Method for determining electrical resistance

Abstract

The invention relates to a method for determining an electrical resistance of at least one component (2, 16, 17, 20, 21, 22) of an electrical circuit (23) which serves to supply electrical energy to a magnetic drive (3) of a circuit breaker (1), wherein a plurality of components (2, 16, 17, 20, 21, 22) are connected in series in the electrical circuit, wherein a first component is a magnetic coil (2) of the magnetic drive (3) and a second component is a voltage source (17), wherein measured values (30 - 33) of a voltage (U) present in the circuit are recorded at two different times, namely before (30) and after (31, 32, 33) closing the circuit (23), wherein a measured value of the current in the circuit (23) is recorded at at least one of the two different times, and wherein an electrical resistance value of at least one component (2, 16, 17, 20, 21, 22) of the circuit (23) is calculated from the detected measured values of voltage and current at the two different times.

Description

Technical FieldThe present invention relates to a method for determining an electrical resistance of at least one component of a circuit which serves for an electrical energy supply of a magnetic drive of a power switch.Background ArtMedium voltage circuit breakers can be operated with high power magnetic drives. During a switching operation in which the circuit breaker is mechanically opened or closed, a relatively high driving current flows through a solenoid of the magnetic drive to generate a magnetic field necessary for the switching operation. The magnetic drives can receive the electrical energy for the switching operation from a capacitor storage, see for example DE 102005013197 A1 (Siemens AG) 28.09.2006.The entire circuit of the magnetic drive, hereinafter referred to simply as a circuit, usually comprises the following circuit components: capacitor storage, cable connections, plug connectors, fuse break switches, semiconductor switches, magnet coils. The total electrical resistance of the circuit, also referred to simply as the circuit resistance, should be as low-ohmic as possible, so that the ohmic losses in the circuit are as small as possible and the voltage provided by the capacitor storage is present at the magnet coil with the smallest possible voltage drop. Namely, the higher the voltage applied to the solenoid coil, the faster the drive current increases, the faster the solenoid drive operates, and the faster the power switch switches.In practice, aging leads to an increase in the circuit resistance, for example, an increase in the internal resistance of the capacitor storage, an increase in the transition resistances in the plug connectors and an increase in the transition resistances in the interrupter switch. This increase in the circuit resistance results in a voltage drop (=voltage loss) in the circuit in the operating case. As a result, the full voltage of the capacitor storage is no longer present at the magnet coil, but a voltage reduced by the voltage drop is present. As a result, the magnetic drive operates more slowly and the intrinsic time of the circuit breaker lengthens or the circuit breaker does not reach its end position (failure) because of the lack of energy.If the circuit breaker is operated at low ambient temperatures, a further factor is added: at low temperatures, the internal resistance of electrolytic capacitors mostly used for the capacitor storage rises sharply. This can result in a considerable voltage drop within the capacitor store and thus the voltage available at the solenoid may be at a critically low level. As a result, the rise of the drive current in the magnet coil takes place significantly more slowly and the intrinsic time of the circuit breaker is extended.It is customary today that the current intensities of the drive current in the circuit achieved in the switching operation and the intrinsic time of the circuit breaker are monitored (monitoring) and, in the event of exceeding or falling below predetermined threshold values, a warning message is generated so that maintenance can take place in good time. Since a magnet coil is usually wound from copper wire, the electrical resistance of which makes up a substantial part of the circuit resistance, a relatively large tolerance range for the circuit resistance must be provided on account of the temperature dependence of the electrical resistance of the copper wire, so that no "false alarm" is triggered in the event of temperature fluctuations. Therefore, relatively small changes in circuit resistance caused by components of the circuit other than the solenoid are often not detected. Therefore, aging effects of these other components of the circuit can surprisingly lead to a disturbance of the circuit without this having been detected in advance by the monitoring.In particular, the internal resistance of the capacitors of the capacitor storage, which has a large variance