Electrical device and method for determining potential functional impairment in an electrical device

Abstract

The invention relates to an electrical device (30) comprising a device housing (20) and electrical components (31, 33, 34), wherein the electrical components (31, 33, 34) are arranged in the device housing (20) and at least two electrical conductors (36, 37) of at least one of the electrical components (31, 33, 34) are electrically insulated from one another by means of an electrical insulator (35), wherein the electrical device (30) comprises a sensor system (40) which is designed to detect the deposition of an electrically conductive foreign body layer on the electrical insulator (35), wherein the sensor system (40) comprises a measuring surface (42) arranged inside the device housing (20) and on which at least two electrodes (43, 44) spaced apart from one another are arranged, and the sensor system (40) comprises a measuring circuit (48) which is designed to measure a parameter which depends on a current flowing between the at least two electrodes (43, 44). The invention also relates to a method for determining a potential functional impairment in an electrical device (30).

Description

Technical Field

[0001] The invention relates to an electrical device having a device housing and electrical components, wherein the electrical components are arranged in the device housing and at least two electrical conductors of at least one of the electrical components are electrically insulated from one another by means of electrical insulators. In addition, the invention relates to a method for determining potential functional impairments in an electrical device. Background Art

[0002] The problem with such electrical devices is that the deposition of conductive foreign matter can lead to functional impairment of the electrical device. Conductive foreign matter can be, for example, dust, in particular metal dust or carbon black, ash, fiber dust, etc., as well as moisture. In addition, combinations of deposited dust and moisture can occur. Here, moisture can be formed, for example, by mist or dew, in particular containing salt. In this case, non-conductive dust also becomes conductive, and conductive dust even more conductive, because the resistance of such a foreign matter layer is reduced. Such foreign matter can, for example, pass through the ventilation grille of the device housing and deposit inside the device housing on electrical components and electrical insulators of the electrical device.

[0003] In particular, the deposition of conductive foreign matter on the surface of an electrical insulator is problematic, on which a conductive foreign matter layer can form. The current of two electrical conductors of one or more components of an electrical device, which are electrically insulated from each other by means of an electrical insulator, can flow along the conductive foreign matter layer. The conductive foreign matter layer becomes critical when the conductive foreign matter layer becomes wet due to condensation of humid air or other input of moisture. Along the current path of the current between the conductors and through the moist conductive foreign matter layer, the moist conductive foreign matter layer is locally heated over time, whereby areas of the moist conductive foreign matter layer are dried. If the dry area is large enough to interrupt the flowing current, a voltage situation occurs on the dry area. Ultimately, at a sufficient voltage, an arc occurs on the dry area until an electric flashover occurs.

[0004] Electrical arcing can lead to short circuits in electrical devices. Short circuits can lead to unexpected interruptions in the operation of electrical devices, in particular by triggering electrical fuses of the electrical device. The causes of short circuits must be investigated with great effort. In addition, short circuits can lead to damage to electrical devices, in particular electrical insulators.

[0005] DE 10 2009 035 296 A1 discloses an electrical switching device having a housing with a detection device which determines the formation of a material layer in a detection region of the detection device within the housing. The detection device is designed with means for optically detecting the foreign body layer.

[0006] It is desirable to provide reliable and accurate detection of conductive foreign material layers in electrical devices at low cost in order to identify potential functional impairment of the electrical devices. Summary of the invention

[0007] The object of the present invention is therefore to provide an electrical device in which potential functional impairments due to electrically conductive foreign matter layers can be detected reliably, precisely and with low outlay.

[0008] Features and details disclosed in connection with the device according to the invention naturally also apply in connection with the method according to the invention, so that reference is always made to one another with regard to the disclosure of the individual inventive aspects.

[0009] According to a first aspect, the technical problem to be solved is solved by an electrical device, which has a device housing and electrical components, wherein the electrical components are arranged in the device housing and at least two electrical conductors of at least one of the electrical components are electrically insulated from each other by means of electrical insulators, wherein the electrical device has a sensor system, which is constructed to detect deposition of a conductive foreign material layer on the electrical insulator, wherein the sensor system has a measuring surface arranged inside the device housing, on which at least two electrodes spaced apart from each other are arranged, and the sensor system has a measuring circuit, which is constructed to measure a parameter that depends on a current flowing between the at least two electrodes.

