Method for evaluating a switching event

Abstract

The invention relates to a method for evaluating a switching event in an electromechanical switching device which is inserted into a load current path, comprising the following steps: - Acquiring temperature-current value pairs (Tm,Im), comprising a temperature measurement (Tm) of a temperature measured at a temperature measuring point (X) of the switching device (10) and a current measurement (Im) of a current (I) flowing through the load current path, which was measured simultaneously with the temperature measurement (Tm); - Recording of said temperature-current value pairs, which were recorded at different times; - Comparison of at least one temperature-current value pair at a time before the switching event with at least one temperature-current value pair at at least one time after the switching event; and - Evaluating the switching event based on comparison.

Description

[0001] The present invention relates to a method for evaluating a switching event.

[0002] Electromechanical switching and protective devices switch using moving contacts. These switching events, on the one hand, and environmental influences such as corrosion, on the other, cause changes in the contact surfaces and thus in the contact resistance. This change occurs more gradually due to environmental influences, but more abruptly during a switching event.

[0003] With every switching event, whether switching on or off, especially at higher currents and voltages, the material on the contact surface is rearranged, which can lead to an abrupt increase or decrease in contact resistance. An increase in contact resistance leads to an increase in power dissipation and consequently in the device temperature. It cannot therefore be ruled out that a switching event could cause a switching device to enter a borderline thermal state, even if sufficient contact material is still present. A switching event can therefore cause the switching device to become so hot that it fails or catches fire.

[0004] To mitigate such risks, determining the current device state after a switching event in an electromechanical switching device can be useful. Therefore, there is a need for a method for evaluating a switching event in an electromechanical switching device.

[0005] The object is achieved by a method according to claim 1. This method is for evaluating a switching event in an electromechanical switching device that is inserted into a load current path. The term “electromechanical switching device” encompasses any electromechanical switching and protective device that has movable switching contacts. It is irrelevant whether it is a multiple-break switching device or a single-break switching device. The type of switch triggering, e.g. actuator, maglatch or switch lock, is also irrelevant. The invention is applicable to all types of switching devices that have movable switching contacts. The contact-based switching devices to which the present invention is applicable follow various basic concepts. On the one hand, there are switching devices that have single-break or multiple-break contacts, whether linear or rotary.Furthermore, these switching devices are operated or driven in different ways. Switchable spring-loaded mechanisms are used, e.g., bistable switch locks such as in MCBs (Miniature Circuit Breakers) and MCCBs (Molded Base Circuit Breakers), or tensionable spring-loaded mechanisms such as in ACBs (Air Circuit Breakers). A contactor contact can also be operated using a magnetic actuator. Even direct switching of blade contacts, such as in LBSs (Load Break Switches), is possible. The force or energy can be introduced manually, by motor, or, in the case of a contactor, by applying voltage. However, all other possible designs of contact-based switching devices are also included.

[0006] The switching device is inserted into a load current path. Via the load current path, electrical energy is transported from an electrical energy source, e.g. an electrical supply network in which a mains voltage is provided, to an electrical load, also referred to as an electrical consumer, e.g. an electric motor. The load current path can be designed, for example, as a 3-phase power line. The switching device can have input terminals (e.g. L1, L2, L3) and outgoing terminals (e.g. T1, T2, T3), with one end of the power line connected to the electrical energy source (mains voltage) being connected to the input terminals and one end of the power line connected to the consumer being connected to the outgoing terminals.An electromechanical switching device is provided inside the switching device, which is designed such that in a first switching state of the switching device (switching state "closed"), a connection between the input terminals and the output terminals is electrically conductive, i.e., an electromechanical switch with closed contacts, and in a second switching state of the switching device (switching state "open"), a connection between the input terminals and the output terminals is electrically non-conductive, i.e., an electromechanical switch with open contacts. A change from one of the two switching states to the other is referred to as a switching event.

[0007] The method includes a step in which temperature-current value pairs are recorded. A temperature-current value pair comprises a temperature measurement value of a temperature measured at a temperature measuring point of the switching device. A temperature-current value pair also comprises a current measurement value of a current flowing through the load current path, which was measured simultaneously with the temperature measurement value.

