A method for estimating a current state of an electrical contact of a switchgear by an electronic computing device, computer program product, computer-readable storage medium, as well as electronic computing device

Abstract

The invention relates to a method for estimating a current state (22) of an electrical contact (12) of a switchgear (10) by an electronic computing device (16), comprising the steps of: providing a temperature model (18) of the electrical contact (12) by the electronic computing device (16); providing an aging model (20) of the electrical contact (12) by the electronic computing device (16); estimating a temperature of the electrical contact (12) depending on at least one parameter (24) of the electrical contact (12) by the temperature model (18); estimating the aging of a contact element (14) of the electrical contact (12) depending on at least the estimated temperature by the aging model (20); and estimating the current state (22) of the electrical contact (12) depending on the estimated aging of the contact element (14) by the electronic computing device (16). Furthermore, the present invention relates to a computer program product, a computer-readable storage medium, as well as to an electronic computing device (16).

Description

[0001] Description

[0002] A method for estimating a current state of an electrical contact of a switchgear by an electronic computing device, computer program product, computer-readable storage medium, as well as electronic computing device

[0003] The present invention relates to a method for estimating a current state of an electrical contact of a switchgear by an electronic computing device according to pending claim 1. Furthermore, the present invention relates to a corresponding computer program product, a corresponding computer-readable storage medium, as well as to a corresponding electronic computing device.

[0004] Thermal faults, especially at fixed, sliding or spring-pressed electrical contacts, are a major root cause compromising the safe operation of switchgears. The faults are costly and need to be prevented.

[0005] The early knowledge of such a fault is therefore of great use. This enables a system operator to send service personal, maintaining the connection. The knowledge of the aging behavior is a very important piece of information to estimate the fault probability. Aging of contacts, depending on temperature, environmental conditions, and other factors, is complicated. Therefore, a robust and reliable model is necessary.

[0006] In the state of the art, temperature sensors are mounted to detect thermal faults. These sensors, located on critical positions like the cable connection, provide a temperature information which can then be further evaluated. Further evaluation can be a comparison to neighboring phases or any kind of statistics as part of a health index.

[0007] The problem there is that the aging information may be contained in the temperature information, but is well hidden, connected via non-linear multiple input relationships. It may be possible to learn such a relationship over time with neural networks. But a sufficiently high amount of training data due to the complexity of the problem would be required.

[0008] It is an object of the present invention to provide a method, a computer program product, a computer-readable storage medium, as well as an electronic computing device, by which a current state of a switching element can be estimated in an improved manner. This object is solved by a method, a computer program product, a computer-readable storage medium, as well as an electronic computing device according to the independent claims. Advantageous embodiments are presented in the dependent claims.

[0009] One aspect of the invention relates to a method for estimating a current state of an electrical contact of a switchgear by an electronic computing device. A temperature model of the electrical contact is provided by the electronic computing device. An aging model of the electrical contact is provided by the electronic computing device. A temperature of the electrical contact is estimated depending on at least one parameter of the electrical contact by the temperature model. The aging of the contact element of the electrical contact is estimated depending on at least the estimated temperature by the aging model. The current state of the electrical contact is estimated depending on the estimated aging of the contact element by the electronic computing device.

[0010] Models for contact aging are already known. Contact aging is represented by an Arrhenius equation from Stephan Schlegel - Kontakt- und Langzeitverhalten stromfuhrender Verbindungen in der Elektroenergietechnik. ISBN 978-3-662-64657-1

[0011] The aging parameters b, m, d are determined experimentally. The problem is that the accelerated aging, which is of interest for condition monitoring / online monitoring, occurs in the nonlinear part of the exponential function. The aging of the contact points is mainly dependent on the activation energy and thus the temperature TE at the contact point and environmental parameters. If one wants to make a statement about the condition of the contacts, the error of such a model can become very large over time.

[0012] The idea is to validate the support points of the exponential function with a measurement adjustment to counteract false-positive or negative model developments. The approach consists of two models, in particular the temperature model and the aging model. Therefore, an accurate prediction of the contact health and aging is provided, and therefore prevention of possible faults is provided.

[0013] The accuracy is even valid for the single asset as no kind of generalizing statistics is used.