[0010] In other words, the parameter is a measure of the electrical conductivity of the foreign body layer between at least two electrodes. The parameter can be, for example, the current intensity. For this purpose, the voltage of the measuring circuit can be predetermined.

[0011] Accordingly, the electrical device can detect potential functional impairments by means of a conductive foreign body layer deposited on the measuring surface. The functional impairment can be, for example, a short circuit in the electrical device. The functional impairment can therefore lead to unplanned downtime of the electrical device. With the aid of the measuring surface of the sensor system arranged in the device housing and the measuring circuit, the deposition of a conductive foreign body layer on the measuring surface can be measured very reliably, precisely and cost-effectively.

[0012] At least two electrical conductors of at least one of the electrical components are electrically insulated from each other by an electrical insulator, which may mean that the at least two electrical conductors come from the same electrical component. However, it may also mean that the at least two electrical conductors come from different electrical components. That is, due to the deposition of a conductive foreign layer, a short circuit may occur not only between the electrical conductors of the same electrical component but also between the electrical conductors of different electrical components. In addition, a plurality of electrical insulators may be arranged between the electrical conductors of the electrical component. With the aid of an electrical device, in principle, potential functional damage can be identified independently of one of the aforementioned configurations. In addition, the present invention enables early identification of potential functional damage due to current from the electrical conductor to ground.

[0013] In an electrical device, a measuring surface can be arranged and constructed so that a conductive foreign layer on one or more electrical insulators between electrical conductors is only indirectly and / or only partially directly collected with the aid of the measuring surface. Indirect means that the measuring surface does not measure the conductive foreign layer on the one or more electrical insulators themselves, but measures the conductive foreign layer deposited on the measuring surface. For this purpose, the measuring surface can be arranged at a distance from one or more electrical insulators. Based on the deposition on the measuring surface, it is possible to estimate with high reliability whether and to what extent a conductive foreign layer is formed on one or more electrical insulators. Alternatively or additionally, the measuring surface can be arranged on the surface of the electrical insulator, or a plurality of measuring surfaces can be arranged on the surface of a plurality of electrical insulators. In this way, the conductive foreign layer can be directly collected.

[0014] Preferably, at least two electrodes are designed as conductor tracks. This allows large measuring areas to be easily covered by means of the at least two electrodes in order to obtain reliable results of the sensor system.

[0015] Furthermore, preferably, at least one of the at least two conductor tracks extends in a comb-like manner. The comb-like shape is formed in particular by at least one outer conductor track and an inner conductor track, which is arranged on the outer conductor track, is spaced apart from one another and extends laterally, in particular perpendicularly, from the outer conductor track. In particular, the two conductor tracks can be designed in a comb-like manner and can be interlaced with one another. In this case, the inner conductor tracks can be arranged alternately side by side, in particular parallel to one another.

[0016] In addition, preferably, at least two conductor tracks are interlaced with each other. Here, the conductor tracks can be arranged side by side, in particular parallel to each other. For example, a plurality of conductor tracks can be interlaced in a comb-shaped conductor track. Here, a plurality of conductor tracks extend beside and in particular parallel to the inner conductor tracks of the comb-shaped conductor track.

[0017] Preferably, at least two electrodes are connected to an AC voltage source in a current-conducting manner. The measuring circuit can include this AC voltage source. In principle, at least two electrodes can be connected to a voltage source (for example, also a DC voltage source) in a current-conducting manner, and the measuring circuit can include this voltage source. However, an AC voltage source has the following advantages over a DC voltage source: no electrolytic corrosion occurs at the electrodes. This can increase the maintenance-freeness and service life of the sensor system.

[0018] Furthermore, the measuring surface is preferably arranged at and / or on the electrical insulator, so that a part of the electrically conductive foreign body layer on the electrical insulator can be directly measured, so that a particularly precise measurement result can be obtained.

[0019] Furthermore, the measuring surface is preferably arranged horizontally or essentially horizontally in the device housing. Horizontal here means an arrangement perpendicular to the direction of gravity. Essentially horizontal means that deviations from the horizontal arrangement of up to 20° are possible. In other words, it can also be said that the measuring surface is arranged parallel to or essentially parallel to the bottom surface. The bottom surface can be, for example, the bottom surface of the device housing, with which the electrical device is placed or mounted on the ground, or can be, for example, the bottom surface of the ground, on which the electrical device is placed or mounted. By means of the horizontal arrangement of the measuring surface, it is possible to measure the largest possible deposition of the conductive foreign matter layer based on foreign matter settling by gravity.

