Aging inspection for low voltage components

Abstract

The invention relates to a method for checking the aging of a low-voltage component designed for placement in an electrical circuit. In this case, first temperature information relating to the low-pressure component is determined for a first time point, second temperature information relating to the low-pressure component is determined for a second time point, and first information representing a measure for the temperature rise between the time points is determined by means of the two pieces of temperature information. The first information is compared with second information representing a measure of similar temperature rise between points in time for a respective low-pressure component in a known state. A conclusion about the aging of the low-voltage component is then derived on the basis of the difference between the first information and the second information. According to the invention, the aging of the low-voltage component can be checked with low cost and high efficiency.

Description

Technical Field

[0001] The invention relates to a method for checking the aging of low-voltage components designed for insertion into a circuit, a device for carrying out the method according to the invention and a computer program product having a computer program which, when run on a processor, carries out the calculation steps of the method according to the invention. Background Art

[0002] In particular, live low-voltage components are subject to aging processes which depend not only on the external conditions but also on the loads during operation.

[0003] Examples of such low-voltage components are fuse applications, which age during operation at high temperatures, during operation with frequent load changes, and during overload operation. Such ageing can lead to changes in the triggering behavior and even to triggering during rated operation.

[0004] Advanced safety device solutions are sometimes equipped with sensor devices and communication devices to monitor usage information, for example.

[0005] For example, WO 2020 / 127486 A1, WO 2020 / 127488 A1, WO 2020 / 148015 A1 and DE 10 2018 213 522 A1 disclose fuse devices with an integrated measuring function.

[0006] When these fuses and low-voltage components in general reach the end of their service life, they need to be replaced. Although components should be replaced before they fail to avoid longer interruptions in operation, premature replacement will result in a waste of resources. It is therefore desirable to check for aging. Summary of the invention

[0007] The technical problem to be solved by the present invention is to make a contribution to this.

[0008] The above-mentioned technical problem is solved by a method according to claim 1 , an apparatus according to claim 13 and a computer program product according to claim 17 .

[0009] According to the invention, it is proposed to check the aging of low-voltage components which are designed to be inserted or introduced into a circuit (eg via corresponding connecting terminals and current paths extending in the low-voltage component). The low-voltage component can be used to monitor or interrupt the circuit.

[0010] Here and below, the conjunction “or” is always to be understood as a non-exclusive “or.” In particular, the conjunction “and” is also to be included here, ie in the above case, the low-voltage component can also be used for monitoring and interruption.

[0011] The low-voltage component can be, in particular, a fuse, a low-voltage switch or a measuring device for energy monitoring (often also referred to as a PMD or power measuring device).

[0012] According to the present invention, first temperature information related to the low-pressure component is determined for a first time point (preferably also at this time point). The first temperature information is, for example, a temperature characteristic of the low-pressure component. The temperature can be a temperature measured by a temperature sensor of the low-pressure component. However, it is also conceivable, for example, that the low-pressure component has a plurality of mutually exclusive temperature sensors, the measured values ​​of which are combined into the first temperature information.

[0013] In addition, for a second time point that is usually later (preferably also at this time point), second temperature information related to the low-voltage component is determined. In order to ensure similarity, it is preferably determined in the same way as for the first temperature information. With the help of these two temperature information, the first information is determined, and the first information represents a measure for the temperature rise between the time points. If the two temperature information represent temperature values, the first information can be the difference between these temperature values. In addition, the second information is determined, and the second information represents a measure for the similar temperature rise between the corresponding low-voltage components in the known state at each time point. The known state of the corresponding low-voltage component can be the end of its service life or new, that is, the purpose is to compare with the corresponding low-voltage component at the beginning or end of its service life. With the help of the difference between the first information and the second information (for example, in the form of the difference of two values), a conclusion about the aging of the low-voltage component is derived. Here, for example, the value of the temperature rise between each time point can be compared. However, it is also feasible, for example, to calculate the temperature value of the second time point with the help of the temperature rise and compare the temperature value.

[0014] Since the current in most circuits with corresponding low-voltage components is also not approximately constant and the temperature rise depends on the current flow, it is usually meaningful to take this into account. Therefore, in one embodiment, the low-voltage component is equipped with at least one current measuring device, and in order to check the aging, the current value is determined by means of a current measurement performed by the current measuring device. This is a suitable value, which can be, for example, the measured current value (possibly for direct current) or the average value of the measured current values ​​(for example the RMS (Root Mean Square) value of alternating current). The second information is then determined based on this current value.

