Detection of thermal overloading of components of switchgear equipment

Abstract

The invention relates to a method and a device (9) for detecting thermal overloading of components of switchgear equipment (1) arranged in an insulating-gas-filled gas chamber (3) of a gas container (5) in the switchgear equipment (1), in which at least one electric current (I) flows in an electric conductor (7). In the method, a gas pressure (p) in the gas chamber (3) is measured, and a comparative value (f) for the gas pressure (p) in the gas chamber (3) is determined. It is concluded that thermal overloading of at least one component of the switchgear equipment (1) arranged in the gas chamber (3) takes place if the gas pressure (p) significantly exceeds the comparative value (f).

Description

[0001] I

[0002] 1

[0003] Description

[0004] Detecting thermal overload of switchgear components

[0005] The invention relates to a method and a device for detecting a thermal overload of components of a switchgear assembly which are arranged in a gas chamber of a gas container of the switchgear assembly which is filled with an insulating gas and in which at least one electric current flows in an electrical conductor.

[0006] To date, temperatures in a switchgear gas compartment have only been recorded locally. For example, temperatures in the gas compartment are measured locally using wireless sensors, or individual components in the gas compartment are monitored by infrared sensors positioned at a safe distance from live parts. Temperature measurements on cables and bushings are also known. However, such local temperature measurements do not allow the entire current path within the gas compartment to be monitored. Monitoring the entire current path using local temperature measurements would require a large number of measuring points and therefore a large number of temperature sensors, which would make the measuring system very complex and expensive.

[0007] The invention is based on the object of specifying an improved method and an improved device for detecting a thermal overload of components of a switchgear which are arranged in a gas space of a gas container of the switchgear which is filled with an insulating gas and in which at least one electrical current flows in an electrical conductor.

[0008] The object is achieved according to the invention by a method having the features of claim 1 and a device having the features of claim 13. I

[0009] 2

[0010] Advantageous embodiments of the invention are the subject of the dependent claims.

[0011] The method according to the invention serves to detect a thermal overload of components of a switchgear assembly that are arranged in a gas chamber of a gas container of the switchgear assembly that is filled with an insulating gas and in which at least one electric current flows in an electrical conductor. In the method, a gas pressure in the gas chamber is measured. Furthermore, a comparison value for the gas pressure in the gas chamber is determined. Thermal overload of at least one component of the switchgear assembly arranged in the gas chamber is concluded if the gas pressure significantly exceeds the comparison value.

[0012] The invention exploits the fact that increases in temperature of the insulating gas in the gas space lead to increases in pressure in the gas space, since the volume of the gas space and the amount of insulating gas in the gas space are constant and the temperature of the insulating gas is therefore proportional to the gas pressure in the gas space according to the thermal equation of state for ideal gases. Local increases in temperature have a direct effect on the gas pressure in the entire gas space, so that a pressure sensor used to measure the gas pressure can also detect increases in temperature at locations in the gas space that are far away from the pressure sensor. A single pressure sensor is therefore sufficient to thermally monitor the entire gas space. The pressure sensor can be wired and designed to be passive in order to achieve a long service life for the pressure sensor. The comparison value is a value that the gas pressure assumes without thermal overload in the gas space.A significant excess of the reference value by the gas pressure measured in the gas space therefore indicates thermal overload of at least one component of the switchgear in the gas space.

[0013] In one embodiment of the invention, all currents flowing in the gas space are measured and the comparison value is I

[0014] 3 is determined as a function of the currents. In addition, the ambient temperature of the switchgear's surroundings can be measured, and the comparison value can also be determined as a function of the ambient temperature.

[0015] The aforementioned embodiment of the invention takes into account that the electrical currents flowing in the gas space influence the temperature and thus the gas pressure in the gas space, since heat is transferred to the insulating gas from the conductors in which the currents flow. A temperature increase in the insulating gas caused solely by the currents therefore does not indicate thermal overload of switchgear components and must be taken into account when determining the comparison value. In other words, the comparison value must be determined as a function of the electrical currents flowing in the gas space in order to avoid misinterpretations of pressure increases in the gas space. The same applies to the ambient temperature of the switchgear's surroundings, since the heat released from the gas space into the surroundings depends on the ambient temperature.However, the influence of the ambient temperature can often be neglected, since the ambient temperature is often at least approximately constant.