[0020] In particular, the measuring surface can be arranged parallel or substantially parallel to the surface of the electrical insulator. In this context, substantially parallel means that deviations from a parallel arrangement of up to 20° are possible. This ensures that the measuring surface has an orientation in the device housing that is as similar as possible to the electrical insulator, so that the conductive foreign matter layer on the measuring surface corresponds with a high probability to the conductive foreign matter layer on the surface of the electrical insulator, for example in terms of dust content, layer thickness and humidity, due to the air circulation that prevails in the device housing. Because depending on the orientation of the measuring surface relative to the surface of one or more electrical insulators and the position in which the measuring surface is arranged relative to the ventilation slots, ventilation channels or ventilation grilles and the device housing, the foreign matter layer deposited thereon can form differently.

[0021] Preferably, the carrier of the measuring surface, on which at least two electrodes are arranged, has the same insulating material as the electrical insulator. In particular, the carrier or the carrier material of the measuring surface is made of the same insulating material as the electrical insulator. Since foreign matter adheres differently to different materials, it can be ensured that the conductive foreign matter layer on the electrical insulator is detected as accurately as possible by measuring the conductive foreign matter layer deposited on the measuring surface.

[0022] Furthermore, the sensor system preferably has a heating device for heating the measuring surface. Since the electrical component and thus the one or more electrical insulators are usually hotter than the measuring surface during operation, condensation of the moist air occurs on the measuring surface before condensation occurs on the one or more electrical insulators. This results in the risk that the sensor system erroneously detects a potential functional impairment despite the fact that no condensation has formed on the one or more electrical insulators (which could cause or increase the conductivity of the foreign body layer). Such erroneous detections can therefore be avoided by means of the heating device by heating the measuring surface.

[0023] In addition, it is preferred that the electrical device has a temperature sensor for collecting the temperature of the electrical device and a regulating device connected to the temperature sensor and the heating device, and the regulating device is configured to regulate the temperature of the measuring surface according to the temperature of the electrical device. The temperature of the electrical device can be, for example, the internal temperature in the device housing. The temperature sensor can be an air temperature sensor in the device housing accordingly. In addition, the temperature of the electrical device can be a temperature measured on one or more electrical components or on one or more electrical insulators. The temperature sensor can be arranged on one or more electrical components or on one or more electrical insulators accordingly. In particular, the sensor system can also have a temperature sensor. In addition, a combination of multiple temperature sensors at different positions in the device housing, for example, on different electrical components and electrical insulators is possible. Here, a temperature value derived from the temperature measured by multiple temperature sensors, such as an average value, can be considered as the temperature of the electrical device. The regulating device is configured to regulate the temperature of the measuring surface according to the temperature of the electrical device, which can mean that the temperature of the measuring surface is regulated to the temperature of the electrical device.

[0024] However, preferably, the regulating device is designed to regulate the temperature of the measuring surface to a temperature below the temperature of the electrical device, so that there is a temperature gap between the temperature of the measuring surface and the temperature of the electrical device. The temperature gap can be a predefined temperature gap. The predefined temperature gap can be an absolute temperature gap or a percentage temperature gap, which is determined as a percentage depending on the temperature of the electrical device. The temperature gap can be, for example, in the range of 1°C to 5°C, in particular 2°C to 4°C. Thus, potential functional damage to the electrical device due to condensation on a non-conductive foreign matter layer or a conductive foreign matter layer in a dry state can be determined by means of the sensor system even before such functional damage occurs. Thus, appropriate measures can then also be taken to avoid functional damage.

[0025] It is also preferred that the evaluation unit is connected to the measuring circuit and the evaluation unit is configured to compare the measured parameter of the current flowing between at least two electrodes with a threshold value and output a message of potential functional damage of the electrical device when the measured parameter has exceeded the threshold value. The threshold value may be a predefined threshold value, which is still below the parameter that would cause functional damage, such as a short circuit. The electrical device, in particular the sensor system, may have an evaluation unit. It is also possible that the sensor system has a wireless communication device, which is configured to communicate wirelessly with the evaluation unit. Accordingly, the evaluation unit may be arranged, for example, in a central computer, which may monitor a plurality of electrical devices with respect to potential functional damage. The message may be output, for example, optically on a screen of the evaluation unit or the electrical device and / or acoustically. The message may also be a control technology message in the form of an indication to the electrical device. For example, the indication may include: adjusting the operation of the electrical device, reducing the operating load of the electrical device, or increasing the speed of one or more fans of the electrical device.

