CIRCUIT BREAKER DEVICE AND METHOD

Abstract

A circuit breaker protects an electrical multi-phase low-voltage AC circuit. The circuit breaker contains series circuits each made up of a mechanical phase contact and an electronic switch. Each series circuit electrically connects a grid-side phase connection to a load-side phase connection. The mechanical phase contacts are opened together to prevent a flow of current or closed together to allow a flow of current. The electronic switches can be switched, by semiconductor-based switching elements, to a high-impedance state of the switching elements to prevent a flow of current or to a low-impedance state of the switching elements to allow the flow of current. The electronic switches are switched independently of one another to a high-impedance or low-impedance state to prevent or enable a phase-conductor-dependent flow of current. A temperature sensor is provided for each series circuit for determining the temperature level of the respective electronic switch.

Claims

1. A circuit breaker for protecting an electrical multi-phase low-voltage AC circuit, the circuit breaker comprising: a housing having grid-side phase connections and load-side phase connections for phase conductors of the electrical multi-phase low-voltage AC circuit; series circuits each having a mechanical phase contact and an electronic switch, wherein each of said series circuits electrically connects one of said grid-side phase connections to one of said load-side phase connections, said mechanical phase contacts being switched to an open state together to prevent a flow of current or to close together to allow the flow of the current; each said electronic switch having semiconductor-based switching elements and being switched, by means of said semiconductor-based switching elements, to a high-impedance state of said semiconductor-based switching elements in order to prevent the flow of the current or to a low-impedance state of said semiconductor-based switching elements in order to allow the flow of the current; the circuit breaker configured such that each said electronic switch being switched independently of one another to the high-impedance state or the low-impedance state; temperature sensors, in each case at least one of said temperature sensors is provided for each of said series circuits; and the circuit breaker being configured such that, when a first temperature threshold value of said at least one temperature sensor of one of said series circuit is exceeded, said electronic switch of said series circuit is switched to the high-impedance state to prevent the flow of the current to prevent overheating.

2. The circuit breaker according to claim 1, further comprising: current sensors, a respective current sensor of said current sensors is provided for each of said series circuits, for determining in each case a level of the current of a respective phase conductor of the phase conductors; and a controller connected to said current sensors, said temperature sensors, said mechanical phase contacts and said electronic switches, the circuit breaker is configured such that a process for preventing the flow of the current in a phase conductor is initiated by said electronic switch, when at least one first current threshold value is exceeded in the phase conductor.

3. The circuit breaker according to claim 1, wherein said mechanical phase contacts are assigned to said load-side connections and said electronic switches are assigned to said grid-side connections.

4. The circuit breaker according to claim 1, further comprising: a grid-side neutral conductor connection and a load-side neutral conductor connection; and a mechanical neutral conductor contact electrically connecting said grid-side neutral conductor connection to said load-side neutral conductor connection, said mechanical neutral conductor contact is switched together with said mechanical phase contacts.

5. The circuit breaker according to claim 1, wherein said mechanical phase contacts are opened in a case of an initiated high-impedance state of said electronic switch to prevent overheating and when a higher second temperature threshold value is exceeded.

6. The circuit breaker according to claim 1, wherein said electronic switch is switched to the low-impedance state in a case of the high-impedance state of said electronic switch to prevent overheating and when a third temperature threshold value is undershot.

7. The circuit breaker according to claim 6, wherein the third temperature threshold value is lower than the first temperature threshold value.

8. The circuit breaker according to claim 1, wherein said electronic switch is switched to the low-impedance state to prevent overheating in a case of the high-impedance state of said electronic switch to prevent overheating and when a first time period since the high-impedance state started has expired.

9. The circuit breaker according to claim 1, wherein said mechanical phase contacts are opened within a first-time frame in an event of a change to the high-impedance state in order to prevent overheating, the change exceeding a first number.

10. The circuit breaker according to claim 2, further comprising a communication unit connected to said controller.

11. The circuit breaker according to claim 10, wherein a warning is issued by means of said communication unit when a fourth temperature threshold value of one of said temperature sensors is exceeded.

12. The circuit breaker according to claim 10, wherein a level of a temperature of at least one of said temperature sensors or an equivalent is issued by means of said communication unit.

13. The circuit breaker according to claim 2, wherein each said mechanical phase contact is opened, but not closed, by way of said controller.

