Method for operating a switching device in a temporary electrical overload

Abstract

The invention relates to a method for operating a switching device (1) in a temporary electrical overload, having the following steps: - detecting (61), by means of a current sensor (7), a temporal current curve (I(t)) of a current (I) that flows through the switching device (1) during operation of the switching device (1); - detecting (62), by means of a second temperature sensor (4), an ambient temperature curve over time (T_amb(t)) of an ambient temperature (T_amb) of the switching device (1) that prevails in the surroundings of the switching device during operation of the switching device (1); - receiving (63) the detected current curve (I(t)) and the detected ambient temperature curve (T_amb(t)) as input values from an electronic computing device (8); - calculating (64), by means of the electronic computing device (8), a temporal component temperature curve (θ(t)) of the component temperature (θ) of the at least one component (11, 12) of the switching device (1) using a thermal model that has been created for the switching device (1) according to a method according to one of claims 1 to 4; and - allowing (65), by means of the electronic computing device (8), an electrical overload operation of the switching device (1) only as long as the component temperature (θ) calculated for the at least one component (11, 12) does not exceed a temperature limit value (θmax) defined for the at least one component (11, 12).

Description

[0001] Description

[0002] Method for operating a switching device in a temporary electrical overload

[0003] Technical field

[0004] The present invention relates to a method for creating a thermal model of a switching device and a method for operating a switching device in a temporary electrical overload.

[0005] Technical background

[0006] Switching devices such as circuit breakers, load switches, and load disconnectors are qualified and approved under maximum load conditions as part of type testing. These type tests verify, among other things, the steady-state (static) conditions of a switching device, such as self-heating, which occur under maximum load conditions, i.e., at a maximum permissible ambient temperature during continuous operation with a maximum permissible current. An electrical current through a switching device, which is interrupted or enabled by a switching operation of the device, is also referred to as primary current or load current.

[0007] In reality, however, switching devices are often operated neither a) at a maximum permissible ambient temperature nor b) continuously, but rather a) at ambient temperatures lower than a maximum permissible ambient temperature and b) intermittently, e.g., in the case of switching devices for arc furnaces. As a result, switching devices often do not heat up to a maximum permissible temperature, but remain significantly cooler. A temporary electrical overload of a switching device, i.e., a temporary operation of a switching device above a current value that a manufacturer specifies as the maximum permissible continuous operating current (usually the rated current), is therefore technically quite possible. Such temporary overload operation is required by many switching device operators from the manufacturers and is also implemented in practice.

[0008] To ensure the safe handling of temporary electrical overloads in switching devices, temperatures at critical components must not reach or exceed predefined limits. Currently, the actual temperature of thermally critical components is measured and monitored by sensors (temperature measurement) to terminate the temporary overload operation if the temperature of a critical component reaches or exceeds a predefined limit. However, since critical components of switching devices can be at high voltage potential during operation, temperature measurement is not straightforward and is often costly. Furthermore, for example, with radio-based temperature measurement, the sampling of temperature values ​​can be susceptible to interference, and the sampling rate can be relatively slow.

[0009] Summary of the invention

[0010] The object of the present invention is to improve the temporary electrical overload operation of switching devices.

[0011] This problem is solved according to the invention by a method with the features specified in claim 1. The method serves to create a thermal model of a switching device using an electronic computing device. The method comprises a step in which a current sensor is used to detect the current profile over time of a current flowing through the switching device during its operation. The method comprises a step in which a second temperature sensor is used to detect the ambient temperature profile over time of the ambient temperature prevailing in the vicinity of the switching device during its operation.The method comprises a step in which a first temperature sensor is used to record the temperature profile of at least one component of the switching device over time. This profile is determined by the current flowing through the switching device, the ambient temperature of the switching device, and the passage of time. The method comprises a step in which the component temperature profile, the current profile, and the ambient temperature profile are received by the electronic processing unit. The method comprises a step in which corresponding tuples of values ​​are generated by the electronic processing unit based on the received component temperature profile, current profile, and ambient temperature profile.And the method includes a step in which a thermal model of the switching device is created using the electronic computing device based on the formed tuples of values, wherein an electronic computing device using the created thermal model is able to calculate a component temperature profile for the at least one component of the switching device based on a given time-dependent current profile of a current through the switching device and a given time-dependent ambient temperature profile of an ambient temperature of the switching device.

