WO2014037030A1

WO2014037030A1 - Method for operating an electrical apparatus and electrical apparatus

Info

Publication number: WO2014037030A1
Application number: PCT/EP2012/067219
Authority: WO
Inventors: Thomas Alfred Paul; Axel Kramer; Eric Killer; Javier Mantilla; Max-Steffen Claessens; Stephan Grob; Hubert Brändle; Oliver Cossalter; Mathias-Dominic Buergler
Original assignee: Abb Technology Ag
Priority date: 2012-09-04
Filing date: 2012-09-04
Publication date: 2014-03-13

Abstract

A method and device for operating a fluid- insulated electrical apparatus (1) are disclosed. The insulation fluid (10) of the electrical apparatus (1) comprises at least two fluid components (A, B) which are a priori ingredients of the insulation fluid (10). The method comprises the step of carrying out at least one optical measurement and/or at least one gas chromatographic measurement on the insulation fluid (10). Using this measurement or these measurements or at least one additional measurement on the insulation fluid (10), a first concentration (c_A) of the first fluid component (A) and a second concentration (c_B) of the second fluid component (B) are derived. Then, using the first concentration (c_A) and the second concentration (c_B), and, advantageously, a dielectric breakdown strength of the insulation fluid (10), an operating state (O) of the electrical apparatus (1) is derived.

Description

Method for operating an electrical apparatus and

electrical apparatus

Technical Field

The present invention relates to a method for operating a fluid-insulated electrical apparatus. Furthermore, it relates to such an electrical apparatus having a control and analysis unit implementing such a method and to a power transmission network comprising such an electrical apparatus.

Introduction and Background Art

Dielectric insulation media in liquid and/or gaseous states (i.e. fluids) are widely applied to insulate an electrically active part in a variety of electri^¬ cal apparatuses, such as switchgears or transformers. For example, the electrically active part in medium or high voltage metal-encapsulated switchgear is arranged in a gas-tight compartment which encloses an insulation gas with a pressure of several bars which electrically separates the compartment of the apparatus from the electrically active part. In other words, the insulation gas does not allow the passage of electrical current from the electrically active part to the compartment. A commonly used dielectric insulation gas is sulfur hexafluoride (SFg) , which exhibits excellent insulation and electric arc extinguishing capabilities. However, SFg is a strong contributor to the green-house effect and thus has a high global warming potential. Therefore alternative insulation fluids should be found.

Several alternative insulation fluids have been identified. Some of these alternatives comprise multi-component fluid mixtures, i.e. they comprise more than one molecular or atomic species. It is found that certain properties of such insulation fluid mixtures are viable for the safe operation of the electrical apparatus. As an example, the dielectric breakdownstrength of the insula- tion fluid is strongly dependent on the concentration ratio of the mixture components and on the total fluid pressure. In order to maintain the mixture's insulating features and thus the safety and functionality of the electrical apparatus, the concentrations of the different fluid components of the insulation fluid and the total number of particles in the fluid must remain constant or at least within certain boundaries. Furthermore, a certain level of purity of the insulation gas mixture needs to be ensured. For this, sensor devices are used for offline monitoring of the insulation fluid.

US 2002/0095262 Al and US 7,184, 895 B2 describe methods and devices for monitoring the proportion of a component in a gaseous insulation medium consisting of at least two components.

The publication "Application of infrared spectroscopy to monitoring gas insulated high-voltage equipment: electrode material-dependent SF6 decomposition" by R. Kurte et al., Anal. Bioanal . Chem. (2002) 373: 639-646 describes the usage of an infrared spectroscopy system to determine contaminants from electrical discharges in an SFg-insulated discharge chamber.

The disclosed methods and devices have the disadvantage, however, that they do not monitor multi- component insulation fluids and do not derive an operating state or various operating states of the electrical apparatus .

Disclosure of the Invention

Hence it is a general objective of the present invention to provide an improved method for operating an electrical apparatus comprising a multi-component insulation fluid, wherein at least one operating state is derived. It is a further object of the invention to provide an electrical apparatus that implements such an operating method. Yet another objective of the invention is to provide a power transmission network comprising such an electrical apparatus. Yet another objective of the invention is to provide a computer program element that implements such a method.

These objectives are achieved by the method and devices of the independent claims.

Accordingly, a method for operating a fluid- insulated electrical apparatus (e.g. gas-insulated medium or high voltage switchgear, a gas-insulated line, or a gas-insulated transformer) comprises the step of carrying out at least one optical measurement and/or at least one gas chromatographic measurement on an insulation fluid of the electrical apparatus. In the case of both an optical measurement and a gas chromatographic measurement, the measurements can be carried out simultaneously or one after another.

The term "optical measurement" herein relates to an experimental quantification of a physical property of the insulation fluid comprising interactions between atoms or molecules of the insulation fluid and photons. Examples are

optical absorption measurements by means of, e.g., a multi-pass spectroscope at, e.g., at least one photon wavelength between 0.2 micrometer (μπι) and 20 micrometer (μηα) , or

fluorescence measurements, e.g., at at least one fluorescence excitation wavelength between 100 nm and 400 nm and/or at at least one fluorescence emission wavelength between 350 nm and 600 nm.

- photoacoustic measurements by means of optical excitation, e.g., in the range between 0.2 μιτι and 20 μιτι, followed by detection of the acoustic response of the insulation fluid using, e.g., a microphone.

The term "gas chromatographic measurement" herein relates to an experimental quantification of a physical property (e.g. a retention time) of at least one fluid component of the insulation fluid comprising interactions between atoms or molecules of the insulation flu- id and a carrier fluid called the "mobile phase" and a fixed material called the "stationary phase". This stationary phase can, e.g., be located in a column of a gas chromatograph .

The insulation fluid comprises at least two fluid components A and B, i.e. it comprises a mixture of at least a first fluid component A and a second fluid component B. This/these fluid component (s) A and/or B can be liquid and/or gaseous under normal operating conditions (e.g. room temperature and pressure) of the electrical apparatus, e.g. fluid component B can be air or technical air and fluid component A can e.g. be one of the partially or fully fluorinated fluoroketones C5, C6, or C7 (see definitions below) . The insulation fluid is enclosed in at least one compartment of the electrical apparatus for insulating, e.g., an electrically active part of the electrical apparatus.

Then, a first concentration of the first fluid component A of the insulation fluid is derived using the optical measurement and/or using the gas chromatographic measurement.

Furthermore, a second concentration of the second fluid component B of the insulation fluid is derived.

The fluid components A and B are not contaminants (e.g. decomposition products from, e.g., the insulation fluid or other parts of the electrical apparatus) . The term "contaminant" or "decomposition product" herein relates to a chemical substance or mixture that is not an a priori or desired ingredient of the insulation fluid. As an example, due to high voltage arcing or partial discharges during operation of the electrical apparatus, such contaminants can be produced from the originally present fluid components of the insulation fluid. In other words, contaminants are chemical substances that are not intentionally present in the insulation fluid of the electrical apparatus. The term "concentration" herein defines

- 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.

Then, an operating state of the electrical apparatus is derived using the first concentration of the first fluid component of the insulation fluid mixture and using the second concentration of the second fluid component of the insulation fluid mixture.

The term "operating state" herein relates to a state of the electrical apparatus indicative of its availability for normal, i.e. undisturbed, operation. The operating states of the electrical apparatus can be selected from a plurality of possible operating states. Possible operating states of the electrical apparatus can, e.g., comprise "operational" and "failure". Thus, the current operating state of the electrical apparatus can be determined using the concentrations of the first and second fluid component of the insulation fluid, and optionally further measures (e.g. an emergency shutdown) can be taken depending on the operating state of the electrical apparatus.

In an embodiment, the method further comprises a step of at least partially filling or replenishing the compartment with the insulation fluid. This step can, e.g., be carried out during commissioning, i.e. installation, of the electrical apparatus, or during maintenance of the electrical apparatus. Then, the step of carrying out the optical measurement and/or the gas chromatographic measurement is or are carried out during and/or after the filling or replenishing of the compartment. Thus, the measurement ( s ) can be carried out on the insulation fluid which is used for actual operation of the electrical apparatus. Thus, potential measurement errors are reduced because the measurement (s) is or are taken within the electrical apparatus and not only on the insulation fluid before filling.

In an embodiment, the optical measurement and/or the gas chromatographic measurement, the deriving of the first concentration, the deriving of the second concentration, and the deriving of the operating state are carried out by the electrical apparatus itself. In other words, no separate sensor device or other measurement unit is necessary, but all the necessary sensors and processing units are permanent parts of the electrical apparatus. Thus, the electrical apparatus provides a "self-diagnostic" or "self-monitoring" functionality, thus reducing maintenance efforts and costs. Furthermore, less additional equipment needs to be carried to the site for commissioning or maintenance.

