Aging check for low-voltage components

Abstract

The invention relates to the checking of the aging of a low-voltage component which is designed to be inserted into a circuit. According to the invention, a first item of temperature information related to the low-voltage component is determined for a first point in time, a second item of temperature information related to the low-voltage component is determined for a second point in time, and a first item of information representing a measure of the heating between the points in time is determined using the two items of temperature information. Said first item of information is compared with a second item of information representing a measure of comparable heating between the points in time for a corresponding low-voltage component in a known state. A statement about the aging of the low-voltage components is then derived using the difference between the first and the second item of information. The invention allows the aging of a low-voltage component to be checked simply and efficiently.

Description

[0001]202219449 1 Description Aging test for low-voltage components The invention relates to a method for checking the aging of a low-voltage component which is designed to be introduced into an electrical circuit, a device for carrying out a method according to the invention and a computer program product with a computer program which carries out the calculation steps of a method according to the invention when it runs on a processor. Current-carrying low-voltage components in particular are subject to an aging process in which the aging depends not only on the external conditions but also on the loads during operation. An example of such low-voltage components are fuse links which age during operation at high ambient temperatures, with frequently occurring alternating loads and during overload operation. This aging results in a change in the tripping characteristic, up to and including tripping during nominal operation.Advanced fuse solutions are sometimes equipped with sensors and communication devices, for example, to monitor consumption information. Fuses with integrated measuring functions are disclosed, for example, in WO 2020 / 127486 A1, WO 2020 / 127488 A1, WO 2020 / 148015 A1, and DE 102018213522 A1. There is a need to replace such fuses and general low-voltage components when they reach the end of their service life. While the components should be replaced before a failure occurs to avoid prolonged interruptions in operation, premature replacement would waste resources. Therefore, monitoring for aging is desirable. The invention aims to contribute to this. This object is achieved by a method according to claim 1, a device according to claim 13 and a computer program product according to claim 17.According to the invention, an aging check of a low-voltage component is proposed, which is designed to be introduced or looped into an electrical circuit (e.g. by means of corresponding connecting terminals and a current path running in the low-voltage component). This low-voltage component can be used to monitor or interrupt the electrical circuit. Here and in the following, the conjunction "or" is always to be understood as a non-exclusive "or". In particular, this should also include the conjunction "and", i.e. in the above case, the low-voltage component can also be used for monitoring and interruption. In particular, the low-voltage component can be a fuse, a low-voltage switch or a measuring device for energy monitoring - often also referred to as a PMD or power measurement device.According to the invention, a first piece of temperature information relating to the low-voltage component is determined for a first point in time (and preferably also at this point in time). This first piece of temperature information is, for example, a temperature characteristic of the low-voltage component. This temperature can be a temperature measured by a temperature sensor of the low-voltage component. However, it is also conceivable, for example, for the low-voltage component to have a plurality of mutually spaced temperature sensors, the measured values ​​of which are linked to form the first piece of temperature information. Furthermore, a second piece of temperature information relating to the low-voltage component is determined for a second, typically later point in time (and preferably also at this point in time).The determination is preferably carried out in the same way as for the first temperature information in order to ensure comparability. Using the two pieces of temperature information, a first piece of information is determined which represents a measure of the heating between the points in time. If the two pieces of temperature information represent temperature values, this first piece of information can be the difference between these temperature values. In addition, a second piece of information is determined which represents a measure of comparable heating between the points in time for a corresponding low-voltage component in a known state. The known state of a corresponding low-voltage component can be the end of its service life or as new, i.e., the aim is to compare it with a corresponding low-voltage component at the beginning or end of its service life. Using the difference (e.g.in the form of a difference between two values) between the first and second pieces of information, a statement is made about the aging of the low-voltage components. In doing so, values ​​for the heating between the points in time can be compared. However, it is also possible, for example, to use the heating to calculate temperature values ​​at the second point in time and to compare these. Since the current in most circuits with corresponding low-voltage components is not even remotely constant and the heating depends on the current flow, it is generally sensible to take this into account. Therefore, in one design, the low-voltage component is provided with at least one current measuring device, and a current value is determined by the current measuring device to check the aging using current measurement. This is a suitable value, which can be, for example, a measured current