Method and device for determining an operating parameter of a fluid insulated electrical apparatus

Abstract

A method for deriving at least one operating parameter of a fluid-insulated electrical apparatus, in particular of gas-insulated switchgear. The operating parameter is dependent on a dielectric breakdown strength of an insulation fluid of the electrical apparatus. The insulation fluid includes at least three components that are assigned to at least a first and a second component group such that at least one component group comprises at least two components. The component groups differ in their weighted average values of the molecular masses of the components in the respective component groups. At least one quantity which is indicative of the concentration of the first component group and of the concentration of the second component group is determined from the insulation fluid, e.g. by measuring one or more measurement variables with one or more sensors. The operating parameter is then derived using the at least one quantity.

Claims

1. A method for deriving at least one operating parameter P of a fluid-insulated electrical apparatus, which is a gas-insulated medium or high voltage switchgear or a transformer and which comprises an insulation fluid with at least three components X, Y, and Z with component concentrations c.sub.X, c.sub.Y, and c.sub.Z, and which derived operating parameter P is dependent on a dielectric breakdown strength E.sub.bd of the insulation fluid of the electrical apparatus and defines an operational operating state or a failure state of the electrical apparatus, the method comprising the method elements of: measuring by means of at least one sensor a plurality of measurement variables, wherein the measurement variables are indicative of at least a pressure and a temperature of the insulation fluid, assigning the at least three components X, Y, and Z to at least a first component group A with a group concentration c.sub.A and to at least a second component group B with a group concentration c.sub.B, wherein at least the first component group A comprises at least two of the components X, Y, and Z or wherein at least the second component group B comprises at least two of the components X, Y, and Z, wherein the at least three components X, Y, and Z are assigned to the at least two component groups A and B in such a way that a weighted average value M.sub.A of a molecular mass of the component or components in the first component group A differs from a weighted average value M.sub.B of a molecular mass of the component or components in the second component group B, deriving the group concentrations c.sub.A and c.sub.B of the component groups A and B by using the measurement variables and at least one relating equation, which is the same or different for each of the component groups A and B, and deriving the operating parameter P using the group concentration c.sub.A and the group concentration c.sub.B; the method further comprising at least one additional method element selected from the group consisting of: increasing at least one of the component concentrations c.sub.X c.sub.Y and/or c.sub.Z of the components X, Y, and/or Z of the insulation fluid by injecting an amount of at least one of the components X, Y, and/or Z from a component reservoir into a compartment of the electrical apparatus, reducing at least one of the component concentrations c.sub.X c.sub.Y, and/or c.sub.Z of the components X, Y, and/or Z of the insulation fluid, reducing a concentration of at least one contaminant in the insulation fluid by means of a filter, at least partially evaporating a condensed amount of at least one of the components X, Y, and/or Z of the insulation fluid by means of a heater, and condensing an amount of at least one of the components X, Y, and/or Z of the insulation fluid by means of a cooler.

2. The method of claim 1, wherein an absolute value |M.sub.AM.sub.B| of the difference between the weighted average values M.sub.AM.sub.B of the molecular masses of the components X, Y, and Z between the first and second component groups A and B is larger than weighted statistical spreads .sub.M,A and .sub.M,B of the molecular masses of the components X, Y, and Z within the first and second component groups A and B.

3. The method of claim 2, wherein the absolute value |M.sub.AM.sub.B| of the difference between the weighted average values M.sub.AM.sub.B of the molecular masses of the components X, Y, and Z between the first and second component groups A and B is larger than 20 g/mol.

4. The method of any of the claims 2 to 3, wherein the second component group B comprises at least one of the components from the group consisting of: sulfur hexafluoride, partially or fully fluorinated ethers, in particular hydrofluoroethers, hydrofluoro monoethers, hydrofluoro monoethers containing at least 3 carbon atoms, perfluoro monoethers, or perfluoro monoethers containing at least 4 carbon atoms, partially or fully fluorinated ketones, in particular hydrofluoro monoketones, perfluoro monoketones, perfluoro monoketones comprising at least 5 carbon atoms, or perfluoro monoketones comprising exactly 5 or 6 or 7 or 8 carbon atoms, and mixtures thereof, and wherein the first component group A comprises at least one of the components from the group consisting of: nitrogen, oxygen, carbon dioxide, nitric oxide, nitrogen dioxide, nitrous oxide, argon, methanes, in particular partially or fully halogenated methanes, in particular tetrafluoromethane or trifluoroiodomethane, air, in particular technical air or synthetic air, and mixtures thereof.

5. The method of claim 2, wherein the absolute value |M.sub.AM.sub.B| of the difference between the weighted average values M.sub.AM.sub.B of the molecular masses of the components X, Y, and Z between the first and second component groups A and B is larger than 50 g/mol.

6. The method of claim 2, wherein the absolute value |M.sub.AM.sub.B| of the difference between the weighted average values M.sub.AM.sub.B of the molecular masses of the components X, Y, and Z between the first and second component groups A and B is larger than 100 g/mol.

7. The method of claim 1, wherein the at least three components X, Y, and Z are assigned to the at least two component groups A and B in such a way that a weighted average value E.sub.crit,A of a critical field strength of the component or components in the first component group A differs from a weighted average value E.sub.crit,B of a critical field strength of the component or components in the second component group B.

8. The method of claim 7, wherein an absolute value |E.sub.crit,AE.sub.crit,B| of the difference between the weighted average values E.sub.crit,AE.sub.crit,B of the critical field strengths of the components X, Y, and Z between the first and second component groups A and B is larger than weighted statistical spreads .sub.Ecrit,A and .sub.Ecrit,B of the critical field strengths of the components X, Y, and Z within the first and second component groups A and B.