[0014] Instead, basic physical formulas are utilized. The free parameters of such a formula are adapted to the specific switchgear. Due to this approach, a high accuracy, in particular better than current solutions based on statistics, can be achieved and a rather low amount of training data, in particular for pure artificial intelligence based approaches, is required. Especially, no fault data is required, often difficult to get.

[0015] In particular, depending on the estimated state of the electrical contact, a state of the switchgear can be estimated. Furthermore, this information can be used in order to generate alarm messages for service personnel or in order to shut down for example the complete switchgear or to initiate counter measures, for example extinguishing counter measures.

[0016] According to an embodiment, the temperature model is provided as a data-based model and / or a three-dimensional multiphysics model and / or a thermal (network) model. Therefore, different models can be used in order to precisely estimate the temperature of the electrical contact. Therefore, an improved estimation of the current state of the electrical contact is provided.

[0017] In another embodiment, the temperature is estimated depending on an electric current and / or an electric voltage and / or an ambient temperature in the electrical contact as the at least one parameter. In particular, the presented parameters are parameters which have a high impact on the aging of the electrical contact. Therefore, by taking into consideration these parameters, a precise estimation of the state of the electrical contact is provided.

[0018] In another embodiment, the temperature model is provided depending on an initial installation of the electrical contact. For example, the temperature model is calibrated during commissioning and forms a so-called ..thermal twin" that accurately replicates the thermal / electrical resistances of the conductors and adapts contact resistances through calibration during commissioning, in particular with no aged contact elements. The model can infer the roughly discretized conductor temperature at specific points of interest using the current and ambient temperature. Therefore, a precise estimating of the state of the electrical contact can be provided.

[0019] In another embodiment, the aging model models a long-term behavior of the electrical contact. Therefore, a long-term behavior of the electrical contact can be provided depending on the before-mentioned parameters. Therefore, the state of the electrical contact can be precisely determined over a long-term life of the electrical contact.

[0020] In another embodiment, the aging model is provided depending on an initial installation of the electrical contact. Therefore, the aging model utilizes commonly used aging models for long- term behavior of electric contacts. The starting values of the contact resistances are approximately known due to the calibration of the temperature model or measurement at commissioning, maintenance or production. The conductor temperatures are known through measurement or modelling. The temperature at the contact spot can be calculated by taking the thermal / electrical resistance of the contact itself into account. By using additional simple thermal network of a contact point and the known current, the expected contact temperature can be inferred, which is used as an input for the aging model.

[0021] In another embodiment in predefined time frames an actual temperature is measured and the actual temperature is compared with an estimated temperature. In particular, at regular time intervals, the actual measured temperature is compared to the temperature of the temperature model and the contact aging model to check for any deviation. This difference can then be used to infer the actual contact aging and improve the ..inaccurate" model.

[0022] In another embodiment, depending on the comparison, the temperature model and the aging model are adapted. In particular, parameters of the aging model and / or the temperature model can be adapted depending on the comparison. Therefore, the models can be adapted and a more precise estimating of the state of the electrical contact can be provided.

[0023] In another embodiment, the comparison is performed during high loads at the electrical contact. In particular, it does not make sense to search for errors at low loads as resistances are not stressed. This can in particular be done by least squares fit or generic algorithms for the parameters d, b, m.

[0024] According to another embodiment, detected events at the electrical contact are taken into consideration by estimating the aging of the contact element. In particular, events are delaying or accelerating aging and these can be included in the models by recalibrating the model parameters m and d. In particular, such events may have physical effects on the electrical contact and therefore can be taken into consideration.

[0025] In another embodiment, an increase of a contact force and / or a decrease of the contact force of the contact element are taken into consideration by estimating the aging of the contact element. Increase or decrease of contact force is changing the current density in the micro-context of the electrical contact. The contact force can decrease, for example due to degradation of springs. Service can reestablish the initial contact force. This may be easy in a sudden decrease of temperature under identical load conditions and can be taken into account automatically by triggering re-calibration.

[0026] In another embodiment, environmental conditions of the electrical contact are taken into consideration by estimating the aging of the contact element. For example, pollution of the contact element, for example with degradation products of polymeric insulators, salt-fog, e.g. in a marine environment, dust, e.g. in an industrial environment, are introducing resistive layers on the clean metal surface. Servicing the contact(s) may remove resistive layers, thus reducing contact resistance. This can automatically be taken into account by triggering re-calibration upon sudden temperature decrease under identical load conditions.