In another embodiment, at least one of or all of: the optical measurement and/or the gas chromatographic measurement, the deriving of the first concentration, the deriving of the second concentration, and the deriving of the operating state are carried out in an add-on device to the electrical apparatus. The add-on device may be installed permanently or temporarily at the electrical apparatus. The add-on device may also be a stand-alone device which is connectable to the electrical apparatus as may be required for measurement or monitoring, e.g. the add-on or stand-alone device may be fluidly connectable, i.e. connectable to extract a sample for analysis, to at least one or each encapsulated compartment, and/or may be connectable electrically or via a data transmission line to a control unit of the electrical apparatus or GIS or substation.

In another embodiment, the second concentration of the second fluid component B of the insulation fluid is also derived using the optical measurement and/or using the gas chromatographic measurement. Thus, no further measurements are necessary and costs and com^¬ plexity are reduced.

Alternatively or additionally, the second concentration of the second fluid component B of the insulation fluid is derived (or additionally derived to an already derived second concentration value) using a density measurement or using a pressure- and a temperature- measurement of the insulation fluid. Thus, an additional measurement principle is employed and second concentration values derived using different measurements can optionally be compared to each other. Thus, potential measurement errors can be reduced and reliability is enhanced.

In the case of a pressure- and/or temperature- and/or density-measurement, the step of deriving the second concentration can comprise the use of an equation of state (i.e. a "thermodynamic equation describing the state of matter under a given set of physical conditions" (from http://en.wikipedia.org/wiki/Equation_ of_state as accessed on May 03, 2012)) which is, e.g., selected from the group consisting of

- the ideal gas law, i.e. pV = nRT with p being an absolute pressure, V being a volume, n being a number of molecules (usually expressed in moles), R being the ideal gas constant, and T being an absolute temperature ,

- the van-der-Waals equation of state, i.e. (p+a/V_m ²) (V_m-b)=RT with V_m being a molar volume and a, b being substance-specific parameters for the respective insulation fluid component,

- the virial equation of state, i.e. pV_m/ (RT) = 1 + B(T)/V_m + C(T)/V_m ² + D(T)/V_m ³ + ... with B(T), C(T), D(T), ... being temperature-dependent terms that correspond to interactions between molecules,

- the Beattie-Bridgeman equation of state, i.e. p = R_uT/(V_m ²) (l-c/(V_mT3) ) (V_m+B)-A/(V_m ²) with A = Ag(l-a/V_m), B = B()(l-b/V_m), R_u being a gas constant in the form R_u = 8.314 kPa m3/(kmol K) , V_m being a molar volume, and a, b, c, Ag, and Bg being substance-specific parameters for the respective insulation fluid component, and

- the Peng-Robinson equation of state, i.e. p = RT/(V_m-e) - d(T) / (V_m(V_m+e) + e(V_m-e)) with d(T) and e being empirical parameters.

When an equation of state other than the ideal gas law is used, the behavior of a gas can be better predicted than with the ideal gas law alone and the prediction can be extended to liquids. This is possible by putting in terms to describe attractions and repulsions between molecules as well as the molecular volume itself which leads to a reduction in the molar volume.

In another embodiment, the operating state of the electrical apparatus is selected from a group of possible operating states consisting of

- normal, i.e. undisturbed, operation of the electrical apparatus,

- uniform leakage of the insulation fluid, i.e. fluid-component-independent loss of insulation fluid from the compartment of the electrical apparatus,

- preferential leakage of one fluid component (A or B) of the insulation fluid, i.e. increased loss of one fluid component compared to the other fluid component, thus leading to a change of a mixing ratio of the insulation fluid,

condensation or preferential condensation of one fluid component of the insulation fluid, e.g. a state transition from gaseous to liquid state or vice versa of only one or at least preferentially one fluid component (A or B) of the insulation fluid,

adsorption or preferential adsorption of one fluid component (A or B) of the insulation fluid, e.g. on a component of the electrical apparatus, e.g. on an inner surface of the compartment of the electrical apparatus ,

- reaction or preferential reaction of one fluid component (A or B) of the insulation fluid, e.g. with a component of the electrical apparatus, e.g. with sealing material,

- appearance of at least one new fluid component in the insulation fluid, e.g. due to arcing, partial discharges, evaporation, light, high temperature, and/or reactions of at least one of the fluid components (A and/or B) with materials in the electrical apparatus, in particular wherein the new fluid component is a contaminant, and

- decomposition or preferential decomposition of at least one fluid component (A and/or B) of the insulation fluid, e.g. due to arcing, partial discharges, light, high temperature, and/or reactions of at least one of the fluid components (A and/or B) with materials in the electrical apparatus.

Thus, a plurality of different fault scenarios for the electrical apparatus can be distinguished and troubleshooting in the case of malfunctions is simplified.

Other optional possible operating states are

- intermolecular reactions between molecules of the at least two fluid components (A, B) of the insulation fluid, and

- removal of at least one of the at least two fluid components (A, B) of the insulation fluid, e.g. due to adsorption onto surfaces.

Thus, even more fault scenarios for the electrical apparatus can be distinguished and troubleshooting in the case of malfunctions is improved and/or simplified.

In another embodiment, the optical measurement and/or the gas chromatographic measurement, the deriving of the first and second concentrations, and - op- tionally - the deriving of the operating state are carried out repeatedly, e.g. at least once a day, preferably at least four times a day, more preferably at least once an hour. Thus, it is possible to derive a trend over a longer period of time thereby improving and/or simplifying predictions of malfunctions and troubleshooting. Alternatively or additionally, in another embodiment of the method, the above mentioned steps are carried out after a triggering event is received by the electrical apparatus, e.g. from a higher-hierarchy monitoring device ("polling") . Thus, an on-demand query of the status of the electrical apparatus becomes possible.

In another embodiment of the method, the first fluid component A is selected from the group consisting of:

- sulfur hexafluoride,

- partially or fully fluorinated ethers, in particular hydrofluoroethers, hydrofluoro monoethers, hy- drofluoro 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 mono- ketones, 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.

The second fluid component B is selected 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 or natural air, and

- mixtures thereof.

Thus, an improved insulation performance can be achieved for the insulation fluid of the electrical apparatus .

In embodiments, the first fluid component A is selected from the group consisting of:

- cyclic and/or aliphatic fluoropentanones, preferably cyclic and/or aliphatic perfluoropentanones , more preferably 1, 1, 1, 3, 4, 4, 4-heptafluoro-3- (tri-fluoro- methyl) butan-2-one,

cyclic and/or aliphatic fluorohexanones , preferably cyclic and/or aliphatic perfluorohexanones, more preferably 1 , 1, 1, 2 , 4 , 4 , 5 , 5, 5-nonafluoro-4- ( tri- fluoromethyl ) pentan-3-one,

- cyclic and/or aliphatic fluoroheptanones , preferably cyclic and/or aliphatic perfluoroheptanones ,

- sulfur hexafluoride, and

- hydrofluoroethers .

In another embodiment, the second fluid component B consists of

nitrogen and oxygen with relative partial pressures between p ( 2 ) / (p (O2 ) +p (N2 ) ) =0.7 , p (0₂ ) / (p (0₂ ) + p(N₂) )=0.3 and p (N₂ ) / (p (0₂ ) +P (N₂ ) ) =0.95 , p (0₂ ) / (p (0₂ ) + p(N₂) )=0.05 or

carbon dioxide and oxygen with relative partial pressures between p (CO2 ) / (p (0₂ ) +p (CO2 ) ) =0.6, p(0₂)/ (p(0₂)+p(C0₂) )=0.4 and p (C0₂ ) / (p (0₂ ) +p (C0₂ ) )=0.99, p(0₂)/ (p(0₂)+ p(C0₂) )=0.01, or carbon dioxide and nitrogen with relative partial pressures between p (CO2 ) / (p ( 2 ) +P (C0₂ ) ) =0.1 , p(N₂)/(p(N₂)+p(C0₂) )=0.9 and p (C0₂ ) / (p (N₂ ) +p (C0₂ ) ) =0.9, p(N₂) /(p(N₂)+p(C0₂) )=0.1.

The first fluid component A comprises at least one 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 (degrees Celsius) ,

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 hydrofluoroethers with a partial pressure between 0.2 bar and 1 bar at a temperature of 20 °C.

In another embodiment, the second fluid component B comprises

nitrogen and oxygen with relative partial pressures between p (N₂ ) / (p (0₂ ) +p (N₂ ) ) =0.75, p (0₂ ) / (p (0₂ ) + p(N₂))=0.25 and p (N₂ ) / (p (0₂ ) +p (N₂ ) ) =0.90 , p (0₂ ) / (p (0₂ ) + p(N₂) )=0.10 and

wherein the first fluid component (A) comprises 1,1,1,3,4,4, 4-heptafluoro-3- (tri-fluoromethyl ) butane-one with a partial pressure between 0.25 bar and 0.5 bar and/or the fluid 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.