9. The method of claim 1, wherein the second component group B comprises at least one of the components from the group consisting of: sulfur hexafluoride, partially or fully fluorinated ethers, in particular hydrofluoroethers, hydrofluoro monoethers, hydrofluoro monoethers containing at least 3 carbon atoms, perfluoro monoethers, or perfluoro monoethers containing at least 4 carbon atoms, partially or fully fluorinated ketones, in particular hydrofluoro monoketones, perfluoro monoketones, perfluoro monoketones comprising at least 5 carbon atoms, or perfluoro monoketones comprising exactly 5 or 6 or 7 or 8 carbon atoms, and mixtures thereof, and wherein the first component group A comprises at least one of the components from the group consisting of: nitrogen, oxygen, carbon dioxide, nitric oxide, nitrogen dioxide, nitrous oxide, argon, methanes, in particular partially or fully halogenated methanes, in particular tetrafluoromethane or trifluoroiodomethane, air, in particular technical air or synthetic air, and mixtures thereof.

10. The method of claim 9, wherein the second component group B comprises at least one component from the group consisting of: cyclic and/or aliphatic fluoropentanones, cyclic and/or aliphatic fluorohexanones, cyclic and/or aliphatic fluoroheptanones, sulfur hexafluoride, and hydrofluoroethers.

11. A computer program element comprising computer program code means for, when executed by a processing unit, implementing a method according to any one of the claims 1, 6 and 10.

12. The method of claim 9, wherein the first component group A comprises: the components nitrogen and oxygen with relative partial pressures between p(N.sub.2)/(p(O.sub.2)+p(N.sub.2))=0.7, p(O.sub.2)/(p(O.sub.2)+p(N.sub.2))=0.3 and p(N.sub.2)/(p(O.sub.2)+p(N.sub.2))=0.95, p(O.sub.2)/(p(O.sub.2)+p(N.sub.2))=0.05, or the components carbon dioxide and oxygen with relative partial pressures between p(CO.sub.2)/(p(O.sub.2)+p(CO.sub.2))=0.6, p(O.sub.2)/(p(O.sub.2)+p(CO.sub.2))=0.4 and p(CO.sub.2)/(p(O.sub.2)+p(CO.sub.2))=0.99, p(O.sub.2)/(p(O.sub.2)+p(CO.sub.2))=0.01, or the components carbon dioxide and nitrogen with relative partial pressures between p(CO.sub.2)/(p(N.sub.2)+p(CO.sub.2))=0.1, p(N.sub.2)/(p(N.sub.2)+p(CO.sub.2))=0.9 and p(CO.sub.2)/(p(N.sub.2)+p(CO.sub.2))=0.9, p(N.sub.2)/(p(N.sub.2)+p(CO.sub.2))=0.1, and wherein the second component group B comprises at least one components of the group consisting of: 1,1,1,3,4,4,4-heptafluoro-3-(tri-fluoro-methyl)butan-2-one with a partial pressure between 0.1 bar and 0.7 bar at a temperature of 20 C., 1,1,1,2,4,4,5,5,5-nonafluoro-4-(tri-fluoromethyl)pentan-3-one with a partial pressure between 0.01 bar and 0.3 bar at a temperature of 20 C., sulfur hexafluoride with a partial pressure between 0.1 bar and 2 bar at a temperature of 20 C., and one or more hydrofluoroethers with a partial pressure between 0.2 bar and 1 bar at a temperature of 20 C.

13. The method of any one of the claims 8, 9, and 12, wherein the dielectric breakdown strength E.sub.bd of the insulation fluid is derivable using a plurality of the component concentrations c.sub.X, c.sub.Y, and c.sub.Z of the components X, Y, and Z according to $E_{bd} = S (c_{X}, c_{Y}, c_{Z}, .Math.) {.Math.}_{i = X, Y, Z, .Math.}^{} c_{i} E_{crit, i}$ with c.sub.X, c.sub.Y, and c.sub.Z being the component concentrations of the components X, Y, and Z; with E.sub.crit,X, E.sub.crit,Y, and E.sub.crit,Z being component-specific critical field strengths of the components X, Y, and Z; with S(c.sub.X, c.sub.Y, c.sub.Z) being a component-specific synergy parameter; and with i being an index for the components X, Y, and Z, wherein the components X, Y, and Z and/or the component concentrations c.sub.X, c.sub.Y, and c.sub.Z are selected such that the synergy parameter S(c.sub.X, c.sub.Y, c.sub.Z) is greater than 1 for at least one combination of the component concentrations c.sub.X, c.sub.Y, and c.sub.Z.

14. The method of any one of the claims 8, 9, and 12, wherein the first component group A comprises the components X and Y and the second component group B comprises at least the component Z, and wherein a component-group-specific critical field strength E.sub.crit,A for the first component group A and/or a component-group-specific critical field strength E.sub.crit,B for the second component group B is or are derivable according to $E_{crit, A} = S_{A} (c_{X}, c_{Y}) {.Math.}_{i = X, Y}^{} c_{i} E_{crit, i}$ $and / or$ $E_{crit, B} = S_{B} (c_{Z}, .Math.) {.Math.}_{i = Z, .Math.}^{} c_{i} E_{crit, i}$ with c.sub.X, c.sub.Y, and c.sub.Z being the component concentrations of the components X, Y, and Z; with E.sub.crit,X, E.sub.crit,Y, and E.sub.crit,Z being component-specific critical field strengths of the components X, Y, and Z; with S.sub.A(c.sub.X, c.sub.Y) and S.sub.B(c.sub.Z, . . . ) being intra-component group synergy parameters of the component groups A and B; and with i being an index for the components X and Y for component group A and for at least the component Z for component group B.