[0008] A temperature measurement is a temperature value determined by a temperature sensor. A temperature measurement point is a position inside the device housing or on an external surface of the device housing of the switching device where a temperature sensor can be positioned to measure the temperature. A current measurement is a current value determined by a current sensor.

[0009] The method includes a step in which said temperature-current value pairs, which were recorded at different times, are recorded. Thus, a time series of temperature-current value pairs is recorded, with a first subset of the time series being recorded before the switching event and a second subset of the time series being recorded after the switching event. A time series of measured values ​​is a chronologically ordered sequence of measured values; the measured values ​​can be recorded at any time intervals.

[0010] The method comprises a step in which at least one temperature-current value pair at a time before the switching event is compared with at least one temperature-current value pair at at least one time after the switching event. The comparison comprises a comparison of the temperature measured values ​​and a comparison of the current measured values.

[0011] The method includes a step in which the switching event is evaluated based on the comparison. The basic principle is that, on average, the change in the contacts caused by a switching event is greater the higher the current (power) switched by the switching event. This means that, on average, a switching event at rated current causes less contact wear than a switching event during an overload, and that a switching event during an overload causes less contact wear than a switching event during a short circuit. The greater the change in the contacts (contact wear) caused by a switching event, the greater the probability that the contact resistance, and thus the heat generated in the switching device, will be greater after the switching event than before the switching event. The result of the evaluation can be used, for example, in a contract wear indicator.

[0012] The invention is based on the idea that, to evaluate a switching event in an electromagnetic switching device, the general condition of the contacts (= contact condition) is considered before and after the switching event. The contact condition in an electromagnetic switching device, in turn, is reflected in the temperature prevailing within the electromagnetic switching device. According to the invention, the measured variable of temperature is used to evaluate a switching event, since this best describes the quality of the general condition of the contacts (= contact condition) in an electromagnetic switching device.A key difference from conventional methods used to evaluate a switching event is that a temperature measurement is used for the assessment and evaluated as a function of time in such a way that a temporal trend and a determination of the thermal service life of the contacts, in particular a remaining thermal service life, is possible. In this way, condition monitoring of a switching device is possible based on a quality characteristic for the switching device, namely the temperature. In addition, a forecast regarding the thermal service life of the contacts can be derived. This predicted service life may be shorter than a service life predicted based on a currently measured temperature, which does not take into account temperature measurements recorded in the past.

[0013] The more measured values ​​are available, the more reliably a trend of the contact condition is depicted; therefore, in order to obtain sufficient smoothing of the measured values, it is advantageous to average the temperature measured values ​​to obtain a temperature mean.

[0014] Advantageous embodiments and further developments of the invention are specified in the dependent claims. The method according to the invention can also be further developed according to the dependent device claims, and vice versa.

[0015] According to a preferred embodiment of the invention, a temperature sensor is arranged in the switching device on the load current path. This is a load current path that can be switched by the switching contacts of the switching device. Since the contact point, i.e., the point where the contacts touch, cannot be selected for temperature measurement in many cases, a nearby suitable point can be chosen instead. This detects a critical thermal location (= hot spot) in the switching device. To assess the contact condition, the temperature at the hot spot is evaluated before and after a switching event.

[0016] According to a preferred embodiment of the invention, the comparison of the temperature-current value pairs before and after the switching event includes a comparison of the absolute temperature values ​​Tabs. The change in the absolute temperature Tabs or a temperature difference ΔT = Tabs - Tamb, where Tamb is the ambient temperature of the switching device, can be used as an indicator of a switching event, i.e., a change in the contact state.

[0017] According to a preferred embodiment of the invention, the temperature measurements are set in relation to various temperature thresholds, which correspond to limit temperatures of the switching device. Since limit temperature values ​​are known for switching devices, these can be used for the evaluation. It is also possible for the operator of the switching device to set limit temperatures or warning thresholds known to the operator of the switching device in the evaluation process.

[0018] The limit temperature value of the switching device can be a permissible temperature of the switching device. The permissible temperature of the switching device is defined by an institution that knows the materials used in the switching device, e.g., a manufacturer or operator of the switching device. The permissible temperature of the switching device represents the upper limit of a first temperature range in which the switching device does not experience accelerated thermal aging. In this first temperature range, the thermal service life decreases in proportion to the passage of time; e.g., in 24 hours, the thermal service life also decreases by 24 hours.