value (possiblyfor a DC current) or an average value from measured current values ​​(e.g. RMS value for AC current). The second piece of information is then determined as a function of this current value. According to a further development of the invention, it is taken into account that the current value used is typically not constant between the two points in time. In principle, it would be possible to track the change in this value and incorporate it into the determination of the second piece of information. However, it is less complex and easier to handle to assume a sufficiently constant current value, i.e., to determine the second piece of information only as a function of a current value. According to one embodiment of the invention, a corresponding procedure is followed, whereby a criterion for a sufficiently constant current value is checked, and the second piece of information is only determined if the criterion is met. Specifically, for example,By means of current measurement by the current measuring device, a current value is determined at times relevant to the method for determining aging (e.g., at the first and second times, but possibly also for times in between). A measure of the change in current between the times based on these current value determinations is then used (e.g., the amount of the difference in the current value at the first and second times). The method is then only carried out, or the results of the method are only output as relevant aging information, if a criterion related to this measure of the change in current (e.g., a threshold criterion for the amount of the difference in the current value at the first and second times) for a small change in current is met.According to a further development of the invention, a value is determined as the second piece of information that represents a measure of comparable heating between the points in time for a corresponding low-voltage component at the end of its service life, and a value is determined as the third piece of information that represents a measure of comparable heating between the points in time for a corresponding new low-voltage component. The difference between the second and third pieces of information is then used as a criterion for the significance of the statement on the aging of the low-voltage components or for information on aging. If this difference is too small (e.g., of the same order of magnitude as the intrinsic inaccuracies due to measurements, approximations, etc.), the results may not be meaningful. This is checked according to the further development.In this development, a current value can be determined by the current measuring device to check for aging by means of current measurement (suitable value, e.g., RMS value for alternating current), and the third piece of information can be determined as a function of this current value (preferably the second piece of information as well). According to one embodiment of the invention, the low-voltage component is provided with at least one temperature sensor, and the first or second piece of temperature information is determined by measuring the temperature using the at least one temperature sensor. The difference between the measured temperatures is then used as the first piece of information, which represents a measure of the heating between the points in time.According to one embodiment of the invention, the first temperature information is the temperature of the first low-voltage component at the first time, and for determining the second information or the third information, the temperature of a comparable low-voltage component in the known state is determined, which the latter would assume based on the temperature of the first low-voltage component after a period determined by the time difference between the first and second time points with a comparable current flow (as a criterion for a comparable current flow, for example, it can be checked whether the current value is sufficiently constant between the two times). For determining the second or third information, the ambient temperature at the first or second time point outside the low-voltage component (e.g.at a central location in a distribution box or by a central communications unit responsible for several low-voltage components) and transmitted to the low-voltage component. According to one embodiment, the second or (if provided) third piece of information is determined by means of a formula-based description of the heating, a table or a neural network. The second or third piece of information can be determined by means of a formula-based description of the heating, for which purpose a final temperature or final heating that is dependent on the current flow (which can be assumed to be constant) is assumed and an empirical approach is established, for example, for this final temperature or this final heating and the approach behavior. The invention also relates to a device that can comprise the low-voltage component.The low-voltage component can be provided with at least one current measuring device (e.g., Rogowski coil, shunt, current transformer, etc.) and with at least one temperature sensor. In addition, the low-voltage component can have a receiver for receiving an ambient temperature measured outside (possibly centrally) of the low-voltage components. The subject matter of the invention further relates to a computer program product with a computer program that carries out the calculation steps of a method according to the invention when it runs on a processor. The invention is explained in more detail below within the framework of an exemplary embodiment. 