15. The method of any of the claims 8, 9, and 12, further comprising the method element of deriving the dielectric breakdown strength E.sub.bd of the insulation fluid according to $E_{bd} = S (c_{A}, c_{B}) {.Math.}_{i = A, B}^{} c_{i} E_{crit, i}$ with E.sub.crit,A and E.sub.crit,B being component-group-specific critical field strengths of the component groups A and B; with c.sub.A and c.sub.B being the group concentrations of the first and second component groups A and B; with S(c.sub.A, c.sub.B) being an inter-component group synergy parameter; and with i being an index for the component groups A and B.

16. The method of claim 9, wherein the first component group A comprises: the components nitrogen and oxygen with relative partial pressures between p(N.sub.2)/(p(O.sub.2)+p(N.sub.2))=0.75, p(O.sub.2)/(p(O.sub.2)+p(N.sub.2))=0.25 and p(N.sub.2)/(p(O.sub.2)+p(N.sub.2))=0.90, p(O.sub.2)/(p(O.sub.2)+p(N.sub.2))=0.10, and wherein the second component group B comprises the component 1,1,1,3,4,4,4-heptafluoro-3-(tri-fluoromethyl)butan-2-one with a partial pressure between 0.25 bar and 0.5 bar and/or the component 1,1,1,2,4,4,5, 5,5-nona-fluoro-4-(tri-fluoromethyl)pentan-3-one with a partial pressure between 0.02 bar and 0.3 bar at a temperature of 20 C.

17. The method of claim 9, wherein the second component group B comprises at least one component from the group consisting of: cyclic and/or aliphatic perfluoropentanones, cyclic and/or aliphatic perfluorohexanones, cyclic and/or aliphatic perfluoroheptanones, sulfur hexafluoride, and hydrofluoroethers.

18. The method of claim 9, wherein the second component comprises 1,1,1,3,4,4,4-heptafluoro-3-(tri-fluoro-methyl)butan-2-one.

19. The method of claim 9, wherein the second component comprises 1,1,1,2,4,4,5,5,5-nonafluoro-4-(tri-fluoromethyl)pentan-3-one.

20. The method of claim 1, wherein the dielectric breakdown strength E.sub.bd of the insulation fluid is derivable using a plurality of the component concentrations c.sub.X, c.sub.Y, and c.sub.Z of the components X, Y, and Z according to $E_{bd} = S (c_{X}, c_{Y}, c_{Z}, .Math.) {.Math.}_{i = X, Y, Z, .Math.}^{} c_{i} E_{crit, i}$ with c.sub.X, c.sub.Y, and c.sub.Z being the component concentrations of the components X, Y, and Z; with E.sub.crit,X, E.sub.crit,Y, and E.sub.crit,Z being component-specific critical field strengths of the components X, Y, and Z; with S(c.sub.X, c.sub.Y, c.sub.Z) being a component-specific synergy parameter; and with i being an index for the components X, Y, and Z, wherein the components X, Y, and Z and/or the component concentrations c.sub.X, c.sub.Y, and c.sub.Z are selected such that the synergy parameter S(c.sub.X, c.sub.Y, c.sub.Z) is greater than 1 for at least one combination of the component concentrations c.sub.X, c.sub.Y, and c.sub.Z.

21. The method of claim 1, wherein the first component group A comprises the components X and Y and the second component group B comprises at least the component Z, and wherein a component-group-specific critical field strength E.sub.crit,A for the first component group A and/or a component-group-specific critical field strength E.sub.crit,B for the second component group B is or are derivable according to $E_{crit, A} = S_{A} (c_{X}, c_{Y}) {.Math.}_{i = X, Y}^{} c_{i} E_{crit, i}$ $and / or$ $E_{crit, B} = S_{B} (c_{Z}, .Math.) {.Math.}_{i = Z, .Math.}^{} c_{i} E_{crit, i}$ with c.sub.X, c.sub.Y, and c.sub.Z being the component concentrations of the components X, Y, and Z; with E.sub.crit,X, E.sub.crit,Y, and E.sub.crit,Z being component-specific critical field strengths of the components X, Y, and Z; with S.sub.A(c.sub.X, c.sub.Y) and S.sub.B(c.sub.Z, . . . ) being intra-component group synergy parameters of the component groups A and B; and with i being an index for the components X and Y for component group A and for at least the component Z for component group B.

22. The method of claim 21, wherein the components X, Y, and Z and/or the component concentrations c.sub.X, c.sub.Y, and c.sub.Z are selected such that the intra-component group synergy parameter or intra-component group synergy parameters S.sub.A(c.sub.X, c.sub.Y) and/or S.sub.B(c.sub.Z, . . . ) is or are equal to 1.

23. The method of claim 1, further comprising the method element of deriving the dielectric breakdown strength E.sub.bd of the insulation fluid according to $E_{bd} = S (c_{A}, c_{B}) {.Math.}_{i = A, B}^{} c_{i} E_{crit, i}$ with E.sub.crit,A and E.sub.crit,B being component-group-specific critical field strengths of the component groups A and B; with c.sub.A and c.sub.B being the group concentrations of the first and second component groups A and B; with S(c.sub.A, c.sub.B) being an inter-component group synergy parameter; and with i being an index for the component groups A and B.

24. The method of claim 23, wherein the components X, Y, and Z and/or the component concentrations c.sub.X, c.sub.Y, and c.sub.Z are selected such that the inter-component group synergy parameter S(c.sub.A, c.sub.B) is greater than 1 for at least one combination of the group concentrations c.sub.A and c.sub.B of the first and second component groups A and B.

25. The method of claim 1, further comprising the method element of deriving the component concentrations c.sub.X, c.sub.Y, and c.sub.Z of the components X, Y, and Z using the measurement variables by using at least one relating equation, wherein the relating equation is the same or different for each of the components X, Y, and Z.