[0019] The limit temperature value of the switching device can be a maximum permissible temperature of the switching device. The maximum permissible temperature of the switching device is defined by an institution that knows the materials used in the switching device, e.g. a manufacturer or an operator of the switching device. The maximum permissible temperature forms the upper limit of a second temperature range in which the switching device thermally ages more quickly due to an increased temperature than in the first temperature range. In this second temperature range, which includes all temperature values ​​that are greater than the permissible temperature and less than or equal to the maximum permissible temperature, the thermal service life decreases faster than time passes, e.g. in 24 hours the thermal service life decreases by more than 24 hours, e.g. by 28 hours. Materials, e.g. plastics, exhibit a specific temperature-time characteristic curve for a material property.This temperature-time characteristic takes into account the safeguarding of important material properties, such as strength or electrical insulation capacity. The temperature-time characteristic can be used to determine the permissible temperature of the material. As long as the permissible temperature is not exceeded, the material can easily withstand this permissible temperature over a long period of time, e.g., 25 years, without sustaining damage. Furthermore, the temperature-time characteristic can also be used to determine the maximum permissible temperature. A design limit for the maximum permissible temperature can be derived from a strength limit value.

[0020] For example, the range between a nominal temperature and a maximum permissible temperature can be divided into three or more evaluation zones. For example, a first evaluation zone is "green" for a slight temperature increase or decrease of, for example, < 10%; a second evaluation zone is "yellow" for a significant temperature increase or decrease of, for example, 10 to 30%; a third evaluation zone is "orange" for a temperature increase or decrease of, for example, 30 to 50%; and a fourth evaluation zone is "red" for a temperature increase or decrease of, for example, > 50%. Alternatively, any other type of visualization can be used.

[0021] According to a preferred embodiment of the invention, the temperature-current value pairs before and after the switching event are compared using calculated values ​​based on the measured temperature values. These calculated values ​​can also be referred to as characteristic values.

[0022] According to a preferred embodiment of the invention, the calculation values ​​are quotients Q, which are calculated from the temperature measured values ​​Tm, which are each divided by an associated current measured value Im: Q = Tm / Im or by a squared associated current measured value Im: Q = Tm / Im 2 are divided. The associated current measurement values ​​Im are the measured values ​​of a current flowing through the load current path, which are each measured simultaneously with the temperature measurement values ​​Tm at a current measurement point Q of the switching device.

[0023] According to a preferred embodiment of the invention, the calculated values ​​are equal to dimensionless quotients Q, which are calculated from the temperature measured values ​​Tm divided by a temperature reference value Tref: Q = Tm / Tref. The quotient Q describes the ratio of the absolutely measured temperature Tm to a reference temperature Tref, e.g. for a brand-new switching device at rated current I_standard: Q = Tm / Tref(@I_standard). It is possible that the reference temperature Tref refers to a brand-new circuit breaker. It is possible that the reference temperature Tref refers to a circuit breaker in the standard test setup of DIN EN 60947-2:2020-11 Low-voltage switchgear and controlgear - Part 2: Circuit breakers. It is also possible that the reference temperature Tref refers to a permissible temperature of a material installed in the switching device that forms a thermal weak point of the switching device.But any other temperature comparison value can also be used as reference temperature Tref.

[0024] According to a preferred embodiment of the invention, the comparison of at least one temperature-current value pair at a time before the switching event with at least one temperature-current value pair at at least one time after the switching event is carried out by dividing a calculated value at one or more measurement times before a switching event by a calculated value at one or more measurement times after the switching event. The switching event is then evaluated based on the comparison.

[0025] According to a preferred embodiment of the invention, the comparison of the temperature-current value pairs before and after the switching event involves dividing the temperature values ​​before and after the switching event. This allows a dimensionless characteristic value to be generated. A value = 1 then means no change due to the switching event, a value < 1 means an improvement in the contact condition, and a value > 1 means a deterioration in the contact condition. Alternatively, a dimensionless characteristic value can also be generated differently, so that other values ​​indicate a constant, improving, or deteriorating contact condition.

