PROTECTIVE SWITCH AND PROCEDURES

Description

[0001] The invention relates to the technical field of a protective switching device for a low-voltage circuit with an electronic interruption unit and a method for a protective switching device for a low-voltage circuit with an electronic interruption unit.

[0002] Low voltage refers to voltages up to 1000 volts AC or up to 1500 volts DC. In particular, low voltage refers to voltages higher than extra-low voltage, defined as 50 volts AC or 120 volts DC.

[0003] Low-voltage circuits, networks, or installations refer to circuits with rated currents of up to 125 amperes, or more specifically, up to 63 amperes. Low-voltage circuits specifically include circuits with rated currents of up to 50 amperes, 40 amperes, 32 amperes, 25 amperes, 16 amperes, or 10 amperes. These current values ​​refer specifically to rated, rated, and / or tripping currents, i.e., the maximum current that normally flows through the circuit or at which the electrical circuit is typically interrupted, for example, by a protective device such as a protective switching device, circuit breaker, or miniature circuit breaker.

[0004] Miniature circuit breakers (MCBs) are long-established overcurrent protection devices used in low-voltage electrical installations. They protect conductors from damage caused by overheating due to excessive current and / or short circuits. A MCB can automatically disconnect the circuit in case of overload and / or short circuit. A MCB is a non-resetting safety device. Circuit breakers, unlike MCBs, are designed for currents greater than 125 A, and sometimes even as low as 63 A. Therefore, MCBs are simpler and more delicate in design. MCBs typically have a mounting option for installation on a DIN rail (also known as a top-mounted rail or TH35).

[0005] Miniature circuit breakers (MCBs) are electromechanical devices. They contain a mechanical switching contact or shunt trip within a housing to interrupt (trigger) the electrical current. Typically, a bimetallic element is used for tripping (interruption) in the event of a prolonged overcurrent (overcurrent protection) or thermal overload (overload protection). An electromagnetic trip with a coil is used for momentary tripping when an overcurrent limit is exceeded or in the event of a short circuit (short-circuit protection). One or more arc-quenching chambers or devices are provided. Furthermore, they include connection elements for conductors of the electrical circuit to be protected.

[0006] Protective switching devices with an electronic interruption unit are relatively new developments. These devices feature a semiconductor-based electronic interruption unit. This means that the electrical current flow of the low-voltage circuit is routed through semiconductor components or semiconductor switches that can interrupt the electrical current flow or be switched to conductivity. Protective switching devices with an electronic interruption unit also frequently feature a mechanical isolating contact system, particularly with isolating characteristics according to relevant standards for low-voltage circuits. The contacts of the mechanical isolating contact system are connected in series with the electronic interruption unit, meaning that the current of the low-voltage circuit to be protected is routed through both the mechanical isolating contact system and the electronic interruption unit.

[0007] In semiconductor-based protective switching devices, also known as solid-state circuit breakers (SSCBs), the switching energy is not converted into an arc as with a mechanical switching device, but rather into heat via an additional circuit called an energy absorber. The switching energy comprises the energy stored in the circuit, i.e., in the network, line, or load impedances (consumer impedances). To reduce the load on the energy absorber, the current flowing at the moment of switching must be as low as possible. This also applies in the case of a short circuit, where the current rises very rapidly. Rapid short-circuit detection allows a short circuit to be identified early and an excessively high short-circuit current to be avoided. The semiconductor-based protective switching device interrupts the circuit almost instantaneously, within microseconds.High currents do not occur, and the load on the energy absorber of a semiconductor-based protective switching device is reduced. Known short-circuit detection and tripping criteria are typically based on determining and evaluating the actual current value.

[0008] The present invention relates to low-voltage alternating current circuits with an alternating voltage, usually a time-dependent sinusoidal alternating voltage with frequency f, typically 50 or 60 Hertz (Hz). The time dependence of the instantaneous voltage value u(t) of the alternating voltage is given by the equation: u t = U * sin 2 π * f * t described. Whereby: u(t) = instantaneous voltage value at time t U = amplitude (maximum value) of the voltage

[0009] A harmonic alternating voltage can be represented by the rotation of a phasor whose length corresponds to the amplitude (U) of the voltage. The instantaneous displacement is the projection of the phasor onto a coordinate system. One oscillation period corresponds to one full rotation of the phasor, and its full angle is 2π (2π) or 360°. The angular frequency is the rate of change of the phase angle of this rotating phasor. The angular frequency of a harmonic oscillation is always 2π times its frequency, i.e., ω = 2 π * f = 2 π / T = Kreisfrequenz der Wechselspannung (T = period of the oscillation)

[0010] The angular frequency (ω) is often preferred over the frequency (f), since many formulas in the theory of oscillations can be represented more compactly using the angular frequency due to the occurrence of trigonometric functions whose period is by definition 2π: u t = U * sin ωt

[0011] In the case of angular frequencies that are not constant over time, the term instantaneous angular frequency is also used.

[0012] For a sinusoidal, especially a time-constant, alternating voltage, the time-dependent value of the angular velocity ω and the time t corresponds to the time-dependent angle φ(t), which is also called the phase angle φ(t). This means that the phase angle φ(t) periodically traverses the range 0...2π or 0°...360°. That is, the phase angle periodically assumes a value between 0 and 2π or 0° and 360° (φ = n*(0...2π) or φ = n*(0°...360°), due to periodicity; simplified: φ = 0...2π or φ = 0°...360°).

[0013] The instantaneous voltage value u(t) therefore refers to the instantaneous value of the voltage at time t, i.e., in the case of a sinusoidal (periodic) alternating voltage, the value of the voltage at the phase angle φ (φ = 0...2π or φ = 0°...360°, of the respective period). Publication US 2020 / 366078 A1 describes a protective switching device that corresponds to the preamble of claim 1.

[0014] Furthermore, DE 2020 / 0366078 A1 discloses an intelligent circuit breaker. US 2017 / 0004948 A1 discloses an electrical circuit protection device. EP 00 516 569 A2 discloses a method and a device for monitoring the network of uninterruptible power supplies. DE 20 2009 014 759 U1 discloses a semiconductor relay with an integrated mechanical switching element for load circuit interruption.

[0015] The object of the present invention is to improve a protective switching device of the type mentioned above, in particular to show a way in which, in the event of a short circuit or overcurrent occurring, i.e., in the event of exceeding at least one current threshold, the electronic interruption unit reliably prevents an electric current flow.

[0016] This problem is solved by a protective switching device having the features of claim 1, and by a method according to claim 13.