[0015] According to the extended design of the present invention, it is considered that the current value used is usually not constant between two time points. In principle, it is feasible to track the change of this value and include it in the determination of the second information. However, it is less expensive and easier to operate to assume that the current value is sufficiently constant, that is, to determine the second information only based on the current value. According to one design of the present invention, a corresponding program is executed, wherein a criterion for whether the current value is sufficiently constant is checked, and the second information is determined only when the criterion is met. Specifically, for example, the current value at a time point related to the method for determining aging (for example, the first and second time points, and also the middle time point) is determined by means of a current measurement performed by a current measuring device. Then, a measure of the change of the current between the time points (for example, the magnitude of the difference of the current value at the first time point and the second time point) determined based on the current value is used. Only when the criterion for a smaller change of the current related to the measure of the change of the current (for example, the threshold value criterion for the magnitude of the difference of the current value at the first and second time points) is met, the method is executed or the result of the method is output as the relevant aging information.

[0016] According to the extended design of the present invention, the following value is determined as the second information, which represents a measure of similar temperature rise between each time point at the end of the service life of the corresponding low-voltage component, and the following value is determined as the third information, which represents a measure of similar temperature rise between each time point for the corresponding new low-voltage component. The difference or difference between the second information and the third information is then used as a criterion for the importance of the conclusion about the aging of the low-voltage component or as a criterion for the indicative information about aging. If the difference is too small (for example, the same order of magnitude as the inherent error caused by measurement, approximation, etc.), the result may not be convincing. This is checked according to the following extended design. In this extended design, in order to check aging, a current value (a suitable value, such as an RMS value in the case of alternating current) can be determined by means of current detection performed by a current measuring device, and the third information is determined based on the current value (preferably the second information is also determined).

[0017] According to one design of the present invention, the low-voltage component is equipped with at least one temperature sensor, and the first or second temperature information is determined by measuring the temperature with the at least one temperature sensor. The difference between the measured temperatures is then used as the first information, which represents a measure of the temperature rise between each time point.

[0018] According to one design of the present invention, the first temperature information is the temperature of the first low-voltage component at a first time point, and in order to determine the second information or the third information, the temperature of a similar low-voltage component in a known state is determined, and the temperature is taken as the starting point when the current is similar (as a criterion for similar currents, for example, it can be checked whether the current value between two time points is sufficiently constant) after a time period given by the time difference between the first time point and the second time point. Here, in order to determine the second or third information, the ambient temperature outside the low-voltage component can be measured at the first or second time point (for example, at a central location of a distribution box or through a central communication unit responsible for multiple low-voltage components) and transmitted to the low-voltage component.

[0019] According to one embodiment, the second or (if present) third information is determined by means of a formula-based description of the temperature increase, a table or a neural network. The second or third information can be determined by means of a formula-based description of the temperature increase, for which a final temperature or a final temperature increase set as a function of the current (which can be assumed to be constant) is assumed and, for example, an empirical formula is established for this final temperature or final temperature increase and an approximate behavior.

[0020] The invention also relates to an arrangement which may include a low-voltage component. The low-voltage component may be equipped with at least one current measuring device (such as a Rogowski coil, a shunt, a current transformer, etc.) and with at least one temperature sensor. In addition, the low-voltage component may also have a receiver for receiving an ambient temperature measured outside the low-voltage component (possibly centrally).

[0021] Furthermore, the technical solution of the present invention also relates to a computer program product having a computer program, which executes the calculation steps of the method of the present invention when running on a processor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be described in more detail in the following embodiments.

[0023] Figure 1 A fuse with a temperature sensor is shown,

[0024] Figure 2 A flow chart for the method according to the invention is shown.

[0025] Figure 3 shows the temperature rise characteristics of the new fuse compared to the temperature rise characteristics of the old fuse of the same design, and

[0026] Figure 4 The dependence of the final temperature rise of the fuse on the load current is shown. DETAILED DESCRIPTION

[0027] Figure 1 A fusible fuse 1 is shown schematically. The fusible fuse has a protective housing 2 and a further housing 12 which are arranged one behind the other in a longitudinal extension direction L and which together reach the height H of a standard NH fuse.

[0028] The fuse 1 has two connecting elements 3, which are made of an electrically conductive material, such as copper. The connecting elements 3 extend into the cavity of the protective housing 2 through openings formed in the closing cover 4. At least one so-called fuse conductor 5 is arranged in the cavity, which electrically connects the two connecting elements 3 to each other.

[0029] Elements 10 for monitoring power consumption parameters are arranged in a further housing 12, and include a current transformer 11 for measuring the 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.