[0026] According to a preferred embodiment of the invention, the evaluation of the switching event comprises classifying the switching event as a switching event at a current during normal operation, as a switching event at an overload current, or as a switching event at a short-circuit current. A switching event at a current during normal operation means that the current strength approximately corresponds to the nominal current; at such current strengths, the contacts generally experience only a small and gradual change. A switching event at an overload current generally only causes the contacts to experience a greater change than a switching event at a nominal current. A switching event at a short-circuit current generally causes the contacts to experience the greatest change; e.g., according to the standard for circuit breakers DIN EN IEC 60947-2, such a switching device is designed for three such maximum switching events.

[0027] According to a preferred embodiment of the invention, the method comprises the following steps: A current range covered by the recorded current measurement values ​​is divided into two or more current classes. A current class is a current range that lies between a lower range limit and an upper range limit. It is possible to form current classes that correspond to a fraction of the rated current range In of the switching device, e.g. (0.5 ± 0.05) × In, (0.6 ± 0.05) × In, (0.7 ± 0.05) × In, etc. An alternative suggestion for the current classes is, for example, 30 - 40% / 40 - 50% / 50 - 60% / 60 - 70% / 70 - 80% / 80 - 90% of In of the switching device. The recorded temperature-current value pairs are each divided into the current class in which the current measured value of the temperature-current value pair.For temperature-current value pairs in the same current class, at least one temperature-current value pair at a time before the switching event is compared with at least one temperature-current value pair at at least one time after the switching event.

[0028] The prevailing temperature is measured for defined time intervals during which a constant current is present. A constant current is present as long as the current is within a predefined current range [I-; I+] between a lower range limit I- and an upper range limit I+. The corresponding temperature-current value pairs are saved. After a switching event, the prevailing temperatures are again recorded for further time intervals during which a constant current is present. The contact condition is assessed after comparing at least one temperature-current value pair at a time after the switching event with at least one temperature-current value pair at a time before the switching event, provided the compared value pairs are in the same current class.

[0029] According to a preferred embodiment of the invention, a temperature-current value pair is only recorded when temperature measurements lie within a defined temperature tolerance band. A query is made as to whether a temperature fluctuation lies within a predefined tolerance band. As long as temperature fluctuations lie outside the tolerance band, the switching device is not yet in a thermally steady state, and no temperature can be assigned to the current value. As soon as temperature fluctuations lie within the tolerance band, the switching device is in a thermally steady state, and the temperature can be assigned to the current value. Only in the thermally steady state can temperature-current value pairs be formed and used in a comparison.

[0030] According to a preferred embodiment of the invention, a temperature-current value pair is formed from an average of several individual measurements. To avoid measurement errors, the measured values, whether of temperature or current, are recorded during periods of approximately constant temperature and current (load). This ensures that no compensating processes distort the evaluation. To further improve the evaluation quality, the calculation of averages over such a period with constant temperature and current measured values ​​is advantageous.

[0031] According to a preferred embodiment of the invention, an estimate is made of when the temperature measurements will reach a predefined limit. By comparing a temperature change caused by a switching event at a specific current intensity with a maximum permissible temperature in the switching device, an estimate can be made of how many shutdowns from a breaking current with a comparable current intensity are still possible before the switching device reaches its maximum permissible temperature and the service life of the switching device ends. Thus, a message can be implemented for an operator of the switching device, indicating to the operator that the switching device will survive the next switching event with a similar current intensity or that it will lead to the switching device reaching its service life.This estimate can be compared with a number of electrical switching cycles specified by the switchgear manufacturer or with an algorithm for determining the remaining service life of the contacts. It is possible that the result of the different calculations indicating the shorter service life will be given priority.

[0032] According to a preferred embodiment of the invention, the method comprises a step in which a temperature sensor for detecting a temperature measurement value is positioned on a current path of a switching contact of the switching device. The measurement temperature is thus determined on a current path of the switching device through which a load current is conducted. In this case, the measurement point is on the current path. If the current sensor is electrically insulated, the measurement point can be directly on the surface of the current path; otherwise, it can be at a sufficiently large distance from the current-carrying current path to prevent electrical flashover from the current path to the temperature sensor. The advantage here is that the measurement temperature can be measured at a primary heat source of the switching device, namely a current path.

