Electrical apparatus, method for determining an occurrence of a hotspot and use of a gas thermometer for determining an occurrence of a hot spot

Abstract

The invention relates to an electrical apparatus (10) comprising an electrically isolated enclosure and at least one electrical component (12) inside the enclosure, wherein the apparatus (10) comprises a gas thermometer (16) for determining a temperature inside the enclosure, wherein the gas thermometer (16) is configured as constant volume thermometer and comprises a sealed tube (18) and a pressure sensor (20) arranged at a first end of the tube (18) for detecting pressure changes of a gas inside the tube (18), and wherein the tube (18) is arranged such that at least the first end is outside the enclosure and further parts of the tube (18) are at least partly arranged in-side the enclosure. Furthermore, the invention relates to a method for determining an occurrence of a hot spot inside an electrically isolated enclosure of the above electrical apparatus (10), comprising the steps of - receiving pressure data from the pressure sensor (20) of the gas thermometer (16), and - determining the occurrence of a hot spot inside the enclosure based on the received pressure data. Furthermore, the invention relates to the use of a gas thermometer (16) configured as constant volume thermometer for determining an occurrence of a hot spot inside an electrically isolated enclosure of an electrical apparatus (10).

Description

[0001] 1 P240081W001

[0002] Description

[0003] Electrical apparatus, method for determining an occurrence of a hotspot and use of a gas thermometer for determining an occurrence of a hot spot

[0004] Technical Field

[0005] The invention relates to an electrical apparatus comprising an electrically isolated enclosure and at least one electrical component inside the enclosure.

[0006] Furthermore, the invention relates to a method for determining an occurrence of a hot spot inside an electrically isolated enclosure of an electrical apparatus.

[0007] Furthermore, the invention relates to a use of a gas thermometer for determining an occurrence of a hot spot inside an electrically isolated enclosure of an electrical apparatus.

[0008] Background Art

[0009] Methods for determining the occurrence of hot spots are of electrical apparatus are known in the art. For example, a temperature with optical means such as an IR camera, or FLIR camera can be use, or a resistance thermometer can be used to measure the temperature at the electrical apparatus.

[0010] However, in case the hot spot occurs inside an enclosure the above methods can either not detect the hot spot at all, or only very delayed at a time when the electrical apparatus may already be in a critical condition due to overheating.

[0011] Moreover, if the hot spot is inside electrically isolated enclosure of an electrical apparatus, in particular for cases where the isolation is performed by liquids, gases, and / or by compartmentalizing the apparatus, hot spot detection becomes even more challenging. In such cases, it is very difficult to detect the hot spot while the electrical apparatus is in operation. Therefore, means to simplify hot spot detection are desirable. 2 P240081W001

[0012] Summary of invention

[0013] It is an object of the invention to provide means to improve the detection of hot spots in particular inside electrically isolated enclosures. It is a further object of the invention to provide means to determining the temperature inside the enclosure.

[0014] The object of the invention is solved by the features of the independent claims. Modified embodiments are detailed in the dependent claims.

[0015] Thus, the object is solved by an electrical apparatus comprising an electrically isolated enclosure and at least one electrical component inside the enclosure, wherein the apparatus comprises a gas thermometer for determining a temperature inside the enclosure, wherein the gas thermometer is configured as constant volume thermometer and comprises a sealed tube and a pressure sensor arranged at a first end of the tube for detecting pressure changes of a gas inside the tube, and wherein the tube is arranged such that at least the first end is outside the enclosure and further parts of the tube are at least partly arranged inside the enclosure.

[0016] Additionally, the object is solved by a method for determining an occurrence of a hot spot inside an electrically isolated enclosure of an electrical apparatus, wherein the electrical apparatus is configured as described above, comprising the steps of

[0017] - receiving pressure data from a pressure sensor of the gas thermometer, and

[0018] - determining the occurrence of a hot spot inside the enclosure based on the received pressure data.