[0027] In particular, the present invention is computer-implemented method. Therefore, another aspect of the invention relates to a computer program product comprising program code means for performing a method according to the preceding aspect.

[0028] A still further aspect of the invention relates to a computer-readable storage medium comprising at least the computer program product according to the preceding aspect.

[0029] Furthermore, the present invention relates to an electronic computing device for estimating a current state of an electrical contact of a switchgear, comprising at least one temperature model of the electrical contact and at least one aging model of the electrical contact, wherein the electronic computing device is configured for performing a method according to the preceding aspect. In particular, the method is performed by the electronic computing device.

[0030] Furthermore, the present invention relates to an electrical contact comprising at least the electronic computing device. Alternatively, the present invention relates to a switchgear comprising an electrical contact according to the preceding aspect and comprising the electronic computing device according to the preceding aspect.

[0031] Advantageous embodiments of the method are to be regarded as advantageous embodiments of the computer program product, the computer-readable storage medium, the electronic computing device, the electrical contact, and the switching gear. The electronic computing device, the electrical contact, as well as the switchgear may comprise means for performing the method. A computing unit / electronic computing device may in particular be understood as a data processing device, which comprises processing circuitry. The computing unit can therefore in particular process data to perform computing operations. This may also include operations to perform indexed accesses to a data structure, for example a look-up table, LUT.

[0032] In particular, the computing unit may include one or more computers, one or more microcontrollers, and / or one or more integrated circuits, for example, one or more applicationspecific integrated circuits, ASIC, one or more field-programmable gate arrays, FPGA, and / or one or more systems on a chip, SoC. The computing unit may also include one or more processors, for example one or more microprocessors, one or more central processing units, CPU, one or more graphics processing units, GPU, and / or one or more signal processors, in particular one or more digital signal processors, DSP. The computing unit may also include a physical or a virtual cluster of computers or other of said units.

[0033] In various embodiments, the computing unit includes one or more hardware and / or software interfaces and / or one or more memory units.

[0034] A memory unit may be implemented as a volatile data memory, for example a dynamic random access memory, DRAM, or a static random access memory, SRAM, or as a non-volatile data memory, for example a read-only memory, ROM, a programmable read-only memory, PROM, an erasable programmable read-only memory, EPROM, an electrically erasable programmable read-only memory, EEPROM, a flash memory or flash EEPROM, a ferroelectric random access memory, FRAM, a magnetoresistive random access memory, MRAM, or a phase-change random access memory, PCRAM.

[0035] For use cases or use situations which may arise in a method according to the invention and which are not explicitly described herein, it may be provided that, in accordance with the method, an error message and / or a prompt for user feedback is output and / or a default setting and / or a predetermined initial state is set.

[0036] Independent of the grammatical term usage, individuals with male, female or other gender identities are included within the term.

[0037] Further features and feature combinations of the invention are obtained from the figures and their description as well as the claims. In particular, further implementations of the invention may not necessarily contain all features of one of the claims. Further implementations of the invention may comprise features or combinations of features, which are not recited in the claims.

[0038] Therefore, the figures show in:

[0039] FIG 1 a schematic block diagram according to the embodiment of a switchgear comprising an embodiment of an electrical contact comprising an embodiment of an electronic computing device; and

[0040] FIG 2 a schematic flow chart according to an embodiment of the method.

[0041] In the following, the invention will be explained in detail with reference to specific exemplary implementations and respective schematic drawings. In the drawings, identical or functionally identical elements may be denoted by the same reference signs. The description of identical or functionally identical elements is not necessarily repeated with respect to different figures.

[0042] FIG 1 shows a schematic block diagram according to an embodiment of a switchgear 10. The switchgear 10 comprises in this embodiment two electrical contacts 12. The electrical contacts 12 are comprising each at least a contact element 14. Furthermore, the switchgear 10 comprises an electronic computing device 16. In an alternative embodiment, the electronic computing device 16 can be formed for and as a part of the electrical contact 12. The electronic computing device 16 comprises at least one temperature model 18 and one aging model 20.