[0012] If the current flowing through the switching device changes, then the power loss released in the switching device also changes according to P. v = I 2* R, where I is the current and R is the electrical resistance of the current path within the switching device. This causes a change in the temperature of the switching device. The higher the temperature rises within the switching device, the greater the temperature difference between the switching device and its surroundings, and consequently, the greater the heat loss from the switching device to the cooler environment via various heat transfer mechanisms (conduction, radiation, convection). A component temperature profile over time for a component of the switching device results from the superposition of heat release and heat loss from the switching device over time. The entire switching device forms a thermal system that can be simulated using a thermal model (thermal simulation). Thermal models for modeling a current-carrying device are known, e.g., thermal motor models (TMMs).The simulation of the thermal behavior of the switching device (thermal simulation) can be carried out, for example, using a thermal network model or a - computationally more complex - numerical FEM and / or FVM and / or CFD modeling (FEM = Finite Element Method, FVM = Finite Volume Method; CFD = Computational Fluid Dynamics).

[0013] Temperature measurements on the components of the switching device are not performed during operation at the customer's site, but only once, preferably during heating tests as part of type testing. A thermal model of the switching device is created based on these temperature measurements, which are preferably carried out during the heating tests of type testing. This thermal model can also be referred to as a thermal image or a thermal simulation model.

[0014] A temperature rise test (TRT) is performed by passing a rated current through the switching device. Due to the ohmic losses of the rated current during the test, the temperature of the switching device rises over time. Only when the switching device has reached a certain temperature above its surroundings can it dissipate heat. The temperature rise test is carried out until the switching device reaches a constant and stable final temperature, which may take several hours; this final temperature must be within the permissible limits specified by the manufacturer. The heating curve over time follows an exponential function. The time it takes to reach the final temperature reveals the thermal time constant T of the switching device; the thermal time constant T is the time it would take for the switching device to reach the final temperature without dissipating heat.

[0015] This problem is further solved according to the invention by a method with the features specified in claim 5. The method serves to operate a switching device under a temporary electrical overload. The method comprises a step in which a current sensor is used to detect the current profile over time of a current flowing through the switching device during its operation. The method comprises a step in which a second temperature sensor is used to detect the ambient temperature profile over time of the ambient temperature prevailing in the vicinity of the switching device during its operation. The method comprises a step in which the detected current profile and the detected ambient temperature profile are received as input values ​​by an electronic computing device.The method comprises a step in which the electronic computing device calculates a time-dependent component temperature profile of the component temperature of the at least one component of the switching device using a thermal model created for the switching device according to a method according to any one of claims 1 to 4. The method also comprises a step in which the electronic computing device permits electrical overload operation of the switching device only as long as the component temperature calculated for the at least one component does not exceed a temperature limit specified for that component. The switching device is operated in electrical overload if the component temperature calculated for the at least one component does not exceed or reach the temperature limit specified for that component.The electrical overload operation of the switching device is terminated if the component temperature calculated for the at least one component exceeds or reaches the temperature limit specified for the at least one component.

[0016] The procedure is carried out in such a way that a temperature limit stored in the microprocessor, which is defined for the component, is not reached, or alternatively, that a temperature limit stored in the microprocessor, which is defined for the component, is not exceeded: which definition of the term "temperature limit" is used (a) The limit must not be reached, or b) The limit must not be exceeded), is at the discretion of the person skilled in the art: ultimately, these are only different aspects of the fact that an upper limit is defined for the component temperature, above which temporary overload operation is not permitted.

[0017] One of the underlying ideas of the invention is to create a thermal model of a switching device based on heating and cooling tests performed as part of a type test. The thermal model represents the thermal behavior of a switching device as a function of its primary current and ambient temperature. Based on a given primary current profile over time, the thermal model is able to calculate the current temperature or temperature rise of a thermally critical component of the switching device relative to the ambient temperature.

[0018] Therefore, during operation of the switching device, it is no longer necessary to measure the component's actual temperature with a temperature sensor: Only the thermal model is used during operation at the customer's site. The thermal model can be used to operate a switching device under temporary electrical overload by calculating the component's current temperature using the thermal model. The switching device is then operated under temporary electrical overload only as long as the component's current temperature does not reach a predefined temperature limit. The various components of the switching device have different thermal sensitivities depending on their construction and therefore also heat up to different temperatures during operation.

[0019] The invention is therefore able to provide thermal protection for switching devices, whereby thermal protection means that a heat-generating current through the switching device is reduced or even switched off in time before unacceptably high temperatures of the individual components are reached in any operating mode.