14. The circuit breaker according to claim 2, further comprising a mechanical handle, wherein said mechanical phase contacts can be operated by way of said mechanical handle to switch between an opening of said mechanical phase contacts or a closing of said mechanical phase contacts.

15. The circuit breaker according to claim 14, wherein said mechanical phase contacts have a release functionality such that said mechanical phase contacts are opened by way of said controller, even if said mechanical handle is blocked.

16. The circuit breaker according to claim 1, wherein when the first temperature threshold value of said at least one temperature sensor of one of said series circuits is exceeded, all of said electronic switches are switched to the high-impedance state to prevent the flow of the current to prevent overheating.

17. A method of using a circuit breaker to protect an electrical multi-phase low-voltage AC circuit, the circuit breaker having series circuits each made up of a mechanical phase contact, an electronic switch and at least one temperature sensor, wherein each of the series circuits connects a grid-side phase connection to a load-side phase connection, which method comprises the steps of: opening the mechanical phase contacts together to prevent a flow of current or closed together to allow the flow of the current; switching electronic switches of the series circuits, by means of semiconductor-based switching elements, to a high-impedance state of the switching elements to prevent the flow of the current or to a low-impedance state of the switching elements to allow the flow of the current, the electronic switches being switched independently of one another to the high-impedance or the low-impedance state in order to prevent or enable a phase-conductor-dependent flow of the current; and switching the electronic switch of the series circuit to the high-impedance state to prevent the flow of the current in order to prevent overheating when a first temperature threshold value of the at least one temperature sensor of a series circuit is exceeded.

18. The method according to claim 17, which further comprises: determining a level of the current of a respective one the series circuits; and initiating a process for preventing the flow of the current in the respective series circuit by way of the electronic switch, if at least one said first current threshold value is exceeded in the respective series circuit.

19. The method according to claim 17, which further comprises opening mechanical phase contacts of the series circuits in a case of an initiated high-impedance state of the electronic switch to prevent overheating when a higher second temperature threshold value is exceeded.

20. The method according to claim 17, which further comprises switching the electronic switch to the low-impedance state in a case of the high-impedance state of the electronic switch to prevent overheating and if a third temperature threshold value is undershot.

21. The method according to claim 17, which further comprises switching the electronic switch to the low-impedance state to prevent overheating in a case of the high-impedance state of the electronic switch to prevent overheating and when a first time period since the high-impedance state started has expired.

22. The method according to claim 17, which further comprises opening the mechanical phase contacts within a first-time frame in an event of a change to the high-impedance state to prevent overheating, the change exceeding a first number.

23. The method according to claim 17, which further comprises issuing a warning when a fourth temperature threshold value of the at least one temperature sensor is exceeded.

24. The method according to claim 17, wherein a level of a temperature of at least one of the at least one temperature sensor or an equivalent is issued.

25. The method according to claim 17, which further comprises switching all of the electronic switches to the high-impedance state to prevent the flow of the current to prevent overheating when the first temperature threshold value of the at least one temperature sensor of the series circuit is exceeded.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0101] FIG. 1 is a schematic diagram of a circuit breaker device;

[0102] FIG. 2 is a schematic diagram of a further embodiment of the circuit breaker device;

[0103] FIG. 3 is a graph;

[0104] FIG. 4 is an illustration of a second graph;

[0105] FIG. 5 is an illustration of a third graph;

[0106] FIG. 6 is an illustration of a fourth graph; and

[0107] FIG. 7 is an illustration of a fifth graph.

DETAILED DESCRIPTION OF THE INVENTION

[0108] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown an exemplary illustration of a 3-pole, for example for 3-phase conductors, circuit breaker device SG for protecting an electrical multi-phase low-voltage AC circuit. In the example according to FIG. 1, a three-phase low-voltage AC circuit, contains:

[0109] a housing GEH having a first, second and third grid-side phase connection LG1, LG2, LG3 and a first, second and third load-side phase connection LL1, LL2, LL3, for a first, second and third phase conductor L1, L2, L3 of the low-voltage AC circuit, an energy source is usually connected to the grid side Grid, and a consumer is usually connected to the load side Load.