[0043] According to an embodiment, a method for estimating a current state 22 of the electrical contact 12 of the switchgear 10 is provided. The temperature model 18 as well as the aging model 20 are provided by the electronic computing device 16. A temperature of the electrical contact 12 is estimated depending on at least one parameter 24 of the electrical contact 12 by the temperature model 18. The aging of the contact element 14 of the electrical contact 12 is estimated depending on at least the estimated temperature by the aging model 20 and the current state 22 is estimated depending on the estimated aging of the contact element 14 by the electronic computing device 16.

[0044] In particular, the temperature model 18 is provided as a data-based model and / or a three- dimensional multiphysics model and / or a thermal (network) model. Furthermore, the temperature may be estimated depending on an electric current and / or an electric voltage and / or an ambient temperature in the electrical contact 12 as the at least one parameter 24. In another embodiment, the temperature model 18 is provided depending on an initial installation of the electrical contact 12. Furthermore, the aging model 20 models a long-term behavior of the electrical contact 12. Furthermore, the aging model 20 is provided depending on an initial installation of the electrical contact 12.

[0045] In another embodiment, in predefined time frames an actual temperature is measured and the actual temperature is compared with the estimated temperature. Therefore, depending on the comparison, the temperature model 18 and / or the aging model 20 may be adapted. Furthermore, the comparison performed during high loads at the electrical contact 12.

[0046] In another embodiment, detected events at the electrical contact 12 are taken into consideration by estimating the aging of the contact element 14. Furthermore, an increase of a contact force and / or a decrease of the contact force of the contact element 14 are taken into consideration by estimating the aging of the contact element 14. Furthermore, environmental conditions of the electrical contact 12 are taken into consideration by estimating the aging of the contact element 14.

[0047] In particular, models for contact aging are already known in the state of the art. Contact aging is represented by for example an Arrhenius equation from Stephan Schlegel - Kontakt- und Langzeitverhalten stromfuhrender Verbindungen in der Elektroenergietechnik. ISBN 978-3-662- 64657-1 :

[0048] The aging parameters b, m, and d are determined experimentally. The problem is that the accelerated aging, which is of interest for condition monitoring / online monitoring, occurs in the nonlinear part of the exponential function. The aging of the contact element 14 is mainly dependent on the activation energy and thus the temperature TE at the contact point and environmental parameters. If one wants to make a statement about the condition of the contact element 14, the error of such a model can become very large over time.

[0049] The idea is to validate the support points of the exponential function with a measurement adjustment to counteract false-positive or negative model developments. The approach consists of two models, in particular the temperature I model 18 and the aging model 20. The temperature model 18 is calibrated during commissioning and forms a ..thermal twin" that accurately replicates the thermal / electrical resistances of the conductors and adapts contact resistances through calibration during commissioning, in particular with a non-aged contact element 14. The temperature model 18 can infer the roughly discretized conductor temperature at specific points of interest using the current and ambient temperature.

[0050] The aging model 20 utilizes commonly used aging models for the long-term behavior of electrical contacts. The starting values of the contact resistances are approximately known due to the calibration of the temperature model 18 or measurement at commissioning / maintenance. The conductor temperatures are known through measurement of modelling. The temperature at the contact element 14 can be calculated by taking the thermal / electrical resistance of the contact itself into account. By using an additional simple temperature model 18 of the contact element 14 and the known current, the expected contact temperature can be inferred, which is used as an input for the aging model 20.

[0051] At regular intervals, the actual measured temperature is compared with the temperature of the estimated temperature model 18 and the aging model 20 to check for any deviation. This difference can then be used to infer the actual contact aging and improve the ..inaccurate" models.

[0052] At specific points, for example every two weeks, the difference between the temperature model 18 and the aging model 20 and the measured values is calculated. This allows for the adjustment of resistances and correction of aging. It does not make sense to search for errors at low loads as resistances are not stressed. This can be done by least squares fit or generic algorithms for d, b, m.

[0053] Therefore, for example the temperature model 18 may report high loads (time) for calibration model reference points. Furthermore, interruptions can be calculated, in particular, when it makes sense to update contacts, in particular constantly, or how big the change has to be. This can then be reported to the aging model 20.

[0054] FIG 2 shows a schematic flow chart according to an embodiment of the method. In a first step S1 the method starts with a good guess of the parameter set. The aging model 20 calculates the aging based on measured temperatures. The first step S1 initiates the second step S2. In the second step S2, the temperature model 18 and the aging model 20 calculate the temperatures of the switchgear 10. Furthermore, a deviation to measured values may be provided in the second step S2. Then, thermal simulation 26 is performed.