[0020] This eliminates the need to perform temperature measurements on switching device components located in high-voltage areas. As a result, expensive and relatively slow-sampling temperature sensors are unnecessary, and interference or measurement inaccuracies of temperature measurement technology do not need to be taken into account.

[0021] One advantage of the invention lies in the creation of a switching device in which unnecessarily high costs due to oversizing can be avoided and, in particular, intelligent adaptation to the existing conditions, especially load and temperature situations, is possible.

[0022] The invention facilitates intelligent load management using overcurrents, as it enables simple and reliable prediction of component temperatures. An overcurrent is defined as a current value exceeding the primary current value specified by the switching device manufacturer as the maximum permissible value for continuous operation.

[0023] The outlined problem is also solved by a thermal modeling device according to the invention, comprising a current sensor, a second temperature sensor, a first temperature sensor, and an electronic computing device, which are adapted to perform the steps of the method according to one of claims 1 to 4.

[0024] The outlined problem is also solved by a switching device according to the invention, comprising a current sensor, a second temperature sensor, and an electronic computing device, which are adapted to perform the steps of the method according to one of claims 5 to 12.

[0025] The outlined problem is also solved by computer program products according to the invention. The computer program product is designed to be executed in a microprocessor. The microprocessor can be arranged in the switching device or in a separate control unit. The computer program product can be designed to be stored as software or firmware in memory. Alternatively or additionally, the computer program product can also be designed, at least partially, as a hard-wired circuit, for example, as an ASIC (application-specific integrated circuit). A first computer program product comprises program code means that cause the device of claim 13 to execute the method steps according to any one of claims 1 to 4. A second computer program product comprises program code means that cause the switching device of claim 16 to execute the method steps according to any one of claims 5 to 12.According to the invention, the first computer program product is configured to implement and execute at least one embodiment of the outlined method for creating a thermal model of a switching device. According to the invention, the second computer program product is configured to implement and execute at least one embodiment of the outlined method for operating a switching device under a temporary electrical overload. The computer program products can integrate all sub-functions of the respective method, i.e., be monolithic. Alternatively, the computer program products can also be segmented, distributing sub-functions across segments that are executed on separate hardware.For example, part of the procedure for creating a thermal model of a switching device can be carried out in a switching device and another part of the procedure for creating a thermal model of a switching device can be carried out in a higher-level control unit, such as a PLC, a protection device or a computer cloud (PLC = Programmable Logic Controller).

[0026] Computer program products are proposed that can be directly loaded into the internal memory of a digital processing unit and comprise software code sections that execute the steps of the methods described herein when the products are running on the processing unit. The processing unit is, in particular, a microprocessor in a switching device according to the invention or in a separate control unit. The computer program products described above can each be stored on a computer-readable storage medium (data carrier), such as a USB flash drive, a DVD or CD-ROM, flash memory, EEPROM, or an SD card (USB = Universal Serial Bus; DVD = Digital Versatile Disc; CD-ROM = Compact Disc Read-Only Memory; EEPROM = electrically erasable programmable read-only memory; SD card = Secure Digital Memory Card).The computer program products can also be in the form of a signal that can be loaded via a wired or wireless network.

[0027] The methods are preferably implemented in the form of computer programs for automatic execution. The invention is thus, on the one hand, a computer program with program code instructions executable by a computer, and on the other hand, a storage medium containing such a computer program, i.e., a computer program product with program code means, and finally, a switching device in whose data storage such a computer program is loaded or loadable as a means of carrying out the methods and their embodiments.

[0028] When procedural steps or sequences of steps are described below, this refers to actions that are carried out by or under the control of the computer program, unless it is expressly stated that individual actions are initiated by a user of the computer program. At a minimum, any use of the term "automatically" means that the action in question is carried out by or under the control of the computer program.

[0029] Instead of a computer program with individual program code instructions, the method described here and below can also be implemented in the form of firmware. It is clear to those skilled in the art that, instead of implementing a method in software, it is always also possible to implement it in firmware, in firmware and software, or in firmware and hardware. Therefore, for the purposes of this description, the terms "software" and "computer program" should be understood to encompass other implementation possibilities, namely, in particular, implementation in firmware, in firmware and software, or in firmware and hardware.

[0030] Embodiments of the invention

[0031] Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0032] According to a preferred embodiment of the method for creating a thermal model of a switching device, the thermal model is created by iteratively optimizing an initial configuration of a thermal model that models a component temperature profile for the at least one component as a function of the input values ​​current profile and ambient temperature profile until the thermal model reproduces the value tuples within predefined tolerance ranges. An advantage of this approach is that the thermal properties can be represented in the thermal model in a simple and adaptable manner.