[0019] Furthermore, the object is solved by the use of a gas thermometer configured as constant volume thermometer for determining an occurrence of a hot spot inside an electrically isolated enclosure of an electrical apparatus. Particularly preferably the object is solved by the use of the gas thermometer configured as constant volume thermometer for determining an occurrence of a hot spot inside an enclosure of a power semiconductor module. 3 P240081W001

[0020] One aspect of the invention is that a gas thermometer configured as constant volume thermometer is used. Such a gas thermometer is also called pressure thermometer and measures the temperature by changes in the pressure of a gas kept at an essentially constant volume. The essentially constant volume is preferably provided by the sealed tube. Essentially constant volume preferably means that the volume is constant ± 5%, preferably constant ± 3%, and even more preferably constant ± 1 % over the temperature range determined by the gas thermometer. Tube in the sense of this application means a geometry that is significantly longer in one dimension than in two other orthogonal dimensions. The tube is preferably hollow and thus provides the essentially constant gas volume. A cross section of the tube can in principle have any form such as oval, round, squarish, and is not necessarily circular. The changes in pressure of the gas inside the tube is preferably detected by the pressure sensor arranged at one end of the tube.

[0021] As the tube of the gas thermometer is arranged such that at least the first end - i.e. the end of the tube where the pressure sensor is arranged - is outside the enclosure and further parts of the tube are at least partly arranged inside the enclosure, it is possible to detect a hot spot inside the electrically isolated enclosure without deteriorating the electrical isolation. Preferably, when the electrical component inside the enclosure generates heat, the part of the tube that is arranged inside the enclosure is heated up, which leads to an expansion of the gas inside the tube. The rise in pressure can easily be detected by the pressure sensor located at the first end of the tube outside of the enclosure. Thus, it is possible to determining the occurrence of a hot spot inside the enclosure based on the pressure data received from the pressure sensor.

[0022] The part of the tube that is arranged inside the enclosure can be arranged inside the enclosure in different patterns. It is possible that the tube meanders within the enclosure or loops horizontally and / or vertically through the enclosure. Preferably, the part of the tube inside the enclosure has a length of at least 30%, preferably at least 50 % of a longest distance across the enclosure. Thus, it is possible to detect the occurrence of a hot spot at different locations inside the enclosure.

[0023] According to a further preferred embodiment of the invention all the further parts of 4 P240081W001 the tube expect for the first end are arranged inside the enclosure. In other words, in this preferred embodiment only the first end is located outside the enclosure. In an alternative embodiment of the invention, the first end and a second end of the tube opposite to the first end are located outside of the enclosure, wherein a middle part of the tube is arranged inside the enclosure.

[0024] According to a preferred embodiment of the invention, an external surface of the tube and / or the tube comprises an electrical insulation material. Further preferably the external surface of the tube and / or the tube consists of the electrical insulation material. This has the advantage that the tube can be arrange in direct contact to the electrical component without disturbing the electrical isolation of the apparatus. The electrical insulation material is preferably a plastic material such as PTFE or PVC, a rubber material, glass and / or ceramics. The tube is preferably configured to provide the essentially constant volume throughout the expected temperature range. The material of the tube can provide the tube with a certain flexibility which may simplify manufacturing of the apparatus. Alternatively, the material of the tube may provide the tube with a rigidity, which may increase the accuracy of the temperature determination.

[0025] According to a preferred embodiment of the invention, the tube is arranged such that the external surface of the tube is in contact to the at least one electrical component inside the enclosure. As the tube and the electrical component are in direct contact the heat transfer from the electrical component as heat source to the tube is high. This has the advantage that detection of the hot spot is fast and the electrical apparatus or its components may be shut down before a critical condition due to overheating is reached.