[0110] In the housing GEH: [0111] a first series circuit SS1 made up of a first mechanical phase contact K1 and a first electronic switch S1, [0112] a second series circuit SS2 made up of a second mechanical phase contact K2 and a second electronic switch S2, [0113] a third series circuit SS3 made up of a third mechanical phase contact K3 and a third electronic switch S3,
wherein: [0114] the first series circuit SS1 electrically connects the first grid-side phase connection LG1 to the first load-side phase connection LL1, [0115] the second series circuit SS2 electrically connects the second grid-side phase connection LG2 to the second load-side phase connection LL2 and [0116] the third series circuit SS3 electrically connects the third grid-side phase connection LG3 to the third load-side phase connection LL3, [0117] the mechanical phase contacts K1, K2, K3 can be switched together, that is to say they are opened together to prevent a flow of current or closed together for allowing a flow of current, that is to say the mechanical contacts are connected to one another via a mechanical coupling (for example a switching shaft), [0118] the electronic switches S1, S2, S3 can be switched, by means of semiconductor-based switching elements, to a high-impedance state of the switching elements in order to prevent a flow of current or to a low-impedance state of the switching elements to allow the flow of current.

[0119] According to the invention, the first, second and third electronic switches can be switched to a high-impedance or low-impedance state independently of one another. That is to say that the first, second and third electronic switches are switched to a high-impedance or low-impedance state independently of one another. In particular, in order to prevent or to enable a phase-conductor-dependent flow of current.

[0120] According to FIG. 1, a first, second and third current sensor unit S11, S12, S13 are provided. The first current sensor unit S11 is provided or arranged in the first series circuit SS1, the second current sensor unit S12 is provided or arranged in the second series circuit SS2, and the third current sensor unit S13 is provided or arranged in the third series circuit SS3, for determining in each case the current level of the first, second and third phase conductors L1, L2, L3, in particular, determining that there are instantaneous current values available.

[0121] According to FIG. 1, the first mechanical phase contact K1, the second mechanical phase contact K2 and the third mechanical phase contact K3 are part of a mechanical isolating contact unit MK, which opens or closes the phase contacts K1, K2, K3 together. The mechanical isolating contact unit MK can have a handle HH accessible on the circuit breaker device for manually opening or closing the phase contacts (operated by a person). The mechanical isolating contact unit MK corresponds, for example, to a conventional unit, as is known from electromechanical circuit breaker devices (miniature circuit breakers, circuit breakers) (however, according to the invention, without elements for overcurrent detection or short-circuit detection, such as bimetal trip, etc.).

[0122] The circuit breaker device is configured, in particular, in such a way that the mechanical isolating contact unit MK can be opened, but not closed, by way of a control unit SE. In particular, closing of the mechanical isolating contact unit MK by way of the handle HH is only possible after release by way of the control unit SE. A release unit LC can be provided for this purpose. That is to say, the contacts can be closed by way of the handle HH only when the enable or the enable signal (from the control unit) is present. Without the enable or the enable signal, although the handle HH can be actuated, the contacts cannot be closed (permanent slider contacts).

[0123] The release unit LC may also be designed such that it is possible to open the contacts K1, K2, K3 of the mechanical isolating contact unit MK by way of a control signal from the control unit SE, as indicated in FIG. 1 by an arrow from the control unit SE to the release unit LC.

[0124] According to FIG. 1, the mechanical phase contacts K1, K2, K3 are assigned to the load-side phase connections/the load side Load and the electronic switches S1, S2, S3 are assigned to the grid-side phase connections/grid side Grid.

[0125] The first electronic switch S1, the second electronic switch S2 and the third electronic switch S3 may be part of an electronic interruption unit EU, wherein the electronic switches S1, S2, S3 can be switched independently of one another.

[0126] The electronic interruption unit/the electronic switches may have a bidirectional dielectric strength. Specifically, overvoltage protection is provided for the semiconductor-based switching elements in order to limit the voltages and thus have protection for the semiconductor-based switching elements.

[0127] A control unit SE is provided (as already partially mentioned), which is connected to the current sensor units S11, S12, S13, the mechanical phase contacts or the mechanical isolating contact unit MK (as shown in FIG. 1) and the electronic switches S1, S2, S3.

[0128] The current sensor units S11, S12, S13 each determine the level of the current of their respective conductor, so that, in particular, instantaneous values of the current are available.

[0129] When at least one first current threshold value in a conductor is exceeded, a process for preventing the flow of current in the conductor in question is initiated by way of the electronic switch coming to have a high impedance.