[0030] The total construction space required by the protective housing 2 and the other housings 12 is the same size as the construction space of a standardized NH fuse, i.e. the sum of the construction spaces required by the protective housing 2 and the other housings 12 corresponds to the predefined construction space of a standardized NH fuse, wherein in addition to the actual fuse, the measuring device is also integrated in this construction space. In this way, the fuse 1 can also be used for retrofit applications within the scope of retrofitting or modernization of existing electrical equipment, wherein a conventional fuse without a measuring device is replaced by the fuse according to the invention.

[0031] The height H of the fuse device 1 is divided into a first height H D The first section and the second section having a second height H M The first height H D Here, it refers to the height of the pressure body 2, that is, the actual protective body 2 of the fuse 1, and the second height H M This refers to the height of the second housing 12 in which the measuring device 10 is arranged. The requirements placed on such a housing with regard to its mechanical stability are also significantly lower.

[0032] The current transformer 11 and the temperature sensor 15 are connected to a processing device 14 for transmitting corresponding current and temperature measurement signals. Figure 1 Schematically shown as a printed circuit board in FIG. The transmission device 13 is connected to the processing device 14 shown as a printed circuit board. The transmission device 13 can be, for example, an RFID module, wherein active RFID and passive RFID solutions are conceivable. For this purpose, other (preferably wireless) transmission technologies such as Bluetooth, Zigbee or Thread can also be considered.

[0033] Figure 2 The flow of the method according to the invention which can be run, for example, in a processing device 14 is shown. The start of the method (step S1) is triggered, for example, by time information. For example, it can be provided that the aging check is carried out at regular time intervals, for example every day. For this purpose, date information of a timer or clock can be transmitted to the processor according to the present invention. Figure 1 Alternatively, according to Figure 1 The processing device itself also includes a clock. If the fuse is in sleep mode in which the processing device is not activated, the date information transmitted from the outside is meaningful. The date information is then compared with the scheduled date for the next aging check and a check is performed if the check date is reached or exceeded.

[0034] Often, a plurality of fuses are installed in a power distribution system (e.g. in a fuse box). It is usually advisable to carry out an aging check on all relevant fuses, since the aging behavior usually differs due to design deviations, different loads or different degrees of aging (e.g. due to replacement of individual fuses). Figure 2 This is illustrated in FIG. 1 by the loop of step S2 . The different fuse types are differentiated by an identifier (eg MLFB or maschinenlesbare Fabrikatsbezeichnung, machine-readable brand name).

[0035] The temperature rise performance of various types of fuses was tested at the factory, and an empirical formula was determined.

[0036] For new fuses, the temperature rise is described as follows. Temperature rise is here referred to as a change in temperature, usually a rise in temperature. Temperature rise is represented by the letter T in the following formulas, while temperature is represented by the Greek letter It means that the temperature rise during the time period Δt=t2-t1 is , where the notation is simplified when t1=0 and t2=t.

[0037] If the current I0 is applied, the fuse heats up. Immediately after the current is applied, the temperature of the fuse is not much different from the ambient temperature. The temperature then rises and approaches a limit value over time, which corresponds to the maximum temperature at the current I0. Experience has shown that the rise or temperature increase can be approximately described with the aid of an exponential function and is therefore proportional to (1-exp(-t / τ)), where exp represents the exponential function, t represents the time, and τ represents a constant characteristic of the temperature increase (thermal time constant). The final temperature increase depends on the current I0. By Taylor expansion of the difference between the final temperature and the ambient temperature according to the current I0, an approximate formula can be established for the final temperature increase. T e(i;I0) represents the final temperature rise of the type i fuse. If the Taylor series terminates after the quadratic term, the following approximation applies:

[0038] (1)

[0039] Before the current flows, the temperature of the fuse corresponds to the ambient temperature. With the above mentioned rising behavior, the heating of the fuse can then be described as follows:

[0040] (2)

[0041] An empirical formula can also be used for the thermal time constant τ. This time constant depends on the current intensity I0, because the larger the current, the faster the temperature rises. Considering the linear dependence of τ on the current intensity, the following formula can be obtained:

[0042] (3)

[0043] The core idea of ​​the invention is that the behavior and ultimate temperature rise of the fuse change over time due to aging. Figure 3 The following figure shows the temperature rise performance of the new fuse, where the lower curve describes the temperature rise performance of the old fuse of the same design. The final temperature rise depends on the load current, such as Figure 4 shown.