[0017] According to the invention, an (electronic) protective switching device for the protection of a low-voltage electrical circuit, in particular a low-voltage alternating current circuit, is provided, comprising: A housing with first, in particular mains-side, and second, in particular load-side, connections for conductors of the low-voltage circuit; a mechanical disconnect contact unit connected in series with an electronic interruption unit, wherein in particular the mechanical disconnect contact unit is assigned to the (second) load-side connections and the electronic interruption unit to the (first) mains-side connections; wherein the mechanical disconnect contact unit can be switched by opening contacts to prevent current flow or closing contacts to allow current flow in the low-voltage circuit; wherein the electronic interruption unit can be switched by semiconductor-based switching elements into a high-resistance state of the switching elements to prevent current flow or a low-resistance state of the switching elements to allow current flow in the low-voltage circuit; a current sensor unit.for determining the magnitude of the current in the low-voltage circuit, such that instantaneous current values ​​are available, in particular in an embodiment of a voltage sensor unit, for determining the magnitude of the voltage in the low-voltage circuit, such that instantaneous voltage values ​​are available, a control unit which is connected to the current sensor unit, (the voltage sensor unit,) the mechanical disconnect contact unit and the electronic interruption unit, wherein, if at least one current threshold is exceeded, a current flow in the low-voltage circuit is prevented (in particular by the electronic interruption unit), wherein the protective switching device is designed in such a way that that at least one current threshold is adjusted depending on the level of current in the low-voltage circuit.

[0018] The minimum current threshold is adjusted depending on the current level such that the minimum current threshold is reduced when the current increases and is increased when the current decreases.

[0019] This has the particular advantage that the protective switching device can reliably prevent an overcurrent or short circuit, especially through its electronic interruption unit, i.e., it can disconnect the circuit. "Reliably" in this context means that the semiconductor-based switching elements (e.g., power semiconductors) are protected from thermal damage. The disconnection capacity of the electronic interruption unit, and in particular its semiconductor-based switching elements (power semiconductors), is limited by the current and / or the temperature of the power semiconductor, especially by the amount of energy supplied at high currents, which could lead to thermal overload.To ensure reliable disconnection (especially when at least one current threshold is exceeded) without oversizing the electronic interruption unit, particularly its semiconductor-based switching elements (power semiconductors), the level of the at least one current threshold is adjusted depending on the current level in the low-voltage circuit. According to the invention, this allows for high efficiency and economic benefits with simply designed units. Advantageously, the current threshold is reduced at high currents, as this allows for greater heat input, which is thus more easily detected, thereby improving the current-carrying capacity.to maximize the use of the heat capacity, in particular of the electronic interruption unit, especially its (power) semiconductor, while simultaneously protecting the (power) semiconductor of the electronic interruption unit from thermal destruction.

[0020] Advantageous embodiments of the invention are specified in the dependent claims.

[0021] In an advantageous embodiment of the invention, the protective switching device is designed such that the at least one current threshold is adjusted depending on the magnitude of the instantaneous current value.

[0022] In an advantageous embodiment of the invention, the protective switching device is designed such that the at least one current threshold value is adjusted depending on the magnitude of the RMS value or an average value of the current.

[0023] In an advantageous embodiment, the current threshold is adjusted depending on the RMS value of the current during a network period, in particular that the current threshold is reduced at higher RMS values ​​compared to the device's rated current. Rated current refers to the current that the protective switching device must be able to carry continuously; it is defined in relevant standards. Common rated currents are, for example, 16 A, 10 A, and 32 A.

[0024] In a further advantageous embodiment, the current threshold is adjusted depending on the average RMS value of the current over a third time period. This third time period is, for example, 3, 4, 5, or 10, 20, 30, or 50 network cycles. For example, with 10 network cycles, an average RMS value is calculated over 200 ms, and the current threshold is reduced, particularly if the average RMS value is higher compared to the rated current of the device.

[0025] This has the particular advantage that an adjustment is made based on current value or effective value (mean value).

[0026] In an advantageous embodiment of the invention, the protective switching device is designed such that, as the current decreases, the at least one current threshold is increased up to a maximum value of the at least one current threshold.

[0027] In an advantageous embodiment of the invention, the protective switching device is configured such that the at least one current threshold is continuously adjusted. Furthermore, adjustment can be carried out, in particular, at intervals faster than 10 s, 5 s, 1 s, 200 ms, 100 ms, 50 ms, 20 ms, 10 ms, or faster than 1 ms (all intermediate values ​​are possible and disclosed).

[0028] This has the particular advantage that the current threshold is quickly updated in order to achieve maximum utilization of the electronic interruption unit, especially its (power) semiconductor / semiconductor-based switching element, and thus high economic utilization.

[0029] In an advantageous embodiment of the invention, the protective switching device is designed such that the instantaneous current value of the determined current magnitude is compared with the at least one current threshold value by means of an analog comparator in such a way that if the (in particular the magnitude) of the (analog) instantaneous current value is exceeded by the (in particular the magnitude of the) at least one (analog) current threshold value, the prevention of the current flow in the low-voltage circuit is initiated.

[0030] In this context, exceeding the magnitude of the current above at least one current threshold sensibly refers to exceeding the current threshold when the current value is positive and falling below a negative (but equal in magnitude) current threshold when the current value is negative (alternating current). This could also be achieved through a comparison of the magnitudes.

[0031] This has the particular advantage that a rapid prevention of current flow (shutdown) is achieved, especially by the electronic interruption unit.

[0032] An instantaneous current value refers, for example, to an analog instantaneous current value that represents the magnitude of the current using an equivalent, such as an electrical voltage (voltage signal), where the voltage level represents the magnitude of the current. For instance, an analog instantaneous current value is an analog measurement of the current, which is represented as an electrical voltage signal that maps the current waveform as an equivalent.

[0033] An instantaneous current threshold, for example, refers to an analog instantaneous current threshold that indicates the current level using an equivalent, such as an electrical voltage (voltage signal), where the voltage level represents the current level. For example, the analog instantaneous current threshold is an analog signal, represented as an electrical voltage signal, that maps the instantaneous current threshold (curve) as its equivalent.

[0034] In an advantageous embodiment of the invention, the protective switching device is designed such that the at least one current threshold is digitally calculated (by the control unit or, for example, by a microprocessor or microcontroller contained therein), the calculated digital current threshold is converted into an analog current threshold using a digital-to-analog converter, and the analog current threshold is supplied to the comparator.

[0035] This has the particular advantage of combining the processing speed of an analog circuit (typically in the range of a few nanoseconds [ns], e.g. 5-10 ns) with the flexibility of a digital programmable and intelligent system (e.g. microprocessor / microcontroller).

[0036] The analog comparator operates continuously in time, meaning it is not discrete in time. This allows for the detection of an overcurrent (exceeding a current threshold) in a very short time. A microprocessor / microcontroller operates as a discrete-time controller, so the response time is limited to the processing clock, which is typically in the range of 10–100 µs.

[0037] This combination allows the flexibility and adaptability of a digital (instantaneous) current threshold to be maintained while simultaneously achieving the high response time of the analog circuit. This is possible because the adjustment of the current threshold does not need to occur in the nanosecond / ns range; only its comparison with the (current) instantaneous value of the current needs to be performed in the ns range, which is made possible by this arrangement / combination.

[0038] In an advantageous embodiment of the invention, the protective switching device is designed such that the (analog) instantaneous current values ​​are converted into digital current values, such that if the RMS value of the current exceeds the rated current of the protective switching device, the at least one current threshold is reduced for a first period of time by a percentage that depends on the extent of the exceedance of the rated current in order to obtain an adapted current threshold.