[0033] According to a preferred embodiment of the method for creating a thermal model of a switching device, the thermal model is a thermal network model, wherein the parameters describing the thermal network model are iteratively optimized until the thermal network model replicates the value tuples within predefined tolerance ranges. The thermal network model can, for example, model the switching device as a network in which heat flows between masses with defined heat capacities, the heat flow being determined by different thermal resistances located between the masses. Parameters describing such a thermal network model include, for example, thermal resistances, heat capacities, heat transfer coefficients, linear temperature coefficients, etc. An advantage of this approach is that the thermal properties can be replicated in the thermal model in a simple and adaptable manner.

[0034] According to a preferred embodiment of the method for creating a thermal model of a switching device, the thermal model is created using at least one heating curve and / or at least one cooling curve of the at least one component. An advantage of this is that the thermal properties can be easily and adaptably reproduced in the thermal model.

[0035] According to a preferred embodiment of the method for operating a switching device in a temporary electrical overload, the calculation is performed by the thermal model in a microprocessor of the switching device. An advantage of this is the availability of high computing power, allowing the use of complex thermal models that permit high reliability of the predicted temperature values.

[0036] According to a preferred embodiment of the method for operating a switching device in a temporary electrical overload, the electronic computing unit uses the thermal model to calculate a maximum time interval for one or more different currents, during which a component temperature calculated for at least one component does not exceed a temperature limit specified for that component. The thermal model applies to every current, regardless of whether it is below or above the maximum permissible continuous load current of the switching device. An advantage of this is that an operator of the switching device can select one of the offered operating options with respect to a time interval, thus optimizing load management by utilizing overcurrents.

[0037] According to a preferred embodiment of the method for operating a switching device in a temporary electrical overload, the electronic computing unit uses the thermal model to calculate a maximum current for the switching device for one or more predetermined, different time intervals, at which a component temperature calculated for at least one component does not exceed a temperature limit specified for that component. An advantage of this method is that an operator of the switching device can select one of the offered operating options with respect to a maximum current value, thus optimizing load management by utilizing overcurrents.

[0038] According to a preferred embodiment of the method for operating a switching device in a temporary electrical overload, tulip contacts of the switching device or a sliding bearing of a vacuum switching tube in which a moving contact rod of the switching device is mounted are components of the switching device for which temperature limits are specified.

[0039] Tulip contacts and a sliding bearing, in which a moving contact rod of the switching device is mounted, are typical components of a vacuum circuit breaker. A key advantage is that component temperatures can be predicted simply and reliably for these components.

[0040] According to a preferred embodiment of the method for operating a switching device in a temporary electrical overload, the ambient temperature of the switching device is used as a starting value for the thermal model's component temperature during the initial switch-on. The initial switch-on of a switching device is defined as switching on a device that is at ambient temperature. The advantage of this is that a realistic starting value accelerates the temperature calculation by the thermal model.

[0041] According to a preferred embodiment of the method for operating a switching device in a temporary electrical overload, when the switching device is switched on after a period of inactivity, a temperature value calculated by the electronic computing unit using the thermal model for the end of an operating period immediately preceding the inactivity period is used as a starting value for the thermal model for the component temperature. The advantage of this is that a realistic starting value speeds up the temperature calculation by the thermal model.

[0042] According to a preferred embodiment of the method for operating a switching device in a temporary electrical overload, the thermal model is calculated even when no current is flowing through the switching device. An advantage of this is that the cooling of the switching device, which occurs while no current is flowing through it, is also calculated, thus providing a realistic initial temperature value when the switching device is switched on again (current flowing through the switching device).

[0043] Exemplary embodiments of the drawing

[0044] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more easily understood through the following description of exemplary embodiments, which will be explained in more detail with reference to the drawings. The drawings are schematic and not to scale.

[0045] Fig. 1 shows a switching device for carrying out a method for creating a thermal model of the switching device;

[0046] Fig. 2 shows a Tt diagram with a typical heating curve and a typical cooling curve;

[0047] Fig. 3 shows a switching device for carrying out a method for operating a switching device in a temporary electrical overload;

[0048] Fig. 4 shows a first table of values;

[0049] Fig. 5 shows another table of values;

[0050] Fig. 6 shows a vacuum switching device in an electrical circuit;

[0051] Fig. 7 shows a temporary overload operation of a switching device;

[0052] Fig. 8 shows a flowchart of a method for creating a thermal model of a switching device; and

[0053] Fig. 9 shows a flowchart of a method for operating a switching device in a temporary electrical overload.

