the invention combines a set of solutions for regulating the heating of the storage means so as to comply with all the constraints and to overcome all the difficulties described above.

[0057] These solutions for regulating the heating operate as follows:

[0058] 1. Regulating the heating of the storage means based on a set value of pressure, the latter being variable and calculated in real time on the basis of weighing, when the change in the set value of pressure is less than 0.2 bar per 1 kilogram per cubic meter of change in density (in other words, when the derivative of the set value of pressure as a function of the density is less than 0.2 bar.kg.sup.1.m.sup.3).

[0059] 2. Regulating the heating of the storage means based on the set value of constant temperature, when the change in the set value of pressure is greater than 0.2 bar per 1 kilogram per cubic meter of change in density (in other words, when the derivative of the set value of pressure as a function of the density is greater than 0.2 bar.kg.sup.1.m.sup.3).

[0060] 3. Calculation of the pressure value set in step 1 so that the temperature remains below the maximum permissible temperature for the storage means, so that the pressure remains below the maximum permissible pressure for the storage means, and so that the pressure & temperature pair never leads to recondensation of the mixture.

[0061] The principle of homogenization of the dielectric mixture used in the method according to the present invention is to heat the storage means until it is in the supercritical range. The properties of supercritical fluids (high internal energy, low viscosity) make it possible to guarantee homogenization of the fluids with one another.

[0062] Supercritical fluids have properties close to gases and liquids. Their viscosity and molecular agitation are close to those of gases. A mixture in the supercritical phase will therefore be intrinsically homogeneous.

[0063] The supercritical state may be attained by exceeding the critical temperature and critical pressure of the mixture. However, this heating must be regulated so that neither the design temperature, nor the design pressure of the storage means is exceeded.

[0064] Two problems arise for ensuring homogenization of the mixture during withdrawal of the latter for filling the high-voltage equipment:

[0065] maintaining homogeneity of the mixture within the storage means despite the decrease in density due to consumption;

[0066] making the mixture suitable for use at a pressure and temperature guaranteeing absence of recondensation and therefore of loss of homogeneity.

[0067] As the mixture is consumed, the density will decrease, so that a higher heating temperature is required. However, this temperature is limited by the design temperature of the storage means (generally 65 C.).

[0068] Expanding the mixture to lower it to the pressure of use will cool the fluid by the Joule-Thomson effect. The invention makes it possible to heat the fluid downstream of the storage means and upstream of the expansion so as to compensate this temperature drop. This solution makes it possible to maintain a very high flow rate.

[0069] The method according to the present invention is based on adjusting the pressure in the storage means by controlling the heating, so as to pass from the supercritical state to the gas phase without passing through the condensation zone.

[0070] This pressure adjustment is carried out based on the density calculated in real time (dynamic weighing of the storage means).

[0071] The mixture in the storage means is therefore at high temperature and pressure (temperature above ambient temperature and pressure of some tens of bar). Simple expansion cannot guarantee homogeneity, as in many cases it is accompanied by partial recondensation of the mixture.

[0072] Moreover, the Joule-Thomson effect of the mixture would lead to a very low temperature of the fluid after expansion.

[0073] The method according to the present invention is based on heating the mixture prior to withdrawal so as then to be able to expand it, avoiding the condensation zone.

[0074] The values for heating and expansion depend on the physical properties of the mixture.

[0075] The gas mixture typically used in the method according to the present invention for distribution of homogeneous liquefied mixtures corresponds to CO.sub.2 and to Novec, a registered trademark of 3M. For example, the mixture comprises 7 mol % of Novec (the mixture range may for example comprise from 2 mol % to 20 mol % of Novec).

[0076] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.