26. The method of claim 1 or 25, wherein the relating equation or relating equations is or are selected from the group consisting of: ideal gas law, van-der-Waals equation of state, virial equation of state, Beattie-Bridgeman equation of state, and Peng-Robinson equation of state.

27. The method of claim 1, wherein at least three measurement variables are measured by means of the at least one sensor and wherein a or the relating equation or relating equations is or are used to derive the group concentrations c.sub.A and c.sub.B of the component groups A and B by using the measurement variables, and wherein the relating equation or relating equations is or are functions of at least one weighted average value of a component-specific parameter, in particular of a molecular mass (M), for the first and second component groups A and B.

28. The method of claim 1, wherein the measurement variables are indicative of at least the pressure (p), the temperature (T) and a density () of the insulation fluid.

29. The method of claim 1 or 28, wherein the measurement variables are additionally indicative of at least one element of the group consisting of: a thermal conductivity (), a viscosity (), and a speed of sound (c.sub.S) of or in the insulation fluid.

30. The method of claim 1, wherein a ratio of the component concentrations of the components in each component group A and B is constant or varies less than 10% over a period of application of the method.

31. The method of claim 1, wherein the operating parameter P of the fluid-insulated electrical apparatus is selected from the group consisting of: the dielectric breakdown strength E.sub.bd itself, a state of an indicator element, the state being dependent on the dielectric breakdown strength E.sub.bd, a change over time of the dielectric breakdown strength E.sub.bd, and a Boolean variable with a variable value being dependent on the dielectric breakdown strength E.sub.bd.

32. The method of claim 1, wherein the insulation fluid comprises at least four components X, Y, Z, and ZZ with component concentrations c.sub.X, c.sub.Y, c.sub.Z, and c.sub.ZZ, the method comprising the method elements of: assigning the at least four components to at least three component groups A, B, and C with group concentrations c.sub.A, c.sub.B, and c.sub.C, wherein at least one of the component groups comprises at least two of the components, determining at least one quantity of the insulation fluid which is indicative of the group concentrations, deriving the dielectric breakdown strength E.sub.bd of the insulation fluid according to $E_{bd} = S (c_{A}, c_{B}, c_{C}, .Math.) {.Math.}_{i = A, B, C, .Math.}^{} c_{i} E_{crit, i}$ with E.sub.crit,i for i=A, B, C, . . . being component group specific critical field strengths of the component groups; with c.sub.i for i=A, B, C, . . . being the group concentrations of the component groups; with S(c.sub.A, c.sub.B, c.sub.C, . . . ) being an inter-component group synergy parameter; and with i being an index for the component groups A, B, C, . . . .

33. A method according to claim 1, wherein whenever the dielectric breakdown strength E.sub.bd of the insulation fluid decreases below a threshold, when the electrical apparatus leaves an operational operating state as defined by the operating parameter P, an alert signal is issued, from a control unit to a user, and/or the electrical apparatus is shut down.

34. A method for operating a fluid-insulated electrical apparatus, in particular gas-isolated medium or high voltage switchgear, using a method of claim 1.

35. The method of claim 34, further comprising a method element of circulating the insulation fluid for homogenizing a density and/or a mixture of the first and/or the second and/or the third components X, Y, and/or Z before carrying out the method element of deriving the group concentrations c.sub.A and c.sub.B of the component groups A and B.

36. A fluid-insulated electrical apparatus, which is a gas-isolated medium or high voltage switchgear or a transformer, comprising: an insulation fluid which comprises at least three components X, Y, and Z, at least one sensor for measuring a plurality of measurement variables, and a control and analysis unit adapted to carry out the steps or method elements of the method of claim 1, including: deriving at least one operating parameter P of the fluid-insulated electrical apparatus, which derived operating parameter P is dependent on a dielectric breakdown strength E.sub.bd of the insulation fluid of the electrical apparatus and defines an operational operating state or a failure state of the electrical apparatus, measuring by means of the at least one sensor the plurality of the measurement variables, wherein the measurement variables are indicative of at least a pressure (p) and a temperature (T) of the insulation fluid, assigning the at least three components X, Y, and Z to at least a first component group A with a group concentration c.sub.A and to at least a second component group B with a group concentration c.sub.B, wherein at least the first component group A comprises at least two of the components X, Y, and Z or wherein at least the second component group B comprises at least two of the components X, Y, and Z, wherein the at least three components X, Y, and Z are assigned to the at least two component groups A and B in such a way that a weighted average value M.sub.A of a molecular mass of the component or components in the first component group A differs from a weighted average value M.sub.B of a molecular mass of the component or components in the second component group B, deriving the group concentrations c.sub.A and c.sub.B of the component groups A and B by using the measurement variables and at least one relating equation, which is the same or different for each of the component groups A and B, and deriving the operating parameter P using the group concentration c.sub.A and the group concentration c.sub.B.

37. The method of claim 1, wherein a ratio of the component concentrations of the components in each component group A and B is constant or varies less than 1% over a period of application of the method.

38. The method of claim 1, wherein the at least one additional method element selected from the group includes the at least partially evaporating the condensed amount of the at least one of the components X, Y, and/or Z of the insulation fluid by means of the heater.

39. The method of claim 1, wherein the at least one additional method element selected from the group includes the condensing the amount of at least one of the components X, Y, and/or Z of the insulation fluid by means of the cooler.