as a result of the capacitor temperature, can increase greatly as a result of aging and at low temperatures. The usual cyclical measurements of the capacitor capacitance for detecting aging effects usually give no evidence of an increased internal resistance.DE 10 2021 203 218 A1 (Siemens AG) 06.10.2022 describes a method for determining an electrical resistance of a component of a circuit. However, the resistance measurement is not based there on measurement values from before and after a closing of the circuit. Instead, a certain voltage is applied and the associated current is measured, and the resistance is calculated directly therefrom, wherein the applied voltage is so low that triggering of a switching operation of the circuit breaker is avoided.DE 10 2014 018 640 B3 (Audi AG) 03.03.2016 describes a determination of an internal resistance of a voltage source and / or a determination of connection resistances in an on-board power supply system of a motor vehicle. The resistance determination is based on measured values that are recorded both in an activated and deactivated (only quiescent current consumption) device, so that the resistances can be calculated from the changes in the voltage measured values.SUMMARY OF THE INVENTIONIt is an object of the present invention to improve the determination of an electrical resistance of at least one component of a circuit which serves for an electrical power supply of a magnetic drive of a circuit breaker.This object is achieved according to the invention by a method having the features specified in claim 1.The method according to the invention serves for determining an electrical resistance of at least one component of a circuit which serves for an electrical energy supply of a magnetic drive of a circuit breaker. In this case, a plurality of components are connected in series in the circuit. A first component is a magnetic coil of the magnetic drive and a second component is a voltage source, for example in the form of a capacitor storage. In this case, measured values of a voltage present in the circuit are recorded at two different points in time, namely before and after a closing of the circuit. In this case, a measured value of the current in the circuit is recorded at at least one of the two different points in time. And in this case, an electrical resistance value of at least one component of the circuit is calculated from the recorded measured values of voltage and current at the two different times.A magnetic drive is a construction for switching devices which is customary in medium-voltage installations, for example, in which a magnetic field which attracts another ferromagnetic metal piece, an armature, is generated under voltage by one or more coils. This attraction causes a movement which is transmitted to a movable contact in the switching device and presses the latter onto the fixed contact. Typically, two coils are used which can be connected in parallel or in series. This has the advantage that the magnetic force can be kept approximately the same, even if the input voltage, as mentioned at the beginning, is different due to different rated voltages of the power supply in different countries or in different application cases for the coils. The two coils of the magnetic drive exert an attracting force on the magnet armature in the switched-on state. The transmission mechanism converts the movement of the magnet armature into a movement of the movable contact toward the fixed contact and for this purpose has, for example, a toggle lever. The magnetic drive has controllable switching devices for the coils.A vacuum switching device in the sense of the invention has, for example, a fluid-tight housing, in the interior of which a vacuum prevails (or an extremely low gas pressure <10 -6 Pa). If a movable contact is pulled away rapidly from a fixed contact, for example by means of a spring force, an arc which is produced is rapidly extinguished, inter alia because there is hardly any ionizable medium for a current flow. Vacuum switching devices are particularly well suited for switching alternating current, because an arc always breaks at the zero crossing of the voltage.The invention enables an increased circuit resistance to be determined during operation of the circuit breaker and limits the components in the circuit to those components which cause the increased circuit resistance. These do not offer the methods known to date.Embodiments of the InventionAdvantageous embodiments and developments of the invention are specified in the dependent claims.According to a preferred embodiment of the invention, the measured values of voltage and current are measured within the scope of normal switching operation. It is advantageous here that the operation of the circuit breaker does not need to be interrupted separately, but rather the determination of an electrical resistance of at least one component of a circuit which serves for an electrical power supply