[0033] According to a preferred embodiment of the invention, a measuring temperature is determined at a measuring point of the switching device, wherein said measuring point is a thermal weak point of the switching device. The thermal weak point is a component near a hotspot or the hotspot itself, wherein the hotspot is the warmest point of the switching device. To determine the thermal weak point, both the temperature conditions of the component and the temperature-time characteristic of the component material must be taken into account. The thermal weak point must be determined individually for each switching device. If the actual hotspot or the actual thermal weak point cannot be selected in a switching device, a suitable measuring point nearby can be chosen as an alternative.

[0034] In the following, the invention is explained using several embodiments with the aid of the accompanying drawings. Each drawing is schematic and not to scale. Fig. 1 a switching device; Fig. 2 a T / It diagram in which the time courses of temperature measurements and current measurements before and after a switching event are plotted; Fig. 3 a Tt diagram in which the time course of temperature averages, which are derived from the measured values ​​of Fig. 2 were formed, is registered; Fig. 4 a T / It diagram in which the time courses of temperature measurements and current measurements before and after three different switching events are plotted; Fig. 5 a Tt diagram in which the temporal course of temperature measurements is entered; Fig. 6 a Qt diagram in which the time course of the dimensionless calculated value Q = T_after / T_before is entered; and Fig. 7 an EV-t-diagram, in which the time course of an evaluation variable EV, which is determined by a quotient of the calculated values ​​of Fig. 6 is formed, is registered; and Fig. 8 a flow chart.

[0035] Fig. 1 shows a switching device 10 for switching a load current flowing through a load current line 16 from a voltage source, e.g., a power transformer, to an electrical load, e.g., an electric motor. The switching device 10 has a housing 20 with load current connections 15, 15', which are divided into input terminals 15 and output terminals 15'. The load current line 16 is electrically connected to the load current connections 15, 15' such that the switching device 10 is connected between two ends of the load current line 16. Inside the housing 20, the load current connections 15 are each electrically connected to a switching contact 11 of a fixed switching contact pair 11 by means of a current path 14.The switching contacts 11 of the fixed switching contact pair 11 are electrically connected by a movable contact bridge 13, which carries switching contacts 12 of a movable switching contact pair 12, if the contact bridge 13 is in a first, closed position; in this position, there is a continuous electrical connection of the load current connections 15. In a second, open position of the contact bridge 13, the two switching contacts 11 of the fixed switching contact pair 11 are electrically separated; in this position, the load current connections 15 are galvanically isolated. An actuator unit 17 is able to move the contact bridge 13 back and forth between the two positions; such a change in position of the contact bridge 13 represents a switching event. Such a switching event is triggered by controlling the actuator unit 17 to change position. The actuator unit 17 can be controlled internally in the switching device 10, e.g.In the case of a circuit breaker, this occurs through thermally or magnetically induced tripping. Such control of the actuator unit 17 can also be achieved through an external control signal, e.g., in the case of a contactor, through a control command that is sent via a control line 19 to a control current connection 18 of the actuator unit 17.

[0036] Inside the housing 20, a temperature sensor 23 is arranged at a first measuring point X, a temperature measuring point. The first measuring point X is located on the current path 14 of the switching device 10. This is the warmest point of the switching device 10, the so-called "hotspot." The temperature measurements recorded by the temperature sensor 23 are transmitted to an evaluation unit 30 via a data line 24.

[0037] Inside the housing 20, a current sensor 21 is also arranged at a second measuring point Y, a current measuring point. The second measuring point Y is located on the current path 14 of the switching device 10. The current measured values ​​detected by the current sensor 21 are transmitted to the evaluation unit 30 via a data line 22.

[0038] The evaluation unit 30 has a computing unit that can compare the received temperature measurements and, if necessary, determine a thermal lifetime LD(T) of the switching device 10. A comparison result determined by the evaluation unit 30 can be transmitted to an HMI 32 via a transmission medium 31 and communicated to a user of the switching device 10 via the HMI 32.

[0039] Fig. Figure 2 shows a T / It diagram in which temperature T and current I are plotted on the y-axis and time t on the x-axis. The diagram shows the temporal progression of temperature measurements Tm and current measurements Im. A switching event occurs at time 35. Switching event 35 is a switching event N at rated current, i.e., the current present in the load current path during switching event N is <= IN (IN = rated current of the switching device).