40. A method for operating a fluid-insulated electrical apparatus, in particular gas-isolated medium or high voltage switchgear comprising an insulation fluid with at least three components X, Y, and Z with component concentrations c.sub.X c.sub.Y and c.sub.Z, using a derived operating parameter P that is dependent on a dielectric breakdown strength E.sub.bd of the insulation fluid of the electrical apparatus and defines an operational operating state or a failure state of the electrical apparatus, the method comprising the steps of: measuring by means of at least one sensor a plurality of measurement variables, wherein the measurement variables are indicative of at least a pressure and a temperature of the insulation fluid; assigning the at least three components X, Y, and Z to at least a first component group A with a group concentration c.sub.A and to at least a second component group B with a group concentration c.sub.B, wherein at least the first component group A comprises at least two of the components X, Y, and Z or wherein at least the second component group B comprises at least two of the components X, Y, and Z; wherein the at least three components X, Y, and Z are assigned to the at least two component groups A and B in such a way that a weighted average value M.sub.A of a molecular mass of the component or components in the first component group A differs from a weighted average value M.sub.B of a molecular mass of the component or components in the second component group B; deriving the group concentrations c.sub.A and c.sub.B of the component groups A and B by using the measurement variables and at least one relating equation, which is the same or different for each of the component groups A and B; and deriving the operating parameter P using the group concentration c.sub.A and the group concentration c.sub.B; wherein the second component group B comprises at least one of the components from the group consisting of: sulfur hexafluoride; partially or fully fluorinated ethers, in particular hydrofluoroethers, hydrofluoro monoethers, hydrofluoro monoethers containing at least 3 carbon atoms, perfluoro monoethers, or perfluoro monoethers containing at least 4 carbon atoms; partially or fully fluorinated ketones, in particular hydrofluoro monoketones, perfluoro monoketones, perfluoro monoketones comprising at least 5 carbon atoms, or perfluoro monoketones comprising exactly 5 or 6 or 7 or 8 carbon atoms; and mixtures thereof; and wherein the first component group A comprises at least one of the components from the group consisting of: nitrogen; oxygen; carbon dioxide; nitric oxide; nitrogen dioxide; nitrous oxide; argon; methanes, in particular partially or fully halogenated methanes, in particular tetrafluoromethane or trifluoroiodomethane; air, in particular technical air or synthetic air; and mixtures thereof; the method further comprising at least one method element of the group consisting of: increasing at least one of the component concentrations c.sub.X c.sub.Y and/or c.sub.Z of the components X, Y, and/or Z of the insulation fluid, in particular by means of injecting an amount of at least one of the components X, Y, and/or Z from a component reservoir into a compartment of the electrical apparatus, reducing at least one of the component concentrations c.sub.X c.sub.Y, and/or c.sub.Z of the components X, Y, and/or Z of the insulation fluid, reducing a concentration of at least one contaminant in the insulation fluid by means of a filter, at least partially evaporating a condensed amount of at least one of the components X, Y, and/or Z of the insulation fluid by means of a heater, and condensing an amount of at least one of the components X, Y, and/or Z of the insulation fluid by means of a cooler.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its embodiments will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings.

(2) FIG. 1 shows a schematic of a fluid-insulated electrical apparatus,

(3) FIG. 2 shows a schematic of an assignment of three components X, Y, and Z to two component groups A and B,

(4) FIG. 3 shows an inter-component group synergy parameter S(c.sub.A, c.sub.B) as a function of the total pressure p with fixed partial pressures p.sub.B for different component groups B, and

(5) FIG. 4 shows an inter-component group synergy parameter S(c.sub.A, c.sub.B) as a function of a mole-fraction of the perfluoroketones C5 or C6 (group B) in air (group A).

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows a schematic of a fluid-insulated electrical apparatus 1, i.e. here a gas insulated switch 1. An electrically active part 60 of the fluid-insulated apparatus 1 is arranged in a gas-tight compartment 50 which encloses an insulation fluid 10 for preventing the passage of electrical current from the electrically active part 60 to the compartment 50. The insulation fluid 10 is an insulation gas 10 comprising the component X which is nitrogen N.sub.2 with a partial pressure p.sub.X=p(N.sub.2)=5.29 bar, the component Y which is oxygen O.sub.2 with a partial pressure p.sub.Y=p(O.sub.2)=1.41 bar and the component Z which is perfluoroketone C5 (see definition below) with a partial pressure p.sub.Z=p(C5)=0.3 bar at a temperature of 20 C. The total filling pressure p=p.sub.X+p.sub.Y+p.sub.Z at filling time is p=p.sub.X+p.sub.Y+p.sub.Z=7 bar, the total volume of the gas-tight compartment 50 (filling volume of the insulation gas 10) is V=2 m.sup.3. As an option, additionally or as replacement for component Z, a component perfluoroketone C6 with a partial pressure p(C6)=0.1 bar and/or a component perfluoroketone C7 can be added to the insulation gas 10 (not shown in FIG. 1). The components X and Y are assigned to the component group A and the component Z is assigned to the component group B (see FIG. 2 below). Thus, a weighted average value M.sub.A of the molecular masses of the two components X and Y in the first component group A differs from a weighted average value M.sub.B of the molecular mass of the component in the second component group B: Here, M.sub.A=28.8 g/mol and M.sub.B=266 g/mol. The measurement variables pressure p, temperature T, and density p (e.g. WO 2010/043268 A1 discloses a suitable density sensor device for this purpose) of the insulation fluid 10 mixture are measured by the sensors 30 and electrical signals indicative of these measurement variables are transmitted to the analysis and control unit 40 comprising a processing unit 41 and a memory 42.