of a magnetic drive of a circuit breaker can take place during the normal switching operation of the circuit breaker.According to a preferred embodiment of the invention, at least one measured value of a temperature of the magnetic drive and / or in the environment of the circuit is recorded and taken into account in the calculation of the electrical resistance value in order to be able to eliminate an influence of the temperature on the electrical resistance. It is advantageous here that the temperature dependence of the electrical resistance of components of the circuit is taken into account and the determination of an electrical resistance of at least one component of a circuit thus becomes more accurate.According to a preferred embodiment of the invention, a difference between a voltage value before and a voltage value after closing the circuit yields a voltage swing ΔU, and an electrical resistance value ΔR of at least one component of the circuit is calculated from the acquired measured values of voltage and current at the two different times: ΔU=ΔR*I. It is advantageous in this case that a determination of an electrical resistance of at least one component of a circuit is reduced to a measurement of a voltage swing: the voltage swing is an indicator of the circuit resistance in the drive circuit. The higher the voltage swing, the higher the circuit resistance.According to a preferred embodiment of the invention, a maintenance message is generated if the ascertained voltage change exceeds a predefined threshold value. It is advantageous in this case that measures against a possibly imminent failure of the circuit can be taken in good time and the occurrence of accidents is thus reduced.According to a preferred embodiment of the invention, measurement values of a voltage present in the circuit are recorded at a measurement point pair, wherein the measurement point pair is selected such that as many components as possible in the circuit are traversed by the current. It is advantageous here that an overall diagnosis of a large part of the circuit takes place with regard to the electrical resistance.According to a preferred embodiment of the invention, measurement values of a voltage present in the circuit are recorded at two measurement point pairs, wherein a first measurement point pair is selected such that the voltage measurement is carried out directly at the voltage source, and a second measurement point pair is selected such that any number of components in the circuit are traversed by the current. It is advantageous in this case that the position of an increased electrical resistance in the circuit and thus the component of the circuit concerned can be restricted.Exemplary Embodiments of the DrawingsThe above-described properties, features and advantages of this invention and the manner in which these are achieved will become clearer and more clearly understood from the following description of the exemplary embodiments, which are explained in more detail with reference to the drawings. It is shown in each case schematically and not to scale FIG. 1 shows a switching arrangement with a vacuum switching device, FIG. 2 shows a circuit, FIG. 3 shows voltage curves over time, FIG. 4 shows an enlarged detail from FIG. 3, FIG. 5 shows a flow diagram of a method, and FIG. 6 is a simplified circuit diagram of a circuit.DETAILED DESCRIPTION OF THE EMBODIMENTSFIG. 1 shows a switching arrangement 1. the switching arrangement 1 has a vacuum switching device 2- 14 with a vacuum switch 11- 13 in a housing 14 in which vacuum 13 prevails. In the interior of the housing 14, a movable contact 11 is pressed against a fixed contact 12 since current flows through a magnet coil 2 of a magnet drive 3 in a first direction; FIG. 1 thus shows a current-conducting state of the vacuum switch 11- 13 with a magnet drive 3 switched on. A switching rod 8 which runs through the housing 14 is connected to the movable contact 11, wherein, for example, a bellows, not shown, ensures the mobility of the switching rod 8 with simultaneous vacuum sealing. For a mechanical separation of the contacts 11, 12 a spring device 10 is provided which is supported on a support plate 9 and is prestressed in the closed state shown.The switching rod 8 is connected to a toggle lever 5- 7, wherein a first leg 6 of the toggle lever 5- 7 and a second leg 5 of the toggle lever 5- 7 are connected in an angularly rigid manner, but are rotatably mounted about a joint 7 of the toggle lever 5- 7. The second leg 5 is connected to a magnet armature 4 made of metal, for example iron. The toggle lever 5- 7 acting as a transmission mechanism converts a movement of the magnet armature 4 into a movement of the movable contact 11 toward the fixed contact 12. Alternative embodiments also exist in which the magnet armature 4 acts directly, without toggle levers 5- 7, on the switching rod 8 of the moving contact 11.The magnetic coil 2 can be electrically connected in a