Thus, an improved insulation performance can be achieved for the insulation fluid of the electrical apparatus . The optical measurement is in an embodiment carried out on the insulation fluid in the compartment. In other words, no insulation fluid needs to be extracted from the compartment of the electrical apparatus for or prior to carrying out the optical measurement. Thus, no insulation fluid is lost for the optical measurement, costs are saved and operation periods without refilling insulation fluid can be prolonged.

As an alternative, an amount (e.g. a rela^¬ tively small amount, e.g. 1 ml at 1 bar) of the insulation fluid is extracted from the compartment of the electrical apparatus prior to carrying out the optical measurement and/or the gas chromatographic measurement. Then, the optical measurement and/or the gas chromatographic measurement is or are carried out on the extracted amount of insulation fluid. Thus, the measurement or measurements can be carried out outside the compartment thus simplifying the setup of the electrical apparatus, because no measurement devices need to be introduced into the compartment. Then, - after the measurement (s) - at least a part of the extracted amount of insulation fluid can optionally be re-injected into the compartment and/or be collected for disposal. Thus, the insulation fluid can (at least in part) be reused and/or disposed of in an environmentally friendly manner thus saving. costs and reducing environmental impact.

In another embodiment, the optical measurement and/or the gas chromatographic measurement, the deriving of the first concentration, and the deriving of the second concentration are carried out for a plurality of compartments of the electrical apparatus . In other words, more than one compartment of the electrical apparatus encloses separate volumes of insulation fluid. The compartments are at least in part sealed with respect to each other. Then, the measurements are independently carried out for each of the compartments and the first concentrations and the second concentrations are inde- pendently derived for each of the compartments. Then, a single operating state of the electrical apparatus can be derived using the first and second concentrations in the different compartments. Thus, the monitoring of insulation fluid in multiple compartments becomes possible.

In embodiments, the optical measurement ( s ) is or are carried out by at least one optical sensor of the electrical apparatus and/or the gas chromatographic measurement (s) is or are carried out by at least one gas chromatograph of the electrical apparatus. Advantageously, the total number of optical sensors and gas chromato- graphs is smaller than or equal to the total number of compartments of the electrical apparatus. In other words, e.g. one optical sensor and/or gas chromatograph can be used for taking measurements of all compartments (multiplexing) . Thus, complexity and costs are reduced.

In another embodiment of the method, the electrical apparatus comprises a or the optical sensor for carrying out the optical measurement. For this, the optical sensor comprises bulk optical components (e.g. lenses, filters, mirrors, beam splitters, etc.) and/or fiber optical components (e.g. solid core optical fibers, hollow core optical fibers, light pipes, etc.) and a measurement cell for receiving an amount of the insulation fluid. Thus, a plurality of optical measurement principles can be employed on the insulation fluid, e.g. each of the above-mentioned compartments can comprise a fiber-optical fluorescence sensor for carrying out a fluorescence measurement on the insulation fluid in the respective compartment.

In embodiments, the measurement cell or - in case of a plurality of measurement cells - the measurement cells is or are at least in part formed by the compartment or compartments of the electrical apparatus. Thus, no separate measurement cells are necessary and the setup of the electrical apparatus is simplified. In embodiments, at least one optical sensor is used for carrying out the optical measurement in the compartment or each of the compartments. Thus, the optical measurement on the insulation fluid in every compartment of the electrical apparatus can be carried out independently .

In another embodiment, the insulation fluid is circulated for homogenizing densities and/or a mixture of its first and second fluid components, in particular before carrying out the optical measurement and/or the gas chromatographic measurement. Thus, a derivation of average fluid component concentrations which are less dependent on local concentration deviations is improved or simplified .

In another embodiment, the method further comprises a step of detecting and/or tracing at least one contaminant and/or a step of distinguishing at least two contaminants. This is achieved using the optical measure^¬ ment and/or using an additional optical measurement (e.g. at a different wavelength) and/or using the gas chromatographic measurement and/or using an additional gas chromatographic measurement (e.g. using at least one different column) and/or using the or an additional gas chromatographic measurement combined with a mass spectrometric measurement (e.g. on the fluid components that have been separated by the or the additional gas chromatographic measurement) . Thus, contaminants can be more easily detected and/or discriminated and the operating state of the electrical apparatus can be more reliably derived taking into account this contaminant or these contaminants .

In an embodiment, the method further comprises a step of deriving a dielectric breakdownstrength Ej^ of the insulation fluid using the first concentration and using the second concentration, e.g. by using the following equation

^Ebd =S(c_A,c_B) ∑CjE_{c t}

i=A,B with E_QJ-^-^ ¾ and E_crj_-t-^g being fluid component specific critical field strengths of the first fluid component A and the second fluid component B; with c^ and eg being the first and second concentrations of the first and second fluid components A and B; with S(c¾, eg) being a synergy parameter; and with i being an index for the fluid components A and B. Then, the operating state can advantageously be derived using the dielectric breakdown- strength of the insulation fluid. Thus, a more reliable derivation of the operating state becomes possible.

In another embodiment, the method further comprises a step of deriving at least a third concentration of at least a third fluid component (which is not a contaminant, i.e. which is meant to be a component of the insulation fluid) of the insulation fluid using the optical measurement and/or using an additional optical measurement and/or using the gas chromatographic measurement and/or using an additional gas chromatographic measurement. Thus, insulation fluids with more than two fluid components can be used.

In another embodiment, the optical measure^¬ ment comprises an optical absorption measurement or an optical fluorescence measurement at at least one wave- number (or wavelength), i.e. at a single wavenumber (or wavelength) or within a wavenumber regime (or wavelength regime) . Depending on the optical properties of the fluid components, suitable wavenumbers (for IR) or wavelengths (for UV) are between 500 cm^~l and 1500 cm-^ and/or be^¬ tween 200 nm and 400 nm, respectively. Preferred wave- numbers for IR are between 600 cm^~l and 800 cm^~l and/or between 940 cm^~l and 1050 cm^~l and/or between 1100 cm^~l and 1400 cm^~l and/or between 1750 cm^_l and 1850 cm^~l. Preferred UV wavelengths are between 225 nm and 375 nm. Preferred absorption signal full-widths-at-half-maximum (i.e. FWHM of the absorption signal) are between 40 cm^~l and 120 cm-l for IR absorption measurements and/or be- tween 50 nm and 100 nm for UV absorption measurements at insulation fluid pressures between 1 bar and 10 bar and at insulation fluid temperatures of 20°C. Thus, the derivation of the fluid component concentration or concentrations is simplified.

In embodiments, the absorption measurement can be carried out by means of a cavity ringdown spectro^¬ scope (see, e.g., http://en.wikipedia.org/wiki/Cavity_ ring-down_spectroscopy as accessed on May 3, 2012), a Lambert-Beer spectroscope (see, e.g., http://en.wiki- pedia . org/wiki/File : IR_spectroscopy_apparatus . svg as accessed on May 3, 2012), a multi-pass spectroscope, a single wavelength (non-continuum) ultraviolet spectroscope, a single wavelength (non-continuum) infrared spectroscope, a Fourier-transform infrared spectroscope (see, e.g. , http: //en . wikipedia . org/wiki/Fourier_transform_ spectroscopy as accessed on May 3, 2012), a Raman spectroscope (see, e.g., http://en.wikipedia.org/wiki/Raman_spectroscopy as accessed on May 3, 2012) or a photoacoustic spectroscope (see, e.g., http : //en . wikipedia . org/wiki/Photoacoustic_spectroscopy as accessed on June 6, 2012) . All methods can be performed in dispersive and nondispersive mode. Thus, the optical absorption measurement is easier to carry out.

In another embodiment, the optical measurement comprises a fluorescence emission measurement, in particular at at least one fluorescence excitation wavelength between 200 nm and 400 nm and/or at at least one fluorescence emission wavelength between 350 nm and 600 nm. Thus, the derivation of the fluid component concentration or concentrations is simplified.

In embodiments, the method is carried out during a regular operation of the electrical apparatus. The term "regular operation" or equivalently "live operation" herein relates to an operation condition of the electrical apparatus in which the electrical apparatus is available to perform its dedicated functionality, e.g. current conduction or high-voltage switching. In other words, the electrical apparatus is not shut-down or disconnected for maintenance. This has the advantage that the method can be applied online (i.e. during live operation) and that maintenance intervals can be increased.

In another embodiment, a pressure of the insulation fluid in the compartment during the optical measurement and/or the gas chromatographic measurement is an operating pressure (e.g. > 1 bar at 20°C) for the electrical apparatus. This has the advantage that the method can be carried out online or in an operation condition or during a regular operation of the electrical apparatus and that the electrical apparatus does not have to be shut down for maintenance to carry out the optical measurement and/or the gas chromatographic measurement.

