Detecting thermal overload of switchgear components

Abstract

The invention relates to a method and a device (9) for detecting a thermal overload of components of a switchgear (1) 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 electric current (I) flows in an electrical conductor (7). In the method, a gas pressure (p) in the gas chamber (3) is measured, and a reference value (f) for the gas pressure (p) in the gas chamber (3) is determined. A thermal overload of at least one component of the switchgear (1) arranged in the gas chamber (3) is concluded if the gas pressure (p) significantly exceeds the reference value (f).

Description

[0001] 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.

[0002] 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 monitoring of the entire current path within the gas compartment. Monitoring the entire current path using local temperature measurements would require a large number of measuring points and thus a large number of temperature sensors, which would make the measuring system very complex and costly.

[0003] JP 2016 - 226 146 A describes a method for detecting contact faults using pressure measurements.

[0004] JP 2009 - 236 719 A discloses a device for detecting pressure anomalies in gas-insulated switchgear.

[0005] 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 assembly which are arranged in a gas space of a gas container of the switchgear assembly filled with an insulating gas, in which at least one electrical current flows in an electrical conductor.

[0006] 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 9.

[0007] Advantageous embodiments of the invention are the subject of the subclaims.

[0008] The method according to the invention is used to detect thermal overload of components of a switchgear assembly arranged in a gas chamber of a gas vessel of the switchgear assembly, filled with an insulating gas, 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 switchgear component arranged in the gas chamber is concluded if the gas pressure significantly exceeds the comparison value.

[0009] The reference value is determined by a thermodynamic simulation of the gas space coupled with a flow simulation of the flow of the insulating gas within 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.

[0010] This aims to accurately determine the comparison function, which also takes into account, for example, the geometry of the gas space and the layout of the electrical conductors within 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 within the gas space.

[0011] The invention exploits the fact that temperature increases of the insulating gas in the gas space lead to pressure increases in the gas space, since the volume of the gas space and the amount of substance of the 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 temperature increases 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 temperature increases at locations in the gas space that are far away from the pressure sensor. Therefore, a single pressure sensor is 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.

[0012] In one embodiment of the invention, all currents flowing in the gas chamber are measured, and the comparison value is determined as a function of the currents. Additionally, an 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.

[0013] 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 from the conductors through which the currents flow to the insulating gas. 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 environment 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.

[0014] 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.

[0015] 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.

[0016] It would also be possible to determine the reference value 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 transfer from the electrical conductors to the insulating gas and from the gas space to the switchgear environment. This differential equation can be conveniently solved using a PT2 element, whose transfer function includes the aforementioned heat transfers.

[0017] 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 to calculate the comparison value. Temperatures measured in the gas space can be used as boundary or support values ​​when determining the comparison value, advantageously improving the accuracy of this determination.

[0018] It would also be possible to measure a gas pressure in other gas compartments of the switchgear filled with an insulating gas, and the reference value would then be determined based on the gas pressures in the other gas compartments. For example, an average of the gas pressures in the other gas compartments could be determined as the reference value.

[0019] The aforementioned design takes into account that a switchgear often comprises several identical or at least similar gas compartments, each filled with the insulating gas. Therefore, the reference value for a gas compartment can also be determined depending on the gas pressures in other gas compartments with similar properties. If the currents in these gas compartments are also identical or similar, the reference value can be determined, in particular, as an average of the gas pressures in the other gas compartments. Otherwise, the reference value is also determined depending on the currents flowing in the other gas compartments.

[0020] 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.

[0021] 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.

[0022] The two aforementioned embodiments of the invention enable a quantitative evaluation of the gas pressure in the gas space by means of threshold values ​​related to the comparison value for the absolute or relative deviation of the gas pressure from the comparison value.

[0023] 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, said gas chamber being filled with an insulating gas and in which at least one electrical current flows in an electrical conductor, comprises a pressure sensor which is configured to measure a gas pressure in the gas chamber, and a computing unit which is configured 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.

[0024] 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.

[0025] 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. Fig. 1 a block diagram of a switchgear and a device for detecting thermal overload of switchgear components, Fig. 2 Time courses 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.

[0026] Corresponding parts are provided with the same reference numerals in the figures.

[0027] Fig. 1 ( Fig. 1) shows a block diagram of a switchgear 1 and a device 9 for detecting a thermal overload of components of the switchgear 1. The switchgear 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 Uan 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.

[0028] The following will be based on Fig. 2 describes 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.