[0039] This has the particular advantage that the current threshold is reduced at high currents, since at high currents there is a higher heat input and thus the current-carrying capacity or heat capacity, in particular of the electronic interruption unit, especially its (power) semiconductor, is used to its maximum extent and at the same time the (power) semiconductor of the electronic interruption unit is protected from thermal destruction.

[0040] In an advantageous embodiment of the invention, the protective switching device is designed such that the instantaneous current values ​​are converted into digital current values, a digital current value is reduced by a correction value, and the result is subtracted from the at least one current threshold value to obtain an adapted current threshold value.

[0041] This has the particular advantage that a further, particularly simple calculation or adjustment of the current threshold is possible depending on the level of the current.

[0042] In an advantageous embodiment of the invention, the protective switching device is designed such that the instantaneous current values ​​are converted into digital current values, an RMS value and / or an RMS value averaged over the first time period is calculated from the digital current values, and the current threshold is adjusted depending on the extent of any exceedance of the RMS value or averaged RMS value over the nominal current in order to obtain an adapted current threshold.

[0043] For example, if the average RMS value exceeds the rated current of the protective switching device by 20%, the current threshold is reduced by 20%. Other scaling of the current threshold is also possible.

[0044] This has the particular advantage that a further, particularly simple calculation or adjustment of the current threshold is possible depending on the level of the current.

[0045] In an advantageous embodiment of the invention, in which a voltage sensor unit connected to the control unit is provided for determining the voltage level of the low-voltage circuit, such that instantaneous voltage values ​​are available, instantaneous current threshold values ​​are available that depend on the (in particular periodic) temporal course of the voltage level (in particular alternating voltage), i.e., on the instantaneous voltage values ​​(in particular periodic).

[0046] The current values ​​are compared (especially with respect to phase) with the current threshold values. If the current threshold value is exceeded (especially in magnitude), an interruption of the low-voltage circuit is initiated.

[0047] This has the particular advantage that threshold values / current thresholds are dependent on the periodicity of the voltage, in order to achieve rapid current flow prevention (tripping), especially by the electronic interruption unit. Small current thresholds are used at high currents.

[0048] In an advantageous embodiment of the invention, the (periodic) instantaneous current thresholds have a minimum value that is greater than zero. In particular, this minimum value is in the range of 5 to 20% of the maximum value, i.e., the maximum current threshold.

[0049] This has the particular advantage that, even with small current thresholds or low voltages, safe and rapid detection of short-circuit currents is possible, and false tripping is avoided.

[0050] In an advantageous embodiment of the invention, the low-voltage circuit exhibits a sinusoidal voltage waveform over time (ideal case). In particular, the low-voltage circuit is a low-voltage alternating current circuit. The instantaneous current thresholds also exhibit a (nearly) sinusoidal current waveform over time, particularly in terms of magnitude. Specifically, the zero crossing or the region of the zero crossing has a minimum value (in magnitude) that is greater than zero; in particular, this minimum value is greater than 5%, 10%, or 20% of the maximum value, and more specifically, this minimum value is in the range of 5% to 20% of the maximum value, i.e., the maximum current threshold. The time-dependent waveforms of the voltage and current thresholds are phase-synchronized such that the time of the voltage amplitude (maximum value) coincides with the time of the current threshold amplitude (maximum value).

[0051] This has the particular advantage of enabling easy detection, especially with sinusoidal voltage waveforms. This is particularly beneficial for low-voltage AC circuits.

[0052] In particular, the region of the zero crossing of the voltage coincides with the region of the minimum value of the current threshold.

[0053] In an advantageous embodiment of the invention, the protective switching device is configured such that the control unit comprises an analog first subunit and a digital second subunit. The first subunit includes an (analog) (current) comparator to which the instantaneous (analog) current values ​​and the instantaneous (analog) current thresholds, the latter in particular from the second subunit, are supplied. The current thresholds are provided by the second subunit in a phase-related manner according to the voltage's time-dependent behavior. This enables a phase-dependent comparison of the instantaneous current values ​​with the instantaneous current thresholds, allowing an interruption of the low-voltage circuit to be initiated when the (instantaneous) current thresholds are exceeded.

[0054] This has the particular advantage of a simple implementation of the solution.

[0055] In an advantageous embodiment of the invention, the protective switching device is configured such that a network synchronization unit is provided. This unit determines at least one phase angle (φ(t)) of the voltage and, alternatively, the amplitude (U) of the voltage from the instantaneous voltage values ​​supplied. A threshold unit is provided, which is connected to the network synchronization unit, so that instantaneous current thresholds are determined using the phase angle (φ(t)) of the voltage, the amplitude (U) of the voltage, and a maximum limit / threshold for the current threshold. The instantaneous current values ​​are compared phase-related with the instantaneous current thresholds to determine when to initiate a current interruption (break).

[0056] This has the particular advantage of further simplifying the implementation of the solution.

[0057] The primary advantage is that the electronic interruption unit prevents current flow. Additionally, or if further criteria are met, a galvanic interruption can be initiated by the mechanical isolating contact system.

[0058] According to the invention, a corresponding method for a protective switching device for a low-voltage circuit with electronic (semiconductor-based) switching elements is claimed, offering the same and further advantages.

[0059] In the method for protecting a low-voltage electrical circuit in a protective switching device with a mechanical disconnecting contact unit connected in series with an electronic interrupting unit, wherein the mechanical disconnect contact unit can be switched by opening contacts to prevent current flow or by closing contacts to allow current flow in the low-voltage circuit, wherein the electronic interruption unit can be switched by semiconductor-based switching elements into a high-resistance state of the switching elements to prevent current flow or a low-resistance state of the switching elements to allow current flow in the low-voltage circuit, wherein the voltage level of the low-voltage circuit is determined such that instantaneous voltage values ​​are available, wherein the current level of the low-voltage circuit is determined such that instantaneous current values ​​are available, wherein if the instantaneous current value (in particular its magnitude) is exceeded compared to (in particular its magnitude) at least one current threshold value, a current flow interruption of the low-voltage circuit is initiated.The minimum current threshold is adjusted depending on the current level in the low-voltage circuit. Specifically, the minimum current threshold is adjusted such that it decreases as the current increases and increases as the current decreases.

[0060] In an advantageous embodiment of the invention, the at least one current threshold is adjusted as a function of the current level such that, as the current decreases, the at least one current threshold is increased up to a maximum value of the at least one current threshold.

[0061] In an advantageous embodiment of the invention, if a rated current of the protective switching device is exceeded, the at least one current threshold is reduced by a percentage that depends on the extent of the exceedance of the rated current in order to obtain an adapted current threshold.

[0062] If the rated current is exceeded, the RMS value or the RMS value averaged over a first period (average of the RMS value over the first period) can be used for comparison with the rated current.