[0016] In a further embodiment of the invention, the comparison value is determined by a transfer function dependent on at least two time elements, wherein a first time element describes a heat transfer from the electrical conductors to the insulating gas in the gas space and a second time element describes a heat transfer from the insulating gas from the gas space into the environment of the switchgear.

[0017] The aforementioned embodiment of the invention also takes into account the above-mentioned influences of the currents flowing in the gas space and the ambient temperature on the temperature of the insulating gas and thus on the gas pressure in the gas space. I

[0018] 4

[0019] In a further embodiment of the invention, the comparison value is determined using a PT2 element. This takes into account that the temperature of the insulating gas in the gas space can be described as a function of time by a differential equation that includes the heat transfers from the electrical conductors to the insulating gas and from the gas space to the environment of the switchgear. This differential equation can be conveniently solved using a PT2 element, whose transfer function includes the aforementioned heat transfers.

[0020] In a further embodiment of the invention, the comparison value is determined by a thermodynamic simulation of the gas space coupled with a flow simulation of the flow of the insulating gas in the gas space. The thermodynamic simulation and the flow simulation can, in particular, take into account the spatial dependence of heat transfer from the electrical conductors in the gas space to the insulating gas.

[0021] The aforementioned embodiment of the invention aims at a precise determination of the comparison function, which also takes into account, for example, the geometry of the gas space and the course of the electrical conductors in the gas space. For this purpose, this embodiment of the invention provides a corresponding thermodynamic simulation of the gas space coupled with a flow simulation of the flow of the insulating gas in the gas space.

[0022] In a further embodiment of the invention, a temperature is measured at at least one location in the gas space, and the measured temperature is used in calculating the comparison value. Temperatures measured in the gas space can be used as boundary or support values ​​in determining the comparison value and advantageously improve the accuracy of this determination. I

[0023] 5

[0024] In a further embodiment of the invention, a gas pressure is also measured in each of the additional gas compartments of the switchgear filled with an insulating gas, and the comparison value is determined as a function of the gas pressures in the additional gas compartments. For example, an average value of the gas pressures in the additional gas compartments is determined as the comparison value.

[0025] The aforementioned embodiment of the invention takes into account that a switchgear often comprises a plurality of identical or at least similar gas compartments, each of which is filled with the insulating gas. Therefore, the comparison value for a gas compartment can also be determined as a function of the gas pressures in other gas compartments with similar properties. If the currents in these gas compartments are also the same or similar, the comparison value can be determined in particular as an average value of the gas pressures in the other gas compartments. Otherwise, the comparison value is also determined as a function of the currents flowing in the other gas compartments.

[0026] In a further embodiment of the invention, a difference threshold value is defined for an exceedance of the comparison value by the gas pressure in the gas space, and an exceedance of the comparison value by the gas pressure is assessed as significant if it exceeds the difference threshold value.

[0027] In a further embodiment of the invention, a ratio threshold value is defined for a ratio of the gas pressure in the gas space to the comparison value, and an exceedance of the comparison value by the gas pressure is assessed as significant if the ratio of the gas pressure in the gas space to the comparison value exceeds the ratio threshold value.

[0028] The two aforementioned embodiments of the invention enable a quantitative evaluation of the gas pressure in the gas space by means of threshold values ​​I related to the comparison value

[0029] 6 for the absolute or relative deviation of the gas pressure from the reference value.

[0030] A device according to the invention for detecting a thermal overload of components of a switchgear assembly which are arranged in a gas chamber of a gas container of the switchgear assembly which is filled with an insulating gas and in which at least one electrical current flows in an electrical conductor, comprises a pressure sensor which is set up to measure a gas pressure in the gas chamber, and a computing unit which is set up to determine a comparison value for the gas pressure in the gas chamber and to conclude that there is a thermal overload of at least one component of the switchgear assembly arranged in the gas chamber if the gas pressure significantly exceeds the comparison value.