In another embodiment, an operating voltage (e.g. > 1 kV or > 50 kV) is applied over primary contacts, e.g. high-voltage contacts, of the electrical apparatus during the optical measurement and/or the gas chromatographic measurement. This has the advantage that the method can be carried out online or in an operation condition or during a regular operation of the electrical apparatus and that the electrical apparatus does not have to be shut down for maintenance to carry out the optical measurement and/or the gas chromatographic measurement.

In another embodiment, the gas chromatographic measurement is carried out by means of a multicolumn gas chromatograph (see, e.g., Agilent 490 Micro GC, http: //www. chem. agilent . com/Library/brochures/ 5990- 6664EN_490%20Micro%20GC.pdf as accessed on June 20, 2012) comprising at least a first and a second column with a first and a second stationary phase. In particular, the first concentration of the first fluid component is then derived using the first column of the multicolumn gas chromatograph and the second concentration of the second fluid component is then derived using the second column of the multicolumn gas chromatograph . Thus, the fluid component concentrations can more easily be derived using the gas chromatographic measurement or measurements for fluid components that are not compatible with a single column gas chromatograph (see, e.g., Agilent 7820A GC, http: //www. chem. agilent . com/Library/Brochures/5990- 3326EN _web.pdf as accessed on June 20, 2012).

In another embodiment, the method further comprises at least one step of the group consisting of

- increasing the first concentration of the first fluid component by means of injecting an amount of the first fluid component from a component reservoir comprising the first fluid component into the compartment of the electrical apparatus,

- increasing the second concentration of the second fluid component by means of injecting an amount of the second fluid component from a component reservoir comprising the second fluid component into the compartment of the electrical apparatus,

- reducing a concentration of at least one contaminant (i.e. an unwanted substance in the insulation fluid) in the insulation fluid, in particular by means of a filter adsorbing the contaminant,

- evaporating a condensed amount of the first and/or the second fluid component, in particular by means of a heater, and

- condensing an amount of the first and/or the second fluid component, in particular by means of a cooler .

Thus, a suitable mixing ratio for the insulation fluid can more easily be maintained.

As another aspect of the invention, an electrical apparatus (e.g. gas-insulated medium or high voltage switchgear) comprises at least one compartment enclosing an insulation fluid comprising at least a first fluid component with a first concentration and at least a second fluid component with a second concentration. The electrical apparatus furthermore comprises an optical sensor for carrying out an optical measurement on the insulation fluid indicative of the first concentration and/or a gas chromatograph for carrying out a gas chromatographic measurement on the insulation fluid indicative of the first concentration. Furthermore, the electrical apparatus comprises an analysis and control unit for carrying out the steps of a method as described above.

The electrical apparatus can more advantageously be connectable to an insulation fluid filler (i.e. filling apparatus) by means of an interface. Thus, the insulation fluid mixing ratio can be monitored during filling of the insulation fluid into the compartment, e.g. during commissioning of the electrical apparatus or during replenishing of insulation fluid during maintenance. Thus, less additional sensor devices are necessary.

As another aspect of the invention, a computer program element comprising computer program code means for, when executed by a processing unit, implementing a method as described above is disclosed. This enables the integration of a method as described above into an electrical apparatus comprising a control and analysis unit.

As another aspect of the invention, a power transmission network is disclosed, in particular a medium or high-voltage power transmission network, which comprises an electrical apparatus as disclosed above.

The described embodiments and/or features similarly pertain to the apparatuses, the methods, and the computer program element. Synergetic effects may further arise from different combinations of these embodiments and/or features although they might not be described in detail. Brief Description of the Drawings

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 .

Fig. 1 shows a schematic of an electrical apparatus according to a first embodiment of the invention, the electrical apparatus comprising two insulation fluid filled compartments with an optical sensor arranged in each compartment;

Fig. 2 shows a schematic of an optical fluorescence sensor as used in the electrical apparatus according to the first embodiment of the invention;

Fig. 3 shows a schematic of an electrical appa^¬ ratus according to a second embodiment of the invention, the electrical apparatus comprising two insulation fluid filled compartments with an insulation fluid extractor arranged in each compartment and with a single optical sensor;

Fig. 4 shows a schematic of an optical absorb- ance sensor as used in the electrical apparatus according to the second embodiment of the invention;

Fig. 5 shows a schematic of an electrical apparatus according to a third embodiment of the invention, the electrical apparatus comprising two insulation fluid filled compartments with an insulation fluid extractor arranged in each compartment and with a single gas chro^¬ matography

Fig. 6 shows a schematic of a gas chromatograph as used in the electrical apparatus according to the third embodiment of the invention, wherein the gas chromatograph comprises two columns and a mass spectrometer behind one column; Fig. 7 shows a chromatogram illustrating the separation of insulation fluid components "N2/O2" and "C5" and "C6";

Fig. 8 shows two chromatograms illustrating loss of a specific fluid component "gas 4";

Fig. 9 shows two chromatograms illustrating detection of a contaminant;

Fig. 10 shows a power transmission network comprising an electrical apparatus according to the invention;

Fig. 11 shows an absorption diagram illustrating characteristic optical absorbance signatures of insulation fluid components "C5" and "C6";

Fig. 12 shows absorption diagrams illustrating the detection of a contaminant "HF" of the insulation fluid;

Fig. 13 shows an absorption diagram in the near UV range for "acetone", "C5", and "C6";

Fig. 14 shows fluorescence emission spectra of the insulation fluid component "C6" for different pressures and temperatures;

Fig. 15 shows an infrared absorption spectrum illustrating characteristic optical absorbance signatures of an insulation fluid component "C5";

Fig. 16 shows infrared absorption spectra illustrating the characteristic optical absorbance signatures of the insulation fluid component "C5" of Fig. 15 as well as characteristic optical absorbance signatures of a contaminant "CF4";

Fig. 17 shows infrared absorption spectra illustrating the characteristic optical absorbance signatures of the insulation fluid component "C5" of Fig. 15 as well as characteristic optical absorbance signatures of a contaminant hexafluoropropene "CF3CF=CF2";

Fig. 18 shows infrared absorption spectra illustrating the characteristic optical absorbance signatures of the insulation fluid component "C5" of Fig. 15 as well as characteristic optical absorbance signatures of a contaminant heptafluoropropane "CF3CFHCF3" ;

Fig. 19 shows a schematic of an optical absorbance measurement comprising a spectrometer;

Fig. 20 shows an "optical absorption" vs. "C5 pressure" diagram as recorded by an optical setup of Fig. 19;

Fig. 21 shows a schematic of an optical absorbance measurement comprising a non-dispersive photodetec- tor and a band-pass filter;

Fig. 22 shows a "transmitted intensity" vs. "C5 pressure" diagram as recorded by an optical setup of Fig. 21; and

Fig. 23 illustrates the dependence of UV absorption of the insulation fluid component "C5" on different insulation fluid mixtures and/or pressures.

Modes for Carrying Out the Invention Description of the Figures:

Fig. 1 shows a schematic of an electrical apparatus (high-voltage switchgear) according to a first embodiment of the invention. In the first embodiment, the electrical apparatus comprises two compartments 11 with electrically active parts 60 arranged inside the compartments 11. The compartments 11 are filled with an insulation fluid 10 for insulating the electrically active parts 60 from the walls of the compartment 11. The insulation fluid 10 comprises a first fluid component A (1,1,1,3,4,4, 4-heptafluoro-3- (tri-fluoromethyl ) butan-2- one) with a partial pressure of 0.3 bar (or equivalently a concentration c¾ of 0.3) at 20 °C and a second fluid component B (nitrogen) with a partial pressure of 0.7 bar (or equivalently a concentration 03 of 0.7) at 20°C. The fluid components A and B are intentional ingredients of the insulation fluid 10, i.e. they are not decomposition products or contaminants of the insulation fluid 10 that are created, e.g., during electrical discharge or other electrical stress.

An optical sensor 20 is arranged in each of the compartments 11 for carrying out an optical measurement on the insulation fluid 10 in the compartments 11 and - specifically - for deriving the concentrations c_¾ and eg of the first and second components A and B, respectively. No insulation fluid 10 is extracted from the compartments 11, but the measurements are carried out on the insulation fluid 10 in the compartments 11 themselves. In this embodiment, the optical sensors 20 can be fluorescence sensors as described below with regard to Fig. 2. Fluorescence excitation light is guided to the optical sensors 20 from a single common light source 22 of the electrical apparatus through optical fibers 23. Measurement values indicative of the fluid component concentrations c¾ and θ are transmitted from the optical sensors to an analysis and control unit 40 of the electrical apparatus.

Furthermore, one of the compartments 11 can comprise an optional pTp sensor 70 (dotted) for additionally measuring the total pressure p, the temperature T, and the density p of the insulation fluid 10 in the respective compartment 11. Values indicative of these parameters are also transmitted to the analysis and control unit 40. The control unit 40 can use these values to additionally derive fluid component concentrations c_¾ and eg using an equation of state (see, e.g., US 7 184 895 B2 for detailed disclosure on how this can be achieved) .