(7) As an option, additionally or as a replacement for the density of the insulation gas 10, other suitable measurement variables like thermal conductivity , viscosity , and/or speed of sound c.sub.S of or in the insulation gas 10 can be measured by the same or a different sensor device 30 (not shown in FIG. 1). The measurement variables can then be related to the concentration values c.sub.A, c.sub.B of the component groups A and B of the insulation fluid 10, e.g. by using the following relating equation (if pressure p, temperature T, and speed of sound c.sub.S are measured):

(8) $c_{S} = \sqrt{\frac{RT (c_{A} c_{pA} + c_{B} c_{pB})}{(c_{A} M_{A} + c_{B} M_{B}) (c_{A} c_{VA} + c_{B} c_{VB})}}$ with c.sub.A and c.sub.B being the desired group concentration values in mole fractions of the component groups A and B with c.sub.A+c.sub.B=1, c.sub.A=p.sub.A/p, and c.sub.B=p.sub.B/p, p.sub.A and p.sub.B being partial pressures of the component groups A and B, R being the ideal gas constant, M.sub.A and M.sub.B being (averaged) molecular masses of the component groups A and B, and c.sub.pA, c.sub.pB, c.sub.VA, and c.sub.VB being known specific heat values of the component groups A and B at constant pressures and constant volumes, respectively.

(9) If pressure p, temperature T, and viscosity are measured, the following relating equation can, e.g., be used:

(10) $(T) = \frac{c_{A}_{A} (T)}{c_{A}_{AA} + c_{B}_{AB}} + \frac{c_{B}_{B} (T)}{c_{B}_{BB} + c_{A}_{BA}}$ $with$ $_{ij} (T) = \frac{1}{2 \sqrt{2}} {{(1 + \frac{M_{i}}{M_{j}})}^{- 1 / 2} [1 + {(\frac{_{i} (T)}{_{j} (T)})}^{1 / 2} {(\frac{M_{j}}{M_{i}})}^{1 / 4}]}^{2}$

(11) and with i=A, B, with j=A, B, with c.sub.A and c.sub.B being the desired group concentration values in mole fractions of the component groups A and B with c.sub.A+c.sub.B=1, c.sub.A=p.sub.A/p, and c.sub.B=p.sub.B/p, p.sub.A and p.sub.B being partial pressures of the component groups A and B, .sub.A(T) and .sub.B(T) being known temperature dependent viscosities of the component groups A and B, and M.sub.A and M.sub.B being (averaged) molecular masses of the component groups A and B.

(12) If pressure p, temperature T, and thermal conductivity are measured, the following relating equation can, e.g., be used:

(13) $(T) = \frac{c_{A}_{A} (T)}{c_{A}_{AA} + c_{B}_{AB}} + \frac{c_{B}_{B} (T)}{c_{B}_{BB} + c_{A}_{BA}} with_{ij} (T) = \frac{1}{2 \sqrt{2}} {{(1 + \frac{M_{i}}{M_{j}})}^{- 1 / 2} [1 + {(\frac{_{i} (T)}{_{j} (T)})}^{1 / 2} {(\frac{M_{j}}{M_{i}})}^{1 / 4}]}^{2}$

(14) and with i=A, B, with j=A,B, with c.sub.A and c.sub.B being the desired concentration values in mole fractions of the component groups A and B with c.sub.A+c.sub.B=1, c.sub.A=p.sub.A/p, and c.sub.B=p.sub.B/p, p.sub.A and p.sub.B being partial pressures of the component groups A and B, .sub.A(T) and .sub.B(T) being known temperature dependent thermal conductivities of the component groups A and B, .sub.A(T) and .sub.B(T) being known temperature dependent viscosities of the component groups A and B, and M.sub.A and M.sub.B being (averaged) molecular masses of the component groups A and B.

(15) E.g. U.S. Pat. No. 6,305,212 B1, U.S. Pat. No. 6,272,905 B1, and T. Lofquist et. al: SPEED OF SOUND MEASUREMENTS IN GAS-MIXTURES AT VARYING COMPOSITION USING AN ULTRASONIC GAS FLOW METER WITH SILICON BASED TRANSDUCERS (e.g. http://pure.ltu.se/portal/files/60931/artikel.pdf as accessed on 18 Nov. 2011) give further examples on how to relate different measurement variables.

(16) In this embodiment, this is not necessary, however, because measurement variables indicative of the pressure p, the temperature T, and the density are measured as discussed above. The analysis and control unit 40 determines the partial pressure p.sub.A of the first component group A and the partial pressure p.sub.B of the second component group B using the following equations:

(17) $\begin{matrix} p_{tot} = p_{A} + p_{B} & Eq . 1 \\ _{tot} = \frac{M_{A} p_{A}}{RT} + \frac{M_{B} p_{B}}{RT} & Eq . 2 \\ P_{A} = \frac{\frac{RT}{M_{A}}_{tot} - \frac{M_{B}}{M_{A}} p_{tot}}{(1 - \frac{M_{B}}{M_{A}})} & Eq . 3 \\ p_{B} = \frac{p_{tot} - \frac{RT}{M_{A}}_{tot}}{(1 - \frac{M_{B}}{M_{A}})} & Eq . 4 \end{matrix}$

(18) with p.sub.tot being the (total) pressure p, p.sub.tot being the (total) density , T being the temperature, R being the ideal gas constant, and M.sub.A and M.sub.B being the weighted average values of the molecular masses of the component groups A and B, respectively. Here, the ideal gas law pV=nRT and the equations n=m/M and m=V with m being a mass and V being a volume are used for both component groups A and B as an approximation. As an alternative, different relating equations could be used for both component groups A and B as discussed above.