circuit to a voltage source in the form of a capacitor storage 17. For this purpose, the capacitor memory 17 is electrically connected to a semiconductor switch 15 by means of a first plug connector 21. The semiconductor switch 15 is electrically connected to a fuse cut switch 16 by a cable connection 20. The fuse cut switch 16 is electrically connected to the solenoid 2. The semiconductor switch 15 can be switched either to conduct current or to block current. In the current-conducting state of the semiconductor switch 15, a circuit 23 is formed, in which current flows from the capacitor storage 17 through the magnetic coil 2 and back to the capacitor storage 17. In the current-blocking state of the semiconductor switch 15, the semiconductor switch 15 interrupts the circuit 23 and no current flows through the magnet coil 2; in addition, depending on the actuation of the semiconductor switch 15, the direction in which current flows through the magnet coil 2 can be reversed, so that the movable contact 11, depending on the current direction, is either pressed against the fixed contact 12 or disconnected from it; an operating state is shown in which the magnet coil 2 through which current flows pulls the magnet armature 4 with a force F into a housing of the magnet drive 3 and the movable contact 11 is thus pressed against the fixed contact 12.The switching arrangement 1 also has a charging voltage source 19 from which the capacitor storage 17 can be charged with electrical charge carriers; for charging, the charging voltage source 19 is electrically connected to the capacitor storage 17.FIG. 2 shows the circuit 23 of FIG. 1 in detail. In the circuit 23, the capacitor storage 17, the first connector 21 disposed in the housing of the capacitor storage 17, the semiconductor switch 15, a second connector 22, the cable connection 20, the fuse breaking switch 16, and the solenoid coil 2 are connected in series.When the semiconductor switch 15 is in a current-conducting switching state for a first current direction I 1, current flows from the capacitor storage 17 via a first current path 23 aof the circuit 23, comprising a first current path 23 aof the first plug connector 21, a first current path 23 aof the semiconductor switch 15, a first current path 23 aof the second plug connector 22, a first current path 23 aof the cable connection 20 and a first current path 23 aof the safety break switch 16, to the magnet coil 2 and from the magnet coil 2 via a second current path 23 bof the circuit 23, comprising a second current path 23 bof the safety break switch 16, a second current path 23 bof the cable connection 20, a second current path 23 bof the second plug connector 22, a second current path 23 bof the semiconductor switch 15 and a second current path 23 bof the first plug connector 21, back to the capacitor storage 17.If the semiconductor switch 15 is in a current-conducting switching state for a second current direction I 2 opposite the first current direction I 1, current flows from the capacitor storage 17 via the second current path 23 bof the circuit 23 comprising the second current path 23 bof the first plug connector 21, the second current path 23 bof the semiconductor switch 15, the second current path 23 bof the second plug connector 22, the second current path 23 bof the cable connection 20 and the second current path 23 aof the safety break switch 16, to the magnet coil 2 and from the magnet coil 2 via the first current path 23 aof the circuit 23 comprising the first current path 23 bof the safety break switch 16, the first current path 23 bof the cable connection 20, the first current path 23 bof the second plug connector 22, the first current path 23 bof the semiconductor switch 15 and the first current path 23 bof the first plug connector 21, back to the capacitor memory 17.The capacitor storage 17 functioning as a voltage source has an electrical capacitance 17C and an ohmic resistor 17R.The first plug connector 21 has an ohmic resistor 21R1in its first current path 23 aand an ohmic resistor 21R2in its second current path 23 b.The semiconductor switch 15 has four controllable HL switching elements S 1, S 2, S 3, S 4, e.g. FETs or IGBTs (HL=conductor; FET=field effect transistor; IGBT=insulated-gate bipolar transistor). The HL switching elements S 1, S 2, S 3, S 4 can be controlled in such a way that the semiconductor switch 15 is switched either to conduct current or to block current. The HL switching elements S 1, S 2, S 3, S 4 are connected as an H bridge; they can be controlled in such a way that the current direction I 1, I 2 of the current flowing through the magnet coil 2 is reversed (polarity reversal). The HL switching elements S 1, S 2, S 3, S 4 can be not only hard-switched on or off, but also controlled via a PWM; as a result, the current flowing through the solenoid coil 2 can be controlled (PWM=pulse width modulation). The two HL switching elements S 2 and S 4, more precisely the source