[0063] According to the invention, a corresponding computer program product is claimed. The computer program product comprises instructions which, when executed by a microcontroller (microprocessor), cause the microcontroller to improve the safety of such a protective switching device or to achieve greater safety in the low-voltage electrical circuit to be protected by the protective switching device, specifically ensuring that the electronic interruption unit reliably prevents the flow of electric current. The microcontroller (microprocessor) is part of the protective switching device, in particular the control unit.

[0064] According to the invention, a corresponding computer-readable storage medium on which the computer program product is stored is claimed.

[0065] According to the invention, a corresponding data carrier signal, which transmits the computer program product, is claimed.

[0066] All embodiments, both in dependent form referring back to claim 1 or 13, and also referring back only to individual features or combinations of features of claims, result in an improvement of a protective switching device for fast and safe shutdown in the event of overcurrents and short circuits and avoids thermal destruction of the semiconductor-based switching elements used in the event of overcurrents or short circuits.

[0067] The described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawing.

[0068] The drawing shows: Figure 1 a first representation of a protective switching device, Figure 2 a second representation of a protective switching device, Figure 3a first design of the protective switching device, Figure 4 a second embodiment of the protective switching device, Figure 5 Voltage and current threshold curves over time.

[0069] Figure 1 Figure 1 shows a representation of a protective switching device SG for the protection of a low-voltage electrical circuit, in particular a low-voltage alternating current circuit, with a housing GEH, comprising: Connections for conductors of the low-voltage circuit, in particular first connections L1, N1 for a network-side, especially energy source-side, connection EQ of the protective switching device SG and second connections L2, N2 for a load-side, especially energy sink-side - in the case of passive loads, connection ES (consumer-side connection) of the protective switching device SG, wherein phase-side connections L1, L2 and neutral-side connections N1, N2 may be provided; the load-side connection may have a passive load (consumer) and / or an active load ((further) energy source), or a load that may be both passive and active, e.g.in temporal sequence; a voltage sensor unit SU, for determining the voltage level of the low-voltage circuit, so that instantaneous voltage values ​​(phase-related voltage values) DU are available; instantaneous (phase-angle-related) voltage values ​​refer in particular to analogous instantaneous voltage values, i.e. .For example, an analog equivalent that indicates the voltage level, for example, an analog voltage whose level corresponds to that of the electrical voltage; a current sensor unit SI for determining the current level of the low-voltage circuit, such that instantaneous (phase-angle-related) current values ​​DI are available; instantaneous (phase-angle-related) current values ​​refer in particular to analogous instantaneous current values, i.e.For example, an analog equivalent that indicates the magnitude of the current, such as an analog voltage whose magnitude corresponds to that of the electric current; an electronic interruption unit EU, which, through semiconductor-based switching elements, has a high-resistance state of the switching elements to prevent (in particular, interrupt) and a low-resistance state of the switching elements to allow current flow in the low-voltage circuit; a mechanical isolating contact unit MK, which can be switched by opening contacts to prevent current flow or closing contacts to allow current flow in the low-voltage circuit; a control unit SE, which is connected to the voltage sensor unit SU, the current sensor unit SI, the mechanical isolating contact unit MK, and the electronic interruption unit EU.

[0070] The mechanical disconnect contact unit MK is electrically connected in series with the electronic interruption unit EU.

[0071] The SE control unit can: * be implemented with a digital circuit, e.g. with a microprocessor (= microcontroller); the microprocessor may also contain an analog part; * be implemented with a digital circuit with analog circuit parts.

[0072] The protective switching device SG, in particular the control unit SE, is designed such that if at least one current threshold is exceeded, the interruption of current flow in the low-voltage circuit is initiated, specifically in a first step by the electronic interruption unit EU. That is, if at least one current threshold is exceeded, which is generally caused by a short circuit, especially on the load side (ES), the electronic interruption unit EU switches from a low-resistance state to a high-resistance state to interrupt the low-voltage circuit.

[0073] The protective switching device is designed in such a way that at least one current threshold is adjusted depending on the magnitude of the current in the low-voltage circuit.

[0074] Specifically, or more generally, the minimum current threshold is adjusted depending on the current value. In one variant, the minimum current threshold can be adjusted depending on the RMS value or an average value of the current.

[0075] This means that at least one current threshold is provided, the exceedance of which triggers the prevention of current flow in the low-voltage circuit. This single current threshold is then adjusted depending on the current level. This would provide a simple solution for the invention.

[0076] Multiple current thresholds can be provided, in particular instantaneous / phase-angle-related current thresholds, so that an instantaneous or phase-angle-related comparison is carried out depending on the phase angle of the electrical voltage or current. These instantaneous or phase-angle-related current thresholds can then be adjusted depending on the current level. Particularly in a low-voltage AC circuit, an adjusted instantaneous or phase-angle-related current threshold can then be quickly provided, for example, for the next half-cycle (or a set of adjusted current thresholds for each half-cycle – adjustment every 10 ms in a low-voltage AC circuit with a mains frequency of 50 Hz).

[0077] A comparison can be made in such a way that (especially periodic) instantaneous current thresholds are available that depend on the (especially periodic) temporal course of the voltage level or the determined instantaneous voltage values.

[0078] The instantaneous current thresholds can be continuous or phase-angle sequential.

[0079] The instantaneous current thresholds can be defined for each individual phase angle, a phase angle range (multiple phase angles), e.g., every 2°, or a phase angle segment (a part of a phase angle), e.g., every 0.5° or 0.1°. A resolution of 1° to 5° is particularly advantageous (this corresponds to a sampling rate of 3.5 to 20 kHz).

[0080] The instantaneous current values ​​are compared phase-related with the instantaneous current thresholds. If the instantaneous current value exceeds the instantaneous current threshold (in magnitude), an interruption of the low-voltage circuit is initiated, e.g., by an initial interruption signal TRIP from the control unit SE to the electronic interruption unit EU, as shown in Figure 1 marked.

[0081] The electronic interruption unit EU is in accordance with Figure 1The block is shown in both conductors. In the first variant, this means that neither conductor is interrupted. At least one conductor, in particular the live conductor or phase conductor, has semiconductor-based switching elements. The neutral conductor can be free of switching elements, i.e., without semiconductor-based switching elements. This means the neutral conductor is directly connected and does not become high-impedance. Therefore, only a single-pole interruption (of the phase conductor) occurs. If further live conductors / phase conductors are present, in a second variant of the electronic interruption unit (EU), the phase conductors have semiconductor-based switching elements. The neutral conductor is directly connected and does not become high-impedance. This is the case, for example, in a three-phase AC circuit.

[0082] In a third variant of the electronic interruption unit EU, the neutral conductor can also have a semiconductor-based switching element, i.e., when the electronic interruption unit EU is interrupted, both conductors become high-resistance.

[0083] The electronic interruption unit EU can comprise semiconductor devices such as bipolar transistors, field-effect transistors (FETs), insulated-gate bipolar transistors (IGBTs), metal-oxide-layer field-effect transistors (MOSFETs), or other (self-commutated) power semiconductors. In particular, IGBTs and MOSFETs are especially well-suited for the protective switching device according to the invention due to their low forward resistance, high junction resistance, and good switching characteristics.