(19) Then, the operating parameter P of the electrical apparatus 1 (which is the dielectric breakdown strength E.sub.bd of the insulation fluid 10 in this embodiment) is derived from the group partial pressures p.sub.A and p.sub.B (which areas it is obvious to a person skilled in the artdirectly linked to the group concentrations c.sub.A and c.sub.B via c.sub.i=p.sub.i/p, i=A, B), from component-group-specific critical field strengths E.sub.crit,A and E.sub.crit,B, and from the inter-component group synergy parameter S(c.sub.A, c.sub.B) according to the following equation:

(20) $E_{bd} = S (c_{A}, c_{B}) {.Math.}_{i = A, B}^{} c_{i} E_{crit, i}$

(21) The component-group-specific critical field strengths E.sub.crit,A and E.sub.crit,B and the inter-component group synergy parameter S(c.sub.A, c.sub.B) can be prestored in the memory 42 of the analysis and control unit 40. The inter-component group synergy parameter S(c.sub.A, c.sub.B) can be prestored as a lookup-table for a plurality of c.sub.A-c.sub.B-combinations, interpolation can additionally be used between prestored values. The intra-component group synergy parameters are equal to 1. Thus,albeit the insulation fluid 10 comprises three components X, Y, and Zthe dielectric breakdown strength E.sub.bd of the insulation fluid 10 can more easily be derived from only three measurement variables pressure p, temperature T, and density . This is possible due to the grouping step as described above.

(22) Whenever the dielectric breakdown strength E.sub.bd of the insulation fluid 10 decreases below a threshold, (i.e. the electrical apparatus 1 leaves an operational operating state as defined by the parameter P), an alert signal can be issued to a user from the control unit 40 and an emergency shutdown of the electrical switch 1 can be initiated.

(23) Furthermore, optionally, depending on the entered operating state, countermeasures can be taken automatically by the electrical apparatus 1: As an example, if the ambient temperature drops severely and component Z partly condenses in the lower part of the compartment 50, heater 80 can be engaged to evaporate at least a part of the condensed component Z, thus ensuring a sufficient gaseous amount of component Z in the gaseous phase of the insulation fluid 10 in the compartment 50.

(24) As another example, if preferential leakage of components A and B occurs, e.g., due to a very small leak in the compartment 50, an amount of these components can be replenished from a pressurized component reservoir 70, thus minimizing downtime of the electrical apparatus 1.

(25) As yet another example, a filter 90 in the compartment 50 can be used to remove an unwanted substance (i.e. a contaminant of the insulation fluid 10, e.g. due to arcing) from the insulation fluid 10.

(26) FIG. 2 shows a schematic of an assignment of the three components X, Y, and Z of FIG. 1 to the two component groups A and B. The components are assigned to the component groups A and B based on their molecular masses of M.sub.X=32 g/mol, M.sub.Y=28 g/mol, and M.sub.Z=266 g/mol, as described above. Thus, weighted average value of the molecular mass of M.sub.A=28.8 g/mol and M.sub.B=266 g/mol result. As a result, an absolute value |M.sub.AM.sub.B| of the difference between the weighted average values M.sub.AM.sub.B is larger than standard deviations of the distributions of the components' values which are .sub.M,A=2.33 g/mol and .sub.M,B=0 g/mol (unweighted standard deviations). Thus, the components X, Y, and Z are assigned to the first and second component groups A and B based on similar molecular masses. A similar approach could be used for grouping by similar component specific critical field strengths E.sub.crit,X, E.sub.crit,Y and E.sub.crit,Z.

(27) Grouping the components based on similar molecular masses has two reasons: (1) The closer the molecular masses of grouped components are, the less will undesired leakage rates between these components differ. Therefore, an approximation, that the relative concentrations of these grouped components (i.e. in each component group) remains constant, is better. (2) Some substance-specific and/or empirical parameters of relating equations will be more similar for grouped components of similar molecular masses.

(28) As an effect of the grouping approach, the dielectric breakdown strength E.sub.bd of the insulation fluid 10 can more easily be derived from only three measurement variables pressure p, temperature T, and density because group-specific parameters can be used.

(29) FIG. 3 shows the inter-component group synergy parameter S(c.sub.A, c.sub.B) as a function of total pressure p=p.sub.A+p.sub.B with fixed partial pressures p.sub.B for different component groups B. The same relation for relating partial pressures to concentrations as discussed above is used. Specifically, the rectangles refer to a component group B comprising the perfluoroketone C6 with a partial pressure p.sub.B=0.1 bar, the diamonds refer to a component group B comprising the perfluoroketone C5 with a partial pressure p.sub.B=0.3 bar, and the triangles refer to a component group B comprising the perfluoroketones C5 and C6 with partial pressures p.sub.B,C5=0.3 bar and p.sub.B,C6=0.1 bar, i.e., p.sub.B=0.4 bar. The component group A of the insulation fluid 10 consists of synthetic air (80% N.sub.2 and 20% O.sub.2). The total pressure p=p.sub.A+p.sub.B (x-axis) is varied by adding more and more synthetic air and the inter-component group synergy parameter S(c.sub.A, c.sub.B) (y-axis) is shown for different total pressures p (and hence different partial pressures p.sub.A or concentrations c.sub.A, respectively). As it can be seen from the figure, for the C5 (diamonds) and for the mixed C5-C6 (triangles) component groups B, the inter-component group synergy parameter S(c.sub.A, c.sub.B) and hence the dielectric breakdown strength E.sub.bd of the insulation fluid 10 increase up to a total pressure of about 2 bar whereas for the C6 (rectangles) component group B, the inter-component group synergy parameter S(c.sub.A, c.sub.B) remains almost constant with increasing total pressure p. Thus, if the partial pressure p.sub.A is increased to a total pressure of about 2 bar for C5 and C5-C6, the dielectric breakdown strength E.sub.bd of the insulation fluid is more and more nonlinearly enhanced.