[0026] The gas inside the tube can in principle be any gas or gas mixture. However, according to a preferred embodiment of the invention the gas inside the tube is selected from air, N2, CO2, SFe, fluoroketons, fluoronitriles, decafluoro-2-methylbutan- 3-one (C5-FK), heptafluoro-2-methylpropanenitrile (C4-FN), and mixtures thereof. Thus, preferably the gas inside the tube is an insulation gas.

[0027] According to another preferred embodiment of the invention, the gas thermometer 5 P240081W001 further comprises a temperature sensor arranged outside of the enclosure for calibrating the gas thermometer. With the temperature sensor outside of the enclosure the environment temperature can be determined. Thus, the gas thermometer not only allows to determine the occurrence of a hot spot inside the enclosure, but also allows to determine the temperature of the hot spot. The temperature outside the enclosure can be configured as electrical temperature sensor, e.g. as thermistor, thermocouple, resistance thermometer or silicon bandgap temperature sensor. In other words, the gas thermometer preferably comprises an additional environment temperature sensor to preferably continuously calibrate the pressure measured by the pressure sensor with the environment temperature. Even though the tube is sealed, the gas inside the tube might dissipate. It is preferred that in cyclic calibration routines, the gas thermometer measures the environment temperature and performs a calibrated with the pressure of the gas in the tube measured by the pressure sensor.

[0028] According to another preferred embodiment of the invention the gas thermometer further comprises a second temperature sensor for determining a gas temperature of the gas inside the tube at the first end. By a combined measurement of the gas pressure over time with the pressure sensor and the gas temperature over time with the second temperature sensor, it is possible to estimate the location of the hot spot along the tube, as pressure expansion and temperature convection spread with different velocities.

[0029] According to another preferred embodiment of the invention the gas thermometer comprises a second pressure sensor at a second end of the tube for detecting pressure changes of the gas inside the tube. A further possibility to determine the location of the hot spot along the tube is by using two pressure sensors at opposite ends of the tube. In other words, by a combined measurement of the gas pressure over time with the two pressure sensors, it is possible to estimate the location of the hot spot along the tube.

[0030] Regarding the electrical apparatus and according to another preferred embodiment of the invention, it is preferred that the electrical apparatus comprises several electrical components inside the enclosure and that the tube is arranged such that an 6 P240081W001 external surface of the tube is in contact to more than one of the electrical components and preferably all the electrical components inside the enclosure. In other words, with this arrangement it is possible to detect the occurrence of a hot spot inside the enclosure comprising multiple electrical components with only one tube. This has the advantage that it is very cost efficient.

[0031] According to an alternative embodiment of the invention, the electrical apparatus comprises several electrical components inside the enclosure and further comprises several gas thermometers, and wherein each tube of each gas thermometer is arranged such that an external surface of the tube is in contact to no more than one of the electrical components inside the enclosure. In this embodiment the temperature of every electrical component is probed by its own gas thermometer. This has the advantage that the determination of the location of the hot spot is very accurate.

[0032] According to another preferred embodiment of the invention, the electrical component is a power component for the control and / or conversion of electric power. Further preferably, the electrical component is a power semiconductor device, and / or the apparatus is a power semiconductor module. In particular for power semiconductor modules the determination of the occurrence of a hot spot inside the module is simplified.

[0033] It is possible that the power semiconductor module may comprise one power semiconductor device. However, it is preferred that the power semiconductor module comprises multiple power semiconductor devices. For example, the power semiconductor module comprises two, three, four, five, six, seven, eight, nine or ten power semiconductor devices. Preferably, the power semiconductor module comprises an even number of power semiconductors devices. Further preferably the power semiconductors devices are connected in parallel.

[0034] Further preferably in case the power semiconductor module comprises multiple power semiconductors devices, it is preferred that the power semiconductor devices are arranged in rows and / or columns on a substrate. This makes it especially easy to bring the tube of the gas thermometer in contact with all the power semiconductor devices. 7 P240081W001

[0035] In a further preferred embodiment of the invention the power semiconductor device is connected to a conductive area of the substrate by bond wires. Furthermore, in case the power semiconductor module comprises multiple power semiconductors devices, it is preferred that the power semiconductor devices are connected to each other by bond wires.