[0130] The high impedance can be achieved, in particular, for a first period of time. After the period of time, the electronic switch in question can come to have a low impedance again.

[0131] Coming to have a low impedance can occur, in particular, in the next zero crossing or before or after the zero crossing of the voltage. (All 3 options: in the zero crossing, before the zero crossing or after the zero crossingare possible, or if the value falls below a voltage threshold, in particular 50 V, 25 V or 10 V). In particular, the first time period may be less than 20 ms, especially less than 10 ms.

[0132] A differential current sensor unit ZCT may be provided, as shown in FIG. 1, for detecting differential currents of the low-voltage AC circuit, as is known, for example, from residual current circuit breakers. The differential current sensor unit ZCT is connected to the control unit SE.

[0133] The current sensor units S11, S12, S13 are arranged in the example according to FIG. 1 between the grid-side connections LG1, LG2, LG3 of the series circuit made up of the electronic switch S1, S2, S3 and the mechanical phase contact K1, K2, K3. Specifically, between grid-side connections LG1, LG2, LG3 and the electronic switches S1, S2, S3. The current sensor units S11, S12, S13 may also be arranged in other ways. For example, between the electronic switch S1, S2, S3 and the mechanical phase contact K1, K2, K3.

[0134] According to the invention, in each case at least one temperature sensor TS1, TS2, TS3 is provided for each series circuit SS1, SS2, SS3.

[0135] The first temperature sensor TS1 is provided in the first series circuit SS1, the second temperature sensor TS2 is provided in the second series circuit SS2, and the third temperature sensor TS3 is provided in the third series circuit SS3. This means that each series circuit has in each case at least one temperature sensor.

[0136] In the example according to FIG. 1, the temperature sensor is provided in each case in (for example on) the electronic switch, in particular on the semiconductor-based switching element(s) thereof.

[0137] The first, second and third temperature sensors TS1, TS2, TS3 are each connected to the control unit SE.

[0138] The temperature sensors TS1, TS2, TS3 are used, in particular, for determining in each case the temperature level of the respective electronic switch, in particular the semiconductor-based switching element.

[0139] This means that the first temperature sensor TS1 determines, for example, the level of the temperature of the first electronic switch S1, in particular the semiconductor-based switching element/semiconductor-based switching elements.

[0140] The second temperature sensor TS2 determines, for example, the level of the temperature of the second electronic switch S2, in particular the semiconductor-based switching element/semiconductor-based switching elements.

[0141] The third temperature sensor TS3 determines, for example, the level of the temperature of the third electronic switch S3, in particular the semiconductor-based switching element/semiconductor-based switching elements.

[0142] The circuit breaker device is designed in such a way that, if a first temperature threshold value 1.SW of a temperature sensor of a series circuit is exceeded, the electronic switch of the series circuit is switched to a high-impedance state in order to prevent a flow of current in order to prevent overheating.

[0143] As an alternative or in addition (for example in a configurable manner), if a first temperature threshold value of a temperature sensor of a series circuit is exceeded, all electronic switches are switched to a high-impedance state to prevent a flow of current in order to prevent overheating.

[0144] FIG. 2 shows an illustration in accordance with FIG. 1, with the following differences.

[0145] A grid-side neutral conductor connection NG and a load-side neutral conductor connection NL are provided for a neutral conductor N of the multi-phase low-voltage AC circuit, in the example according to FIG. 2 a three-phase low-voltage AC circuit with neutral conductors. According to FIG. 2, the grid-side neutral conductor connection NG is connected to the load-side neutral conductor connection NL via a neutral conductor contact KN.

[0146] As an alternative, the grid-side neutral conductor connection NG can also be connected directly (that is to say without a switchable contact) to the load-side neutral conductor connection NL.

[0147] In this example, an electronic switch is not provided in the neutral conductor path in the housing of the circuit breaker device. This means that the neutral conductor connection between the grid-side neutral conductor connection NG and the load-side neutral conductor connection NL is free of electronic switches (electronic switch-free).

[0148] The mechanical neutral conductor contact KN can advantageously be connected together with the phase contacts K1, K2, K3. This means that the mechanical neutral conductor contact KN can be opened or closed together with the phase contacts K1, K2, K3, as described further above in relation to the contacts K1, K2, K3.