[0055] In a third step S3, aging parameters are matched to the actual values. Based on high points in time where high current was measured the third step S3 is performed. Then an aging simulation 28 is performed and after that a fourth step S4 is performed.

[0056] In the fourth step S4 the aging model 20 calculates the aging based on the temperature model 18 or measured temperatures. After the fourth step S4 a recalibration 30 may be performed and the method starts again with the second step S2.

[0057] In particular, events delaying or accelerating aging can be included in the models 18, 20 by recalibrating the model parameters m, and d. Such events or physical effects are for example the increase or decrease of contact force changing the current density in the micro-contacts. The contact force can decrease, for example due to degradation of springs. Service can be reestablish the initial contact force. This would easily be seen in a sudden decrease of temperature under identical load conditions and can be taken into account automatically by triggering recalibration. Furthermore, the pollution of the contact element 14 may have a physical effect, for example with the degradation products of polymeric insulators, salt-fog, dust, introducing resistive layers on the clean metal surface. Servicing the contact would remove resistive layers, thus reducing contact resistance. This can automatically be taken into account by triggering recalibration upon sudden temperature decrease under identical load conditions.

[0058] List of Reference

[0059] 10 switchgear

[0060] 12 electrical contact

[0061] 14 contact element

[0062] 16 electronic computing device

[0063] 18 temperature model

[0064] 20 aging model

[0065] 22 state

[0066] 24 parameter

[0067] 26 thermal simulation

[0068] 28 aging simulation

[0069] 30 recalibration

[0070] S1-S4 steps of the method

Claims

Patent claims1. A method for estimating a current state (22) of an electrical contact (12) of a switchgear (10) by an electronic computing device (16), comprising the steps of:- providing a temperature model (18) of the electrical contact (12) by the electronic computing device (16);- providing an aging model (20) of the electrical contact (12) by the electronic computing device (16);- estimating a temperature of the electrical contact (12) depending on at least one parameter (24) of the electrical contact (12) by the temperature model (18);- estimating the aging of a contact element (14) of the electrical contact (12) depending on at least the estimated temperature by the aging model (20); and- estimating the current state (22) of the electrical contact (12) depending on the estimated aging of the contact element (14) by the electronic computing device (16).

2. The method according to claim 1 , wherein the temperature model (18) is provided as a data-based model and / or a three-dimensional multiphysics model and / or a thermal model.

3. The method according to claim 1 or 2, wherein the temperature is estimated depending on an electric current and / or an electric voltage and / or an ambient temperature in the electrical contact (12) as the at least one parameter (24).

4. The method according to any one of claims 1 to 3, wherein the temperature model (18) is provided depending on an initial installation of the electrical contact (12).

5. The method according to any one of claims 1 to 4, wherein the aging model (20) models a long-term behavior of the electrical contact (12).

6. The method according to any one of claims 1 to 5, wherein the aging model (20) is provided depending on an initial installation of the electrical contact (12).

7. The method according to any one of claims 1 to 6, wherein in predefined time frames an actual temperature is measured and the actual temperature is compared with the estimated temperature.

8. The method according to claim 7, wherein depending on the comparison the temperature model (18) and / or the aging model (20) are adapted.

9. The method according to claim 7 or 8, wherein the comparison is performed during high loads at the electrical contact (12).

10. The method according to any one of claims 1 to 9, wherein detected events at the electrical contact (12) are taken into consideration by estimating the aging of the contact element (14).

11. The method according to any one of claims 1 to 10, wherein an increase of a contact force and / or a decrease of the contact force of the contact element (14) are taken into consideration by estimating the aging of the contact element (14).

12. The method according to any one of claims 1 to 11 , wherein environmental conditions of the electrical contact (12) are taken into consideration by estimating the aging of the contact element (14).

13. A computer program product comprising program code means for performing a method according to any one of claims 1 to 12.

14. A computer-readable storage medium comprising at least the computer program product according to claim 13.

15. An electronic computing device (16) for estimating a current state (24) of an electrical contact (12) of a switchgear (10), comprising at least one temperature model (18) of the electrical contact (12) and at least one aging model (20) of the electrical contact (12), wherein the electronic computing device (16) is configured for performing a method according to any one of claims 1 to 12.

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