[0040] For time intervals Δt1 to Δt7, in which the current Im in the load current path is approximately constant, the temperature and current measured values ​​are recorded, and temperature-current value pairs [Tm_i, Im_i] are generated. For this purpose, the current range covered by the recorded current measured values ​​Im is divided into several current classes 46, each of which corresponds to a fraction of the rated current range In of the switching device, e.g., (0.5 ± 0.05) × In, (0.6 ± 0.05) × In, (0.7 ± 0.05) × In, etc. The recorded temperature-current value pairs are each assigned to the current class 46 in which the current measured value of the temperature-current value pair lies. For temperature-current value pairs in the same current class 46, a comparison is made of at least one temperature-current value pair at a time before the switching event 35 with at least one temperature-current value pair at at least one time after the switching event.

[0041] Fig. 3 shows that after the switching event 35, temperature mean values ​​Tx, Ty, Tz before the switching event 35 are compared with temperature mean values ​​Tx1, Ty1, Tz1 after the switching event 35, whereby all temperature mean values ​​Tx, Ty, Tz, Tx1, Ty1, Tz1 were formed from the temperature measured values ​​Tm within time intervals Δt in which approximately the same current strength prevailed, namely, in this example, temperature mean values ​​that all fall into the current class 0.5 In, thus being directly comparable with each other. Fig. Figure 3 shows that switching event 35 did not cause any significant change in temperature; this is evident from the fact that all temperature mean values ​​lie within a tolerance band [T-; T+].

[0042] Fig. Figure 4 shows a T / It diagram in which temperature T and current I are plotted on the y-axis and time t on the x-axis. The time profiles of temperature measurements Tm and current measurements Im are plotted in the diagram. For time intervals Δt1 to Δt6, during which the current Im in the load current path is approximately constant, the temperature measurements and current measurements are recorded, and temperature-current value pairs [Tm_i, Im_i] are formed.

[0043] A switching event occurs at times 35, 36, and 37. Switching event 35 is a switching event N at rated current, i.e., the current present in the load current path at switching event N is <= IN (IN = rated current of the switching device). Switching event 36 is a switching event 0 at overload current, i.e., the current present in the load current path at switching event O is in the range between IN and 6 IN. Switching event 37 is a switching event S at short-circuit current, i.e., the current present in the load current path at switching event S is > 6 IN.

[0044] The current range covered by the recorded current measurements is divided into several current classes 46. The temperature-current value pairs [Tm_i, Im_i] are assigned to current classes 46, each corresponding to a fraction of the rated current range In of the switching device, e.g., (0.5 ± 0.05) × In, (0.6 ± 0.05) × In, (0.7 ± 0.05) × In, etc.

[0045] The recorded temperature-current value pairs are each assigned to the current class in which the current measurement of the temperature-current value pair lies. For temperature-current value pairs in the same current class, a comparison is made between at least one temperature-current value pair at a time before the switching event and at least one temperature-current value pair at at least one time after the switching event. After a switching event (OFF / ON), a temperature measurement before the switching event is compared with a temperature measurement after the switching event, provided both temperature measurements were recorded at approximately the same current.

[0046] Fig. Figure 5 shows a Tt diagram plotting the temporal progression of temperature measurements after a switching event 35. Immediately after the switching event 35, the temperature values ​​are still outside a specified tolerance band [Tmax; Tmin]. As long as the temperature fluctuation lies outside this tolerance band, the switching device is not yet in a thermally steady state, and a comparison of the temperature measurements before and after the switching event is not meaningful. As soon as the temperature measurements are within the tolerance band for a specified time interval Δt_in, the thermally steady state is reached, and the temperature measurements can be recorded in a time measurement interval Δt_mess, min = [t_start; t_end].The temperature measurements taken in the time measurement interval Δt_mess, min can be averaged and used for subsequent comparison with temperature measurements taken before the switching event.