[0149] Specifically, the mechanical isolating contact unit MK can be designed in such a way that the neutral conductor contact KN is closed before the phase contacts K1, K2, K3 are closed. Similarly, the neutral conductor contact KN can be opened after the phase contacts K1, K2, K3 have been opened.

[0150] Furthermore, an energy supply NT is provided, such as a power supply unit provided for the supply of energy to the circuit breaker device SG, in particular to the control unit SE.

[0151] In the example, the energy supply NT is connected on one side to the phase conductors L1, L2, L3 and (if necessary) to the neutral conductor N. It can also only be connected to some of the conductors (at least two) for the purpose of supplying energy. In the example, the energy supply NT is connected on the other side to the control unit SE.

[0152] On the other hand, the control unit SE is illustrated combined with the electronic switches S1, S2, S3, the temperature sensors TS1, TS2, TS3 and the current sensor units S11, S12, S13.

[0153] Furthermore, in each case a voltage sensor unit is provided between each phase conductor and the neutral conductor. A first voltage sensor unit SU1 is provided between the first phase conductor L1 and the neutral conductor N, a second voltage sensor unit SU2 is provided between the second phase conductor L2 and the neutral conductor N, and a third voltage sensor unit SU3 is provide between the third phase conductor L3 and the neutral conductor N for determining the level of the voltage between the respective phase conductors and neutral conductors, in particular determining that there are instantaneous voltage values available. The voltage sensor units SU1, SU2, SU3 are connected to the control unit SE.

[0154] In the case of the electronic switches S1, S2, S3 coming to have a low impedance, which is initiated by way of the control unit SE, for example: [0155] if the change to low impedance is initiated by a user or, [0156] if the change to low impedance is initiated by the circuit breaker device, specifically if a third temperature threshold value 3.SW is undershot, [0157] the electronic switch in question can come to have a low impedance at (in the range of, see above) the respective zero crossing of the voltage.

[0158] As already mentioned, the voltage sensor units SU1, SU2, SU3 are to this end connected to the control unit SE, which is also connected to the current sensor units S11, S12, S13, the temperature sensors TS1, TS2, TS3, the mechanical phase contacts K1, K2, K3 (or mechanical isolating contact unit MK) and the electronic switches. The circuit breaker device can also advantageously be designed in such a way that a process for preventing a flow of current in a phase conductor is initiated by the electronic switch in question if at least one first current threshold value (specifically instantaneous value of the current) is exceeded in the phase conductor in question. At the next or next but one zero crossing of the voltage, the electronic switch comes to have a low impedance again to allow a flow of current.

[0159] This can be done several times until a first number of repetitions are exceeded. Then: [0160] a) all of the electronic switches may come to have a high impedance, or (/and) [0161] b) the contacts may be opened (galvanic isolation).

[0162] Any combinations (intermediate combinations) from the illustrations of the exemplary circuit breaker devices according to FIGS. 1 and 2 are possible (for example energy supply NT from FIG. 2 in FIGS. 1, etc.).

[0163] High impedance is used to mean a state in which only a current of a negligible magnitude flows. In particular, high impedance is used to mean resistance values of greater than 1 kilohm, preferably greater than 10 kilohms, 100 kilohms, 1 megaohm, 10 megaohms, 100 megaohms, 1 gigaohm or greater.

[0164] Low impedance is used to mean a state in which the current value indicated on the circuit breaker device could flow. In particular, low impedance is used to mean resistance values of less than 10 ohms, preferably less than 1 ohm, 100 milliohms, 10 milliohms, 1 milliohm or less.

[0165] The electronic switches S1, S2, S3 and the electronic interruption unit EU may have semiconductor components such as bipolar transistors, field-effect transistors (FET), isolated gate bipolar transistors (IGBT), metal oxide layer field-effect transistors (MOSFET) or other (self-commutated) power semiconductors. In particular, IGBTs and MOSFETs are particularly well suited to the electronic switches (as semiconductor-based switching elements) on account of low forward resistances, high junction resistances and good switching behavior.

[0166] Mechanical contacts or a mechanical isolating contact unit MK is used to mean, in particular, a (standards-compliant) isolating function implemented by the isolating contact unit MK. An isolating function is used to mean the following points: [0167] minimum clearance in air according to the standard (minimum distance between the contacts), [0168] contact position indication of the contacts of the mechanical isolating contact system, [0169] actuation/interruption of the contacts of the mechanical isolating contact system (by the control unit) always possible (no (permanent) blocking of the contacts in the closed state by the handle possible).