The control unit 40 then derives an operating state 0 of the electrical apparatus 1 using the first concentrations c_¾ and using the second concentrations C-_Q of the insulation fluid components A and B in each compartment 11. Specifically, a dielectric breakdown strength of the insulation fluid 10 can be derived according to

^Ebd =S(c_A,c_B) J CjEcrjt,i with Ec t, A ^{anc E}crit,B being known and preset fluid component specific critical field strengths of the fluid components A and B. S(c¾, eg) is a known and preset synergy parameter and i is an index running over the fluid components A and B. From this dielectric breakdown- strength of the insulation fluid 10, an operating state 0 is derived which is indicative of the availability of the electrical apparatus for normal operation, e.g. for high-voltage switching or for carrying nominal currents and/or nominal voltages.

The dielectric breakdownstrength of the insulation fluid 10, the fluid component concentrations c^ and CQ and the operating state O are also fed to an in^¬ terface 41 which is adapted to be connectable to a separate insulation fluid filler 42 (dotted) . Such an insulation fluid filler 42 can, e.g. during maintenance of the electrical apparatus, replenish insulation fluid 10 to one or both compartments 11 if necessary. As an example, if the total amount of insulation fluid 10 in one compartment 11 decreases below a threshold for safe operation of the electrical apparatus, the analysis and control unit 40 detects this "failure" operating state 0 of the electrical apparatus 10 (a too low dielectric breakdownstrength of the insulation fluid 10 in the respective compartment 11) and shuts down the electrical apparatus 1. Then, during maintenance, it triggers via the interface 41 (via a triggering event G) the insulation fluid filler 42 to replenish insulation fluid 10 to the affected compartment 11 (dotted lines) . As another example, it is also possible to provide feedback to the insulation fluid filler 42 during commissioning of the electrical apparatus 1 to trigger a signal to the insulation fluid filler 42 as soon as operating pressures and/or operating dielectric breakdown strengths E^ of the insulation fluid 10 in the compartments 11 are reached . Fig. 2 shows a schematic of an optical fluorescence sensor 20 as it is useful in the electrical apparatus 1 according to the first embodiment of the invention (see above with regard to Fig. 1) . Here, fluorescence excitation light from an external light source 22 (not shown) is guided to the optical sensor 20 through an optical fiber 23. The light emerging from the tip of the fiber 23 is then collimated by a lens 24 and passes a dichroic beam splitter 28. It then passes through the wall of a glass tube whose inner volume is connected to the compartment^■ 11 of the electrical apparatus 1, is filled with to-be-measured insulation fluid 10, and forms the measurement cell 21 of the optical sensor 20. In another embodiment, the measurement cell 21 of the optical sensor 20 can be formed by the compartment 11 itself, i.e. fluorescence is then measured in the compartment 11 itself. The fluorescence excitation light then excites molecules of the insulation fluid 10 and resulting fluorescence emission light is in part travelling back towards the beam splitter 28. To increase light collection efficiency, a mirror 27 is arranged on a side of the glass tube opposing the beam splitter 28. Fluorescence emission photons are then deflected by the dichroic beam splitter 28, pass an emission filter 26 (which blocks leftover excitation light), and are focused onto a detector 25 (e.g an avalanche photodiode or a photomultiplier tube) by a collection lens 24. The electrical fluorescence signal (indicative of c¾ and eg) from the detector 25 is then read out, optionally preprocessed (not shown) , and transmitted to the analysis and control unit 40 of the electrical apparatus 1 for further processing. It should be noted that different light sources and optical setups are possible, e.g. monochromatic light at one or more wavelengths (e.g. at 305 nm) from one or more laser (s) 22, narrow spectrum light from a narrow band LED light source 22 (e.g. in the near UV range), or polychromatic or white light (optionally with a monochromator such as a grating) from a conventional light source 22. It is also possible to use different optical sensors 20 for the different fluid components A and B.

Fig. 3 shows a schematic of an electrical apparatus according to a second embodiment of the invention. This embodiment is very similar to the first embodiment described above with regard to Fig. 1 except for the following differences: While in the first embodiment, the optical fluorescence measurements were carried out inside each compartment 11 by means of separate optical sensors 20 inside the compartments 11, here, a single common optical sensor 20 is used for carrying out the optical measurements one after another (multiplexing) . For this, a small amount, e.g. 1 ml at 1 bar at room temperature, of the insulation fluid 10 is extracted from each com^¬ partment 11 by means of an insulation fluid extractor 80 arranged in each compartment 11. This insulation fluid 10 is then transferred to the common optical sensor 20 through tubings 81. After the optical measurements, the insulation fluid 10 is at least in part reinjected into the compartments 11. As another differences to the first embodiment, the measurement principle of the optical sensor 20 can also be different (e.g. can be an absorption measurement as described further below in connection with Fig. 4) .

The insulation fluid 10 that is used in the second embodiment can be composed of a different fluid component mixture compared to the insulation fluid 10 of the first embodiment. Here, the first component A has a partial pressure of only 0.2 bar at 20°C wherein an additional third fluid component C (1,1,1,2,4,4,5,5,5- nonafluoro-4- (tri-fluoromethyl) pentan-3-one) has a partial pressure of 0.1 bar (or, equivalently, a concentration cc of 0.1) at 20°C. Measurement values indicative of the fluid component concentrations c¾, CB, and C_Q are transmitted from the optical sensor 20 to an analysis and control unit 40 of the electrical apparatus 1. As another difference, a circulator 90 can be arranged in one compartment 11 near the insulation fluid extractor 80 for homogenizing the density and/or the mixture of the insulation fluid components A, B, and C prior to extracting the to-be-measured insulation fluid 10 and prior to carrying out the optical measurement.

As yet another difference the electrical apparatus 1 according to the second embodiment comprises an optional filter 51 (dotted) for reducing a concentration of at least one contaminant in the insulation fluid 10. Such a contaminant can, e.g., be created from electrical discharge or from any other sources or chemical processes. Furthermore, the electrical apparatus according to the second embodiment comprises an optional heater 52 (dotted) for evaporating a condensed amount of at least one fluid component, e.g. when the ambient temperature of the electrical apparatus 1 drops below a condensation threshold for the respective fluid component. Thus, the condensed fluid component can be brought back to its gaseous form and thus the mixing ratio of the insulation fluid 10 can be preserved. In addition, the electrical apparatus 1 according to the second embodiment comprises an optional cooler 53 (dotted) for intentionally condensing an amount of at least one fluid component and/or of a contaminant by reducing the insulation fluid temperature below a condensation threshold for the respective substance .

As another difference, the electrical apparatus 1 according to the second embodiment can comprise a component reservoir 50 which can replenish certain amounts of insulation fluid components A and/or B and/or C etc. to one or more compartments 11. As an example, when the analysis and control unit 40 detects a decrease in the fluid component concentration c_¾ in one compartment 11, the right amount of fluid component A is replenished to the respective compartment 11 and thus the mixing ratio of the insulation fluid 10 is brought back to normal. Thus, normal operation of the electrical apparatus 1 can automatically be restored and apparatus downtime is reduced .

With regard to the first and second embodiment, advantages of using an optical sensor or optical measurement for deriving the fluid component concentrations c¾, c_Q- , and/or c^ are (i) high specificity to individual fluid components, (ii) high sensitivity, and (iii) broad applicability to any insulation fluid mixture comprising optical absorption or fluorescence.

Fig. 4 shows a schematic of an optical absorb- ance sensor 20 as it is used in the electrical apparatus 1 according to the second embodiment of the invention (see above with regard to Fig. 3) . Here, light is mono- chromized inside a light source 22 by a grating (only schematically shown) and split into two beams by a 50:50 beam splitter 28. One light beam is guided through a reference cell 21a with a known absorbance per wavelength. The other light beam is guided through a measurement cell 21 of the optical sensor into which the extracted amount of insulation fluid 10 is transferred prior to carrying out the optical measurement. After traveling through the measurement cell 21 or the reference cell 21a, respectively, both light beams are propagated through band-pass filters 29 and focused onto photodetectors 25 (e.g. avalanche photodiodes) by lenses 24. By tuning the wavelength from the light source 22, an absorbance spectrum of the insulation fluid 10 over wavelength which is indicative of the fluid component concentrations c¾, CB, and C_Q is measured. As discussed above with regard to the fluorescence optical sensor 20, it should again be noted that different light sources and optical setups are possible, as well.