terminal (FET) and the emitter (IGBT), are electrically connected to a ground potential 15E (GND or 0V potential) of the circuit 23 (GND=ground, reference potential in electrical technology).The second plug connector 22 has an ohmic resistor 22R 1 in its first current path 23 aand an ohmic resistor 22R 2 in its second current path 23 b.The cable connection 20 has an ohmic resistor 20R1in its first current path 23 aand an ohmic resistor 20R2in its second current path 23 b.The fuse breaking switch 16 has an ohmic resistor 16R in its first current path 23 a.The solenoid coil 2 has an ohmic resistor 2R and an electric inductance 2L.The circuit 23 has a plurality of voltage measurement points at which a voltage measurement can be carried out in the circuit 23. A first voltage measurement point 21M is arranged in the first current path 23 abetween the first plug connector 21 and the semiconductor switch 15. A second voltage measurement point 22M+ is arranged in the first current path 23 abetween the semiconductor switch 15 and the second plug connector 22. A third voltage measuring point 20M+ is arranged in the first current path 23 abetween the second plug connector 22 and the cable connection 20. A fourth voltage measurement point 16M+ is arranged in the first current path 23 abetween the third voltage measurement point 20M+ and the ohmic resistor 16R of the fuse break switch 16. A fifth voltage measuring point 16M- is arranged in the first current path 23 abetween the ohmic resistor 16R of the fuse break switch 16 and the magnet coil 2. A sixth voltage measuring point 2M+ is arranged in the solenoid coil 2, namely in the first current path 23 abetween the fifth voltage measuring point 16M- and the series connection of the ohmic resistor 2R with the electrical inductance 2L of the solenoid coil 2; a seventh voltage measuring point 2M- is arranged in the solenoid coil 2, namely in the second current path 23 bbetween the series connection of the ohmic resistor 2R with the electrical inductance 2L of the solenoid coil 2 and the safety break switch 16; an eighth voltage measuring point 20M- is arranged in the second current path 23 bbetween the cable connection 20 and the second plug connector 22. A ninth voltage measuring point 22M- is arranged in the second current path 23 bbetween the second plug connector 22 and the semiconductor switch 15.In addition, a current measuring device 24 is present, with which a current measurement can take place in the circuit 23, here for example at the first voltage measurement point 21M.A temperature measuring device 25 is also present, with which a temperature measurement can take place in or on the magnet coil 2.FIG. 3 shows voltage profiles 31- 34 of a voltage U over time t. FIG. 4 shows an enlarged section from FIG. 3.In the context of the switching operation, the voltage is measured immediately before and after a switching on or before and after a switching off of a drive current of the solenoid coil and the voltage swing ΔU is determined, i.e. a decrease in the voltage U or an increase in the voltage U. The voltage swing ΔU is an indicator of the circuit resistance: the higher the voltage swing ΔU, the higher the circuit resistance ΔR: I=const=U / R; i.e. as R increases, U also increases.The voltage provided from the capacitor memory 17 is about U 0= 160 V. However, the capacitor voltage is not always exactly 160 V, but may be higher or lower. Higher, if e.g. a capacitor test is carried out and switched in the process, and lower, for example if - allowed - is already switched before the 160 V are reached. Therefore, measurement of the voltage provided by the capacitor storage 17 in the circuit-free state (I=0) is also necessary in order to have a voltage reference value.The voltage curves 31- 33 show the voltage U, which is applied between the third voltage measurement point 20M+and the ninth voltage measurement point 22M-, in three different ageing states. The voltage curve 34 shows the voltage U which is applied between the second voltage measurement point 22M+ and the ninth voltage measurement point 22M- in the same three different ageing states.First (t<approximately 10 ms), the HL switch 15 is switched to a current-blocking state, so that no voltage is still present between the third voltage measurement point 20M+and the ninth voltage measurement point 22M- as well as between the second voltage measurement point 22M+and the ninth voltage measurement point 22M-. At the time of the current being switched on at t=approximately 10 ms, the HL switch 15 is switched to conduct current, so that the voltage between the third voltage measurement point 20M+and the ninth voltage measurement point 22M- decreases in a first aging state 31 with a lowest aging to a value of U 31= approximately 155 V, decreases in a second aging state 32 with a medium aging to a value of U 32= approximately 153 V, and decreases in a third aging state 33 with a highest aging to a value of U 33= approximately 