[0026] It is also preferred that the electrical device is a transformer. The transformer may be, for example, a power transformer, a distribution transformer or the like. The transformer may in particular be a dry-type transformer, very particularly a resin-cast transformer. Unlike oil-filled transformers, these transformers are particularly sensitive to contamination. Transformers are used in different environments and may be exposed to very low temperatures, very high temperatures, temperature fluctuations, weather conditions, humid air, salty air or otherwise polluted air, for example by dust, which may support or cause functional impairment. Alternatively, the electrical device may be, for example, a converter, a switchgear or a switch device.

[0027] According to a second aspect, the technical problem to be solved is solved by a method for determining potential functional damage in an electrical device, wherein the method has the following steps: measuring a parameter of an electric current between at least two electrodes; comparing the measured parameter with a threshold value; and when the measured parameter exceeds the threshold value, outputting a message of potential functional damage to the electrical device.

[0028] Preferably, the method further comprises the following steps: determining the increase in the parameter between the measured measurement time points; and calculating the threshold time point at which the parameter is expected to exceed the threshold value based on the increase in the parameter. In other words, the temporal increase in the parameter is taken into account for predicting the expected threshold time point. This makes it possible, for example, to determine more economically the necessary maintenance time point at which the electrical device must be cleaned.

[0029] Furthermore, the method may preferably include the following steps: acquiring the temperature of the electrical device; and adjusting the temperature of the measuring surface according to the temperature of the electrical device. In particular, the temperature of the measuring surface may be adjusted to a temperature lower than the temperature of the electrical device, so that there is a temperature gap between the temperature of the measuring surface and the temperature of the electrical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further measures for improving the invention are obtained from the following description of various embodiments of the invention, which are schematically shown in the drawings. All features and / or advantages resulting from the invention, including structural details and spatial arrangements, are important to the invention not only per se but also in various combinations.

[0031] The present invention is described in detail below based on the accompanying drawings. In this regard, in the accompanying drawings:

[0032] Figure 1 A perspective side view of an embodiment of an electrical device having a device housing according to the present invention is shown,

[0033] Figure 2 Shows the case without the device Figure 1 A three-dimensional side view of an electrical device,

[0034] Figure 3 Shown according to Figure 2 a perspective side view of a sensor system of an electrical device, and

[0035] Figure 4 Shows the Figure 3 View of a cross section of a sensor system.

[0036] exist Figures 1 to 4 In the drawings, elements having the same function and mode of action are provided with the same reference numerals. DETAILED DESCRIPTION

[0037] Figure 1 The figure shows a perspective side view of an exemplary embodiment of an electrical device 30 according to the invention having a device housing 20. In this exemplary embodiment, the electrical device 30 is designed as a transformer, in particular a cast-resin transformer.

[0038] The electrical device 30 is surrounded by a housing 20. The housing 20 is shown here with the doors 21.1, 21.2 removed and is therefore in an open state, in which the electrical device 30 can be seen. The housing 20 is used, among other things, to prevent external weather influences and the deposition of foreign matter on the electrical device 30. In order to enable ventilation of the electrical installation 30, a plurality of ventilation grilles 22.1, 22.2, 22.3, 22.4, 22.5, 22.6, 22.7, 22.8, 22.9, 22.10 are arranged in the housing 20. Despite the presence of the housing 20, moist air, salty air and at least a small amount of conductive and non-conductive foreign matter can reach the electrical device 30 through the ventilation grilles 22.1, 22.2, 22.3, 22.4, 22.5, 22.6, 22.7, 22.8, 22.9, 22.10.