[0084] The protective switching device SG may preferably have a mechanical isolating contact system MK according to the standard with standard-compliant isolating properties, for galvanic isolation of the circuit, in particular for standard-compliant disconnection (as opposed to switching off) of the circuit. The mechanical isolating contact system MK is connected to the control unit SE, as shown in Figure 1 drawn in such a way that the control unit SE can initiate a galvanic isolation of the circuit.

[0085] Specifically, a further evaluation can be implemented that, upon fulfillment of other criteria, brings about galvanic isolation. For example, overcurrent detection can be provided, for instance in the control unit SE, which, in the event of overcurrents—i.e., when current-time limits are exceeded, meaning when a current exceeding a current limit is present for a certain time, i.e., when a certain energy threshold is exceeded—in which case a semiconductor-based and / or galvanic interruption of the circuit occurs.

[0086] Alternatively or additionally, galvanic isolation can be initiated, for example, in the event of a detected short circuit.

[0087] The initiation of the galvanic interruption of the low-voltage circuit is achieved, for example, by a further second interruption signal TRIPG, which is sent from the control unit SE to the mechanical isolating contact system MK, as shown in Figure 1marked.

[0088] The MK mechanical disconnect contact system can, in one variant, interrupt a single pole. This means that only one of the two conductors, specifically the live conductor or phase conductor, is interrupted, i.e., it has a mechanical contact. The neutral conductor is then without contact, i.e., the neutral conductor is directly connected.

[0089] If additional active conductors / phase conductors are provided, in a second variant the phase conductors have mechanical contacts of the mechanical disconnect contact system. In this second variant, the neutral conductor is directly connected. For example, in a three-phase AC circuit.

[0090] In a third variant of the mechanical disconnect contact system MK, the neutral conductor also has mechanical contacts, as in Figure 1 marked.

[0091] The term "MK mechanical disconnect contact system" refers specifically to a (standard-compliant) disconnect function, implemented by the MK disconnect contact system. The following points are included with the disconnect function: Minimum air gap according to standard (minimum distance between contacts), contact position indicator of the contacts of the mechanical disconnect contact system, opening of the mechanical disconnect contact system always possible (no blocking of the disconnect contact system by the handle), so-called free release is meant.

[0092] The minimum air gap between the contacts of the isolating contact system is essentially voltage-dependent. Other parameters include the degree of pollution, the type of field (homogeneous, inhomogeneous), and the air pressure or altitude above sea level.

[0093] There are corresponding regulations and standards for these minimum clearances or creepage distances. For example, these regulations specify the minimum clearance for an inhomogeneous and a homogeneous (ideal) electric field, depending on the degree of pollution, to ensure shock voltage withstand capability. Shock voltage withstand capability is the resistance to being applied when a corresponding shock voltage is applied. Only if this minimum length (minimum distance) is present does the isolating contact system or protective switching device exhibit a disconnecting function (isolating property).

[0094] For the purposes of the invention, the standards DIN EN 60947 and IEC 60947 are relevant for the separator function and its properties, and reference is made to them here.

[0095] The isolating contact system is advantageously characterized by a minimum air gap between the open isolating contacts in the OFF position (open position, contacts open), depending on the rated impulse withstand voltage and the degree of pollution. The minimum air gap is, in particular, between (at a minimum) 0.01 mm and 14 mm. . In particular, the minimum air gap is advantageously between 0.01 mm at 0.33 kV and 14 mm at 12 kV, especially for pollution degree 1 and especially for inhomogeneous fields.

[0096] Advantageously, the minimum air gap can have the following values: E DIN EN 60947-1 (VDE 0660-100):2018-06 Table 13 Minimum air distances - Design impulse stress resistance Minimum air gaps (mm) U imp Case A Case B inhomogeneous field homogeneous field, ideal conditions kV (see 3763) (see 3.7.62) Pollution level Pollution level 1 2 3 4 1 2 3 4 0,33 0,01 0,01 0,5 0,04 0,2 0,04 0,2 0,8 0,1 0,6 0,1 0,8 1,6 1,5 0,5 0,5 1,6 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 air gaps are based on the 1.2 / 50 µs impulse voltage at an air pressure of 80 kPa, which corresponds to the air pressure at 2 000 m above sea level.

[0097] The pollution levels and field types correspond to those defined in the standards. This advantageously allows for the creation of a standard-compliant protective switching device dimensioned according to the rated impulse withstand voltage.

[0098] Figure 2 shows a representation according to Figure 1The difference is that, advantageously (in the series connection of mechanical disconnect contact unit MK and electronic interrupt unit EU), the mechanical disconnect contact unit MK is assigned to the load-side terminals and the electronic interrupt unit EU to the network-side terminals. Furthermore, the electronic interrupt unit EU is designed as a single-pole electronic interrupt unit, i.e., in this example, it is located in the phase conductor, i.e., between terminals L1 and L2. The electronic interrupt unit EU also has (at least) one semiconductor-based switching element (= power semiconductor), which is indicated in Figure 2. The semiconductor-based switching element also has an overvoltage protection element, which is shown in Figure 2. Figure 2as also indicated. The control unit SE comprises an analog first subunit SEA and a digital second subunit SED. The digital second subunit SED can, for example, be a microprocessor or digital signal processor (DSP). The analog first subunit SEA comprises at least one (current) comparator, as shown in Figure 2 hinted at.

[0099] Figure 3 shows a representation according to Figure 1 and 2, with a further detailed embodiment. The control unit SE comprises two subunits: a first subunit SEA, preferably analog, and a second subunit SED, preferably digital. The first subunit SEA includes an analog (current) comparator CI. This comparator receives, on the one hand, the instantaneous current values ​​DI from the current sensor unit SI, specifically analog instantaneous current values. On the other hand, the current comparator CI (in this example) receives (a current threshold or) the instantaneous current thresholds SWI from the second subunit SED. A current comparator, in this context, refers to a comparator that compares two (current) quantities, in particular comparing equivalents of the current magnitude (e.g., two voltages whose voltage amplitude represents the current magnitude or the current threshold, respectively).

[0100] The (analog) instantaneous current thresholds are, in particular, an analog voltage curve.

[0101] The current comparator CI compares the (analog) instantaneous current values ​​DI with the (analog) instantaneous current threshold values ​​SWI and, as described, outputs a first current interruption signal TI to initiate an interruption of the low-voltage circuit if (especially in magnitude) the threshold is exceeded.

[0102] The current interruption signal TI can be fed to a logic unit LG, which combines it with other interruption signals and outputs the first interruption signal TRIP to the electronic interruption unit EU for semiconductor-based interruption or high-impedance interruption.

[0103] With the analog (current) comparator, immediate, i.e., very fast, detection of the exceedance is particularly possible; this usually takes place in the nanosecond range. . between 1 and 100 ns.

[0104] In comparison, a digital system would currently react in the µs range, for example between 2 - 100 µs, due to the calculation and reaction times.

[0105] In one embodiment, the current comparator CI stores the current threshold values ​​SWI in order to have the values ​​constantly available.