[0031] A device according to the invention enables the implementation of the method according to the invention. Therefore, the advantages of the device correspond to the above-mentioned advantages of the method according to the invention.

[0032] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of exemplary embodiments, which are explained in more detail in conjunction with the drawings.

[0033] FIG 1 is a block diagram of a switchgear and a device for detecting thermal overload of switchgear components,

[0034] FIG 2 temporal progressions of a temperature and a gas pressure in a gas compartment of a switchgear, an ambient temperature in the environment of the switchgear and a comparison value for the gas pressure. I

[0035] 7

[0036] Corresponding parts in the figures are provided with the same reference symbols.

[0037] Figure 1 (FIG. 1) shows a block diagram of a switchgear assembly 1 and a device 9 for detecting a thermal overload of components of the switchgear assembly 1. The switchgear assembly 1 comprises a gas chamber 3 of a gas container 5 filled with an insulating gas and an electrical conductor 7 extending into the gas chamber 3. The device 9 comprises a current sensor 11, a pressure sensor 13, a temperature sensor 15 and a computing unit 17. The current sensor 11 is configured to measure a current I flowing in the conductor 7. The pressure sensor 13 is configured to measure a gas pressure p in the gas chamber 3. The temperature sensor 15 is configured to measure an ambient temperature T yan environment of the switchgear 1. The computing unit 17 is configured to determine a comparison value f for the gas pressure p according to the method described below and to conclude that there is a thermal overload of at least one component of the switchgear 1 arranged in the gas space 3 if the measured gas pressure p significantly exceeds the comparison value f.

[0038] In the following, an embodiment of the method according to the invention for detecting a thermal overload of components of the switchgear 1 which are arranged in the gas space 3 is described with reference to Figure 2.

[0039] Figure 2 (FIG 2) shows curves of the temperature T of the insulating gas and the gas pressure p in the gas space 3, the ambient temperature Tu and a comparison value f for the gas pressure p as a function of time t.

[0040] The gas pressure p in the gas space 3 and the ambient temperature Tu are measured.

[0041] The comparison value f is a calculated value of the gas pressure in the gas space 3 in the fault-free case, that is, in the case I that there is no thermal overload in the gas space 3. For example, the comparison value f is calculated in the manner described below using a PT2 element whose transfer function depends on two time elements, wherein a first time element describes a heat transfer from the conductor 7 to the insulating gas in the gas space 3 and a second time element describes a heat transfer from the insulating gas from the gas space 3 into the environment of the switchgear 1.

[0042] The heat transfer from the conductor 7 to the insulating gas in the gas space 3 depends on a power loss P vof the conductor 7. A portion of this power loss is transferred from the conductor 7 to the insulating gas in the gas chamber 3. Heat is transferred from the insulating gas in the gas chamber 3 to the environment of the switchgear 1, which heat depends on the ambient temperature Tu. The reference value f (t) as a function of time thus depends on the power loss Pv(t) as a function of time and on the ambient temperature Tu(t) as a function of time. The relationship between f (t) , P v (t) and Tu(t) is described, for example, by the following equations [1] , [2] , [3] :

[0043] [1] : Pv(t) = Cx -dTu / dt + (T L -T) / R thi

[0044] [2] : (T L -T) / R thi = C2-dT / dt + (T-Tu) / R t h2

[0045] [3] : f -V = n -R -T

[0046] The following terms were used:

[0047] Ci : heat capacity of the conductor 7

[0048] C2: Heat capacity of the insulating gas TL : Temperature of conductor 7

[0049] Rthi : thermal resistance between the conductor 7 and the insulating gas R t h2 : Thermal resistance between the insulating gas and the environment V: Volume of the gas space 3 n: Amount of substance of the insulating gas R: Universal gas constant dT L / dt: derivative of T L after time t dT / dt: derivative of T after time t I