Fig. 5 shows a schematic of an electrical apparatus 1 according to a third embodiment of the invention. This embodiment is very similar to the first embodiment described above with regard to Fig. 1 and to the second embodiment described above with regard to Fig. 3. However, as a difference, a gas chromatograph 30 (see below with regard to Fig. 6) can be utilized for carrying out a gas chromatographic measurement on extracted amounts of insulation fluid 10 from compartments 11. Due to the measurement principle used, the extracted amount of insulation fluid 10 is not reinjected into the chamber after the measurement in the third embodiment. The gas chromatographic measurement again produces measurement values indicative of the fluid component concentrations c¾ and eg which are transmitted from the gas chromatograph 30 to the analysis and control unit 40 of the electrical apparatus 1 for further processing. Advantages of using a gas chromatographic measurement for deriving the fluid component concentrations c¾, eg, and/or CQ are (i) good separation and quantification capability to individual fluid components, (ii) very good sensitivity, and (iii) the ability to diagnose unknown contaminants, e.g. optionally using an additional mass spectrometer (see below) .

Fig. 6 shows a schematic of a gas chromatograph 30 as useful in the electrical apparatus 1 according to the third embodiment of the invention as described with regard to Fig. 5. The gas chromatograph 30 comprises a carrier gas reservoir 31 and a sample injector 32 which accepts a small amount (e.g. 0.5 ml at 1 bar at 20 °C) of the insulation fluid 10 (see description of Fig. 3 on details of the extraction of the sample from the compartments 11) . This insulation fluid 10 is then injected into the flowing carrier gas and propagated through two columns 33 onto detectors 34 (e.g. thermal conductivity detector, flame ionization detector, or electron capture detector) . Due to different retention times of the fluid components A, B, and C with a stationary phase in the columns, the concentrations values c¾, eg, and CQ can be measured. For example, the column Fluorocol from the company Supelco can separate a mixture of N2/O2 and C5/C6. A mass spectrometer 35 can optionally be arranged behind one column 33 for carrying out an additional mass spec- trometric measurement for detecting and/or discriminating contaminants in the insulation fluid.

Fig. 7 shows a chromatogram (i.e. a chromato- graph detector signal as a function of retention time in the column) illustrating the separation of insulation fluid components "N2/O2" (technical air) and "C5" and "C6", which all appear as single separate peaks in the chromatogram. A Fluorocol column (FC column) from the manufacturer Supelco can, e.g., be used for such a separation .

Fig. 8 shows two chromatograms illustrating electrical stress-induced loss of a specific fluid component (gas 4, peak drops, see arrow and dotted lines). An FC column can, e.g., be used for such a measurement.

Fig. 9 shows two chromatograms illustrating detection of a contaminant of the insulation fluid 10. An additional peak (arrow, dotted circle) appears after a fresh insulation gas mixture (fresh gas mixture) has undergone electrical stress (aged gas mixture) . An FC column can, e.g., be used for such a measurement.

Fig. 10 shows a power transmission network 200 comprising an electrical apparatus 1 according to the invention. The electrical apparatus is exemplarily used for switching a high-voltage connection between two bus bars 201 and 202 of the power transmission network 200.

Fig. 11 shows an infrared absorption spectrum illustrating characteristic signatures of insulation fluid components C5 and C6. The use of infrared spectroscopy offers an easy, specific, and accurate method for the determination (type and concentration) and monitoring of the fluid components that make up the insulation fluid 10. Many molecules, such as C5 and C6, show characteristic spectral signatures (spectral fingerprint) in the infrared region which are, e.g., due to vibrational excitation. Specifically, measurements of the bands labeled C5- signature and C6-signature in the spectrum of the insula- tion fluid unambiguously indicate the presence and allow the concentration determination of C5 and/or C6, respectively. Note that the spectrum in the region 1200 cm^~l to 1350 cm^~l is partially saturated.

Fig. 12 shows absorption diagrams illustrating the detection of a contaminant "HF" of the insulation fluid 10. Specifically, after electrical stress induced aging of an insulation fluid component "C5", clear absorption signatures of the contaminant "HF" can be seen in the spectrum. An HF reference spectrum is given for comparison. Using calibrated HF spectra, the concentration of the contaminant HF can also be derived. Analogous procedures exist for other contaminants, as well.

Fig. 13 shows an absorption diagram in the UV range for acetone, C5, and C6 together with reference data for acetone .

Fig. 14 shows fluorescence emission spectra of C6 for different pressures and temperatures. By taking the pressure and temperature variations into account, a direct derivation of the insulation fluid pressure and temperature becomes possible. This figure is taken from J. Gustavsson, C. Segal, "Characterization of a Perfluor- inated Ketone for LIF Applications", 46th AIAA Aerospace Sciences Meeting and Exhibit, 7-10 January 2008, Reno, Nevada, USA.

Fig. 15 shows an infrared absorption spectrum illustrating characteristic optical absorption signatures of an insulation fluid component "C5". It is found that the insulation fluid component "C5" shows absorption peaks that do not overlap with spectral signatures of contaminants (see, e.g., arrow, see below). Therefore, by selecting such an appropriate spectral signature, the insulation fluid component "C5" can unambiguously be monitored without cross-sensitivity to contaminants.

Fig. 16 shows infrared absorption spectra illustrating the characteristic optical absorbance signatures of the insulation fluid component "C5" of Fig. 15 as well as characteristic optical absorbance signatures of a contaminant "CF4" (see arrow) . Because these peaks do not overlap, they allow an unambiguous detection of the contaminant "CF4", even in the presence of "C5".

Fig. 17 shows infrared absorption spectra illustrating the characteristic optical absorbance signatures of the insulation fluid component "C5" of Fig. 15 as well as characteristic optical absorbance signatures of a contaminant hexafluoropropene "CF3CF=CF2" (see arrows) . Similar to the situation in Fig. 16, these signatures allow an unambiguous detection of the contaminant "CF3CF=CF2", even in the presence of "C5".

Fig. 18 shows infrared absorption spectra illustrating the characteristic optical absorbance signatures of the insulation fluid component "C5" of Fig. 15 as well as characteristic optical absorbance signatures of a contaminant heptafluoropropane "CF3CFHCF3". Similar to the situation in Figs. 16 and 17, these signatures allow an unambiguous detection of the contaminant heptafluoro- propane "CF3CFHCF3", even in the presence of "C5".

Fig. 19 shows a schematic of an optical absorbance measurement comprising a spectrometer, i.e. a wavelength-discriminating or dispersive photodetector 25. Light from a light source 22 (e.g. a deuterium light source) is propagated through an optical fiber 23 and a measurement cell 21 comprising the insulation fluid 10. Then, a part of the light that has not been absorbed in the measurement cell 21 is detected by photodetector 25.

Fig. 20 shows an "optical absorption" vs. "C5 pressure" diagram as recorded by an optical setup of Fig. 19. In other words, absorption A in arbitrary units is plotted versus pressure p in mbar of pure insulation fluid component C5. The graph shows measured data (diamonds) together with a linear fit line (slope a = 0.009872, offset A_offset = -0.019615) as well as relative errors of measured values compared to the fit. Each data point corresponds to the area of the absorption peak for the re- spective "C5" concentration. The inset shows a typical absorption spectrum (i.e. wavelength in nm on x-axis, (wavelength-dependent) absorption in arbitrary units a.u. on y-axis, here for a partial pressure of C5- perfluoroketone of e.g. p(C5) = 91.5 mbar) of insulation fluid component "C5" where the hatched region (240 nm < λ < 350 nm) represents the integration area which is used to measure an (integral) absorption A. The relative error dA/A ≤ +2% demonstrates that a concentration of insulation fluid component "C5" can be determined with high sensitivity and high precision by using simple calibration methods. The used equipment comprises: Light source 22: Deuterium light source, DT-MINI-2-GS, Ocean Optics. Gas cell 21: Stainless steel cell (with optical path length 47 cm) "Expando" from Solvias. Fiber-optic cables 23: length 0.5 m, core diameter 600 μιη, UV-0.5m/1204191 from Solvias. Detector 25: High-resolution spectrometer, HR4000 from Ocean Optics.

Fig. 21 shows a schematic of an optical absorb- ance measurement comprising a non-dispersive photodetec- tor 25 and a band-pass filter 29. Light from a light source 22 (e.g. a deuterium light source) is propagated through an optical fiber 23 and a measurement cell 21 comprising the insulation fluid 10. Then, a part of the light that has not been absorbed in the measurement cell 21 propagates through a band-pass filter 29 and is detected in a non-wavelength-discriminating-fashion by photodetector 25.

Fig. 22 shows a "transmitted intensity" vs. "C5 pressure" diagram as recorded by an optical setup of Fig. 21. In other words, transmitted intensity I in pW is plotted versus pressure p in mbar of pure insulation fluid component C5. The graph shows measured data (diamonds) together with exponential fit (line, Lambert-Beer law; with offset intensity I_offset = 21.9 μΐΛί, intensity coefficient I_0 = Io = 35.8 μϊί, and exponential coefficient ε = 0.0032 1/mbar) and relative error dl/I of measurement I compared to fit. Each data point corresponds to the total integrated intensity I measured by the silicon photo- detector 25. Most of the light of the Deuterium light source 22 which has a larger wavelength than the insulation fluid components' absorption peaks is blocked by a filter 29 (the light which is not blocked contributes to the offset loffset) · ^The relative error dl/I ≤ ±1% demon^¬ strates that concentration of insulation fluid component "C5" can be determined with high sensitivity and high precision .