[0106] The instantaneous current thresholds (SWI) are synchronized with the time course of the instantaneous voltage values ​​(the voltage's time course). This means that low instantaneous current thresholds (SWI) are used (or present) at low instantaneous voltages (phase angle of a sinusoidal AC voltage of, for example, -30° to 0° to 30°) and high instantaneous current thresholds (SWI) are used (or present) at high instantaneous voltages (phase angle of a sinusoidal AC voltage of, for example, 60° to 90° to 120°). This advantageously makes the tripping time largely independent of the voltage phase angle, so that the tripping time is below a certain initial threshold value.

[0107] The (analog) instantaneous current values ​​DI and the (analog) instantaneous voltage values ​​DU are also fed to the second subunit SED. In a preferred embodiment, the instantaneous current values ​​DI and / or instantaneous voltage values ​​DU are digitized there by an analog-to-digital converter (ADC) and fed to a microprocessor (microcontroller) CPU. The CPU determines or calculates the instantaneous current threshold values ​​SWI, depending on the magnitude of the current / the supplied instantaneous current values ​​DI. The instantaneous current threshold values ​​SWI determined by the second subunit SED, or in particular by the microprocessor CPU, are then fed (via a digital-to-analog converter DAC) to the first subunit SEA, in particular to the current comparator CI, to perform the comparison described above.

[0108] The second subunit SED or the first subunit SEA can include a digital-to-analog converter (DAC) to convert the (digital) current thresholds SWI calculated in the second subunit SED into analog current thresholds SWI for analog comparison in the first analog subunit SEA. In the example according to Figure 3 The digital-to-analog converter (DAC) is part of the second (digital) subunit (SED) (or assigned to it).

[0109] Advantageously, the determination of the instantaneous current thresholds SWI in the second subunit SED can be performed digitally, or at a slower processing speed, than the continuous comparison of analog instantaneous current values ​​DI with the analog instantaneous current thresholds SWI in the first subunit SEA. This is advantageous because the analog comparison of the current value is faster than the processing or calculation time of the digital second subunit SED.

[0110] Phase-accurate comparison is generally ensured by the fast processing speeds of analog-to-digital converters (ADCs), microprocessors (=microcontrollers) (CPUs), and digital-to-analog converters (DACs) compared to the frequency of the low-voltage circuit, which is typically 50 Hertz in Europe.

[0111] In an advantageous embodiment of the invention, the first subunit SEA can comprise a voltage comparator CU. On the one hand, the instantaneous voltage values ​​DU from the voltage sensor SU are supplied to this comparator. On the other hand, instantaneous voltage threshold values ​​SWU from the second subunit SED are supplied to the voltage comparator CU.

[0112] The voltage comparator CU compares the instantaneous voltage values ​​DU with the instantaneous voltage threshold values ​​SWU and, in case of exceedance or undershooting or range check, outputs a voltage interruption signal TU to initiate an interruption of the low-voltage circuit.

[0113] The voltage interruption signal TU can be fed to the logic unit LG, which combines it with the (other) interruption signal(s) and outputs the first interruption signal TRIP to the electronic interruption unit EU for semiconductor-based interruption or high-impedance interruption.

[0114] In one embodiment, the voltage comparator CU stores the current threshold values ​​SWU in order to have the values ​​constantly available.

[0115] In one embodiment, the microprocessor CPU determines or calculates the instantaneous voltage thresholds SWU. The instantaneous voltage thresholds SWU determined by the second subunit SED, and in particular by the microprocessor CPU, are then fed back to the first subunit SEA, specifically the voltage comparator CU, to perform the comparison described above. The digital instantaneous voltage thresholds SWU can be converted into analog instantaneous voltage thresholds SWU by a further digital-to-analog converter (not shown). These are then compared with the analog instantaneous voltage values ​​DU by the voltage comparator CU.

[0116] Advantageously, the determination of the instantaneous voltage thresholds SWU in the second subunit SED can be carried out digitally or with a slower processing speed than the continuous comparison of instantaneous voltage values ​​DU and instantaneous voltage thresholds SWU in the first subunit SEA.

[0117] Depending on the configuration, a second interruption signal TRIPG can be output from the second sub-unit SED of the control unit SE, in particular from the microprocessor CPU, to the mechanical isolating contact system MK for galvanic interruption of the low-voltage circuit, as shown in Figure 3 marked.

[0118] The design of the control unit with an analog first subunit and a digital second subunit offers the particular advantage of an efficient architecture. The first analog subunit can perform a very fast comparison of instantaneous values ​​and threshold values, thus enabling rapid short-circuit detection. The second subunit can perform an independent threshold calculation or adjustment, dependent on the current level, which does not need to be performed as quickly as the detection. The threshold values ​​can, for example, be temporarily stored to be available for quick comparison. The threshold values ​​do not need to be constantly adjusted.

[0119] Figure 4 shows a further design or variant according to the Figures 1 to 3 . Figure 4shows part of a simple variant of the first subunit SEAE, preferably analog, and part of an alternative variant of the second subunit SEDE, preferably digital.

[0120] The simplified version of the first subunit SEAE includes the current comparator CIE, to which the instantaneous current values ​​DI, in particular their magnitude, and the instantaneous current threshold values ​​SWI, also in magnitude, are fed. In this example, the current comparator CIE directly outputs the first interrupt signal TRIP to interrupt the low-voltage circuit, analogous to the preceding figures. The magnitude calculation can be performed by one or more units not shown.

[0121] The alternative version of the second subunit SEDE includes a network synchronization unit NSE. This unit receives the (analog) instantaneous voltage values ​​DU. The network synchronization unit NSE determines the phase angle φ(t) of the voltage from the supplied (analog) instantaneous voltage values ​​DU, which are, for example, a sinusoidal alternating voltage from the low-voltage circuit.

[0122] Alternatively, the amplitude U and an expected time value of the voltage UE or expected value of the voltage UE can also be determined.

[0123] The expected value of the voltage UE is here a kind of filtered or regenerated or generated equivalent instantaneous voltage value DU.

[0124] The phase angle φ(t) (as well as the expected value of the voltage UE or the amplitude U) of the voltage DU can be determined, for example, by a so-called phase-locked loop (PLL). A PLL is an electronic circuit arrangement or a software-programmed variant in a microcontroller that influences the phase and, consequently, the frequency of a variable oscillator via a closed control loop in such a way that the phase deviation between an external periodic reference signal (instantaneous voltage values) and the oscillator or a signal derived from it is as constant as possible.

[0125] This allows, among other things, the phase angle φ(t), the fundamental frequency and its amplitude of the supplied mains voltage, i.e., the determined voltage values, to be determined, i.e., also the (undisturbed or filtered) expected value of the (mains) voltage.

[0126] The phase angle φ(t) determined by the network synchronization unit (NSE) (and possibly the amplitude U and / or the expected time value of the voltage UE) are fed to a threshold unit (SWE). The threshold unit SWE can display a (scaled) curve for the (phase-related) instantaneous current thresholds SWI. For example, in the case of a sinusoidal AC voltage in the low-voltage circuit, this could be an (approximately) sinusoidal current threshold curve, i.e., a sinusoidal progression of the instantaneous current thresholds SWI over the phase angle from 0° to 360° or the period (or the corresponding time).