202219449 7 Fig. 1: a fuse with a temperature sensor, Fig. 2: a flow chart for a method according to the invention, Fig. 3: a comparison of the heating behavior of a new fuse and the heating behavior of an identically constructed, aged fuse, and Fig.4: the dependence of the final heating of a fuse on the load current. In Fig. 1, a fuse 1 is shown schematically. The fuse has a protective housing 2 and another housing 12, which are arranged one behind the other in the longitudinal direction L and together reach the height H of a standardized NH fuse. The fuse 1 has two connection elements 3, which consist of an electrically conductive material, for example copper. The connection elements 3 each extend through an opening formed in the closure caps 4 into the cavity of the protective housing 2. In this cavity, at least one so-called fusible element 5 is arranged, which electrically conductively connects the two connection elements 3 to one another.Elements 10 for monitoring consumption parameters are arranged in the further housing 12, comprising a current transformer 11 for measuring an electrical current I flowing through the fuse 1 and a transmission device 13 for transmitting the measured value to a receiving device (not shown) arranged outside the fuse 1. A temperature sensor 15 is also provided. 202219449 8 The total installation space required for the protective housing 2 and the further housing 12 is exactly the same size as the installation space of a standardized NH fuse, ie the installation space required by the protective housing 2 and the further housing 12 corresponds in total to the predefined installation space of a standardized NH fuse, wherein the measuring device is now integrated in this installation space in addition to the actual fuse.In this way, the fuse 1 can also be used for retrofitting applications as part of retrofitting or modernizing existing electrical systems, in which a conventional fuse without a measuring device is to be replaced by the fuse according to the invention. The height H of the fuse 1 is divided into a first section with a first height H. D and a second section with a second height H M With the first height H D is the height of the pressure body 2, ie the actual protective body 2 of the fuse 1, the second height H Mrefers to the height of the second housing 12 in which the measuring device 10 is arranged. This housing also has significantly lower requirements with regard to its mechanical stability. The current transformer 11 and a temperature sensor 15 are connected to the processing device 14, which is shown schematically as a circuit board in Fig. 1, for transmitting the corresponding current and temperature measurement signals. The transmission device 13 is connected to the processing device 14 shown as a circuit board. The transmission device 13 can be an RFID module, for example, with both active RFID and passive RFID solutions being possible. Other – advantageously wireless – transmission technologies such as Bluetooth, Zigbee or Thread are also suitable for this purpose. Fig.Fig. 2 shows the sequence of a method according to the invention, as it can run, for example, in the processing device 14. The start of the method (step S1) is triggered, for example, by time information. It can be provided, for example, that an aging check is carried out at regular intervals, e.g. daily. For this purpose, date information from a timer or clock can be transmitted to a fuse according to Fig. 1. Alternatively, the processing device according to Fig. 1 itself comprises a clock. Externally transmitted date information is useful if the fuse has a sleep mode in which the processing device is not active. The date information is then compared with a target date for the next aging check, and the check is carried out when the check date has been reached or exceeded.Typically, a large number of fuses are installed in power distribution systems (e.g., in a fuse box). It is usually sensible to perform an aging test for all relevant fuses, as aging behavior will usually vary due to structural deviations, different loads, or different ages (e.g., due to the replacement of individual fuses). This is illustrated in Fig. 2 by the loop of step S2. Different fuse types are differentiated by an identifier (e.g., the MLFB or machine-readable manufacturer's designation). The heating behavior of the individual fuse types was tested at the factory, and empirical formulas were determined. For a new fuse, the heating can be approximately described as follows. Heating refers to a change in temperature, typically a rise in temperature.Heating is denoted below by the letter T in the formulas, while the Greek letter ϑ is used for temperatures. ie, heating during a period Δt = t2–t1 would then be T(t2–t1) = 202219449 10 ϑ(t2) – ϑ(t1), where, for simplicity of notation, t1 = 0 and t2 = t are set where possible. If a current I0 is applied, the fuse heats up. Immediately after the current is applied, the temperature of the fuse will not differ greatly from the ambient temperature. The temperature then rises and, over time, will approach a limit value corresponding to the maximum temperature at a current I0. Experience has shown that the increase or heating can be roughly described using an exponential function and is then proportional to (1 – exp (-t / τ)), where exp is the exponential function, t is the time and τ is a constant characteristic of the heating (thermal time constant).The final heating depends on the current I0. An approximate formula can be established for it by performing a Taylor expansion for the difference between the final temperature and the ambient temperature with respect to the current I0. Let it be T. e (i;I0) is the final heating for fuse type i. If the Taylor series is terminated after the quadratic term, then the approximation T e (i;I0) = a e,i *I0 2 +b e,i *I0+c e,i (1) Before the current flows, the temperature of the fuse corresponds to the ambient temperature. Using the rise behavior discussed above, the heating of the fuse can then be described as follows: T(i;I0;t) = T e(i;I0)*(1–exp(-t / τ)) (2) An empirical approach can also be used for the thermal time constant τ. This time constant will depend on the current I0, because the higher the current, the faster the heating occurs. Taking into account the linear dependence of τ on the current, the following approach is obtained: 202219449 11 τ(i;I0)=a τ,i *I0+b τ,i A central idea of ​​the invention is that the course and final heating of the fuse change over time due to aging. This is shown in Fig. 3, where the lower curve describes the heating behavior of a new fuse and the upper curve the heating behavior of an identically constructed aged fuse. The final heating depends on the load