151 V. In contrast, the voltage 34 between the second voltage measurement point 22M+ and the ninth voltage measurement point 22M- decreases to a value of U 34= approximately 157 V in all three aging states. After the HL switch 15 has been switched back to a current-blocking state (t=approximately 60 ms), no voltage is present any longer at the two voltage measurement points under consideration.By measuring the voltage U which is present between the third voltage measurement point 20M+ and the ninth voltage measurement point 22M-, the increased voltage drop ΔU and thus the increased resistance value ΔR can be detected during the switching operation. The voltage upstream of the first resistor 22R1 of the second connector 22, which is measured between the second voltage measurement point 22M+ and the ninth voltage measurement point 22M-, is not affected by the increase in resistance. Thereby, the increased resistance value ΔR can be accurately assigned to the first resistor 22R 1 of the second connector 22 or the second resistor 22R 2 of the second connector 22.If an adjustable threshold value of the voltage swing ΔU or of the increased resistance value ΔR is exceeded, a maintenance message is generated in order to prompt an operator to take measures.A voltage measurement can be carried out in different ways.According to a first type of stress measurement, a measurement offset in time is carried out at a measurement point pair. The voltage measurement points are selected such that as many components as possible in the circuit are traversed by the current, e.g. capacitor storage devices, lines, plugs, safety switches. The voltage is measured immediately before the semiconductor switch in this case. For example, the voltage is measured from the first voltage measurement point 21M to the ground potential 15E, i.e., in front of the semiconductor switch 15.It is also possible that, in order to determine the aging of the capacitor storage 17, the voltage is measured directly at the electrical terminals of the capacitor storage 17, in order to determine only an increase in the internal resistance of the capacitor storage 17. It is possible that the special case of low ambient temperatures must be taken into account. If an increased internal resistance of capacitor storage 17 is detected, heating of capacitor storage 17 can take place by means of cyclic discharging and charging of capacitor storage 17, and the temperature-induced increased internal resistance can thus be lowered again. The discharge takes place, for example, via the magnet coil 2, which is switched on for a period of time which does not yet lead to a movement of the magnet armature 4. Charging takes place as in normal operation via charging electronics of the capacitor store 17. alternatively, a rectified alternating voltage source can be connected to the capacitor store 17 to heat the capacitor store 17, so that a cyclical current direction change takes place through the voltage ripple, which heats the capacitor store 17.According to a second type of stress measurement, a measurement offset in time is carried out at two measurement point pairs. The voltage is carried out directly on the capacitor storage 17 and additionally as described above in the first type of voltage measurement. This can limit the position of the increased circuit resistance and thus the component of the circuit affected by excessive aging. For example, the voltage between the second voltage measurement point 22M+ and the ninth voltage measurement point 22M-, the voltage between the third voltage measurement point 20M+ and the ninth voltage measurement point 22M-, the voltage between the fourth voltage measurement point 16M+ and the eighth voltage measurement point 20M-, the voltage between the fourth voltage measurement point 16M+ and the fifth voltage measurement point 16M-, or the voltage between the sixth voltage measurement point 2M+ and the seventh voltage measurement point 2M- are detected.In order to be able to calculate a temperature influence on the circuit resistance, a temperature measurement in the magnet coil 2 can be carried out with the aid of the temperature measuring device 25.FIG. 5 shows a flow diagram of a method according to the invention. In a first step 51, measured values of a voltage present in the circuit are recorded at a first point in time, namely before the circuit is closed. In a second step 52, measured values of a voltage present in the circuit are recorded at a second point in time, namely after the circuit has been closed. In a third step 53, a measurement value of the current in the circuit is recorded at at least one of the two different points in time. In a fourth step 54, an electrical resistance value of at least one component of the circuit is calculated from the recorded measured values of voltage and current at the two different points in time.FIG. 6 shows a circuit 60 in which a voltage source S provides a voltage U 0 at the connection points M 1, M 2. An electrical load C which is connected to the voltage source S via power lines 60 a, 60 band itself has an electrical resistance R c "sees" a reduced voltage ΔU c= U 0- ΔU at its connections M 3, M 4 during operation, i.e. when the circuit is closed, because a total voltage drop ΔU occurs at the total electrical resistance R of the power lines 60 a, 60 b. The total electrical resistance R is composed of the electrical resistances R 1 to R 6 of all circuit components of the circuit, such as cable connections, plug connectors, switches, etc.:The same current flows through all components of the circuit 60, so the current intensity I at each point of the circuit 60 is the same. The current intensity is not influenced by a fluctuating voltage of the voltage source S, for example a capacitor, because the current intensity I is regulated in the circuit 60. The voltage source S can also supply a multiple of the required current intensity I. At each circuit component R 1 to R 6 of the circuit 60, the voltage drops by a specific voltage drop ΔU i= R i×I. The total voltage drop ΔU at the total electrical resistance R is composed of the sum of all individual voltage drops ΔU iBy detecting the individual voltage drops ΔU i one can detect a change in resistance (increase or decrease) of each individual circuit component R 1 to R 6 with time.List of reference characters1 Switching arrangement 2 Magnet coil 3 Magnet drive 4 Magnet armature 5 Leg, second 6 Leg, first 7 Joint 8 Switching rod 9 Support plate 10 Spring device 11 Contact, movable 12 Fixed contact 13 Vacuum 14 Switch housing 15 Semiconductor switch 15E Ground potential 16 Safety break switch 17 Voltage source, capacitor memory 19 Charging voltage source 20 Cable connection 21 Plug connector, first 22 Plug connector, second 23 Circuit 24 Current measuring device 25 Temperature measuring device 30 Voltage value 31 Voltage value 32 Voltage value 33 Voltage value 34 Voltage value 51 Method step 52 Method step 53 Method step 54 Method step C Load F Force, attracting force

Claims

Method for determining an electrical resistance of at least one component (2, 16, 17, 20, 21, 22) of a circuit (23) which serves for supplying an electrical energy to a magnetic drive (3) of a circuit breaker (1), wherein a plurality of components (2, 16, 17, 20, 21, 22) are connected in series in the circuit, wherein a first component is a magnetic coil (2) of the magnetic drive (3) and a second component is a voltage source (17), wherein measured values (30-33) of a voltage (U) present in the circuit are detected at two different points in time, namely before (30) and after (31, 32, 33) a closing of the circuit (23), wherein a measured value of the current in the circuit (23) is detected at at least one of the two different points in time, and wherein an electrical resistance value of at least one component (2, 16, 17, 20, 21, is detected, 22) of the circuit (23) is calculated from the detected measured values of voltage and current at the two different points in time.Method according to claim 1, wherein the voltage and current measurement values are measured in the course of normal switching operation.Method according to one of the preceding claims, wherein at least one measurement value of a temperature of the magnetic drive (3) and / or in the environment of the circuit (23) is detected and taken into account in the calculation of the electrical resistance value in order to be able to eliminate an influence of the temperature on the electrical resistance.Method according to one of the preceding claims, wherein a difference between a voltage value before (30) and a voltage value after (31, 32, 33) closure of the circuit (23) yields a voltage swing ΔU, and wherein an electrical resistance value ΔR of at least one component (2, 16, 17, 20, 21, 22) of the circuit (23) is calculated from the detected measurement values of voltage and current at the two different times: ΔU = ΔR * IMethod according to one of the preceding claims, wherein a maintenance message is generated if the ascertained voltage change exceeds a predefined threshold value.Method according to one of the preceding claims, wherein the measurement values (30-33) of a voltage (U) present in the circuit (23) are recorded at a measurement point pair, wherein the measurement point pair is selected such that as many components (2, 16, 17, 20, 21, 22) as possible in the circuit (23) are traversed by the current.Method according to one of the preceding claims, wherein the measurement values (30-33) of a voltage (U) present in the circuit are recorded at two measurement point pairs, wherein a first measurement point pair is selected such that the voltage measurement is carried out directly at the voltage source, and a second measurement point pair is selected such that any number of components (2, 16, 17, 20, 21, 22) in the circuit (23) are traversed by the current.

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