[0127] The protective switching device SG may have one, and in particular only one, setting element. This setting element, and in particular only one, on the protective switching device SG may be used to set a limit value or maximum value for the current threshold. Alternatively, the limit value or maximum value for the current threshold may also be fixed or programmed.

[0128] According to the invention, the current threshold curve is then scaled with respect to this limit value or maximum value for the current threshold, which is set or fixed by means of the adjustment element. For example, the amplitude (i.e., the maximum value) of the current threshold curve can be scaled with the limit value / maximum value for the current threshold.

[0129] For example, the maximum current threshold value can be four times the amplitude of the rated current (i.e., at least the current that the protective device must be able to carry continuously, depending on the standards) of the protective device. For example, typical protective devices have a rated current of, say, 16 A. In this example, this results in a maximum current threshold value of: 90 A = Wurzel 2 * 16 A * 4 . (Square root of 2 => Amplitude of the nominal current value)

[0130] The instantaneous current threshold values ​​SWI can be transmitted from the threshold unit SWE to the current comparator CIE synchronously with the instantaneous current value DI by the presence of the phase angle φ(t) of the voltage in the threshold unit SWE, so that a phase-related (phase-angle-related) comparison between instantaneous current value DI and instantaneous current threshold value SWI can be carried out.

[0131] Figure 5The graph shows, on the one hand, the voltage level Vgrid in volts [V] on the left vertical axis, and, on the other hand, the period of a sinusoidal alternating voltage over time t in seconds [s] on the horizontal axis. For example, a sinusoidal alternating voltage in a low-voltage AC circuit. The instantaneous voltage values ​​over time are shown, where time is proportional to the phase angle (f = 50 Hz).

[0132] On the other hand, a phase-angle-related or phase-angle-dependent (magnitude-dependent) scaled (0 to 1) instantaneous current threshold is plotted on the right vertical axis over time t in s [s]. The time-dependent (scaled) course of the instantaneous current thresholds corresponds to the (phase-related) instantaneous current thresholds SWI.

[0133] The temporal profile of the instantaneous current threshold is determined by the magnitude profile of the voltage, i.e., the profile in the area of ​​the positive voltage half-wave is the same as the profile in the area of ​​the negative voltage half-wave.

[0134] The temporal (scaled) progression of the instantaneous current threshold values ​​is scaled according to the invention according to the limit / maximum value for the current threshold set or fixed by means of the adjustment element. For example, the amplitude (scaling 1) is set to 100 A, or, for example, 5 times the rated current. With a rated current of, for example, 16 A, the amplitude is set to, for example, 100 A. . 5 * 16 A * 1,414 Wurzel 2 = 113 A (Square root of 2 => peak value of the instantaneous value of the current).

[0135] In general, the behavior of the instantaneous current thresholds corresponds to the behavior of the voltage in the circuit, as shown in Figure 5This is illustrated. For example, a triangular voltage waveform would be used with a triangular current threshold curve. The rationale is that the voltage level determines the level of the (short-circuit) current. According to the invention, low thresholds are therefore used at high currents and high thresholds at low currents to enable fast, phase-angle-independent short-circuit detection.

[0136] According to Figure 5 The (periodic) instantaneous current threshold values ​​(SWI) exhibit a minimum value. This means the sine wave is not ideal (only approximately sinusoidal). The minimum value is greater than zero. In particular, the minimum value is greater than 5%, 10%, or 20% of the maximum value. More specifically, this minimum value can lie in the range of 5% to 20% of the maximum value, for example, at 10% or 15% of the threshold amplitude.

[0137] The minimum value takes the place of, or is located in the area of, the zero crossing of the (sine) curve for the current thresholds.

[0138] In a low-voltage alternating current circuit with a sinusoidal voltage waveform, the time-dependent waveforms of voltage and current thresholds are phase-synchronized such that the time of the voltage amplitude (maximum value) coincides with the time of the current threshold amplitude (maximum value), as shown in Figure 5 shown.

[0139] Furthermore, the region of the zero crossing of the voltage coincides with the region of the minimum value of the current threshold.

[0140] The phase angle resolution determines the speed of threshold calculation. With a phase angle resolution of 1°, meaning a threshold value is available for every full phase angle of the voltage, i.e., an instantaneous threshold value is available approximately every 55.5 µs. Switch-off is preferably achieved via an analog comparator, i.e., continuously, and is therefore significantly faster (e.g., in the nanosecond range) than the phase angle resolution.

[0141] Alternatively, the following time course applies to fully digital processing. The phase angle resolution determines the detection speed. With a phase angle resolution of 1°, meaning a threshold value exists for each full phase angle of the voltage (i.e., an instantaneous threshold value occurs approximately every 55.5 µs), this means that a shutdown can occur after a minimum of approximately 60 µs. Shorter shutdown times can be achieved with higher phase angle resolutions.

[0142] In this example, the values ​​are then processed at a minimum of 18 kHz.

[0143] The current threshold values ​​can also be stored (scaled) in a table, in which case the value may be adjusted.

[0144] Current thresholds can be calculated generally or using tables as follows: Variant A (slow, average of the RMS value): Specifically, an RMS value averaged over a first period is calculated from the instantaneous digital current values. This averaged RMS value is then compared to the rated current of the protective device to determine if it has been exceeded. The current threshold is adjusted depending on the extent to which the averaged RMS value exceeds the rated current. Specifically, at least one current threshold is reduced by a percentage dependent on the extent to which the rated current is exceeded, in order to obtain an adjusted (reduced) current threshold.

[0145] For example, if the average RMS value exceeds the nominal current by 20%, the current threshold is reduced by, say, 30%. Other scaling factors for the current threshold are also possible (for example, a 30% exceedance could also result in a 20% reduction). A possible general approach: Percentage of threshold reduction = Percentage of exceedance multiplied by an initial scaling factor.

[0146] The first scaling factor can be, for example, 1, greater than one, less than one.

[0147] The first time interval can be one network period (20ms at 50 Hz) or a multiple (up to 50 times, i.e. 1 s) of a network period.

[0148] Variant B (fast, instantaneous value): A current value averaged over a second time period is calculated from the instantaneous digital current values. This averaged current value is compared to the rated current of the protective device to determine if it has exceeded the rated current. The current threshold is adjusted depending on the extent to which the averaged current value exceeds the rated current. Specifically, at least one current threshold is reduced by a percentage dependent on the extent to which the rated current is exceeded, in order to obtain an adjusted (reduced) current threshold.

[0149] For example, if the average current exceeds the nominal current by 100%, the current threshold is reduced by, say, 20%. Other scaling factors for the current threshold are also possible (for example, a 200% exceedance could result in a 30% reduction). A possible general approach: Percentage of threshold reduction = percentage of exceedance multiplied by a second scaling factor.