The used equipment comprises: Light source 22: Deuterium light source, DT-MINI-2-GS, Ocean Optics. Gas cell 21: Stainless steel cell (with optical path length 47cm) «Expando» from Solvias . Fiber-optic cables 23: length 0.5 m, core diameter 600 μιη, UV-0.5m/1204191 from Solvias. Filter 29, UG-11 from Schott. Detector 25: Si Photodiode, UV-818 from Newport.

Fig. 23 illustrates the dependence of UV absorption of the insulation fluid component "C5" from insulation fluid mixtures and/or from insulation fluid pressure. In other words, the absorption of pure insulation fluid component "C5" in gaseous form and of two different insulation fluid mixtures consisting of insulation fluid component "C5" and insulation fluid component "synthetic air" with different mixture ratios and total pressures is acquired with the optical setup of Fig. 19. The absolute amount of insulation fluid component "C5" for all 3 samples (i.e. 3 graphs, only two are distinguishable here) is constant: p(C5)=91.5 mbar . The amount of synthetic air differs between 0 and 5775 mbar. The graph illustrates that absorption values for all 3 insulation fluid mixtures do not or not significantly deviate for high or low pressures when synthetic air is added to the insulation fluid component "C5". This shows that a concentration of an insulation fluid component "C5" using a C5 UV- absorption peak can be determined independently from the admixture of synthetic air. No effect is observed even up to a total insulation fluid pressure of p_tot = 8.9 bar (data not shown) .

The used equipment comprises: Light source 22: Deuterium light source, DT-MINI-2-GS, Ocean Optics. Gas cell 21: Stainless steel cell (with optical path length 47cm) "Expando" from Solvias. Fiber-optic cables 23: length 0.5 m, core diameter 600 μιη, UV-0.5m/1204191 from Solvias. Detector 25: High-resolution spectrometer, HR4000 from Ocean Optics.

Definitions :

The term "air" herein shall include "technical air", i.e. pressurized and dried ambient air, or "synthetic air", i.e. mixtures of nitrogen (¾) and oxygen (O2) with various mixing ratios, or ambient air.

The term "aliphatic" herein shall relate to both "linear aliphatic" and "branched aliphatic".

The term "fluid" herein shall relate 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 9/11/2011) .

The term "high-voltage" herein shall relate to voltages larger than 50 kV.

The term "medium-voltage" herein shall relate to voltages larger than 1 kV.

As it is apparent from the description above, the term "method for operating a fluid-insulated electrical apparatus" herein relates to a method for making the electrical apparatus available and/or maintaining the operation of the electrical apparatus.

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

The compound "C5" herein particularly relates to a 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 or are substituted with a fluorine atom or fluorine atoms:

O (Ic), and

0 ^? (Id) .

The compound "C6" herein particularly relates to a 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

(lid) ,

O (Ilf), and

The compound "C7" herein particularly relates to a 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 or fluorine atoms:

(Hie) ,

(IHf) ,

( Illm) , and

(Illn), named dodecafluoro-cycloheptanone

Note :

C5 or "C5", C6 or "C6", C7 or "C7" etc. denote partially or fully fluorinated fluoroketones that have 5, 6, 7 etc. interconnected carbon atoms.

While there are shown and described embodiments or presently preferred or advantageous embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims .

Reference numbers

1: electrical apparatus

10: insulation fluid

11: compartment of the electrical apparatus 1

A, B, C: fluid components of the insulation fluid 10

^CA'^CB'^CC^: fluid component concentrations

0: operating state of the electrical apparatus 1 F>hd^: dielectric breakdown strength

20: optical sensor

21: measurement cell of optical sensor 20

21a: reference cell of optical sensor 20

22: light source

23: optical fiber

24: lens

25: photodetector of optical sensor 20

26: emission filter

27: mirror

28 : beam splitter

29: band-pass filter

30: gas chromatograph

31: carrier gas reservoir

32: sample injector

33: column of gas chromatograph 30

34: detector of gas chromatograph 30

35: mass spectrometer

40: analysis and control unit

41: interface

42: insulation fluid filler, filling apparatus

50: component reservoir

51: filter

52 : heater

53: cooler : electrically active part: pTp sensor

triggering event: insulation fluid extractor: tubing

: circulator

: power transmission network , 202: bus bars

Claims

1. A method for operating a fluid-insulated electrical apparatus (1), in particular a gas-insulated medium or high voltage switchgear (1), wherein an insulation fluid (10) in at least one compartment (11) of the electrical apparatus (1) comprises at least a first fluid component (A) and at least a second fluid component (B) , the method comprising method elements of:

carrying out at least one optical measurement and/or at least one gas chromatographic measurement on the insulation fluid (10),

deriving a first concentration (c¾) of the first fluid component (A) using the optical measurement and/or using the gas chromatographic measurement,

deriving a second concentration (eg) of the second fluid component (B) ,

wherein the first fluid component (A) and the second fluid component (B) are not contaminants, and

the method further comprises a method element of deriving an operating state (0) of the electrical apparatus (1) using the first concentration (c¾) and/or using the second concentration (eg) .

2. The method of claim 1, further comprising a method element of filling an amount of the insulation fluid (10) into the compartment (11) of the electrical apparatus (1) , wherein the method element of carrying out the optical measurement and/or the gas chromatographic measurement is or are carried out during and/or after the method element of filling the compartment (11) with the insulation fluid (10).

3. The method of any of the preceding claims, wherein the method elements of carrying out the optical measurement and/or the gas chromatographic measurement, of deriving the first concentration (c¾) , of deriving the second concentration (eg) , and of deriving the operating state (0) are carried out by the electrical apparatus (1) ·

4. The method of any of the preceding claims, wherein the second concentration (eg) is derived using the optical measurement and/or using the gas chromatographic measurement.

5. The method of any of the preceding claims, wherein the second concentration (eg) is derived using a density measurement and/or using a pressure- and a temperature-measurement of the insulation fluid (10).

6. The method of any of the preceding claims, wherein the operating state (0) of the electrical apparatus (1) is selected from a group of possible operating states consisting of:

normal operation,

uniform leakage of all fluid components (A, B) of the insulation fluid (10),

- preferential leakage of a fluid component (A, B) of the insulation fluid (10),

- condensation or preferential condensation of a fluid component (A, B) of the insulation fluid (10),

- adsorption or preferential adsorption of a fluid component (A,B) of the insulation fluid (10),

- reaction or preferential reaction of one fluid component (A or B) of the insulation fluid (10),

- decomposition or preferential decomposition of a fluid component (A, B) of the insulation fluid (10), and

- appearance of at least an additional fluid component (D) in the insulation fluid (10), in particular wherein the additional component (D) is a contaminant.

7. The method of any of the preceding claims, wherein the method elements of carrying out the optical measurement and/or the gas chromatographic measurement, of deriving the first concentration (c¾) , and of deriving the second concentration (eg) are carried out repeatedly, in particular at least once a day, preferably at least four times a day, more preferably at least once an hour.

8. The method of any of the preceding claims, wherein the method elements of carrying out the optical measurement and/or the gas chromatographic measurement, of deriving the first concentration (c¾) , and of deriving the second concentration (eg) are carried out after a triggering event (G) is received by the electrical apparatus (1) .

9. The method of any of the preceding claims, wherein the first fluid component (A) is selected from the group consisting of:

- sulfur hexafluoride,

- mixtures thereof, and

wherein the second fluid component (B) is selected 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 first fluid component (A) is selected from the group consisting of:

- cyclic and/or aliphatic fluoropentanones, preferably cyclic and/or aliphatic perfluoropentanones , more preferably 1 , 1 , 1 , 3 , 4 , 4 , 4-heptafluoro-3- (tri-fluoro- methyl) butan-2-one,

cyclic and/or aliphatic fluorohexanones , preferably cyclic and/or aliphatic perfluorohexanones , more preferably 1, 1, 1, 2, 4, 4, 5, 5, 5-nonafluoro-4- (tri- fluoromethyl ) pentan-3-one,

- cyclic and/or aliphatic fluoroheptanones , preferably cyclic and/or aliphatic perfluoroheptanones,

- sulfur hexafluoride, and

- hydrofluoroethers .