[0044] The temperature rise of the fuse at the end of its service life can also be calculated using the formula corresponding to formula (1). e,tot represents the final temperature rise of the fuse at the end of its service life. Thus, equation (1) applies analogously:

[0045] (4)

[0046] The coefficients of equations 1, 3, and 4 are determined at the factory through testing and are entered according to Figure 2 These coefficients are either already present in the fuse's memory upon delivery or are transferred to the fuse from a central location before the start of the method (the provision of the coefficients is Figure 2 In step S3 of the embodiment). In step S4, the charging current I0 of the fuse and the current temperature of the fuse are measured. If there are I0 and If the value is not found, the timer or timer is reset to zero (t=0, step S5). Then the load factor k is calculated, which is defined as the ratio of the charging current I0 to the rated current I r(steps S6 and S7). In the next step S8, it is checked whether the load factor is greater than 0.4. If the load factor is not greater than 0.4, wait for 10 seconds (step S9) and then continue with step S4. At low load (here defined as k≤0.4), Figure 3 The deviation of the heating curve shown is very small and the method reaches its limits due to tolerances or inaccuracies. It is therefore reasonable to carry out the method according to steps S10-S21 only when the load exceeds the threshold value. Depending on the fuse and the application scenario, other threshold values ​​other than k=0.4 and other waiting times other than 10 seconds are naturally conceivable or may be more advantageous. If the load is high enough, T is determined in step S10 or S11 according to formulas (1), (3) and (4) by the coefficients according to step S3. e , T e,tot and τ. Then, before re-measuring the load current and the fuse temperature and additionally measuring the ambient temperature, wait for 10 seconds (step S12) and increment the timer accordingly (step S13). The ambient temperature does not have to be measured by the fuse itself, but can be measured at a central location and transmitted to the fuse. Central measurement can be performed, for example, by means of a communication module described in DE 202021000293 U1. The ambient temperature can also be measured centrally in a switch cabinet with multiple fuses and then transmitted from there to the fuses of the switch cabinet. A data collector can also be responsible for multiple fuses, which transmits the value of the ambient temperature measured by itself or obtained from the measuring location to multiple fuses. The measurement or its time point is marked with the subscript 1, and the corresponding values ​​of the load current, ambient temperature and fuse temperature are marked as I1, I2, I3, I4, I5, I6, I7, I8, I9, I10, I21, I22, I11, I23, I24, I25, I26, I27, I28, I29, I30, I31, I32, I33, I34, I35, I36, I37, I38, I39, I40, I41, I42, I43, I44, I45, I46, I47, I48, I49, I50, I51, I52, I53, I54, I55, I56, I57, I58, I59, I60, I61, I62, I63, I64, I65, I66, I71, I72, I73, I74, I80, I81, I82, I83, I84, I85, I86, I87, I88, I89, I90, I91, I92, I93, I94, I95 and (Steps S14 and S15). In step S16, it is checked whether the load current has changed significantly compared to I0 measured in step S4. The criterion is that the deviation is less than 5%, i.e. If the deviation is too great, a waiting period of 10 seconds is followed (step S9 ) and the process then continues with step S4 . Otherwise, a value for assessing the aging of the fuse is calculated in step S17 .

[0047] The starting point of the calculation according to step S17 is here the value of the charging current I0 obtained in step S4 and the current temperature of the fuse The value of . It is taken into account that the fuse continues to heat up during the time t between step S4 and the measurement of the corresponding variable in step S14. This temperature increase depends on the aging of the fuse. For new fuses, the following formula can be established, which can be used to calculate the predetermined temperature The starting point is thus the temperature of the fuse measured in step S4 or at time zero. When the limit value t→∞, the temperature of the fuse is close to the limit temperature or termination temperature. The limit temperature is determined by the ambient temperature and the final temperature rise T e The above gives the difference T e Assuming that the temperature rise from step S4 (zero time point) conforms to (1-exp(-t / τ)), then :

[0048] (5)

[0049] (At time t=0, the temperature is , at time t=∞, the temperature is +T e , the heating process starting from time zero has a behavior that can be described by (1-exp(-t / τ))).

[0050] The fuse has a higher final temperature rise near the end of its service life. Analogously to equation (2), we obtain:

[0051] (6)

[0052] A measure T for the difference in the temperature rise of a type i fuse in the new state and at the end of its service life is introduced as a function of the temperature rise duration t. tot :

[0053] (7)

[0054] In step S17 or S18, define the parameter

[0055] (8).

[0056] This parameter is used in the query according to step S19, namely to inquire whether

[0057] ΔT ≥ T tot (9)

[0058] and whether

[0059] ΔT ≥ 2.5 K (10).