[0036] In this regard and according to another preferred embodiment of the invention, the electrical apparatus comprises a bond wire for electrical connection of the electrical component and the tube is arranged in direct contact to the bond wire, and preferably in between the bond wire and the electrical component. In other words, the tube is preferably integrated with the bond wire positioned on the power semiconductor device.

[0037] According to another preferred embodiment of the invention, the electrically isolated enclosure is a molded housing and the tube is integrated into the molded housing. In particular for power semiconductor modules this an easy way to mechanically affix the tube inside the enclosure.

[0038] According to a preferred embodiment of the invention the power semiconductor device is selected from any of MOSFET, IGBT, BJT, Thyristor, GTO, JFET, and diodes. Further preferably the power semiconductor device is a Silicon power semiconductor device, or a wide-bandgap power semiconductor device, for example a Silicon-Carbide power semiconductor device and / or a Gallium-Nitride power semiconductor device. This has the advantage that fast switching can be achieved.

[0039] Further preferably the power semiconductor module configured for a voltage in between 600 V to 20 kV. Further preferably the power semiconductor module comprises only few - i.e. less than 20 - wide-band gap semiconductor devices connected in parallel. 8 P240081W001

[0040] Further technical aspects and advantages of the invention will be apparent for the skilled person from the following description of the method for determining the occurrence of a hot spot inside the electrically isolated enclosure of the electrical apparatus.

[0041] As already mentioned, the object is solved by the method for determining the occurrence of a hot spot inside the electrically isolated enclosure of the above-described electrical apparatus, comprising the steps of

[0042] - receiving pressure data from the pressure sensor of the gas thermometer, and

[0043] - determining the occurrence of a hot spot inside the enclosure based on the received pressure data.

[0044] The sensitive pressure sensor will detect the pressure difference generated from temperature changes.

[0045] According to another preferred embodiment of the invention, the method further comprises the steps of

[0046] - receiving environment temperature data from a temperature sensor arranged outside of the enclosure, and

[0047] - determining a temperature of the hot spot based on the received pressure data and the received environment temperature data.

[0048] With the help of model calculations and a calibration with the environment temperate, it is possible to determine the temperature at the hot spot.

[0049] According to a preferred embodiment of the invention, the step of receiving pressure data from the pressure sensor of the gas thermometer, comprises receiving time resolved pressure data. This makes it possible to determine how fast the pressure inside the tube and thus the temperature inside the enclosure changes. Preferably the time resolved pressure data is taken into account for determining the occurrence of the hot spot inside the enclosure. To take the change of the pressure into account makes the method less sensitive to potential diffusion processes of the gas through the wall of the tube. Even though the tube is sealed, some gas might get lost by 9 P240081W001 propagating through the walls of the tube by diffusion. However, as diffusion of gas is a slower process than the pressure change inside the tube, the determination of the hot spot is possible despite potential diffusion by taking the time resolved pressure data into account. Additionally, to take the change of the pressure into account makes the method also less sensitive to potential thermal contraction / elongation of the tube material, as the pressure change happens on a faster timescale than the thermal contraction / elongation.

[0050] Furthermore, it is preferred that the step of receiving environment temperature data from the temperature sensor arranged outside of the enclosure comprises receiving time resolved environment temperature data. By comparing the change of the pressure and / or temperature inside the enclosure to the change of the environment temperature, it is possible to determine if the temperature development of the hot spot is critical to the electrical component and / or the apparatus.