[0029] Fig. 2 ( Fig. 2) shows the temperature T of the insulating gas and the gas pressure p in the gas space 3, the ambient temperature T U and a comparison value f for the gas pressure p as a function of time t.

[0030] The gas pressure p in the gas space 3 and the ambient temperature TU are measured.

[0031] The comparison value f is a calculated value of the gas pressure in the gas chamber 3 in the fault-free case, i.e., in the case where there is no thermal overload in the gas chamber 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, where a first time element describes a heat transfer from the conductor 7 to the insulating gas in the gas chamber 3, and a second time element describes a heat transfer from the insulating gas from the gas chamber 3 to the environment of the switchgear 1.

[0032] 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. The insulating gas in the gas chamber 3 transfers heat to the environment of the switchgear 1, which depends on the ambient temperature T U The comparison value f(t) as a function of time therefore depends on the power loss P V (t) as a function of time and ambient temperature T U (t) as a function of time. The relationship between f(t), P V (t) and T U (t) is described, for example, by the following equations [1], [2], [3]: PV(t)=C1⋅dTL / dt+(TL−T) / Rth1 (TL−T) / Rth1=C2⋅dT / dt+(T−TU) / Rth2 f⋅V=n⋅R⋅T

[0033] The following terms were used: C1: Heat capacity of conductor 7 C2: Heat capacity of the insulating gas T L : Temperature of conductor 7 R th1: Thermal resistance between the conductor 7 and the insulating gas R th2 : Thermal resistance between the insulating gas and the environment V: Volume of gas space 3 n: amount of insulating gas R: universal gas constant dT L / dt: derivative of T L after time t dT / dt: derivative of T with respect to time t

[0034] Equation [1] describes the power loss P V (t) depending on T L and T. Equation [2] describes the relationship between T, T L and T U and is used to T L in equation [1]. This yields a second-order differential equation for the temperature T(t) as a function of time t, into which the power loss P V (t) as a function of time and the ambient temperature T U(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 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, into which the power loss P V (t) as a function of time and the ambient temperature T U (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 U (t)) which depends on the power loss P V (t) as a function of time and ambient temperature T U (t) as a function of time: f(t)=w(PV(t),TU(t))

[0035] Often the ambient temperature T U 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 ohm the square of the current I flowing in the conductor 7 and the ohmic resistance R Ohm of conductor 7. Then the comparison value f depends essentially on the square of the current I.

[0036] The comparison value f is used to detect a thermal overload of components of the switchgear 1 arranged in the gas chamber 3. Thermal overload of at least one component of the switchgear 1 arranged in the gas chamber 3 is inferred 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 chamber 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 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.

[0037] Fig. Figure 2 shows, by way of example, 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 T U(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 chamber 3 without any significant time delay. In this example, the gas pressure p(t) corresponds very well to the reference value f(t), so that no thermal overload of the components of the switchgear 1 arranged in the gas chamber 3 can be concluded.

[0038] The calculation of the comparison value described above is only an example of 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 of the insulating gas in the gas space 3. Other data sources can also be taken into account, for example measurement signals from a temperature sensor arranged in the gas space 3.The calculation of the comparison value f can then, for example, be carried out location-dependently, so that the calculation yields a result according to equation [5] instead of equation [4]:. f(t,x)=w(PV(t,x),TU(t),TS(t))

[0039] Here, x denotes a location coordinate from which the power loss P V and the comparison value f depend, and T S refers 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).

[0040] 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.

[0041] 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.

[0042] Regardless of the grammatical gender of a particular term, it includes persons with male, female or other gender identities. List of reference symbols 1 switchgear 3 Gas chamber 5 gas tanks 7 ladders 9 Device for detecting thermal overload of switchgear components 11 Current sensor 13 Pressure sensor 15 Temperature sensor 17 Computing unit f comparison value I Current p gas pressure t time T Temperature T U Ambient temperature

Claims

[1] Method 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), 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 reference value (f), characterized by that 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). [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 (T U ) of an environment of the switchgear (1) and the comparison value (f) is determined as a function of the currents (I) flowing in the gas space (3) and the ambient temperature (T U ) is determined. [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 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. [6] 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). [7] 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. [8] 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. [9] Device (9) for carrying out the method according to one of the preceding claims 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 electric current (I) flows in an electrical conductor (7), the device (9) comprising - a pressure sensor (13) which is arranged to measure a gas pressure (p) in the gas space (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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