[0060] Criterion (9) applies to the question of whether the temperature increase indicates the end of the service life of the fuse, while criterion (10) is introduced to ensure that the temperature increase is significant enough to draw conclusions about the service life. If both conditions are met, the end of the service life is inferred (step S22) and the method ends (step S23). It is sensible to send the end of the service life to a central monitoring location and request replacement of the fuse. If both criteria are not met, it can be checked whether criterion (10) itself is met (step S20) and, if met, a warning is issued that the fuse is significantly aged (step S21). Then continue with step S12.

[0061] The measures according to the invention are not limited to this embodiment, but can be used for other low-voltage components, such as the circuit breaker with temperature detection device described in DE 102021 203 050 B3. The calculation step does not have to be performed by the above formula. Not only can these formulas be modified (for example, more terms of the Taylor expansion of formula (1) are considered), but also different methods in principle can be considered. For example, a properly trained neural network or a pre-calculated or predetermined table can be used.

Claims

1. A method for checking the aging of a low-voltage component designed for placement in an electrical circuit, wherein - determining first temperature information associated with the low-pressure component for a first point in time, - determining second temperature information associated with the low-pressure component for a second point in time, - determining first information with the aid of two pieces of temperature information, said first information representing a measure for the temperature increase between said points in time, - determining second information, which represents a measure of a similar temperature increase between said points in time for the corresponding low-pressure component in the known state, and - Drawing conclusions about the aging of the low-voltage component using the difference between the first information and the second information.

2. The method according to claim 1, characterized in that The known state of the corresponding low-voltage components is end of service life or new.

3. The method according to claim 1 or 2, characterized in that: - low voltage components are equipped with current measuring devices, - to check for aging, the current value is determined by means of a current measurement using a current measuring device, and - determining second information based on the current value.

4. The method according to claim 3, characterized in that - determining a current value at a point in time that is relevant to the method for determining aging by means of a current measurement by means of a current measuring device, - using a measure for the change in current between said points in time determined based on the current values ​​performed, and The method is only carried out or the result of the method is output as relevant aging information if a criterion for a small change in the current, which is correlated with the measure for the change in the current, is met.

5. The method according to any one of the preceding claims, characterized in that - determining as second information a value which represents a measure of the similarity of the temperature increase between the points in time for the respective low-voltage component at the end of its service life - determining a value as third information which represents a measure of the similarity of the temperature increase between the points in time for the respective new low-pressure component, and - using the difference between the second information and the third information as a criterion for the significance of the conclusion regarding the aging of the low-voltage component or as a criterion for the indicative information regarding the aging.

6. The method according to claim 5, characterized in that - to check for aging, the current value is determined by means of a current measurement using a current measuring device, and - determining third information based on the current value.

7. The method according to any one of the preceding claims, characterized in that - the low-voltage components are equipped with at least one temperature sensor, - determining the first or second temperature information by measuring the temperature by means of at least one temperature sensor, and - using the difference between the measured temperatures as first information, said first information representing a measure for the temperature rise between said points in time.

8. The method according to any one of the preceding claims, characterized in that - the first temperature information is the temperature of the first low-pressure component at a first time point, - In order to determine the second information or the third information, the temperature or temperature increase of a similar low-voltage component in a known state is determined, which temperature or temperature increase adopts the temperature after a period of time given by the time difference between the first time point and the second time point when the current is similar, starting from the temperature of the first low-voltage component, or experiences a temperature increase after a period of time given by the time difference between the first time point and the second time point when the current is similar, starting from the temperature of the first low-voltage component.

9. The method according to claim 8, characterized in that In order to determine the second or third information, the ambient temperature is measured outside the low-voltage component at the first or second time and transmitted to the low-voltage component.

10. The method according to claim 8 or 9, characterized in that: The second or third information is determined with the aid of a formula-based description of the temperature rise, a table or a neural network.

11. The method according to claim 10, characterized in that - determine the second or third information with the aid of a formula-based description of the temperature rise, - for this purpose it is assumed that the resulting temperature rise due to the current - Determine the formula for the final temperature rise and approximate performance.

12. The method according to any 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 the method according to one of claims 1 to 12.

14. The device according to claim 13, characterized in that The device comprises low pressure components.

15. The device according to claim 14, characterized in that The low-voltage component is equipped with a current measuring device and at least one temperature sensor.

16. The device according to claim 14 or 15, characterized in that The low-pressure component has a receiver for receiving an ambient temperature measured outside the low-pressure component. 17 . A computer program product comprising a computer program which, when executed on a processor, performs the calculation steps of the method according to claim 1 .

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