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. A method of distributing an electrically insulating liquefied gas mixture to high-voltage electrical equipment from a storage means containing an electrically insulating liquefied gas mixture, the method comprising the following steps: Step a): heating the electrically insulating liquefied gas mixture to a temperature such that the contents of the storage means are a homogeneous fluid; Step b): withdrawing the electrically insulating liquefied gas mixture resulting from step a) to fill high-voltage electrical equipment by raising the temperature of the electrically insulating liquefied gas 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.

2. The method of claim 1, wherein step a) comprises heating the electrically insulating liquefied 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.

3. The method of claim 1, wherein, during step b), the electrically insulating liquefied gas mixture undergoes expansion to a pressure between 0 bar and 12 bar relative.

4. The method of claim 3, wherein the temperature of the electrically insulating liquefied gas mixture resulting from step a) is raised to a temperature between 65° C. and 90° C. during withdrawal in step b).

5. The method of claim 1, wherein the pressure inside the storage means between step a) and step b) is between 15 bar and 90 bar relative.

6. The method of claim 1, wherein the temperature of the electrically insulating liquefied gas mixture inside the storage means between step a) and step b) is between 40° C. and 65° C.

7. The method of claim 1, wherein said storage means comprises heating means consisting of electromagnetic induction means capable of heating the electrically insulating liquefied gas mixture inside the storage means.

8. The method of claim 1, wherein the electrically insulating liquefied 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.

9. The method of claim 8, wherein that the electrically insulating liquefied gas mixture comprises at least one component selected from the fluoronitriles having at least four carbon atoms.

10. The method of claim 9, wherein the electrically insulating liquefied gas mixture comprises between 2 and 20 mol % of said component selected from the fluoronitriles having at least four carbon atoms.

11. The method of claim 1, wherein said storage means has a capacity for storage of the electrically insulating liquefied gas mixture between 30 L and 700 L.

12. The method of claim 1, wherein, in step b), the rate of withdrawal of the electrically insulating liquefied gas mixture resulting from step a) is between 10 Nm.sup.3/h and 50 Nm.sup.3/h.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawing, in which like elements are given the same or analogous reference numbers and wherein:

(2) FIG. 1 is a schematic representation the method of distributing an electrically insulating liquefied gas mixture to high-voltage electrical equipment, in accordance with one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Element Numbers

(3) 101=storage means 102=high-voltage electrical equipment 103=electrically insulating liquefied gas mixture 104=heating means for storage means 105=heating means downstream of storage means (upstream of Joule Thompson valve) 106=weighing means 107=temperature sensor for gas mixture inside storage means 108=temperature sensor for gas mixture outside storage means upstream of Joule-Thompson valve 109=temperature sensor for gas mixture outside storage means downstream of Joule-Thompson valve 110=pressure sensor for gas mixture inside storage means 111=pressure sensor for gas mixture outside of storage means upstream of Joule-Thompson valve 112=pressure sensor for gas mixture outside of storage means downstream of Joule-Thompson valve 113=flowmeter for electrically insulating liquefied gas mixture 114=Joule-Thompson valve 115=controller (regulator)

(4) One of the problems solved by the method according to the invention is to homogenize the mixture in the storage means 101 and then transfer it into the high-voltage equipment 102 without any loss of homogeneity.

(5) The present inventors have elaborated a solution allowing the aforementioned problems to be solved.

(6) The present invention relates to a method of distributing an electrically insulating liquefied gas mixture 103 to high-voltage electrical equipment 102 from a storage means 101 containing an insulating gas mixture 103, said method comprising the following steps: Step a): heating 104 said insulating gas mixture 103 to a temperature 107 such that the contents of the storage means 101 are a homogeneous fluid; Step b): withdrawing the insulating mixture 103 resulting from step a) to fill high-voltage electrical equipment 102 by raising the temperature 108 of said mixture resulting from step a);
characterized in that, during step b), a set value for regulation is applied at variable pressure 110, calculated in real time 115 based on weighing 106 the storage means 101, when the change in the set value of pressure 110 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 108 until the storage means 101 is emptied of its contents.

(7) According to other embodiments, the invention also relates to:

(8) A method as defined above, characterized in that step a) consists of heating 104 said insulating gas mixture 103 to a temperature 107 greater than or equal to its critical temperature in order to obtain a homogeneous supercritical fluid inside said storage means 101.

(9) A method as defined above, characterized in that, during step b), the insulating mixture 103 undergoes expansion to a pressure 112 between 0 bar and 12 bar relative, preferably from 5 bar to 10 bar relative.

(10) A method as defined above, characterized in that the temperature 107 of the insulating mixture 103 resulting from step a) is raised to a temperature 108 between 65° C. and 90° C. during withdrawal in step b).

(11) A method as defined above, characterized in that the pressure 110 inside the storage means 101 between step a) and step b) is between 15 bar and 90 bar relative.

(12) A method as defined above, characterized in that the temperature 107 of the insulating mixture 103 inside the storage means 101 between step a) and step b) is between 40° C. and 65° C.