[0050] Equation [1] describes the power loss Pv(t) as a function of T L and T. Equation [2] describes the relationship between T, T L and Tu and is used to T Lin equation [1]. This yields a second-order differential equation for the temperature T(t) as a function of time t, which includes the power loss Pv(t) as a function of time and the ambient temperature Tu(t) as a function of time. Equation [3] is the thermal equation of state for an ideal gas with the reference value f as the pressure. Equation [3] is used to substitute T(t) by f(t), which is easily possible since the volume V of the gas space 3 and the amount of substance n of the insulating gas are constant over time. This results in a second-order differential equation for the reference value f(t) as a function of time t, which includes the power loss Pv(t) as a function of time and the ambient temperature Tu(t) as a function of time. This differential equation is solved, for example, with a PT2 element. The solution f(t) of this differential equation can thus be written as a function w(P v (t ) , T y(t ) ) which depends on the power loss Pv(t) as a function of time and the ambient temperature Tu(t) as a function of time :

[0051] [4] : f (t) = w(P v (t) ,Tu(t) )

[0052] Often the ambient temperature T y to a good approximation, is time-independent and can therefore be replaced by a constant value. The power loss P v is usually proportional to the product I 2 -R O hm of the square of the current I flowing in the conductor 7 and the ohmic resistance Rohm of the conductor 7. Then the comparison value f depends essentially on the square of the current I.

[0053] The comparison value f is used to detect a thermal overload of components of the switchgear 1 arranged in the gas space 3. In this case, a thermal overload of at least one I arranged in the gas space 3

[0054] 10

[0055] Component of the switchgear 1 is closed if the measured gas pressure p significantly exceeds the comparison value f. For example, a difference threshold is defined for an exceedance of the comparison value f by the gas pressure p in the gas space 3, and an exceedance of the comparison value f by the gas pressure p is assessed as significant if it exceeds the difference threshold. Alternatively or additionally, a ratio threshold is defined for a ratio of the gas pressure p in the gas space 3 to the comparison value f, and an exceedance of the comparison value f by the gas pressure p is assessed as significant if the ratio of the gas pressure p in the gas space 3 to the comparison value f exceeds the ratio threshold.

[0056] Figure 2 shows an example of the result of a calculation of the comparison value f ( t ) in comparison to the measured gas pressure p ( t ) in the gas space 3 . Also shown are the average temperature T ( t ) of the insulating gas in the gas space 3 and the ambient temperature Tu ( t ). It can be clearly seen that the gas pressure p ( t ) changes proportionally to the temperature T ( t ) of the insulating gas in the gas space 3 without any great time delay. In this example, the gas pressure p ( t ) agrees very well with the comparison value f ( t ), so that it can be concluded that there is no thermal overload of components of the switchgear 1 arranged in the gas space 3.

[0057] The calculation of the comparison value described above is only an example for the calculation of the comparison value in a simple case or under simplifying assumptions. In reality, for example, the gas container 5 can also have a relevant thermal mass, which must be taken into account in the calculation. Furthermore, for example, a location dependence of the heat transfer from the conductor 7 to the insulating gas in the gas space 3 and / or, if appropriate, the presence of several conductors 7 in the gas space 3 can be taken into account. In such cases, the comparison value f is determined, for example, by a thermodynamic simulation of the gas space 3 coupled with a flow simulation of the flow I

[0058] 11 of the insulating gas in the gas chamber 3. Other data sources can also be taken into account, for example, measurement signals from a temperature sensor located in the gas chamber 3. The calculation of the comparison value f can then be performed, for example, depending on the location, so that the calculation yields a result according to equation [5] instead of equation [4]:

[0059] [5] : f (t,x) = w (P v (t, x) , Tu (t) , T s (t) )

[0060] Here, x denotes a location coordinate from which the power loss P v and the comparison value f depend, and T srefers to a temperature in the gas space 3 detected by a temperature sensor. In such a case, the gas pressure p in the gas space 3 is measured, for example, at several locations, and the value of the gas pressure p is compared with the reference value f calculated for the respective location. Alternatively, a value of f (t, x) averaged over the location coordinate x is used as the reference value f (t).

[0061] Alternatively, the reference value f can also be determined in a different way. If switchgear 1 has additional gas compartments filled with an insulating gas, for example, a gas pressure is measured in each of the additional gas compartments, and the reference value f is determined as a function of the gas pressures in the additional gas compartments. For example, an average of the gas pressures in the additional gas compartments is determined as the reference value f.