[0051] It is not only possible to determine the temperature of the hot spot but also the location of the hot spot along the tube can be determined. In this regard and according to another preferred embodiment of the invention the step of receiving pressure data from the pressure sensor of the gas thermometer, comprises receiving time resolved pressure data, and wherein the method comprises the further steps of

[0052] - receiving time resolved gas temperature data from a temperature sensor for determining a gas temperature of the gas inside the tube at the first end, and / or

[0053] - receiving time resolved pressure data from a second pressure sensor arranged at the second end of the tube, and

[0054] - determining a location of the hotspot along the tube based on the received time resolved pressure data from the two pressure sensors and / or based on the received time resolved pressure data from the pressure sensor and the temperature sensor.

[0055] In other words, by time resolved measurements of the pressure from two pressure sensors, and / or by time resolved measurements of the pressure sensor and the temperatures sensor, it is possible to determine the location of the hot spot. 10 P240081W001

[0056] According to another preferred embodiment of the invention, the information relating to the temperature of the hot spot and / or the location of the hot spot is digitized and communicated to a user, preferably wireless, to prevent damaging the electrical component and / or in order to maintain the energy efficiency of the electrical apparatus.

[0057] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0058] In the drawings:

[0059] Fig. 1 schematically shows an electrical apparatus with multiple electrical components according to a preferred embodiment of the invention,

[0060] Fig. 2 schematically shows a cross section through one of the electrical components of figure 1 .

[0061] Description of embodiments

[0062] Figure 1 schematically shows an electrical apparatus 10 comprising six electrical components 12. The electrical apparatus 10 is configured as power semiconductor module 10, and the electrical components 12 are power semiconductor devices 12 - in this example MOSFETs that are attached to a conductive area 14 of the apparatus 10. Even though not directly shown in figure 1 , the power semiconductor devices 12 are enclosed in an electrically isolated enclosure, in this embodiment a molded housing of the power semiconductor module.

[0063] The power semiconductor module 10 comprises a gas thermometer 16 for determining a temperature inside the housing. In particular the gas thermometer 16 is configured as constant volume thermometer and comprises a sealed tube 18 and a pressure sensor 20 arranged at a first end of the tube 18 for detecting pressure changes of a gas inside the tube. As can be seen in figure 1 , the tube 18 is arranged such that at least the first end is outside the housing and that the further parts of the tube 18 are arranged inside the housing. The tube 18 is also arranged such that it 11 P240081W001 meanders inside the housing, and further such that all of the six semiconductor devices 12 are in contact to the tube 18.

[0064] As also seen in figure 2, which shows a cross section through one of the power semiconductor devices 12, in this embodiment the tube 18 is arranged such that an external surface 22 of the tube 18 is in contact to the power semiconductor device 12. In order not to disturb the electrical isolation, the external surface 22 of the tube is made of an insulating material, in this embodiment PTFE. The power semiconductor device 12 is connected to the conductive area 14 of by bond wires 24. The tube 18 is arranged in direct contact to the bond wire 24, and in between the bond wire 24 and the power semiconductor device 12.

[0065] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosed, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.

[0066] 12 P240081W001

[0067] Reference signs list

[0068] Reference signs list

[0069] 10 electrical apparatus, power semiconductor module

[0070] 12 electrical component, power semiconductor device

[0071] 14 conductive area

[0072] 16 gas thermometer 18 tube

[0073] 20 pressure sensor

[0074] 22 external surface of tube

[0075] 24 bond wires

Claims

13 P240081W001Claims1. Electrical apparatus (10) comprising an electrically isolated enclosure and at least one electrical component (12) inside the enclosure, wherein the apparatus (10) comprises a gas thermometer (16) for determining a temperature inside the enclosure, wherein the gas thermometer (16) is configured as constant volume thermometer and comprises a sealed tube (18) and a pressure sensor (20) arranged at a first end of the tube (18) for detecting pressure changes of a gas inside the tube (18), and wherein the tube (18) is arranged such that at least the first end is outside the enclosure and further parts of the tube (18) are at least partly arranged inside the enclosure.