(30) Similar to FIG. 3, FIG. 4 shows an inter-component group synergy parameter S(c.sub.A, c.sub.B) as a function of the mole fraction c.sub.B/(c.sub.A+c.sub.B) of the perfluoroketone C5 or the perfluoroketone C6 which is (one at a time, no mixture in component group B in this embodiment) comprised in component group B. The component group A of the insulation fluid 10 consists of synthetic air (80% N.sub.2 and 20% O.sub.2). The mole fraction (x-axis) defines a ratio of number of particles. E.g., a mole fraction of component group B of 0.5 means that half of the molecules in the compartment 50 of the electrical apparatus 1 belong to component group B. The diamonds show experimental values for S(c.sub.A, c.sub.B) whereas the line refers to a fit function for the experimental synergy datapoints of the form S(c.sub.A, c.sub.B)=a*exp(x/x1)exp(x/x2)]+b with a=0.37, x1=0.3, x2=0.026, and b=1 being fit parameters and x being the mole fraction x=c.sub.B/(c.sub.A+c.sub.B) of the perfluoroketones C5 or C6 (experimental datapoints for both components are shown) which areone at a timecomprised in component group B. As it can be seen from the figure, the inter-component group synergy parameter S(c.sub.A, c.sub.B) and hence the achievable dielectric breakdown strength E.sub.bd of the insulation fluid 10 increases up to a mole fraction of component group B of about 0.1 and then decreases. Thus, if the mole fraction (or, equivalently, the concentration c.sub.B) of component group B is increased to about 0.1 the dielectric breakdown strength E.sub.bd of the insulation fluid is maximally nonlinearly enhanced.

Definitions

(31) The term aliphatic relates to both linear aliphatic and branched aliphatic.

(32) The term fluid relates to a substance, such as a liquid [and/] or gas, that can flow, has no fixed shape, and offers little resistance to an external stress (from http://www.thefreedictionary.com/fluid, accessed on Sep. 11, 2011).

(33) The term weighted average value of a property N of the components in a component group relates to a statistical average (such as the median or the mean) of the property N of all the components in the component group. This statistical average is weighted by the concentrations of the components that form the respective component group. If the term weighted average value of a property N of a single component that forms a component group is used, the property N of the single component itself is referred to. Similar definitions apply for the statistical spread. In particular, a statistical spread of a property N in a component group consisting of only a single component is 0.

(34) The term high-voltage relates to voltages larger than 50 kV.

(35) The term medium-voltage relates to voltages larger than 1 kV.

(36) The term concentration herein shall define a quantity (with units) which is indicative of an amount per volume unit, e.g. a particle number per volume unit, moles per volume unit, or a number density, or a number (without units) which is indicative of a ratio such as a mole fraction, a pressure-normalized partial pressure, a volume fraction, a mass fraction, or a density fraction.

(37) The compound class hydrofluoroethers relates to specific partially or fully fluorinated ethers as, e.g., available from 3M.

(38) The compound C5 particularly relates to a partially or fully fluorinated fluoroketone selected from the group consisting of the compounds defined by the following structural formulae in which at least one hydrogen atom, preferably all hydrogen atoms, is/are substituted with a fluorine atom/fluorine atoms:

(39) ##STR00001##

(40) The compound C6 particularly relates to a partially or fully fluorinated fluoroketone selected from the group consisting of the compounds defined by the following structural formulae in which at least one hydrogen atom, preferably all hydrogen atoms, is/are substituted with a fluorine atom/fluorine atoms:

(41) ##STR00002##

(42) The compound C7 particularly relates to a partially or fully fluorinated fluoroketone selected from the group consisting of the compounds defined by the following structural formulae in which at least one hydrogen atom, preferably all hydrogen atoms, is/are substituted with a fluorine atom/fluorine atoms:

(43) ##STR00003## ##STR00004##

(44) Note:

(45) While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may otherwise variously be embodied and practiced within the scope of the following claims. Therefore, terms like preferred, advantageous or the like denote optional features or embodiments only. Method step generally means method element, i.e. does not imply that the steps shall be executed in the order as they are listed.

REFERENCE NUMBERS

(46) 1: electrical apparatus 10: insulation fluid A, B: component groups of the insulation fluid 10 X, Y, Z: components of the insulation fluid 10 , p, T, , , c.sub.S: measurement variables 30: sensors 40: control and analysis unit 41: processing unit 42: memory 50: gas-tight compartment 60: electrically active part c.sub.X, c.sub.Y, c.sub.Z: component concentrations, e.g. expressed in mol/m.sup.3 or without units, of components X, Y, Z c.sub.A, c.sub.B: group concentrations of component groups A, B E.sub.crit,X, E.sub.crit,Y, E.sub.crit,Z: component-specific critical field strengths, e.g. expressed in kV/(cm*(mol/m3)) E.sub.crit,A, E.sub.crit,B: component-group-specific critical field strengths, e.g. expressed in kV/(cm*(mol/m.sup.3)) S(c.sub.X, c.sub.Y, c.sub.Z): synergy parameter S.sub.A(c.sub.X, c.sub.Y), S.sub.B(c.sub.Z, . . . ): intra-component group synergy parameters S(c.sub.A, c.sub.B): inter-component group synergy parameter Ebd: dielectric breakdown strength of the insulation fluid 10 of the electrical apparatus 1, e.g. expressed in kV/cm. 70: component reservoir 80: heater 90: filter

Method and device for determining an operating parameter of a fluid insulated electrical apparatus

Assignee

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Cpc classification

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H01H33/563

ELECTRICITY

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G01R31/1281

PHYSICS

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G01R31/3275

PHYSICS

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H01H2033/566

ELECTRICITY

International classification

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G01R31/00

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H01H33/56

ELECTRICITY

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G01R31/06

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G01R31/327

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G01R31/12

PHYSICS

Abstract

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Description