[0054] Detailed description of the embodiments: Fig. 1 shows a switching device 1 connected in a primary current line 2 between a voltage source 5 and a load 6. The switching device 1 has a switch 13 with which the primary current line 2 running through the switching device 1 can be switched; in a conducting state of the switch 13, current I flows through the primary current line 2; in a blocking state of the switch 13, no current I can flow through the primary current line 2. The switching device 1 has a first component 11, which is part of the primary current line 2; this means that the component 11 is part of the current path between the voltage source 5 and the load 6 and carries the current I through it in the conducting state of the switch 13. The switching device 1 also has a second component 12. A first temperature sensor 3 is arranged on the first component 11, which detects the temperature 0 of the first component 11.A second temperature sensor 4 is arranged in the vicinity of the switching device, which detects the temperature of the area surrounding the switching device 1. A current sensor 7 detects the current I flowing through the primary current line 2 running through the switching device 1.

[0055] To create a thermal model of the switching device 1, the temperatures 0 of the first component 11, which change depending on the current I detected by the current sensor 7 through the primary current line 2 running through the switching device 1, the ambient temperature T_amb of the switching device detected by the second temperature sensor 4, and the time t, are measured by the first temperature sensor 3. The measured values ​​can be acquired as part of a type test of the switching device. In a microprocessor 8, corresponding value tuples (0, I, T_amb, t) are generated from the acquired measured values. The microprocessor 8 can be located in the switching device 1 or in a separate control unit. Based on the generated value tuples (0, I, T_amb, t), a thermal model of the switching device 1 is created using a suitable modeling method, e.g., an iterative method, which is performed in the microprocessor.The thermal model is able to calculate a temperature profile 0(t) for at least one component 11 of the switching device 1 based on a given time profile l(t) of the current I through the switching device 1 and a given time profile T_amb(t) of an ambient temperature of the switching device 1.

[0056] Fig. 2 shows a Tt diagram in which temperature T is plotted against time t. The Tt diagram depicts a typical heating curve 21 and a typical cooling curve 22 of a component of a switching device. The environment surrounding the component is at ambient temperature T_amb. First, the heating of the component is described. At a time before current I flows through the switching device, the component is at the same temperature T_amb as the environment surrounding the switching device 1: the switching device 1 is in thermal equilibrium with its environment. The heating 21 of the component is caused by ohmic losses of the current I through the switching device. The heating begins at time t=0, when the switch 13 of the switching device 1 switches to a conducting state and the current flow I through the switching device is enabled.After a time interval greater than five times a time constant T, the component reaches a thermal equilibrium state in which the heat input due to ohmic losses is equal to the heat output of the component; this constant temperature of the component in thermal equilibrium during current flow through the switching device is called the component's final temperature 0fin. The difference between the component's final temperature 0fin and the ambient temperature T_amb is denoted by A0. The heating curve 21 can be described by the following function f(t): f(t) = T_amb + A0 (1 - exp(-t / T)).

[0057] The cooling of the component is now described. Before the current I is interrupted by the switching device, the component is at a constant final component temperature 0fin: the heat input to the component from the ohmic losses of the current-carrying primary current line is identical to the heat losses of the component to its surroundings. The cooling of the component is caused by the cessation of the heat input. The cooling begins at time t=0, when the current I is interrupted by the switching device and thus the heat input from the ohmic losses ends. After a time interval greater than five times a time constant T, the component returns to a thermal equilibrium state in which the constant temperature of the component corresponds to the ambient temperature T_amb; unlike the initial thermal equilibrium state, the component temperature is now lower.The cooling curve 22 can be described by the following function g(t): g(t) = T_amb + A0 exp(-t / T).

[0058] The time constants T of the heating curve 21 and the cooling curve 22 can be different. For simplicity, they are assumed to be identical in Fig. 1. Such heating curves 21 and cooling curves 22 of a component are one of the foundations for thermal modeling of the component.

[0059] Fig. 3 shows a switching device 1 intended for operation under temporary electrical overload. It is identical to the switching device 1 shown in Fig. 1, which underwent type testing and for which a thermal model was developed, except that the switching device 1 shown in Fig. 3 does not have a temperature sensor on component 11.