[0039] Figure 2 The device housing 20 is shown without Figure 1 3D side view of an electrical device 30. The electrical device 30 has a plurality of electrical components, of which a first electrical component 31, a second electrical component 33 and a third electrical component 34 are shown. In the present embodiment of the resin cast transformer, the first electrical component 31 is a three-phase core, the second electrical component 33 is a low voltage winding, and the third electrical component 34 is a high voltage winding. The second electrical component 33 and the third electrical component 34 are part of a component device 32.1, which is a coil device here. Component devices 32.2 and 32.3 of the same structure in the form of coil devices are arranged on other core columns of the first electrical component 31. The electrical components 31, 33, and 34 are electrically insulated from each other, of which only one electrical insulator 35 is shown. The electrical insulator 35 is arranged around the third electrical component 34 and insulates the two first electrical conductors 36.1 and 36.2 of the third electrical component 34 from each other. The first electrical conductors 36.1, 36.2 are designed here as current connections for two second electrical conductors 37.1, 37.2 of the electrical conductors 37.1, 37.2, 37.3, which are designed as conductor rails. The electrical insulator 35 is based on epoxy resin in the present exemplary embodiment.

[0040] A measuring surface 42 of a sensor system 40 is arranged on the electrical insulator 35. Alternatively, the measuring surface 42 can also be arranged at other locations in the device housing 20, for example on the device housing 20 or on other areas or other components of the electrical device 30, for example on the first electrical component 31. In addition, the measuring surface 42 can be arranged not parallel to the surface of the electrical insulator 35 as shown, but perpendicular to the surface, that is, in particular relatively horizontally in the device housing 20. With the aid of the sensor system 40, the deposition of conductive foreign matter layers on the electrical insulator 35 can be detected. In this case, for example, a conductive foreign matter layer between the first electrical conductors 36.1, 36.2 can be critical, because this foreign matter layer can lead to a short circuit in the event of an electrical arc.

[0041] Figure 3 Shown according to Figure 2 3D side view of a sensor system 40 of an electrical device 30. The sensor system 40 has a sensor housing 41 and a measuring surface 42 arranged thereon. The measuring surface 42 is formed by a carrier 45, which is formed here from the same material as the electrical insulator 35, so that the measuring surface 42 has the same adhesion properties for foreign bodies as the electrical insulator 35. A first electrode 43 in a comb-like manner and configured as a conductor track is arranged on the carrier 45. In addition, further conductor tracks 44.1, 44.2, 44.3, 44.4, 44.5, 44.6, 44.7, 44.8 of a second electrode 44 are arranged on the carrier 45 and are interlaced with the first electrode 43. The conductor tracks 44.1, 44.2, 44.3, 44.4, 44.5, 44.6, 44.7, 44.8 of the first electrode 43 and the second electrode 44 are spaced apart from each other.

[0042] Figure 4 shows that along line XX through the Figure 3 4. A cross-sectional view of the sensor system 40. It can be seen here that the sensor system 40 also has a heating device 46, a regulating device 47 connected to the heating device 46, a measuring circuit 48 connected to the conductor tracks 44.1, 44.2, 44.3, 44.4, 44.5, 44.6, 44.7, 44.8 of the first electrode 43 and the second electrode 44, which has an AC voltage source 49, as well as an evaluation unit 50 and a wireless communication device 51.

[0043] In the present exemplary embodiment, the AC voltage source 49 is designed as an AC voltage source and outputs a current having an AC voltage to the first electrode 43 and the second electrode 44 . Here, since the conductor tracks 43.1, 43.2, 43.3, 43.4, 43.5, 43.7, 43.8, 43.9 of the first electrode 43 and the conductor tracks 44.1, 44.2, 44.3, 44.4, 44.5, 44.5, 44.6, 44.7, 44.8 of the second electrode 44 are alternately spaced apart, when there is no conductive foreign layer on the measuring surface 42, especially between the conductor tracks 43.1, 43.2, 43.3, 43.4, 43.5, 43.6, 43.8, 43.9 of the first electrode 43 and the conductor tracks 44.1, 44.2, 44.3, 44.4, 44.5, 44.6, 44.7, 44.8 of the second electrode 44, only a small amount of current or no current is transmitted between the conductor tracks. However, when a conductive foreign layer is deposited on the measuring surface 42, the current or the change in the current is measured by the measuring circuit 48. The parameters of the current measured by the measuring circuit 48, such as the current intensity, provide information about the conductivity of the conductive foreign layer and therefore about the risk of functional impairment of the electrical device due to a short circuit.