11. The method of any of the claims 9 to 10, wherein the second fluid component (B) consists of

nitrogen and oxygen with relative partial pressures between p ( 2 ) / (p (O2 ) +P (N2 ) ) =0.7 , (O2 ) / ( (O2 ) + p(N₂))=0.3 and p (N₂ ) / (p (0₂ ) +P (N₂ ) ) =0.95 , p (0₂ ) / (p (0₂ ) + p(N₂) )=0.05 or

carbon dioxide and oxygen with relative partial pressures between p (C0₂ ) / (p (0₂ ) +p (C0₂ ) ) =0.6, p(0₂)/ (p(0₂)+p(C0₂) )=0.4 and p (C0₂) / (p (0₂) +p (C0₂) ) =0.99, p(0₂) /(p(0₂)+ p(C0₂) )=0.01, or carbon dioxide and nitrogen with relative partial pressures between p (CO2 ) / (p (N2 ) +P (CO2 ) ) =0.1 , p(N₂)/(p(N₂)+p(C0₂) )=0.9 and p (C0₂) / (p (N₂) +p (C0₂) ) =0.9, p(N₂)/(p(N₂)+p(C0₂) )=0.1, and

wherein the first fluid component (A) comprises at least one 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,

12. The method of any of the claims 9 to 11 wherein the second fluid component (B) comprises

nitrogen and oxygen with relative partial pressures between p ( 2 ) / (p (O2 ) +p (N2 ) ) =0. 5 , p (O2 ) / (p (0₂ ) + p(N₂))=0.25 and p (N₂ ) / (p (0₂ ) +P (N₂ ) ) =0.90 , p (0₂ ) / (p (0₂ ) + p(N₂) )=0.10 and

wherein the first fluid component (A) comprises 1,1,1,3,4,4, 4-heptafluoro-3- (tri-fluoromethyl) butane-one with a partial pressure between 0.25 bar and 0.5 bar and/or the fluid 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.

13. The method of any of the preceding claims, wherein the optical measurement is carried out on the insulation fluid (10) in the compartment (11).

14. The method of any of the claims 1 to 12, further comprising a method element of extracting, in particular by means of the electrical apparatus (1), an amount of the insulation fluid (10) from the compartment (11) prior to carrying out the optical measurement and/or the gas chromatographic measurement, wherein the optical measurement and/or the gas chromatographic measurement is or are carried out on the extracted amount of the insulation fluid (10) .

15. The method of claim 14, further comprising a method element of re-injecting, in particular by means of the electrical apparatus (1) , at least a part of the extracted amount of the insulation fluid (10) into the compartment (11) after carrying out the optical and/or the gas chromatographic measurement.

16. The method of any of the preceding claims, wherein the method elements of carrying out the optical measurement and/or the gas chromatographic measurement, of deriving the first concentration (<¾) , and of deriving the second concentration (eg) are carried out for a plurality of compartments (11) of the electrical apparatus (1), and wherein the first concentration (c¾) and the second concentration (eg) are derived for each of the compartments (11).

17. The method of claim 16, wherein the method element of carrying out the optical measurement is carried out by at least one optical sensor (20), and/or wherein the method element of carrying out the gas chromatographic measurement is carried out by at least one gas chromatograph (30) , and in particular wherein a total number of optical sensors (20) and gas chromatographs (30) is smaller than or equal to a total number of the compartments (11).

18. The method of any of the preceding claims, wherein the electrical apparatus (1) comprises a or the optical sensor (20) for carrying out the optical measurement, wherein the optical sensor (20) comprises a measurement cell (21) for receiving at least a part of the insulation fluid (10), and wherein the optical sensor (20) further comprises bulk optical components and/or fiber optical components.

19. The method of claim 18, wherein the measurement cell (21) of the optical sensor (20) is at least in part formed by a part of the compartment (11) of the electrical apparatus (1) .

20. The method of any of the claims 16 to 17 and of any of the claims 18 to 19, wherein at least one optical sensor (20) is used for carrying out the optical measurement for each of the compartments (11) .

21. The method of any of the preceding claims, further comprising a method element of circulating the insulation fluid (10) for homogenizing densities and/or a mixture of the first and second fluid components (A,B), in particular before carrying out the optical measurement and/or the gas chromatographic measurement.

22. The method of any of the preceding claims, further comprising a method element of detecting and/or tracing at least one contaminant and/or a method element of distinguishing at least two contaminants, thereby using at least one of the group consisting of: the optical measurement, an additional optical measurement, the gas chromatographic measurement, an additional gas chromatographic measurement, and the or an additional gas chromatographic measurement combined with a mass spectrometric measurement.

23. The method of any of the preceding claims, further comprising a method element of deriving a dielectric breakdown strength of the insulation fluid (10) using the first concentration (C_j_J and using the second concentration (eg) , in particular according to equation

^Ebd =S(c_A,c_B) J CjEgrit,i

i=A,B

with E_crit ¾ and E_crj__†-^B being fluid- component-specific critical field strengths of the fluid components A and B; with c^ and eg being the first and second concentrations of the first and second fluid components A and B; with S (c¾, eg) being a synergy parameter; and with i being an index for the fluid components A and B, and in particular wherein the operating state (0) is derived using the dielectric breakdownstrength of the insulation fluid (10) .

24. The method of any of the preceding claims, wherein the insulation fluid (10) comprises at least a third fluid component (C) which is not a contaminant, and wherein the method further comprises a method element of deriving a third concentration (CQ) of the third fluid component (C) by using at least one of the group consisting of: the optical measurement, an additional optical measurement, the gas chromatographic measurement, and an additional gas chromatographic measurement.

25. The method of any of the preceding claims, wherein the optical measurement comprises an absorption measurement, in particular at at least one wave- number between 500 cm-l and 1500 cm^~l and/or at at least one wavelength between 200 nm and 400 nm, preferably at at least one wavenumber between 600 cm^~l and 800 cm^~l and/or between 940 cm^~l and 1050 cm^~l and/or between 1100 cm^~l and 1400 cm^~l and/or between 1750 cm^~l and 1850 cm^~l and/or at at least one wavelength between 225 nm and 375 nm.

26. The method of claim 25, wherein the absorption measurement is carried out by means of a cavity ringdown spectroscope, a Lambert-Beer spectroscope, a multi-pass spectroscope, a single wavelength ultraviolet spectroscope, a single wavelength infrared spectroscope, a Fourier-transform infrared spectroscope, a Raman spectroscope, or a photoacoustic spectroscope.

27. The method of any of the claims 25 to 26, wherein an absorption signal full-width-at-half-maximum is between 40 cm^~l and 120 cm^~l and/or between 50 nm and 100 nm at an insulation fluid pressure between 1 bar and 10 bar and at an insulation fluid temperature of 20°C.

28. The method of any of the preceding claims, wherein the optical measurement comprises a fluorescence emission measurement, in particular at at least one fluorescence emission wavelength between 350 nm and 600 nm.

29. The method of any of the preceding claims, wherein the method is carried out during a regular operation of the electrical apparatus (1) .

30. The method of any of the preceding claims, wherein a pressure of the insulation fluid (10) in the compartment (11) during the carrying out the optical measurement and/or the gas chromatographic measurement is an operating pressure for the electrical apparatus (10), and in particular wherein the pressure of the insulation fluid is > 1 bar at an insulation fluid temperature of 20°C.

31. The method of any of the preceding claims, wherein an operating voltage, in particular > 1 kV, preferably > 50 kV, is applied over an electrically active part (60) of the electrical apparatus (10) during the carrying out the optical measurement and/or the gas chromatographic measurement.

32. The method of any of the preceding claims, wherein the gas chromatographic measurement is carried out by means of a multicolumn gas chromatograph (30) .

33. The method of any of the preceding claims, further comprising at least one method element of the group consisting of:

- increasing the first concentration (c¾) of the first fluid component (A) by means of injecting an amount of the first fluid component (A) from a component reservoir (50) into the compartment (11),

- increasing the second concentration (eg) of the second fluid component (B) by means of injecting an amount of the second fluid component (B) from a component reservoir (50) into the compartment (11),

- reducing a concentration of at least one contaminant in the insulation fluid (10), in particular by means of a filter (51) ,

- evaporating a condensed amount of the first and/or the second fluid component (A, B) , in particular by means of a heater (52) , and

- condensing an amount of the first and/or the second fluid component (A, B) , in particular by means of a cooler (53) .

34. An electrical apparatus (1), in particular gas-insulated medium or high voltage switchgear, comprising

at least one compartment (11) filled with an insulation fluid (10) comprising at least a first fluid component (A) with a first concentration (c^) and at least a second fluid component (B) with a second concentration (CQ) ,

an optical sensor (20) for carrying out an optical measurement indicative of the first concentration (c¾) and/or

a gas chromatograph (30) for carrying out a gas chromatographic measurement indicative of the first concentration (c¾) ,

an analysis and control unit (40 for carrying out the steps of a method of any of the preceding claims.

35. The electrical apparatus (1) of claim 34, further comprising an interface (41) for connecting the electrical apparatus (1) to an external insulation fluid filler (42) and for transmitting the first and second concentrations (c¾, eg) to the insulation fluid filler (42) .

36. A power transmission network (200), in particular a medium or high-voltage power transmission network (200), comprising an electrical apparatus (1) of any of the claims 34 to 35.

37. A computer program element comprising computer program code means for, when executed by a processing unit, implementing a method according to any of the claims 1 to 33.