[0060] To operate the switching device under a temporary electrical overload, the current sensor 7 records the time-dependent profile l(t) of the current I flowing through the switching device during operation. Additionally, the temperature sensor 4 records the time-dependent profile T_amb(t) of the ambient temperature of the switching device during operation. The recorded time-dependent profile l(t) of the current I and the time-dependent profile T_amb(t) of the ambient temperature of the switching device are transmitted to a microprocessor 8 and used by the microprocessor 8 as input values ​​for a thermal model created for the switching device and calculated within the microprocessor 8. The thermal model calculates a time-dependent temperature profile 9(t) for component 11 of the switching device 1.Electrical overload operation of the switching device 1 is permitted as long as the temperature 0 calculated for the component 11 does not exceed a temperature limit 0max stored in the microprocessor 8, which is defined for the component 11.

[0061] A first example of overload operation involves a power line with a rated current of 3000 A. Temperature tests have shown that a switch on the power line can withstand a current of 3500 A for a short period, e.g., 15 minutes. In a temporary overload operation, the power line is thus operated at 3500 A for 15 minutes; only after these 15 minutes does the thermal model indicate that the switch is approaching a predetermined temperature limit, necessitating the current reduction back to 3000 A. This first example is a temporary overload operation resulting from prior operation of the switching device with a current below its rated current at a maximum permissible ambient temperature. In this scenario, the thermal capacity of the switching device's components is utilized.Another example of overload operation is the operation of a switching device with a rated current of 3000 A at 3500 A for an arbitrarily long period of time, because the ambient temperature of the switching device is significantly below the maximum permissible ambient temperature of the switching device.

[0062] Another example of overload operation involves an electric arc furnace that is cyclically switched on and off by a switch, with several switching operations per hour. There are pauses of approximately 5 minutes between the arc phases. The rated current is 3000 A. The thermal model indicates that the switch can temporarily operate at 4000 A or that the length of the pauses can be reduced.

[0063] Fig. 4 shows a first table of values ​​calculated by the thermal model: for several different currents I, which are above a maximum permissible continuous load current of the switching device, a maximum time interval Atmax is specified; a current I may flow through the switching device for a maximum of a time interval Atmax so that a temperature 0 calculated for the component 11 does not exceed a temperature limit 0max that is specified for the component 11.

[0064] Fig. 5 shows a second table of values ​​calculated by the thermal model: For several time intervals At, a maximum current Imax is specified; over the length of a time interval At, at most a current Imax may flow through the switching device so that a temperature 0 calculated for the component 11 does not exceed a temperature limit 0max that is defined for the component 11.

[0065] Fig. 6 shows a movable vacuum switching device 1 with tulip contacts 9 and a sliding bearing 10, wherein a moving contact rod 14 of the vacuum switching device 1, movable against a fixed contact rod 16 by a motor M, is mounted in the sliding bearing 10. Contact pieces 20, 21, arranged on the opposing ends of the fixed contact rod 16 and the moving contact rod 14, are arranged in a vacuum switching tube 18. The contact rods 14, 16 and the contact pieces 20, 21 form a switch 13 of the vacuum switching device 1. The tulip contacts 9 of the vacuum switching device 1 serve to connect a primary current line 2 of the vacuum switching device 1, connected to the contact rods 14, 16, with electrical mating contacts 15 in order to establish an electrical circuit. For this purpose, the vacuum switching device 1 is moved 25 so that the tulip contacts 9 enclose the mating contacts 15, which can be pin- or tube-shaped.The tulip contacts 9 of the switching device 1 and the sliding bearing 10 of the switching device 1 are thermally critical components of the switching device 1: the temperature limit values ​​θmax specified for these components 9, 10 must also be observed if the switching device 1 is temporarily operated in an electrical overload, otherwise damage to components 9, 10 is imminent.

[0066] Fig. 7 shows a temporary overload operation of a switching device at an ambient temperature below the maximum permissible ambient temperature. The switching device is located in an environment with an ambient temperature T_amb. At time t=0, current begins to flow through the switching device at its rated current, and a component of the switching device reaches its final temperature 0fin after a sufficiently long period of time operating at its rated current. At time t1, an overload operation of the switching device 1 begins, i.e., a temporary operation of the switching device with a current value above the rated current. Consequently, from time t1 onwards, the temperature of the thermally critical component under consideration rises above the final temperature 0fin and approaches the temperature limit 0max, which is specified for the component. As soon as the component temperature reaches the temperature limit 0max, the overload operation is terminated at time t2, and the current is reduced back to the rated current.Consequently, from time t2 the component temperature drops again until, after a sufficiently long period, it reaches the final temperature 0fin again at nominal current.

[0067] Figure 8 shows a flowchart of a method for creating a thermal model of a switching device. The method is used to create a thermal model of a switching device. The method is implemented as a computer program for automated execution.The method comprises a first step 51 in which a current profile over time is recorded by means of a current sensor, a current flowing through the switching device during its operation is recorded, a second temperature sensor is used to record an ambient temperature profile over time, and a first temperature sensor is used to record a component temperature profile over time of at least one component of the switching device, which changes depending on the current flowing through the switching device, the ambient temperature of the switching device and time.The method includes a further step 52 in which an electronic computing device receives the component temperature profile, the current profile, and the ambient temperature profile and forms corresponding tuples of values. The method also includes a further step 53 in which an electronic computing device creates a thermal model of the switching device based on the formed tuples of values. Using this thermal model, the electronic computing device is then able to calculate a temperature profile for at least one component of the switching device based on a given time profile of the current through the switching device and a given time profile of the ambient temperature of the switching device.

[0068] Fig. 9 shows a flowchart of a method for operating a switching device under a temporary electrical overload. The method is implemented as a computer program for automatic execution. The method comprises a first step 61 in which the current flowing through the switching device during its operation is recorded over time. The method also comprises a further step 62 in which the ambient temperature of the switching device is recorded over time.The method comprises a further step 63 in which the recorded temporal profile of the current and the recorded temporal profile of the ambient temperature of the switching device are received by an electronic computing device as input values ​​of a thermal model created for the switching device according to a method according to claim 1. The method comprises a further step 64 in which the electronic computing device uses the thermal model to calculate a temporal temperature profile for the at least one component of the switching device. The method comprises a further step 65 in which the electronic computing device permits electrical overload operation of the switching device only as long as the temperature calculated for the at least one component does not exceed a temperature limit specified for the at least one component.

[0069] Reference symbol list

[0070] 1 switching device

[0071] 2 Primary power line

[0072] 3 Temperature sensor, first

[0073] 4. Temperature sensor, second

[0074] 5 Voltage source

[0075] 6 Last

[0076] 7 Current sensor

[0077] 8 microprocessor

[0078] 9 Tulip contact

[0079] 10 plain bearings

[0080] 11th component, first

[0081] 12th component, second

[0082] 13 switches

[0083] 14 Moving contact rod

[0084] 15 counter-contact

[0085] 16 fixed contact rod

[0086] 18 Vacuum switching tube

[0087] 20 contact pieces

[0088] 21 contact piece

[0089] 25 Shift of 1

[0090] 51st procedure step

[0091] 52nd process step

[0092] 53 Procedure step

[0093] 61st step of the process

[0094] 62nd process step

[0095] 63 Procedure step

[0096] 64th process step

[0097] 65th process step

Claims

Patent claims 1. Method for creating a thermal model of a switching device (1), comprising the following steps: - Detect (51), by means of a current sensor (7), a time-dependent current profile (l(t)) of a current (I) flowing through the switching device (1) during operation; - Detect (51), by means of a second temperature sensor (4), a time-dependent ambient temperature profile (T_amb(t)) of an ambient temperature (T_amb) of the switching device (1) which prevails in the vicinity of the switching device (1) during the operation of the switching device (1); Detect (51) a component temperature profile (9(t)) of at least one component (11, 12) of the switching device (1) by means of a first temperature sensor (3), which is determined as a function of the said current (I) through the switching device (1), as a function of the said ambient temperature (T_amb) of the switching device (1) and as a function of time (t); - Receiving (52) the component temperature profile (9(t)), the current profile (l(t)) and the ambient temperature profile (T_amb(t)) using an electronic computing device (8); - Forming (52), based on the received component temperature profile (9(t)), current profile (l(t)) and ambient temperature profile (T_amb(t)), of corresponding value tuples (9, I, T_amb, t) using the electronic computing device (8); and Creating (53) a thermal model of the switching device (1) using the electronic computing device (8) based on the formed tuples of values ​​(9, I, T_amb, t), wherein an electronic computing device (8) using the created thermal model is able to calculate a component temperature profile (9(t)) for the at least one component (11, 12) of the switching device (1) based on a given time current profile (l(t)) of a current (I) through the switching device (1) and a given time ambient temperature profile (T_amb(t)) of an ambient temperature (T_amb) of the switching device (1).