current, as shown in Fig. 4. For the heating behavior at the end of the service life of a fuse, an approach according to formula (1) can now also be used. In the following, T e,totis the final heating of a fuse at the end of its service life. Then, analogously to equation (1), T e,tot (i;I0) = a tot,i *I0 2 +b tot,i *I0+c tot,i (4) The coefficients of equations 1, 3, and 4 are determined at the factory through tests and are input for the process shown in Fig. 2. They are either already present in a memory of the fuse upon delivery or are transferred to the fuse by a central location before the process (the provision of the coefficients is step S3 in Fig. 2). In step S4, the charging current I0 and the current temperature ϑ a of the fuse. If the values ​​of I0 and ϑ a present, a timer is set to zero (t=0, step S5). A load factor k is then calculated, which is the quotient between the charging current I0 and the rated current I ris defined (steps S6 and S7). In the following step S8, it is checked whether the load factor is greater than 0.4. If not, a wait of 10 seconds is made (step S9) and then step S4 is continued. At a low load (here defined as k ≤ 0.4), the shift in the heating curve shown in Fig. 3 is small, and due to tolerances or inaccuracies, the method reaches its limits. Therefore, it is advisable to only carry out the procedure according to steps S10 - S21 if the load has exceeded a threshold value. Of course, depending on the security and application scenario, other threshold values ​​than k = 0.4 and other waiting times than 10 seconds may be conceivable or more favorable. If the load is high enough, the values ​​of T e , T e,totand τ are determined from the values ​​obtained with the coefficients in step S3 using formulas (1), (3), and (4). A 10 second delay is then observed (step S12), and the timer is incremented accordingly (step S13) before the load current, fuse temperature, and ambient temperature are measured again. The ambient temperature does not have to be measured by the fuse itself, but can be measured centrally and transmitted to the fuse. The central measurement can be performed, for example, using a communication module as described in DE 202021000293 U1. The ambient temperature can also be measured centrally in a control cabinet with multiple fuses, and from there the data can then be communicated to the fuses in the control cabinet.A data collector can also be responsible for a plurality of fuses, transmitting an ambient temperature value measured by itself or received from a measuring point to the plurality of fuses. This measurement or its time is referenced with the index 1, and the associated values ​​of load current, ambient temperature, and fuse temperature are labeled I1, ϑ. U1 and ϑ1 (steps S14 and S15). In step S16, it is checked whether the load current has changed compared to the measurement of I0, has changed significantly in step S4. The criterion for this is a deviation of less than 5%, ie, 0.95*I0< I1> 1.05*I0. If the deviation is too large, the system waits 10 seconds (step S9) and then continues with step S4. Otherwise, values ​​are calculated in step S17, which are used to assess the aging of the fuse. 202219449 13 The starting point for the calculation in step S17 are the values ​​for the charging current I0 and the current fuse temperature ϑ obtained in step S4. a . The consideration is that in the time t between step S4 and the measurement of the corresponding quantities in step S14, the fuse has continued to heat up. This heating will depend on how much the fuse has aged. For a new fuse, the following approach can be used, which then allows the calculation of a target temperature ϑ soll enables .The starting point is then the temperature of the fuse ϑ measured in step S4 or at time zero. a . In the limit t ∞, the temperature of the fuse approaches a limit or final temperature. This limit temperature is composed of the ambient temperature and the final temperature rise T e . Formula (1) for this difference T e Assuming that the heating from step S4 (time zero) exhibits a behavior according to (1 – exp (-t / τ)), one obtains for ϑ soll : ϑ soll = ϑ a + (ϑ U1 +T e -ϑ a )*(1–exp(-t / τ)) (5) (At time t=0 the temperature ϑ a , at time t = ∞ the temperature ϑ U1 + T e, and the heating curve from time zero has a behavior that can be described by (1–exp(-t / τ)). A fuse has a higher final heating towards the end of its service life. Analogous to equation (2), one then obtains: T(i;I0;t) = T e,tot (i;I0)*(1–exp(-t / τ)) (6) A measure T which depends on the heating time t is calculated. tot for the difference in temperature for the fuse i in new condition and at the end of its service life: T tot (i;I0;t) = (T e,tot -T e )*(1–exp(-t / τ)) (7) In step S17 or S18 the quantity 202219449 14 ΔT = ϑ 1 - ϑ soll (8). This value is used in the query according to step S19, namely whether ΔT ≥ T tot(9) and ΔT ≥ 2.5 K (10). Criterion (9) addresses the question of whether the heating indicates the end of the fuse's service life, and criterion (10) was introduced to ensure that the heating is significant enough to provide a statement about the service life. If both conditions are met, the end of service life is concluded (step S22) and the process is terminated (step S23). It is useful to send the end of service life to a central monitoring location and indicate a need to replace the fuse. If both criteria are not met, it can be checked whether criterion (10) is met (step S20), and if so, a warning can be issued that the fuse is significantly aged (step S21). The process then continues with step S12.The inventive approach is not limited to this exemplary embodiment, but can be used for other low-voltage components, e.g., the circuit breaker with temperature detection described in DE 102021 203 050 B3. Furthermore, the calculation steps do not necessarily have to be performed using the above formulas. Not only modifications of these formulas (e.g., considering more terms of the Taylor expansion of formula (1)) but also fundamentally different methods are conceivable. For example, it is possible to use a suitably trained 202219449 15 neural network or precalculated or predetermined tables.