[0170] The minimum clearance in air between the contacts of the isolating contact system is substantially voltage-dependent. Further parameters are the pollution degree, the type of field (homogeneous, inhomogeneous) and the barometric pressure and the height above sea level.

[0171] There are corresponding rules or standards for these minimum clearances in air or creepage distances. These rules specify, for example in air for an impulse withstand voltage, the minimum clearance in air for an inhomogeneous and a homogeneous (ideal) electrical field on the basis of the pollution degree. The impulse withstand voltage is the strength when a corresponding impulse voltage is applied. The isolating contact system or circuit breaker device has an isolating function (isolator property) only when this minimum length (minimum distance) is present.

[0172] In the sense of the invention, the DIN EN 60947 or IEC 60947 series of standards, to which reference is made here, is relevant in this case to the isolator function and its properties.

[0173] The isolating contact system is advantageously characterized by a minimum clearance in air of the open isolating contacts in the OFF position (open position, open contacts) on the basis of the rated impulse withstand voltage and the pollution degree. The minimum clearance in air is, in particular, between (a minimum of) 0.01 mm and 14 mm.

[0174] In particular, the minimum clearance in air is advantageously between 0.01 mm at 0.33 kV and 14 mm at 12 kV, in particular for pollution degree 1 and in particular for inhomogeneous fields.

[0175] The minimum clearance in air can advantageously have the following values:

E DIN EN 60947-1 (VDE 0660-100):2018-06

TABLE-US-00001 TABLE 13 Minimum clearances in air U.sub.imp Minimum clearances in air Mm Case B Case A inhomogeneous Rated inhomogeneous field, ideal impulse field conditions withstand (see 3.7.63) (see 3.7.62) voltage pollution degree pollution degree kV 1 2 3 4 1 2 3 4 0.33 0.01 0.2 0.8 1.6 0.01 0.2 0.8 1.6 0.5 0.04 0.04 0.8 0.1 0.1 1.5 0.5 0.5 0.3 0.3 2.5 1.5 1.5 1.5 0.6 0.6 4.0 3 3 3 3 1.2 1.2 1.2 6.0 5.5 5.5 5.5 5.5 2 2 2 2 8.0 8 8 8 8 3 3 3 3 12 14 14 14 14 4.5 4.5 4.5 4.5 NOTE The specified minimum clearances in air are based on the 1.2/50 s impulse voltage at an atmospheric pressure of 80 kPa, which corresponds to the atmospheric pressure at 2000 m above sea level

[0176] The pollution degrees and types of field correspond to those defined in the standards. This advantageously allows a standards-compliant circuit breaker device dimensioned according to the rated impulse withstand voltage to be achieved.

[0177] In particular, a mechanical isolating contact unit does not mean a relay contact.

[0178] The control unit SE may have a microcontroller (microcontroller unit).

[0179] The circuit breaker device may have an (in particular wireless) communication unit COM, which is connected to the control unit SE or is a part of it.

[0180] A warning can be issued by means of the communication unit COM when a fourth temperature threshold value is exceeded. As an alternative or in addition, the level of the temperature of at least one temperature sensor, some of the temperature sensors or all of the temperature sensors can be issued (communicated) by means of the communication unit COM (or an equivalent of this).

[0181] A display unit AE can also be provided. The display unit AE can be configured as a combined display and input unit. The display unit AE (display and input unit) is connected to or is part of the control unit SE. The display unit has display means visible on the circuit breaker device, in particular for displaying the high-impedance or low-impedance state of the electronic switches. As an alternative or in addition, for displaying the exceeding of temperature limits (first or/and second or/and third or/and fourth) or (and) the level of the temperature of at least one temperature sensor, some of the temperature sensors, or all of the temperature sensors.

[0182] FIG. 3 shows an illustration of a graph or coordinate system in which the level of the current I (for example as the root mean square value of an alternating current) of the low-voltage circuit is plotted on the horizontal axis (abscissa) and the level of the temperature TTS of a temperature sensor (for example TS1, TS2 or TS3) is plotted on the vertical axis (ordinate) (which is set at the temperature sensor after a period of time, for example in the thermal steady state).

[0183] The profile of the temperature TTS of the temperature sensor is shown as a function of the level of the current I of the phase conductor of the low-voltage circuit.