2. Electrical apparatus (10) according to claim 1 , wherein an external surface (22) of the tube (18) and / or the tube (18) comprises, and preferably consists of an electrical insulation material.

3. Electrical apparatus (10) according to any of the previous claims, wherein the tube (18) is arranged such that an external surface (22) of the tube (22) is in contact to the at least one electrical component (12) inside the enclosure.

4. Electrical apparatus (10) according to any of the previous claims, wherein the gas inside the tube (18) is selected from air, N2, CO2, SFe, fluoroketons, fluoronitriles, decafluoro-2-methylbutan-3-one (C5-FK), heptafluoro-2-methylpro- panenitrile (C4-FN), and mixtures thereof.

5. Electrical apparatus (10) according to any of the previous claims, wherein the gas thermometer (16) further comprises a temperature sensor arranged outside of the enclosure for calibrating the gas thermometer (16).

6. Electrical apparatus (10) according to any of the previous claims, wherein the14 P240081W001 gas thermometer (16) further comprises a second temperature sensor for determining a gas temperature of the gas inside the tube (18) at the first end.

7. Electrical apparatus (10) according to any of the previous claims, wherein the gas thermometer (16) comprises a second pressure sensor at a second end of the tube (18) for detecting pressure changes of the gas inside the tube (18).

8. Electrical apparatus (10) according to any of the previous claims, wherein the electrical apparatus (10) comprises several electrical components (12) inside the enclosure and wherein the tube (18) is arranged such that an external surface (22) of the tube (18) is in contact to more than one of the electrical components (12) and preferably all the electrical components (12) inside the enclosure.

9. Electrical apparatus (10) according to any of claims 1 to 7, wherein the electrical apparatus (10) comprises several electrical components (12) inside the enclosure and further comprises several gas thermometers (16), and wherein each tube (18) of each gas thermometer (16) is arranged such that an external surface (22) of the tube (18) is in contact to no more than one of the electrical components (12) inside the enclosure.

10. Electrical apparatus (10) according to any of the previous claims, wherein the electrical component (12) is a power component for the control and / or conversion of electric power, and / or wherein the electrical component is a power semiconductor device (12), and / or wherein the apparatus (10) is a power semiconductor module (10).

11. Electrical apparatus (10) according to any of the previous claims, wherein the electrical apparatus (10) comprises a bond wire (24) for electrical connection of the electrical component (12) and wherein the tube (18) is arranged in direct contact to the bond wire (24).

12. Method for determining an occurrence of a hot spot inside an electrically isolated enclosure of an electrical apparatus (10), wherein the electrical apparatus (10) is configured according to any of the preceding claims, comprising the steps of15 P240081W001- receiving pressure data from the pressure sensor (20) of the gas thermometer (16), and- determining the occurrence of a hot spot inside the enclosure based on the received pressure data.

13. Method according to the previous claim, wherein the method further comprises the steps of- receiving environment temperature data from a temperature sensor arranged outside of the enclosure, and- determining a temperature of the hot spot based on the received pressure data and the received environment temperature data.

14. Method according to any of the previous method claims, wherein the step of receiving pressure data from the pressure sensor (20) of the gas thermometer (16), comprises receiving time resolved pressure data.

15. Method according to the previous method claim, and wherein the method comprises the further steps of- receiving time resolved gas temperature data from a temperature sensor for determining a gas temperature of the gas inside the tube (18) at the first end, and / or- receiving time resolved pressure data from a second pressure sensor arranged at the second end of the tube (18), and- determining a location of the hotspot along the tube (18) based on the received time resolved pressure data from the two pressure sensors and / or based on the received time resolved pressure data from the pressure sensor (20) and the temperature sensor.

16. Use of a gas thermometer (16) configured as constant volume thermometer for determining an occurrence of a hot spot inside an electrically isolated enclosure of an electrical apparatus (10), and preferably inside an enclosure of a power semiconductor module (10).

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