Claims

202219449 16 patent claims 1. Method for checking the aging of a low-voltage component which is designed for introduction into an electrical circuit, in which - a first piece of temperature information relating to the low-voltage component is determined for a first point in time, - a second piece of temperature information relating to the low-voltage component is determined for a second point in time, - using the two pieces of temperature information, a first piece of information is determined which represents a measure of the heating between the points in time, - a second piece of information is determined which represents a measure of a comparable heating between the points in time for a corresponding low-voltage component in a known state, and - using the difference between the first and the second piece of information, a statement on the aging of the low-voltage components is derived. 2.Method according to claim 1, characterized in that the known condition of a corresponding low-voltage component is the end of its service life or new condition.

3. Method according to claim 1 or 2, characterized in that - the low-voltage component is provided with a current measuring device, - a current value is determined for checking aging with the aid of current measurement by the current measuring device, and - the second piece of information is determined as a function of this current value. 202219449 17 4. The method according to claim 3, characterized in that - by means of current measurement by the current measuring means, a current value is determined at times relevant for the method for determining aging, - a measure of the change in current between the times based on these current value determinations is used, and - the method is only carried out or the results of the method are only output as relevant aging information if a criterion for a small change in current related to this measure of the change in current is met. 5.Method according to one of the preceding claims, characterized in that - a value is determined as second information which represents a measure of comparable heating between the points in time for a corresponding low-voltage component at the end of its service life, - a value is determined as third information which represents a measure of comparable heating between the points in time for a corresponding new low-voltage component, and - the difference between the second and third pieces of information is used as a criterion for the significance of the statement on the aging of the low-voltage components or for information on aging, the difference between the second and third pieces of information is used.

6. Method according to claim 5, characterized in that - a current value is determined for checking the aging with the aid of current measurement by the current measuring device, and - the third piece of information is determined as a function of this current value. 202219449 18 7. Method according to one of the preceding claims, characterized in that - the low-voltage component is provided with at least one temperature sensor, - the first or second temperature information is determined by measuring the temperature using the at least one temperature sensor, and - the difference between the measured temperatures is used as the first information, which represents a measure of the heating between the points in time. 8.Method according to one of the preceding claims, characterized in that - the first temperature information is the temperature of the first low-voltage component at the first point in time, - to determine the second information or the third information, the temperature or heating of a comparable low-voltage component in the known state is determined, which it would assume or experience based on the temperature of the first low-voltage component after a period determined by the time difference between the first and second points in time with a comparable current flow.

9. Method according to claim 8, characterized in that to determine the second or third information, the ambient temperature at the first or second point in time outside the low-voltage component is measured and transmitted to the low-voltage component. 10.Method according to one of claims 8 or 9, characterized in that the determination of the second or third information is carried out by means of a formula-based description of the heating, a table or a neural network. 202219449 19 11. The method according to claim 10, characterized in that - the second or third piece of information is determined using a formula-based description of the heating, - a final heating that occurs as a function of the current flow is assumed for this purpose, and - an approach for this final heating and the approximation behavior is established.

12. The method according to one of the preceding claims, characterized in that the low-voltage component is a fuse, a low-voltage switch, or an energy monitoring device.

13. A device designed to carry out a method according to one of claims 1 to 12.

14. The device according to claim 13, characterized in that it comprises the low-voltage component. 15.Device according to claim 14, characterized in that the low-voltage component is provided with a current measuring means and at least one temperature sensor.

16. Device according to claim 14 or 15, characterized in that the low-voltage component has a receiver for receiving an ambient temperature measured outside the low-voltage components.

17. Computer program product comprising a computer program that performs the calculation steps of a method according to one of claims 1 to 12 when running on a processor.

Images