(13) A method as defined above, characterized in that said storage means 101 comprises heating means 104 consisting of electromagnetic induction means capable of heating the insulating mixture 103 inside said storage means 101.

(14) A method as defined above, characterized in that the insulating gas mixture 103 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.

(15) A method as defined above, characterized in that the insulating mixture 103 comprises at least one component selected from the fluoronitriles having at least four carbon atoms.

(16) A method as defined above, characterized in that the insulating mixture 103 comprises between 2 and 20 mol % of said component selected from the fluoronitriles having at least four carbon atoms.

(17) A method as defined above, characterized in that said storage means 101 has a capacity for storage of said insulating mixture between 30 L and 700 L.

(18) A method as defined above, characterized in that, in step b), the rate of withdrawal 113 of the insulating mixture 103 resulting from step a) is between 10 Nm.sup.3/h and 50 Nm.sup.3/h, and preferably between 15 and 30.

(19) 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.

(20) It is therefore a method of regulating 115 the heating 105 of means of storage 101 of liquefied mixtures 103 in order to make these mixtures 103 homogeneous before and during transfer. This method of regulating 115 heating 104 is useful and effective throughout transfer, i.e. from the storage means 101 full state to the storage means 101 empty state.

(21) Heating 104 the storage means 101 makes it possible to exceed the critical temperature of the mixture 103 and obtain a homogeneous dielectric mixture in situ.

(22) When the density of the mixture 103 inside the storage means 101 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.

(23) The invention allows high-voltage equipment 102 to be filled from a storage means 101 of liquefied dielectric gas mixture 103 without changing the initial proportions of the mixture, in conditions of temperature 108 and pressure 111 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).

(24) The solution for making the mixture 103 homogeneous consists of heating 104 the storage means 101.

(25) For this purpose, the invention combines a set of solutions for regulating 115 the heating 104 of the storage means 101 so as to comply with all the constraints and to overcome all the difficulties described above.

(26) These solutions for regulating 115 the heating operate as follows:

(27) 1. Regulating 115 the heating 104 of the storage means 101 based on a set value of pressure 110, the latter being variable and calculated 115 in real time on the basis of weighing 105, when the change in the set value of pressure 110 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.Math.kg.sup.−1.Math.m.sup.3).

(28) 2. Regulating 115 the heating 104 of the storage means 101 based on the set value of constant temperature 107, when the change in the set value of pressure 110 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.Math.kg.sup.−1.Math.m.sup.3).

(29) 3. Calculation of the pressure 110 value set in step 1 so that the temperature 107 remains below the maximum permissible temperature for the storage means 101, so that the pressure 110 remains below the maximum permissible pressure for the storage means, and so that the pressure 110 & temperature 107 pair never leads to recondensation of the mixture 103.

(30) The principle of homogenization of the dielectric mixture used in the method according to the present invention is to heat 104 the storage means 101 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.

(31) 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.

(32) The supercritical state may be attained by exceeding the critical temperature and critical pressure of the mixture 103. However, this heating 104 must be regulated 115 so that neither the design temperature, nor the design pressure of the storage means 101 is exceeded.

(33) Two problems arise for ensuring homogenization of the mixture 103 during withdrawal of the latter for filling the high-voltage equipment 102: maintaining homogeneity of the mixture 103 within the storage means 101 despite the decrease in density due to consumption; making the mixture 103 suitable for use at a pressure 111 and temperature 108 guaranteeing absence of recondensation and therefore of loss of homogeneity.

(34) As the mixture 103 is consumed, the density will decrease, so that a higher heating temperature 107 is required. However, this temperature 107 is limited by the design temperature of the storage means 101 (generally 65° C.).

(35) Expanding 114 the mixture 103 to lower it to the pressure 112 of use will cool the fluid by the Joule-Thomson effect. The invention makes it possible to heat 105 the fluid 103 downstream of the storage means 101 and upstream of the expansion 114 so as to compensate this temperature drop. This solution makes it possible to maintain a very high flow rate.

(36) The method according to the present invention is based on adjusting the pressure 110 in the storage means 101 by controlling 115 the heating 104, so as to pass from the supercritical state to the gas phase without passing through the condensation zone.

(37) This pressure adjustment 115 is carried out based on the density calculated in real time (dynamic weighing 106 of the storage means 101).

(38) The mixture 103 in the storage means 101 is therefore at high temperature 107 and pressure 110 (temperature above ambient temperature and pressure of some tens of bar). Simple expansion 114 cannot guarantee homogeneity, as in many cases it is accompanied by partial recondensation of the mixture.

(39) Moreover, the Joule-Thomson effect 114 of the mixture 103 would lead to a very low temperature 109 of the fluid 103 after expansion.

(40) The method according to the present invention is based on heating 104 the mixture 103 prior to withdrawal so as then to be able to expand it 114, avoiding the condensation zone.

(41) The values for heating 104, 105 and expansion 114 depend on the physical properties of the mixture.

(42) The gas mixture 103 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®).

(43) 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.