[0150] The second scaling factor can be, for example, 1 or less than one.

[0151] The second time interval can be a fraction of a network period (20 ms at 50 Hz). For example, less than 10 ms, 5 ms, in particular less than 2 ms, 1 ms or 0.1 ms (any intermediate value is possible and disclosed).

[0152] Although the invention has been illustrated and described in detail by the exemplary embodiment, the invention is not limited by the disclosed examples and other variations can be derived by the person skilled in the art without leaving the scope of protection of the invention as defined by the attached claims.

Claims

1. Circuit breaker (SG) for protecting an electrical low-voltage circuit, having: - a housing (GEH), having first (L1, N1) and second (L2, N2) connections for conductors of the low-voltage circuit, - a series circuit of a mechanical isolating contact unit (MK) and an electronic interruption unit (EU), which series circuit electrically connects the first and second connections, - the mechanical isolating contact unit (MK) being able to be switched by opening contacts to prevent a flow of current or by closing the contacts to allow a flow of current in the low-voltage circuit, - the electronic interruption unit (EU) being able to 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 a flow of current in the low-voltage circuit, - a current sensor unit (SI) to ascertain the level of the current in the low-voltage circuit such that instantaneous current values are available, - a control unit (SE) that is connected to the current sensor unit (SI), the mechanical isolating contact unit (MK) and the electronic interruption unit (EU), wherein, in the event of at least one current threshold value being exceeded, prevention of a flow of current in the low-voltage circuit is initiated, - the circuit breaker being designed such that the at least one current threshold value is adapted on the basis of the level of the current in the low-voltage circuit, characterized in that the at least one current threshold value is adapted on the basis of the level of the current such that, when the current is increasing, the at least one current threshold value is reduced and, when the current is decreasing, the at least one current threshold value is increased.

2. Circuit breaker (SG) according to Patent Claim 1, characterized in that the circuit breaker is designed such that the at least one current threshold value is adapted on the basis of the level of the instantaneous current value.

3. Circuit breaker (SG) according to Patent Claim 1, characterized in that the circuit breaker is designed such that the at least one current threshold value is adapted on the basis of the level of the RMS value or an average value of the current.

4. Circuit breaker (SG) according to one of the preceding patent claims, characterized in that the first connections (L1, N1) are grid-side connections and the second connections (L2, N2) are load-side connections, in that the mechanical isolating contact unit (MK) is assigned to the load-side connections and the electronic interruption unit (EU) is assigned to the grid-side connections.

5. Circuit breaker (SG) according to one of the preceding patent claims, characterized in that, when the current is decreasing, the at least one current threshold value is increased up to a maximum value of the at least one current threshold value.

6. Circuit breaker (SG) according to one of the preceding patent claims, characterized in that the circuit breaker is designed such that the instantaneous current value of the ascertained level of the current is compared with the at least one current threshold value by means of an analogue comparator and, in the event of the at least one current threshold value being exceeded, the prevention of the flow of current in the low-voltage circuit is initiated.

7. Circuit breaker (SG) according to Patent Claim 6, characterized in that the circuit breaker is designed such that the at least one current threshold value is computed digitally, the computed digital current threshold value is converted into an analogue current threshold value by a digital-to-analogue converter (DAC), the analogue current threshold value is supplied to the comparator.

8. Circuit breaker (SG) according to one of the preceding patent claims, characterized in that the circuit breaker is designed such that the instantaneous current values are converted into digital current values, in that an RMS value or an RMS value averaged over a first time interval is computed from the digital current values, the current threshold value is reduced on the basis of the level by which the RMS value or averaged RMS value exceeds a rated current in order to obtain an adapted current threshold value.

9. Circuit breaker (SG) according to one of the preceding Patent Claims 1 to 8, characterized in that the circuit breaker is designed such that the instantaneous current values are converted into digital current values, in that a current value averaged over a second time interval is computed from the digital current values, the current threshold value is reduced on the basis of the level by which the averaged current value exceeds a rated current in order to obtain an adapted current threshold value.

10. Circuit breaker (SG) according to one of the preceding patent claims, characterized in that there is provision for a voltage sensor unit (SU) connected to the control unit, to ascertain the level of the voltage of the low-voltage circuit such that instantaneous voltage values are available, in that instantaneous current threshold values (SWI), in particular periodic ones, that are dependent on the, in particular periodic, time characteristic of the instantaneous voltage values are available, in that the instantaneous current values (DI) are compared, in particular in terms of phase, with the instantaneous current threshold values (SWI), and in that, in the event of the absolute value of the instantaneous current threshold value (SWI) being exceeded, interruption of the low-voltage circuit is initiated.

11. Circuit breaker (SG) according to Patent Claim 10, characterized in that the low-voltage circuit has a voltage characteristic that is sinusoidal over time, in that the instantaneous current threshold values (SWI) have a current threshold value characteristic, in particular in terms of absolute value, that is approximately sinusoidal over time, with a minimum value that is greater than zero, in particular greater than 5, 10, 15 or 20% of the maximum value, in that the time characteristics of voltage (DU) and current threshold values (SWI) are synchronized in terms of phase such that the time of the amplitude of the voltage (DU) matches the time of the amplitude of the current threshold value (SWI).

12. Circuit breaker (SG) according to Patent Claim 11, characterized in that the region of the zero crossing of the voltage (DU) matches the region of the minimum value of the current threshold value (SWI).

13. Method for protecting an electrical low-voltage circuit in a circuit breaker having a mechanical isolating contact unit (MK) that is connected in series with an electronic interruption unit (EU), the mechanical isolating contact unit (MK) being able to be switched by opening contacts to prevent a flow of current or by closing the contacts to allow a flow of current in the low-voltage circuit, the electronic interruption unit (EU) being able 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 a flow of current in the low-voltage circuit, wherein the level of the current in the low-voltage circuit is ascertained such that instantaneous current values are available, wherein, in the event of the instantaneous current value exceeding compared to at least one current threshold value, prevention of the flow of current in the low-voltage circuit is initiated, wherein the at least one current threshold value is adapted on the basis of the level of the current in the low-voltage circuit, characterized in that the at least one current threshold value is adapted on the basis of the level of the current such that, when the current is increasing, the at least one current threshold value is reduced and that, when the current is decreasing, the at least one current threshold value is increased.

14. Method according to Patent Claim 13, characterized in that, when the current is decreasing, the at least one current threshold value is increased up to a maximum value of the at least one current threshold value.

15. Method according to Patent Claim 13 or 14, characterized in that in the event of a rated current of the circuit breaker being exceeded, the at least one current threshold value is reduced by a percentage that is dependent on the level by which the rated current is exceeded in order to obtain an adapted current threshold value.

16. Computer program product comprising commands that, when the program is executed by a microcontroller, cause the microcontroller to support, in particular to carry out, the method according to one of Patent Claims 13 to 15 using a circuit breaker according to one of Patent Claims 1 to 12.

17. Computer-readable storage medium on which the computer program product according to Patent Claim 16 is stored.

18. Data carrier signal that transmits the computer program product according to Patent Claim 16.