[0044] The evaluation unit 50 is connected to the measuring circuit 48 and evaluates the measured parameter, here the current intensity. The evaluation unit compares the measured current intensity with a predefined threshold value and, if the measured current intensity exceeds the threshold value, outputs a message of potential functional impairment of the electrical device to a central computer (not shown) of the electrical device 30 by means of a wireless communication device 51 connected to the evaluation unit 50. Measures for preventing functional impairment can thus be initiated from the central computer.

[0045] In order to detect potential functional impairment before it occurs, the control device 47 controls the heating of the measuring surface 42 by means of the heating device 46 (here, the heating device can be designed as a heating coil, for example) so that the temperature of the measuring surface 42 is lower than the temperature of the electrical device 30, so that there is a temperature gap between the temperature of the measuring surface 42 and the temperature of the electrical device 30. As a result, potential functional impairment due to condensation on the measuring surface 42 can be detected before condensation occurs on the electrical insulator 35 and thus before functional impairment occurs, so that countermeasures can be taken in time to prevent functional impairment.

Claims

1. An electrical device (30) comprising a device housing (20) and electrical components (31, 33, 34), wherein: The electrical components (31, 33, 34) are arranged in the device housing (20), and at least two electrical conductors (36, 37) of at least one of the electrical components (31, 33, 34) are electrically insulated from each other by means of an electrical insulator (35). The electrical device (30) comprises a sensor system (40) which is configured to detect the deposition of a conductive foreign body layer on the electrical insulator (35), wherein the sensor system (40) comprises a measuring surface (42) arranged inside the device housing (20), at least two electrodes (43, 44) spaced apart from each other are arranged on the measuring surface, and the sensor system (40) comprises a measuring circuit (48) which is configured to measure a parameter which depends on a current flowing between the at least two electrodes (43, 44), and the electrical device (30) comprises a temperature sensor for acquiring the temperature of the electrical device. It is characterized in that The sensor system (40) comprises a heating device (46) for heating the measuring surface (42) and a regulating device (47) connected to the temperature sensor and the heating device (46), wherein the temperature of the measuring surface (42) is regulated to a temperature lower than the temperature of the electrical device (30) by means of the regulating device (47), so that a temperature gap exists between the temperature of the measuring surface (42) and the temperature of the electrical device (30), wherein the temperature gap is in the range of 1° C. to 5° C.

2. The electrical device (30) according to claim 1, characterized in that The at least two electrodes (43, 44) are designed as conductor tracks.

3. The electrical device (30) according to claim 2, characterized in that At least one of the at least two conductor tracks extends in a comb-like manner.

4. The electrical device (30) according to claim 2 or 3, characterized in that: The at least two conductor tracks are interlaced with each other.

5. The electrical device (30) according to any one of claims 1 to 3, characterized in that: The at least two electrodes (43, 44) are connected to an AC voltage source (49) in a current-conducting manner.

6. The electrical device (30) according to any one of claims 1 to 3, characterized in that: The measuring surface (42) is arranged at and / or on the electrical insulator (35).

7. The electrical device (30) according to any one of claims 1 to 3, characterized in that: The measuring surface (42) is arranged horizontally or substantially horizontally in the device housing (20).

8. The electrical device (30) according to any one of claims 1 to 3, characterized in that: A carrier (45) of the measuring surface (42) comprises the same insulating material as the electrical insulator (35), and the at least two electrodes (43, 44) are arranged on the carrier (45).

9. The electrical device (30) according to any one of claims 1 to 3, characterized in that: An evaluation unit (50) is connected to the measuring circuit (48) and is configured to compare a measured parameter of the current flowing between the at least two electrodes (43, 44) with a threshold value and to output a message of potential functional damage to the electrical device (30) when the measured parameter exceeds the threshold value.

10. The electrical device (30) according to any one of claims 1 to 3, characterized in that: The electrical device (30) is a transformer.

11. A method for determining a potential functional impairment in an electrical device (30) according to any one of the preceding claims, wherein: The method comprises the following steps: - measuring a parameter of an electric current between at least two electrodes (43, 44), - comparing the measured parameter to a threshold value, and - outputting a message about a potential functional impairment of the electrical device (30) when the measured parameter exceeds the threshold value.

12. The method according to claim 11, wherein: The method further comprises the following steps: - determining an increase in said parameter between the measuring time points of said measurements, and - calculating a threshold time point based on the rise of said parameter, at which threshold time point said parameter is expected to exceed said threshold value.

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