[0047] Fig. 6 shows that a comparison of temperature measurements before the switching event with temperature measurements after the switching event is made using calculated values ​​that were calculated based on the temperature measurements. Fig. 6 shows calculated values ​​Q1, Q2, Q3, Q1N, Q2N, Q3N, which are formed by dividing a temperature measurement value Tm or a temperature average value formed from several temperature measurements by a temperature reference value Tref(@I_standard): Q=Tm / Tref(@I_standard)

[0048] A distinction is made between calculated values ​​Q1, Q2, Q3 before a switching event 35, 36, 37 to be evaluated and calculated values ​​Q1N, Q2N, Q3N after the switching event 35, 36, 37 to be evaluated.

[0049] Fig. 7 shows a further step of the comparison, whereby a calculated value QiN after the switching event 35, 36, 37 to be evaluated is divided by a calculated value Qi before the switching event 35, 36, 37 to be evaluated in order to obtain an evaluation value EV: EV=QiN / Qi

[0050] A value of 1 means no change due to the switching event, a value of < 1 means an improvement in the contact condition and a value of > 1 means a deterioration in the contact condition. Fig. Figure 7 shows that a first quotient Q1N / Q1 related to a first current class is slightly greater than 1, that a second quotient Q2N / Q2 related to a second current class is approximately equal to 1, and that a third quotient Q3N / Q3 related to a third current class is slightly greater than 1. An assessment of the switching event based on the comparison could therefore be that a temperature increase due to the switching event is likely, but very small. Therefore, the switching event could be a switching event N in the rated current range.

[0051] Fig.8 is a flowchart of a method according to the invention for evaluating a switching event in an electromechanical switching device that is inserted into a load current path. In a first step 601, temperature-current value pairs are acquired, comprising a temperature measurement value of a temperature measured at a temperature measuring point of the switching device and a current measurement value of a current flowing through the load current path, which was measured simultaneously with the temperature measurement value. In a second step 602, said temperature-current value pairs, which were acquired at different times, are recorded. In a third step 603, at least one temperature-current value pair at a time before the switching event is compared with at least one temperature-current value pair at at least one time after the switching event. And in a fourth step 604, the switching event is evaluated based on the comparison.

Claims

[1] Method for evaluating a switching event in an electromechanical switching device which is inserted into a load current path, comprising the following steps: - detecting temperature-current value pairs (Tm,Im), comprising a temperature measurement value (Tm) of a temperature measured at a temperature measuring point (X) of the switching device (10) and a current measurement value (Im) of a current (I) flowing through the load current path, which was measured simultaneously with the temperature measurement value (Tm); - Recording of said temperature-current value pairs recorded at different times; - comparing at least one temperature-current value pair at a time before the switching event with at least one temperature-current value pair at at least one time after the switching event; and - Evaluate the switching event based on the comparison. [2] The method of claim 1, wherein the comparison of the temperature-current value pairs before and after the switching event comprises a comparison of the absolute temperature values. [3] Method according to one of the preceding claims, wherein the comparison of the temperature-current value pairs before and after the switching event is carried out on the basis of calculated values which were calculated on the basis of the temperature measured values. [4] Method according to one of the preceding claims, wherein the evaluation of the switching event comprises classifying the switching event as a switching event in normal operation, as an overload switching event or as a short-circuit switching event. [5] Method according to one of the preceding claims, wherein the method comprises the following steps: Dividing a current range covered by the recorded current measurements into two or more current classes; Classifying the recorded temperature-current value pairs into the current class in which the current measured value of the temperature-current value pair lies; For temperature-current value pairs in the same current class, comparison of at least one temperature-current value pair at a time before the switching event with at least one temperature-current value pair at at least one time after the switching event. [6] Method according to one of the preceding claims, wherein a temperature-current value pair (Tm, Im) is only detected when temperature measured values (Tm) are within a defined temperature tolerance band. [7] Method according to one of the preceding claims, wherein a temperature-current value pair is formed from an average of several individual measurements. [8] Method according to one of the preceding claims, wherein the temperature measurement values are related to different temperature threshold values which correspond to limit temperatures of the switching device. [9] A method according to claim 8, wherein it is estimated when the temperature measurements will reach a predefined limit. [10] Method according to one of the preceding claims, comprising the following step: positioning a temperature sensor (23) for detecting a temperature measurement value (Tm) on a current path (14) of a switching contact of the switching device (10).

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