[0062] Although the invention has been illustrated and described in detail by means of preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

[0063] Regardless of the grammatical gender of a particular term, persons with male, female, or other gender identities are included. I

[0064] 12

[0065] Reference symbol list

[0066] I Switchgear

[0067] 3 Gas chamber

[0068] 5 gas tanks

[0069] 7 ladders

[0070] 9 Device for detecting thermal overload of switchgear components

[0071] II Current sensor

[0072] 13 Pressure sensor

[0073] 15 Temperature sensor

[0074] 17 Calculation unit f comparison value

[0075] I current p gas pressure t time

[0076] T Temperature

[0077] Tu ambient temperature

Claims

I 13 Patent claims 1. Method for detecting a thermal overload of components of a switchgear assembly (1) which are arranged in a gas chamber (3) of a gas container (5) of the switchgear assembly (1) filled with an insulating gas, in which at least one electrical current (I) flows in an electrical conductor (7), wherein - a gas pressure (p) is measured in the gas space (3), - a comparison value (f) for the gas pressure (p) in the gas space (3) is determined and - a thermal overload of at least one component of the switchgear (1) arranged in the gas space (3) is concluded if the gas pressure (p) significantly exceeds the comparison value (f).

2. Method according to claim 1, wherein all currents (I) flowing in the gas space (3) are measured and the comparison value (f) is determined as a function of the currents (I).

3. Method according to claim 2, wherein an ambient temperature (Tu) of an environment of the switchgear (1) is measured and the comparison value (f) is determined as a function of the currents (I) flowing in the gas space (3) and the ambient temperature (Tu).

4. Method according to one of the preceding claims, wherein the comparison value (f) is determined by a transfer function dependent on at least two time elements, wherein a first time element describes a heat transfer from the electrical conductors (7) to the insulating gas in the gas space (3) and a second time element describes a heat transfer from the insulating gas from the gas space (3) into the environment of the switchgear (1).

5. Method according to one of the preceding claims, wherein the comparison value (f) is determined with a PT2 element. I 14 6. Method according to one of claims 1 to 4, wherein the comparison value (f) is determined by a thermodynamic simulation of the gas space (3) coupled with a flow simulation of the flow of the insulating gas in the gas space (3).

7. The method according to claim 6, wherein the thermodynamic simulation and the flow simulation take into account a location dependence of a heat transfer from the electrical conductors (7) in the gas space (3) to the insulating gas.

8. Method according to one of the preceding claims, wherein a temperature is measured at at least one location in the gas space (3) and the measured temperature is used in determining the comparison value (f).

9. Method according to claim 1, wherein in further gas spaces of the switchgear (1) filled with an insulating gas, a gas pressure is also measured in each case and the comparison value (f) is determined as a function of the gas pressures in the further gas spaces.

10. The method according to claim 9, wherein an average value of the gas pressures in the further gas spaces is determined as the comparison value (f).

11. Method according to one of the preceding claims, wherein a difference threshold value is defined for an exceedance of the comparison value (f) by the gas pressure (p) in the gas space (3) and an exceedance of the comparison value (f) by the gas pressure (p) is assessed as significant if it exceeds the difference threshold value.

12. Method according to one of the preceding claims, wherein a ratio threshold value is defined for a ratio of the gas pressure (p) in the gas space (3) to the comparison value (f), and an exceedance of the comparison value (f) by the gas pressure (p) is assessed as significant if the ratio of the gas pressure (p) in the gas space (3) to the comparison value (f) exceeds the ratio threshold value.

13. Device (9) for detecting a thermal overload of components of a switchgear (1) which are arranged in a gas chamber (3) of a gas container (5) of the switchgear (1) filled with an insulating gas, in which at least one electrical current (I) flows in an electrical conductor (7), the device (9) comprising - a pressure sensor (13) which is designed to measure a gas pressure (p) in the gas chamber (3), and - a computing unit (17) which is designed to determine a comparison value (f) for the gas pressure (p) in the gas space (3) and to conclude that there is a thermal overload of at least one component of the switchgear (1) arranged in the gas space (3) if the gas pressure (p) significantly exceeds the comparison value (f).

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