2. The method of claim 1, wherein the thermal model is created by generating a start configuration of a thermal model that provides a component temperature profile (9(t)) for the at least one component (11, 12) as a function of the input values ​​current profile (l(t)) and ambient temperature profile. (T_amb(t)) is modeled and iteratively optimized until the thermal model replicates the value tuples (0, I, T_amb, t) within specified tolerance ranges.

3. Method according to claim 2, wherein the thermal model is a thermal network model, wherein the parameters describing the thermal network model are iteratively optimized until the thermal network model replicates the value tuples (0, I, T_amb, t) within specified tolerance ranges.

4. Method according to one of claims 1 to 3, wherein the thermal model is created using at least one heating curve (21) and / or at least one cooling curve (22) of the at least one component (11 , 12).

5. Method for operating a switching device (1) in a temporary electrical overload, comprising the following steps: - Detecting (61) a current waveform (l(t)) of a current (I) flowing through the switching device (1) during operation of the switching device (1) using a current sensor (7); - Detect (62), by means of a second temperature sensor (4), a time-dependent ambient temperature profile (T_amb(t)) of an ambient temperature (T_amb) of the switching device (1) which prevails in the vicinity of the switching device during the operation of the switching device (1); - Receiving (63) the recorded current profile (l(t)) and the recorded ambient temperature profile (T_amb(t)) as input values ​​from an electronic computing device (8); - Calculating (64) by the electronic computing device (8) a time-dependent component temperature profile (0(t)) of the component temperature (0) of the at least one component (11, 12) of the switching device (1) using a thermal model created for the switching device (1) according to a method according to any one of claims 1 to 4; and - Allowing (65) by the electronic computing device (8) an electrical overload operation of the switching device (1) only as long as the component temperature (0) calculated for the at least one component (11, 12) does not exceed a temperature limit (0max) that is specified for the at least one component (11, 12).

6. Method according to claim 5, the calculation is performed by the thermal model in a microprocessor (8) of the switching device (1).

7. Method according to one of claims 5 or 6, wherein the electronic computing device (8) uses the thermal model to calculate a maximum time interval (Atmax,1 ; Atmax,2; Atmax,3) for one or more different currents (11 , I2, I3) in which a component temperature (0) calculated for at least one component (11, 12) does not exceed a temperature limit (0max) that is defined for the at least one component (11 , 12).

8. Method according to one of claims 5 to 7, wherein the electronic computing device (8) uses the thermal model to calculate a maximum current (lmax,1 ; lmax,2; lmax,3) of the switching device (1) for one or more predetermined different time intervals (At1 , At2, At3) at which a component temperature (0) calculated for at least one component (11 , 12) does not exceed a temperature limit (0max) that is defined for the at least one component (11 , 12).

9. Method according to one of claims 5 to 8, wherein tulip contacts (9) of the switching device (1) or a sliding bearing (10) in which a moving contact rod (14) of the switching device (1) is mounted are components (11, 12) of the switching device (1) for which temperature limit values ​​(0max) are specified.

10. Method according to one of claims 5 to 9, wherein, upon first switching on the switching device (1), an ambient temperature (T_amb) of the switching device (1) is used as a starting value of the thermal model for the component temperature (0).

11. Method according to one of claims 5 to 10, wherein when the switching device (1) is switched on after an interruption period of the switching device in which the operation of the switching device was interrupted, a temperature value which had been calculated by the electronic computing device (8) using the thermal model for the end of an operating period of the switching device which immediately preceded the interruption period is used as a starting value of the thermal model for the component temperature (0).

12. Method according to any one of claims 5 to 11, wherein the calculation of the thermal model is also carried out when no current (I) flows through the switching device (1).

13. Thermal modeling device comprising - a current sensor (7), - a second temperature sensor (4), - a first temperature sensor (3), and - an electronic computing device (8) adapted to perform the steps of the method according to any one of claims 1 to 4.

14. Computer program product comprising program code means that cause the device of claim 13 to perform the method steps according to any one of claims 1 to 4.

15. Computer-readable storage medium on which the computer program according to claim 14 is stored.

16. Switching device, comprising - a current sensor (7), - a second temperature sensor (4), and - an electronic computing device (8) adapted to perform the steps of the method according to any one of claims 5 to 12.

17. Computer program product comprising program code means that cause the switching device of claim 16 to perform the method steps according to any one of claims 5 to 12.

18. Computer-readable storage medium on which the computer program according to claim 17 is stored.

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