[0184] It is assumed that the heating in the circuit breaker device, specifically in the electronic switch, specifically the semiconductor-based switching elements thereof, is dependent on the level of the current I of the respective (relevant) phase conductor of the low-voltage circuit through the circuit breaker device (the circuit breaker device is to protect the low-voltage circuit). As the level of the current I in the phase conductor increases, the temperature of the temperature sensor of the electronic switch in question and, as a result, the circuit breaker device, specifically the semiconductor-based switching elements thereof, rises. Thus, the temperature TTS determined by the temperature sensor increases. The temperature increases in a monotonically rising manner with the level of the current. (In addition to the level of the current, the ambient temperature also has an influence on the heating in the circuit breaker device. This is not shown in FIG. 3 for simpler illustration.)

[0185] According to FIG. 3, various temperature threshold values are plotted. A first temperature threshold value 1.SW, in the example 100 C., a second temperature threshold value 2.SW, in the example 110 C., a third temperature threshold value 3.SW, in the example 80 C.

[0186] FIG. 4 shows an illustration according to FIG. 3, with the difference that three, correlated graphs are shown, wherein the time t is plotted on the horizontal axis (abscissa).

[0187] In the upper region of FIG. 4, the temperature TTS of the temperature sensor TS is plotted as a function of the time t. The first temperature threshold value 1.SW and the third temperature threshold value 3.SW are shown.

[0188] In the middle region of FIG. 4, the level of the current I is plotted as a function of the time t.

[0189] In the lower region of FIG. 4, the switching state SZ of the electronic switch in question is plotted as a function of the time t. A low-impedance state of the electronic switch is denoted by on. A high-impedance state of the electronic switch is denoted by off.

[0190] For example, a (constant) current I or a current I with a constant root mean square value of a first level for a certain time (center of FIG. 4) flows. Corresponding heating occurs in the circuit breaker device SG. The temperature in the circuit breaker device/the determined level of the temperature TTS of the temperature sensor increases until the first temperature threshold value 1.SW is reached (top of FIG. 4) at the first time t1.

[0191] When the first temperature threshold value 1.SW is reached or exceeded, in the example 100 C., the electronic switch in question is switched to a high-impedance state off (of the switching elements) in order to prevent a flow of current, first time t1 (bottom of FIG. 4). This prevents further heating and overheating (and associated damage) of the electronic switch or circuit breaker device.

[0192] The circuit breaker device can cool down. At a second time t2, the third temperature threshold value 3.SW, in the example 80 C., is reached or undershot. When the third temperature threshold value 3.SW is reached or undershot, the electronic switch is (again) switched (at the second time t2) to a low-impedance state on (for allowing a flow of current in the low-voltage circuit) (bottom of FIG. 4). The current I can (from the second time t2) flow again (center of FIG. 4). If necessary, the temperature can rise again (top of FIG. 4).

[0193] The third temperature threshold value is lower than the first temperature threshold value.

[0194] As an alternative or in addition, instead of the third temperature threshold value 3.SW, it is possible to wait for a first period of time since the high-impedance state of the switching elements started to elapse. After a first period of time since the high-impedance state of the electronic switch started has elapsed, the electronic switch is switched to the low-impedance state (not shown).

[0195] If the change between the high-impedance state to prevent overheating and back to the low-impedance state is too frequent, the mechanical contacts (if applicable, the mechanical isolating contact unit MK) are opened. This means that the mechanical contacts are opened within a first time frame in the event of a change (toggle) between the high-impedance state in order to prevent overheating and back to the low-impedance state, said change exceeding a first number.

[0196] FIG. 5 shows an illustration according to FIG. 4, with the difference that it shows a fourth graph that correlates to the three upper graphs.

[0197] The fourth graph in the lowest region of FIG. 5 shows the switching state of the mechanical contacts SZK as a function of the time t. A closed state of the contacts is denoted by closed. An open state of the contacts is denoted by open.

[0198] Furthermore, the upper region of FIG. 5 shows the first temperature threshold value 1.SW and the second temperature threshold value 2.SW.

[0199] For example, a (constant) current I of a first level for a certain time (center of FIG. 5) flows. Corresponding heating occurs in the electronic switch. The temperature/the determined level of the temperature TTS of the temperature sensor increases until the first temperature threshold value 1.SW is reached (top of FIG. 5) at the first time t1.

[0200] When the first temperature threshold value 1.SW is reached or exceeded, in the example 100 C., the electronic switch is switched to a high-impedance state off (of the switching elements) in order to prevent a flow of current, first time t1 (bottom of FIG. 5).

[0201] The current is reduced (center of FIG. 5).

[0202] Even though the electronic switch is switched to a high impedance, if the temperature now rises further, for example because the electronic switch is defective (that is to say the high-impedance state is initiated, but for example is not or not fully effective) and a (lower) current flows, the contacts are opened when the second temperature threshold value 2.SW, in the example 110 C., is reached or exceeded (bottom of FIG. 5), third time t3.

[0203] The second temperature threshold value 2.SW is higher than the first temperature threshold value 1.SW.

[0204] FIG. 6 shows an illustration according to FIG. 4, with the difference that the middle area of FIG. 6 shows the issue of a warning Warn. as a function of the time t.

[0205] Furthermore, the upper region of FIG. 6 shows the first temperature threshold value 1.SW and the fourth temperature threshold value 4.SW. If the fourth temperature threshold value is exceeded at the fourth time t4, a warning Warn. is issued (wirelessly/in wired fashion) by means of the communication unit COM. For example, to a higher-level management system. As an alternative or in addition, the warning can be displayed, for example using the display unit AE. The fourth temperature threshold value is lower than the first temperature threshold value.

[0206] The electronic switch remains in the low-impedance state on.

[0207] As an alternative or in addition, the level of the temperature can be issued (wirelessly/in wired fashion) by means of the communication unit COM. For example, to a higher-level management system. As an alternative or in addition, the level of the temperature can be displayed, for example using the display unit AE.

[0208] FIG. 7 shows an illustration according to FIG. 6, with the difference that the warning Warn. is issued with a time offset (time delay) tv. This means that when the fourth temperature threshold value 4.SW is exceeded at the fourth time t4, no warning Warn. will be issued, but the warning Warn. is only issued at a fifth time t5, as shown in FIG. 7. It is thus possible, for example, to avoid warnings based on short-term warming due to briefly increased start-up or switching currents. When the temperature TTS drops below the fourth temperature threshold value 4.SW again before reaching the fifth time t5, no warning Warn. is issued.

[0209] The time offset (time delay) tv is in the range from one second, . . . 5 seconds, . . . 10 seconds, . . . 1 minute.

[0210] Individual monitoring of the temperature of the respective electronic switch can advantageously be carried out for each phase conductor and the current of the phase conductor can be reduced individually. The circuit is interrupted (mechanically/electrically) only if the heating continues, which indicates a fault in the electronic switch.

[0211] The invention is explained again in other words below.

[0212] An electrical (sub)distribution system contains a large number of different protective and switching devices, which are connected to one another via appropriate cables. When designing such a subdistribution system, thermal considerations and calculations must also be carried out, as losses occur in the subdistribution system due to ohmic losses on the lines and the electrical equipment. This heats up the subdistribution system. Today, thermal overload is prevented by appropriate (over)dimensioning (in accordance with standards, guidelines or regulations). Novel electronic protection and switching devices use electronic switching elements (power semiconductors) in the main current path, which also cause increased ohmic losses in the subdistribution system. This will exacerbate the problem of the thermal design of a subdistribution system.

[0213] The existing load current (through the device) significantly influences the temperature of the circuit breaker device and thus also the temperature increase. When a critical temperature is reached, a high-impedance state is initiated. This means that current can no longer flow on the conductor in question (through the circuit breaker device) and cool the device (and the subdistribution system).

[0214] An appropriate warning message can also be issued.

[0215] Since no current flows on the conductor in question, the electronic switch/the circuit breaker device cools down again. After a certain temperature has been undershot, the electronic switch can automatically switch back to the low-impedance state for allowing a flow of current (hysteresis).

[0216] Depending on the device configuration, an opening of the contacts (of the mechanical isolating contact unit) can also be initiated instead of the low-impedance state. An automatic restart after cooling is then not possible. It is necessary to manually close the contacts again.

[0217] The present invention describes a solution that simplifies the thermal design, avoids overdimensioning and prevents a dangerous state in the subdistribution system due to overheating.

[0218] Although the invention has been described and illustrated in more detail by way of the exemplary embodiment, the invention is not restricted by the disclosed examples and other variations may be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention.