EP4241291A1

EP4241291A1 - Circuit breaker device and method

Info

Publication number: EP4241291A1
Application number: EP21844264.8A
Authority: EP
Inventors: Marvin TANNHÄUSER; Fabian Döbler; Dominic Malane
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2020-12-21
Filing date: 2021-12-21
Publication date: 2023-09-13
Also published as: US20240047152A1; WO2022136424A1

Abstract

The invention relates to a circuit breaker device for a low-voltage circuit comprising a mechanical isolating contact unit (MK) which is connected in series with an electronic disconnection unit (EU). The mechanical isolating contact unit (MK) can be switched by opening contacts to prevent current flow or closing the contacts for current flow in the low-voltage circuit. The electronic disconnection circuit (EU) can be switched by semiconductor-based switching elements into a high-resistance state of the switching elements to prevent current flow or into a low-resistance state of the switching elements for current flow in the low-voltage circuit. The magnitude of the voltage of the low-voltage circuit is determined such that instantaneous voltage values are available. The magnitude of the current of the low-voltage circuit is determined such that instantaneous current values are available. If the amount of the instantaneous current value exceeds at least one current threshold value, prevention of the current flow of the low-voltage circuit is initiated. The at least one current threshold value is adjusted according to the magnitude of the voltage of the circuit breaker device.

Description

description

Protective switching device and method

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

By low voltage is meant voltages of up to 1000 volts AC or up to 1500 volts DC. Low voltage refers in particular to voltages that are greater than extra-low voltage, with values of 50 volts AC or 120 volts DC, are .

With low-voltage circuit or network or system are circuits with rated currents or Rated currents of up to 125 amps, more specifically up to 63 amps. Low-voltage circuits are circuits with rated currents or Rated currents of up to 50 amps, 40 amps, 32 amps, 25 amps, 16 amps or 10 amps are meant. The current values mentioned mean in particular nominal, rated and/or cut-off currents, i. H . the maximum current that is normally conducted through the circuit or . where the electrical circuit is usually interrupted, for example by a protective device such as a protective switching device, miniature circuit breaker or circuit breaker.

Miniature circuit breakers have long been known overcurrent protection devices that are used in electrical installation technology in low-voltage circuits. These protect lines from damage caused by heating due to excessive current and/or short circuits. A circuit breaker can switch off the circuit automatically in the event of an overload and/or short circuit. A circuit breaker is a non-automatically resetting safety element. In contrast to miniature circuit breakers, circuit breakers are intended for currents greater than 125 A, sometimes even from 63 amperes. Miniature circuit breakers are therefore simpler and more filigree in construction. Miniature circuit breakers usually have a mounting option for mounting on a so-called top-hat rail (mounting rail, DIN rail, TH35).

Miniature circuit breakers are built electromechanically. In a housing, they have a mechanical switching contact or Shunt trip for interrupting (tripping) the electrical current on . A bimetallic protective element or Bimetallic element used to trigger (interruption) in the event of prolonged overcurrent (overcurrent protection) or in the event of thermal overload (overload protection). An electromagnetic release with a coil is used for short-term release when an overcurrent limit value is exceeded or used in the event of a short circuit (short circuit protection). One or more arc quenching chamber(s) or Arc extinguishing devices are provided. Furthermore, connection elements for conductors of the electrical circuit to be protected.

Protective switching devices with an electronic interrupting unit are relatively new developments. These have a semiconductor-based electronic interruption unit. D. H . the flow of electrical current in the low-voltage circuit is routed via semiconductor components or semiconductor switches, which interrupt or switch off the flow of electrical current. can be switched to be conductive. Protective switching devices with an electronic interrupting unit also often have a mechanical isolating contact system, in particular with isolating properties in accordance with relevant standards for low-voltage circuits, the contacts of the mechanical isolating contact system being connected in series with the electronic interrupting unit, i. H . the current of the low-voltage circuit to be protected is carried both via the mechanical isolating contact system as well as via the electronic interrupting unit.

In the case of semiconductor-based protective switching devices or protective devices, the new German Solid State Circuit Breaker, SSCB for short, the switching energy does not have to be converted into an arc as with a mechanical switching device, but rather into heat by means of an additional circuit, the energy absorber. The shutdown energy includes the energy stored in the circuit, i.e. in the network, line or load impedances (consumer impedances). In order to relieve the energy absorber, the current that flows when it is switched off must be as low as possible. This also applies in the event of a short circuit. Here the current rises very quickly. Fast short-circuit detection means that a short-circuit can be detected early and a short-circuit current that is too high can be avoided. The semiconductor-based protective switching device interrupts the circuit almost instantaneously, within ps, in the sense of a switch-off process. There are no high currents and the load on the energy absorber of a semiconductor-based protective switching device is reduced. Known short-circuit detections or switch-off criteria are usually based on the determination and evaluation of the actual current value.

The present invention relates to low voltage AC circuits having an AC voltage, typically a time dependent sinusoidal AC voltage of frequency f, typically 50 or 60 Hertz (Hz). The time dependency of the instantaneous voltage value u(t) of the AC voltage is described by the equation: u(t)=U*sin(2n*f*t). Where: u(t) = instantaneous voltage value at time t

U = amplitude (maximum value) of the voltage A harmonic AC voltage can be represented by rotating a pointer whose length corresponds to the amplitude (U) of the voltage. The instantaneous deflection is the projection of the pointer onto a coordinate system. A period of oscillation corresponds to a full revolution of the pointer and its full angle is 2n (2Pi) 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 2n times its frequency, ie: w = 2n*f = 2n/T = angular frequency of the AC voltage (T = period of the oscillation)

The specification of the angular frequency (w) is often preferred to the frequency (f), since many formulas of vibration theory can be represented more compactly with the help of the angular frequency due to the occurrence of trigonometric functions whose period is by definition 2n: u ( t ) = U * sin (wt)

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

In the case of a sinusoidal alternating voltage, in particular one that is constant over time, the time-dependent value from the angular velocity w and the time t corresponds to the time-dependent angle cp(t), which is also referred to as the phase angle cp(t). I.e. the phase angle cp ( t ) periodically runs through the range 0...2n or 0°...360°. This means that the phase angle periodically assumes a value between 0 and 2n or 0° and 360° (cp = n* (0...2n) or cp = n* (0°...360°) because of periodicity; abbreviated: cp = O...2n or cp = 0°...360° ) .

The instantaneous voltage value u(t) is consequently the instantaneous value of the voltage at time t, ie in the case of a sinusoidal (periodic) alternating voltage, the value of the voltage at Phase angle cp meant ( cp = 0...2n or cp = 0°...360°, of the respective period).

The object of the present invention is to improve a protective switching device of the type mentioned, in particular to show a possibility that when a short circuit or overcurrent occurs, d. H . if at least one current threshold value is exceeded, the electronic interruption unit reliably prevents an electrical current flow.

This object is achieved by a protective switching device having the features of patent claim 1 and by a method according to patent claim 12 .

According to the invention, an (electronic) protective switching device is provided for protecting an electrical low-voltage circuit, in particular a low-voltage alternating current circuit, having:

- A housing with first, in particular the mains side, and second, in particular the load side, connections for conductors of the low-voltage circuit,

- a mechanical isolating contact unit, which is connected in series with an electronic interrupting unit, in particular the mechanical isolating contact unit being assigned to the (second) load-side connections and the electronic interrupting unit to the (first) network-side connections,

- that the mechanical isolating contact unit can be switched by opening contacts to avoid a current flow or by closing the contacts for a current flow in the low-voltage circuit,

- that the electronic interruption unit can be switched by semiconductor-based switching elements to a high-impedance state of the switching elements to avoid current flow or a low-impedance state of the switching elements to current flow in the low-voltage circuit, - A current sensor unit for determining the level of the current of the low-voltage circuit, such that the instantaneous current values are available,

- a voltage sensor unit, for determining the level of the voltage of the low-voltage circuit, such that the current voltage values are present,

- A control unit, which is connected to the current sensor unit, the voltage sensor unit, the mechanical isolating contact unit and the electronic interrupter unit, wherein when at least one current threshold value is exceeded (in particular in terms of amount), avoidance of a current flow in the low-voltage circuit is initiated,

- that the protective switching device is designed in such a way that the at least one current threshold value is adjusted as a function of the magnitude of the voltage in the low-voltage circuit.

This has the particular advantage that the protective switching device is switched off in the event of an overcurrent or Short circuit this can be safely avoided in particular by the electronic interruption unit, d. H . can turn off . In this context, safe means that the semiconductor-based switching elements (e.g. power semiconductors) are protected from thermal destruction. The breaking capacity of the electronic interruption unit, in particular its (power) semiconductor, is limited by the (current) voltage, in particular by the amount of energy provided at high voltages, which could lead to thermal overload. In order to achieve safe disconnection (when at least one current threshold value is exceeded) without oversizing the electronic interruption unit, in particular its (power) semiconductor, the level of the at least one current threshold value is adjusted depending on the level of the voltage in the low-voltage circuit. Thus, according to the invention, a high level of efficiency and a high economic benefit can be achieved with simple units. Advantageous configurations of the invention are specified in the dependent claims.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that the at least one current threshold value is adjusted as a function of the magnitude of the voltage in such a way that the at least one current threshold value is reduced as the voltage decreases and that the at least one current threshold value is increased as the voltage increases. is increased in particular up to a maximum value of the at least one current threshold value.

In this way, the current threshold value (the current threshold) is advantageously reduced at low voltages, since at low voltages and high currents there can be a greater heat input, which is then better recognized in order to improve the current-carrying capacity or Heat capacity, in particular of the electronic interruption unit, more specifically its (power) semiconductor, to the maximum.

In the case of alternating voltages (AC voltages), there is the possibility that only a very small voltage, e.g. B. 10V, at the connection on the energy source side (mains connection) . As a result, a shutdown does not take place immediately when the short circuit occurs, since only a small short-circuit current flows due to the low voltage. After a short time, typically in the range of 1-3 ms, the AC voltage at the connection on the energy source side (mains connection) increases, so that a sufficiently large current flows for the shutdown. This delayed shutdown represents an increased thermal load for the electronic interruption unit, in particular its semiconductor-based switching elements (the electronic switch), since the semiconductor chip used in the semiconductor-based switching elements of the electronic interruption unit has a very small thermal capacity and thus a very small thermal time constant (typically less than 1 ms ) . The solution described reduces at low torque tan value of the voltage is the current threshold for switching off the electronic interruption unit, so that it also switches off quickly at low voltages and the semiconductor-based switching elements or the semiconductor chip of the electronic interruption unit is protected against thermal destruction.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that the at least one current limit value is continuously adapted. Furthermore, an adaptation can in particular take place which is carried out faster than 20 ms, more specifically faster than 10 ms or preferably faster than 1 ms.

This has the particular advantage that the current threshold value is carried along quickly in order to achieve maximum utilization of the electronic interruption unit, in particular its (power) semiconductor, and thus achieve high economic utilization.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that the instantaneous current value of the determined level of the current is compared with the at least one current threshold value by means of an analog comparator in such a way that if the amount of the current exceeds the amount of the at least one current threshold value, the avoidance of the current flow of the low-voltage circuit is initiated.

Exceeding the magnitude of the current by the magnitude of the at least one current threshold value in this context means exceeding the current threshold value when the current value is positive and falling below a negative current threshold value (the same amount) when the current value is negative (alternating current). This could also be realized by comparing the amounts. This has the particular advantage that rapid avoidance of a current flow (switching off) is achieved, in particular by the electronic interruption unit.

By instantaneous current value is meant, for example, an analog instantaneous current value that represents the magnitude of the current by an equivalent, such as an electrical voltage (voltage signal), with the magnitude of the voltage representing the magnitude of the current. For example, an analog instantaneous current value is an analog measured value of the current, which is present as an electrical voltage signal, which depicts the course of the current as an equivalent.

By instantaneous current threshold is meant, for example, an analog instantaneous current value threshold that indicates the magnitude of the current by an equivalent, such as an electrical voltage (voltage signal), where the magnitude of the voltage represents the magnitude of the current. For example, the analog instantaneous current threshold value is an analog signal, which is present as an electrical voltage (ssignal), which maps the instantaneous current threshold value (curve) as an equivalent.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that the at least one current threshold value is calculated digitally (by the control unit or, for example, by a microprocessor or microcontroller/microcontroller contained therein), the calculated digital current threshold value with a digital analog -Converter is converted into an analog current threshold value, the analog current threshold value is supplied to the comparator.

This has the particular advantage that the processing speed of an analog circuit (typically in the range of a few nanoseconds [ns], e.g. 5-10 ns) is combined with the flexibility of a digitally programmable and intelligent system (e.g. microprocessor/micro controllers) is combined. The analog comparator works in a time-continuous manner, i.e. not in a time-discrete manner. The detection of an overcurrent (exceeding current threshold value) is hereby possible in a very short time. A microprocessor / microcontroller works as a time-discrete controller, so that the reaction time is limited to the processing cycle, which is typically in the range of 10-100 ps.

With this combination, the flexibility and adaptability of a digital (instantaneous) current threshold value can be retained and at the same time the high response time of the analog circuit can be achieved . This is possible because the adjustment of the current threshold value does not have to happen in the nanosecond range/ns, only its comparison with the (current) instantaneous value of the current value should be carried out in the ns range, which is possible with this arrangement/combination.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that the level of the voltage is converted into a digital voltage value, the digital voltage value is normalized to its amplitude value, the amount is then formed, then the amount is multiplied by a first factor (kl) multiplied and then a minimum value (k2) added, the resulting result gives a scaling factor (FM(t)) for the at least one current threshold value, which is multiplied by the at least one current threshold value in order to obtain a (time-varying) adjusted current threshold value .

This has the particular advantage that a particularly simple calculation or Adaptation of the current threshold depending on the level of the voltage is given.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that the level of the voltage is converted into a digital voltage value, the amount of the voltage value is determined by the amplitude of the voltage voltage value is subtracted, then the result is multiplied by a factor (k3), the resulting result gives a correction value which is subtracted from the at least one current threshold value in order to obtain a (time-varying) adjusted current threshold value.

This has the particular advantage that another particularly simple calculation or Adaptation of the current threshold depending on the level of the voltage is given.

In an advantageous embodiment of the invention are from the (periodic) time course of the level of the voltage (AC voltage), d. H . of the instantaneous voltage values, dependent (periodic) instantaneous current threshold values before .

The instantaneous current values are compared (particularly phase-related) with the instantaneous current threshold values. If the instantaneous current threshold value is exceeded (in terms of absolute value), an interruption of the low-voltage circuit is initiated.

This has the particular advantage that there are threshold values/current threshold values that are dependent on the periodicity of the voltage, in order to achieve rapid avoidance of current flow (tripping), in particular by the electronic interruption unit. Small current threshold values are used for low voltages and large current threshold values are used for high voltages.

In an advantageous embodiment of the invention, the (periodic) instantaneous current threshold values 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, ie. H . the maximum current threshold value.

This has the particular advantage that with small current threshold values or small voltages a safe and rapid detection of short-circuit currents is made possible and false tripping can be avoided.

In an advantageous embodiment of the invention, the low-voltage circuit has a voltage profile that is sinusoidal over time (ideal case). In particular, the low-voltage circuit is a low-voltage AC circuit. The instantaneous current threshold values likewise have a time-related, in particular amount-related, (approximately) sinusoidal current curve. In particular, the zero crossing or the area of the zero crossing has a (absolute) minimum value that is greater than zero, in particular this minimum value is in the range of 5 to 20% of the maximum value, d. H . the maximum current threshold value. The time curves of voltage and current threshold values are phase-related such that the point in time of the amplitude (maximum value) of the voltage corresponds to the point in time of the amplitude (maximum value) of the current threshold value.

This has the particular advantage that simple detection is made possible in the case of (particularly) sinusoidal voltage curves. This is particularly advantageous for low-voltage AC circuits.

In particular, the range of the zero crossing of the voltage corresponds to the range of the minimum value of the current threshold value.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that the control unit has an analog first subunit and a digital second subunit. The first sub-unit has an (analog) (current) comparator to which the instantaneous (analog) current values and the instantaneous (analog) current threshold values, the latter in particular from the second sub-unit, are supplied. The current threshold values are provided phase-related according to the time profile of the voltage from the second subunit. This becomes a enables a phase-related comparison of the instantaneous current values with the instantaneous current threshold values based on the time profile of the voltage. With which an interruption of the low-voltage circuit can be initiated when the (instantaneous) current threshold values are exceeded.

This has the special advantage of a simple implementation of the solution.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that a network synchronization unit is provided. From the instantaneous voltage values supplied, this determines at least one phase angle (cp(t)) of the voltage and alternatively the amplitude (U) of the voltage. A threshold value unit is provided, which is connected to the grid synchronization unit, so that the phase angle (cp(t)) of the voltage, the amplitude (U) of the voltage and a maximum limit value/threshold value for the current threshold value => instantaneous current threshold values are determined. The instantaneous current values are compared phase-related with the instantaneous current threshold values to determine the initiation of avoidance of a current flow (interruption).

This has the special advantage of a further simple implementation of the solution.

Advantageously, an avoidance of the current flow is primarily initiated by the electronic interruption unit. In addition, or if other criteria are present, a galvanic interruption can be initiated by the mechanical isolating contact system.

According to the invention, a corresponding method for a protective switching device for a low-voltage circuit with electronic (semiconductor-based) switching elements with the same and additional advantages is claimed. In the method for protecting an electrical low-voltage circuit in a protective switching device with a mechanical isolating contact unit, which is connected in series with an electronic interrupting unit, the mechanical isolating contact unit being switched by opening contacts to prevent a current flow or by closing the contacts for a current flow in the low-voltage circuit can be switched by semiconductor-based switching elements in a high-impedance state of the switching elements to avoid a current flow or in a low-impedance state of the switching elements for current flow in the low-voltage circuit, the level of the voltage of the low-voltage circuit being determined such that the instantaneous voltage values are present, the magnitude of the current in the low-voltage circuit being determined in such a way that the (analog) instantaneous current values are present, with when it is exceeded (in particular the amount) of the instantaneous current value compared with (in particular the amount of) at least one current threshold value to prevent the flow of current in the low-voltage circuit is initiated, the at least one current threshold value is adjusted depending on the magnitude of the voltage of the protective switching device.

In an advantageous embodiment of the invention, the at least one current threshold value is adjusted as a function of the level of the voltage in such a way that the at least one current threshold value is reduced as the voltage decreases and that the at least one current threshold value is increased as the voltage increases, in particular up to a maximum value of the at least a current threshold is increased.

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

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

According to the invention, a corresponding data carrier signal that transmits the computer program product is claimed.

All configurations, both in dependent form based on patent claim 1 or 12, as well as referring back only to individual features or feature combinations of patent claims, bring about an improvement in 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.

The described properties, features and advantages of this invention and the manner in which they are achieved become clearer and more clearly understandable in connection with the following description of the exemplary embodiments, which are explained in more detail in connection with the drawing.

The drawing shows:

Figure 1 is a first representation of a protective switching device,

Figure 2 shows a second representation of a protective switching device,

Figure 3 shows a first embodiment of the protective switching device, FIG. 4 shows a second embodiment of the protective switching device,

Figure 5 voltage and current threshold curves over time.

FIG. 1 shows a representation of a protective switching device SG for protecting an electrical low-voltage 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 LI, NI for a network-side, in particular energy-source-side, connection EQ of the protective switching device SG and second connections L2, N2 for a load-side, in particular energy-sink side - in the case of passive loads, connection ES (consumer-side connection ) of the protective switching device SG, with special connections LI, L2 on the phase conductor side and connections NI, N2 on the neutral conductor side being able to be provided; the load-side connection can have a passive load (consumer) and/or an active load ((further) energy source, or a load that can be both passive and active, eg in a chronological sequence;

- A voltage sensor unit SU, for determining the magnitude of the voltage of the low-voltage circuit, so that instantaneous voltage values (phase-related voltage values) DU are present, instantaneous (phase-angle-related) voltage values mean in particular analog instantaneous voltage values, d. H . for example an analogue equivalent that indicates the magnitude of the voltage, for example an analogue voltage whose magnitude corresponds to that of the electrical voltage,

- A current sensor unit SI, for determining the level of the current of the low-voltage circuit, such that instantaneous (phase angle-related) current values DI are present, instantaneous (phase angle-related) current values mean in particular analog instantaneous current values, d. H . for example an analogue equivalent that indicates the magnitude of the current, for example an analogue voltage whose magnitude corresponds to that of the electric current, - An electronic interruption unit EU, which has a high-impedance state of the switching elements to avoid (in particular interruption) a current flow and a low-impedance state of the switching elements to current flow in the low-voltage circuit due to semiconductor-based switching elements,

- A mechanical isolating contact unit MK, which can be switched by opening contacts to avoid a current flow or by closing the contacts for a current flow in the low-voltage circuit,

- A control unit SE, which is connected to the voltage sensor unit SU, the current sensor unit S I, the mechanical isolating contact unit MK and the electronic interruption unit EU.

The mechanical isolating contact unit MK is electrically connected in series with the electronic interruption unit EU.

The control unit SE can :

* with a digital circuit, e.g. B. with a microprocessor; the microprocessor can also contain an analog part;

* Be realized with a digital circuit with analog circuit parts.

The protective switching device SG, in particular the control unit SE, is designed such that when at least one current threshold value is exceeded, avoidance of a current flow in the low-voltage circuit is initiated, in particular initiated in a first step by the electronic interruption unit EU.

D. H . if at least one current threshold value is exceeded, which is usually caused by a short circuit, in particular on the load side (ES), the electronic interruption unit EU is switched from the low-impedance state to the high-impedance state to interrupt the low-voltage circuit. The protective switching device is designed in such a way that the at least one current threshold value is adjusted as a function of the level of the voltage in the low-voltage circuit.

D. H . at least one current threshold value is provided, when it is exceeded (in particular in terms of absolute value) an avoidance of a current flow in the low-voltage circuit is initiated. This one current threshold value is then adjusted as a function of the level of the voltage. This would provide a simple solution for the invention.

Several current threshold values can also be provided, in particular instantaneous/phase angle-related current threshold values can be provided, so that depending on the phase angle of the electrical voltage or of the electric current a momentary resp. phase angle-related comparison is carried out. These current or Phase angle related current thresholds can then be adjusted depending on the magnitude of the voltage. In a low-voltage AC circuit in particular, an adapted instantaneous or phase angle-related current threshold can be made available (or a set of adjusted current thresholds for each half-wave - adjustment every 10 ms in a low-voltage AC circuit with a mains frequency of 50 Hz).

A comparison can be made to the effect that the (periodic) time profile of the level of the voltage or (periodic) instantaneous current threshold values dependent on the determined instantaneous voltage values are present.

The instantaneous current thresholds may be continuous or phase angle wise.

The instantaneous current threshold values can be per individual phase angle, a phase angle range (several phase angles), z. B. every 2°, or a phase angle intercept (a Part of a phase angle), for example every 0.5° or 0.1°. In particular, a resolution of 1° to 5° is particularly advantageous (this corresponds to a sampling rate of 3.5 to 20 kHz).

The instantaneous current values are compared phase-related with the instantaneous current threshold values. If the amount of the instantaneous current threshold value is exceeded by the amount of the instantaneous current value, an interruption of the low-voltage circuit is initiated, e.g. by a first interruption signal TRIP from the control unit SE to the electronic interruption unit EU, as shown in FIG.

The electronic interruption unit EU is shown in FIG. 1 as a block in both conductors. In a first variant, this means that there is no interruption in both conductors. At least one conductor, in particular the active 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. I.e. the neutral conductor is directly connected, i.e. it does not become highly resistive. I.e. there is only a single-pole interruption (of the phase conductor). If further active conductors/phase conductors are provided, in a second variant of the electronic interruption unit EU the phase conductors have semiconductor-based switching elements. The neutral conductor is connected directly, i.e. it does not become highly resistive. For example, for a three-phase AC circuit.

In a third variant of the electronic interruption unit EU, the neutral conductor can also have a semiconductor-based switching element, i.e. if the electronic interruption unit EU is interrupted, both conductors become highly resistive.

The electronic interruption unit EU can 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. IGBTs and MOSFETs in particular are particularly well suited for the protective switching device according to the invention due to low flow resistances, high junction resistances and good switching behavior.

The protective switching device SG can preferably have a mechanical isolating contact system MK in accordance with the standard with standard-compliant isolating properties for galvanic isolation of the circuit, in particular for standard-compliant isolating (as opposed to disconnecting) the circuit. The mechanical isolating contact system MK is connected to the control unit SE, as shown in FIG. 1, so that the control unit SE can initiate a galvanic isolation of the circuit.

In particular, a further evaluation can be implemented, which brings about a galvanic isolation when other criteria are met. For example, an overcurrent detection can be provided, for example in the control unit SE, in the event of overcurrents, d. H . if current time limits are exceeded, i .e . H . if a current that exceeds a current limit value is present for a certain time, d. H . For example, a certain energy threshold value is exceeded, a semiconductor-based and/or galvanic interruption of the circuit occurs.

Alternatively or in addition, if a short circuit is detected, for example, galvanic isolation can also be initiated.

The galvanic interruption of the low-voltage circuit is initiated, 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 FIG. In a first variant, the MK mechanical isolating contact system can interrupt on a single pole. D. H . only one conductor of the two conductors, in particular the active conductor or phase conductor, is interrupted, d . H . has a mechanical contact. The neutral conductor is then contact-free, i. H . the neutral wire is directly connected .

If further active conductors/phase conductors are provided, in a second variant the phase conductors have mechanical contacts of the mechanical isolating contact system. The neutral conductor is directly connected in this second variant. For example, for a three-phase AC circuit.

In a third variant of the mechanical isolating contact system MK, the neutral conductor also has mechanical contacts, as shown in FIG.

The mechanical isolating contact system MK means, in particular, a (standard-compliant) isolating function, implemented by the isolating contact system MK. The isolating function means the points: -minimum clearance according to the standard (minimum distance between the contacts), -contact position display of the contacts of the mechanical isolating contact system, -opening of the mechanical isolating contact system is always possible (no blocking of the isolating contact system by the handle), so-called trip-free release.

With regard to the minimum clearance between the contacts of the isolating contact system, this is essentially dependent on the voltage. Other parameters are the degree of contamination, the type of field (homogeneous, inhomogeneous) and the air pressure or the height above sea level.

For these minimum clearances or Creepage distances, there are corresponding regulations or norms . These regulations specify, for example, air for a surge voltage the minimum clearance for an inhomogeneous and a homogeneous (ideal) electric field depending on the degree of contamination. The impulse withstand voltage is the strength when a corresponding impulse voltage is applied. The isolating contact system or protective switching device only has an isolating function (isolating property) if this minimum length (minimum distance) is present.

In terms of the invention, the isolating function and its properties are based on the DIN EN 60947 or IEC 60947 series of standards, to which reference is made here.

The isolating contact system is advantageously characterized by a minimum clearance of the open isolating contacts in the exhibition (open position, open contacts) as a function of the rated impulse withstand voltage and the degree of pollution. The minimum clearance is in particular between (at least) 0.01 mm and 14 mm. In particular, the minimum clearance 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.

The minimum clearance can advantageously have the following values:

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

Table 13 - Minimum clearances

The pollution degrees and field types correspond to those defined in the standards. As a result, a standard-compliant protective switching device dimensioned according to the rated surge withstand voltage can advantageously be achieved.

Figure 2 shows an illustration according to Figure 1, with the difference that advantageously (with the series connection of mechanical isolating contact unit MK and electronic interruption unit EU), the mechanical isolating contact unit MK is assigned to the load-side connections and the electronic interruption unit EU is assigned to the network-side connections. Furthermore, the electronic interruption unit EU is designed as a single-pole electronic interruption unit EU, i. H . is in the phase conductor in the example, i . H . provided between the terminals LI, L2. The electronic interruption unit EU also has (at least) one semiconductor-based switching element (=power semiconductor), which is indicated in FIG. The semiconductor-based switching element also has an overvoltage protection element, which is also indicated in FIG. The control unit SE has an analog first sub-unit SEA and a digital second sub-unit SED. The digital second sub-unit SED can be a microprocessor or digital signal processor (DSP), for example. The analog first subunit SEA has at least one (current) comparator, as indicated in FIG.

FIG. 3 shows an illustration according to FIGS. 1 and 2, with a further detailed configuration. The control unit SE has two sub-units, a preferably analog, first sub-unit SEA and a preferably digital, second sub-unit SED. The first sub-unit SEA has an analog (current) comparator CI. On the one hand, the instantaneous current values DI of the current sensor unit SI are fed to this. On the other hand, the current comparator CI (in the example) is fed (a current threshold value or) the instantaneous current threshold values SWI from the second subunit SED.

The term current comparator means a comparator that compares two (current) variables with one another, in which case in particular equivalents of the level of the current are compared with one another (e.g. two voltages whose voltage level each represents the current level or the level of the current threshold value).

The (analog) instantaneous current threshold values are, in particular, an analog voltage profile.

The current comparator CI compares the instantaneous current values DI with the instantaneous current threshold values SWI and, as described, emits a first current interruption signal TI for initiating an interruption of the low-voltage circuit if the limit is exceeded (particularly in terms of amount).

The current interruption signal TI can be fed to a logic unit LG, which communicates with other interruption signals combined and emits the first interrupt signal TRIP for the semiconductor-based interrupt or high-impedance interrupt to the electronic interrupt unit EU.

With the analog (current) comparator, immediate, i.e. very fast, detection of exceeding is possible, this usually takes place in the ns range, i.e. between 1 and 100 ns.

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

In one embodiment, the current comparator CI temporarily stores the instantaneous (current) threshold values SWI in order to have the values constantly available.

The instantaneous current threshold values SWI are synchronized with the time curve of the instantaneous voltage values (the time curve of the voltage). As a result, with a low instantaneous voltage (phase angle of a sinusoidal AC voltage of e.g. -30° to 0° to 30°), small instantaneous current threshold values SWI are used (or are available) and with a high instantaneous voltage (phase angle of a sinusoidal AC voltage of e.g. 60° to 90 ° to 120 °) high current threshold values SWI used (or are available). As a result, for example, the tripping time is advantageously largely independent of the phase angle of the voltage, so that the tripping time is below a first temporal threshold value.

The analog instantaneous current values DI and the analog instantaneous voltage values DU are also supplied to the second sub-unit SED. In a preferred embodiment, the instantaneous current values DI and/or instantaneous voltage values DU are digitized there by an analog/digital converter ADC and fed to a microprocessor (=microcontroller) CPU. This carried out a determination or calculation of the instantaneous current threshold values SWI, depending on the height of the voltage / the instantaneous voltage values DU supplied. The through the second sub-unit SED or. The instantaneous current threshold values SWI determined in particular by the microprocessor CPU are in turn supplied by a digital-to-analog converter (DAC) to the first subunit SEA, in particular to the current comparator CI, in order to carry out the comparison described above.

The second sub-unit SED or the first sub-unit SEA can have a digital-to-analog converter DAC in order to convert the (digital) current threshold values SWI calculated in the second sub-unit SED into analog current threshold values SWI in order to carry out an analog comparison in the first analog sub-unit SEA. In the example according to FIG. 3, the digital-to-analog converter DAC is part of the second (digital) sub-unit SED (or assigned to it).

Advantageously, the instantaneous current threshold values SWI can be determined digitally in the second sub-unit SED. with a slower processing speed than the continuous comparison of analog instantaneous current values DI with the analog instantaneous current threshold values SWI in the first sub-unit SEA. This is advantageous because the analog comparison of the current values with the current threshold values using the comparator takes place faster than the processing time or Calculation time in the digital second subunit SED.

The phase-accurate comparison is usually ensured by the fast processing speeds of analog-digital converter ADC, microprocessor (= microcontroller) CPU and digital-analog converter DAC compared to the frequency of the low-voltage circuit, which is usually 50 Hertz in Europe.

In an advantageous embodiment of the invention, the first sub-unit SEA can have a voltage comparator CU. On the one hand, the instantaneous voltage values DU des Voltage sensor SU supplied. On the other hand, instantaneous voltage threshold values SWU are supplied to the voltage comparator CU by the second sub-unit SED.

The voltage comparator CU compares the instantaneous voltage values DU with the instantaneous voltage threshold values SWU and, if they are exceeded or fallen below or Range check a voltage interrupt signal TU to initiate an interrupt of the low voltage circuit from .

The voltage interrupt signal TU can be fed to the logic unit LG, which combines it with the (n) (other) interrupt signal(s) and uses the first interrupt signal TRIP to semiconductor-based interrupt or emits high-impedance interruption to the electronic interruption unit EU.

In one embodiment, the voltage comparator CU temporarily stores the instantaneous threshold values SWU in order to have the values constantly available.

In one embodiment, the microprocessor CPU performs a determination or Calculation of the instantaneous voltage threshold values SWU by . The through the second sub-unit SED or. In particular, the instantaneous voltage threshold values SWU determined by the microprocessor CPU are in turn supplied to the first subunit SEA, in particular to the voltage comparator CU, in order to carry out the comparison described above. The digital instantaneous voltage threshold values SWU can be converted into analog instantaneous voltage threshold values SWU by a further digital-to-analog converter (not shown). These are compared with the analog instantaneous voltage values DU using the voltage comparator CU.

Advantageously, the instantaneous voltage threshold values SWU can be determined digitally in the second sub-unit SED. with a slower processing speed speed as the continuous comparison of instantaneous voltage values DU and instantaneous voltage threshold values SWU in the first sub-unit SEA.

Depending on the configuration, a second interrupt signal TRIPG can be emitted by the second subunit SED of the control unit SE, in particular by the microprocessor CPU, to the mechanical isolating contact system MK for galvanic interruption of the low-voltage circuit, as shown in FIG.

The configuration of the control unit with an analog first sub-unit and a digital second sub-unit has the particular advantage that an efficient architecture is present. The first analog sub-unit can carry out a very quick comparison of analog instantaneous values and analog threshold values, as a result of which quick short-circuit detection is possible. The second sub-unit can perform a threshold value calculation or Carry out adjustment, according to the invention depending on the level of the voltage, which does not have to be carried out as quickly as the detection. The threshold values can be temporarily stored, for example, in order to be available for a quick comparison. The threshold values do not have to be constantly adjusted.

Figure 4 shows a further embodiment or. Variant according to Figures 1 to 3. FIG. 4 shows part of a simple variant of the preferably analog first subunit SEAE and part of an alternative variant of the preferably digital second subunit SEDE.

The part of the simple variant of the first sub-unit SEAE has the current comparator CIE, to which the instantaneous current values DI, in particular their amount, and the instantaneous current threshold values SWI, in particular also related to the amount, are supplied. In this example, the current comparator CIE directly outputs the first interrupt signal TRIP for breaking of the low-voltage circuit, analogous to the previous figures. The amount can be formed by one or more units that are not shown.

The part of the alternative variant of the second subunit SEDE has a network synchronization unit NSE. The (analogue) instantaneous voltage values DU are supplied to this.

The network synchronization unit NSE determines the phase angle cp ( t ) of the voltage from the supplied (analog) instantaneous voltage values DU, which are e.g. a sinusoidal AC voltage of the low-voltage circuit.

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

The expected value of the voltage UE is a type of filtered or regenerated or generated equivalent instantaneous voltage value DU.

The phase angle cp(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 or phase-locked loop, PLL for short. A PLL is an electronic circuit arrangement (or a software-programmed variant in the microcontroller) that influences the phase position and the associated 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.

In this way, among other things, the phase angle cp(t), the fundamental frequency and its amplitude of the mains voltage supplied, ie the determined voltage values, can be determined, ie for example also the (undisturbed or filtered) expected value of the (mains) voltage.

The phase angle cp(t) determined by the network synchronization unit NSE (and possibly the amplitude U and/or the expected time value of the voltage UE) are supplied to a threshold value unit SWE. The threshold value unit SWE can have a (scaled) curve for the (phase-related) instantaneous current threshold values SWI. For example, in the case of a sinusoidal AC voltage in the low-voltage circuit, an (approximately) sinusoidal current threshold value curve, i.e. a sinusoidal course of the instantaneous current threshold values SWI over the phase angle 0° to 360° or the period duration (or the (corresponding) time).

The protective switching device SG can have one, in particular a single, setting element. A limit value or maximum value for the current threshold value can be set with this, in particular single, setting element on the protective switching device SG. Alternatively, the limit value or maximum value for the current threshold value can also be permanently specified or programmed.

According to the invention, the current threshold value curve is then scaled with regard to this limit value or maximum value for the current threshold value, which is set or permanently predetermined by means of the setting element. For example, the amplitude (i.e. maximum value) of the current threshold curve can be scaled with the limit/maximum value for the current threshold.

For example, the maximum value of the current threshold value can be four times the amplitude of a rated current (i.e. at least the current that the protective switching device must carry continuously, depending on the standard) of the protective switching device, for example, conventional protective switching devices have a rated current of e.g. 16 A. In the example, this results in a maximum value of the current threshold of:

90A = (root 2) * 16A * 4. (root 2 => amplitude of the nominal current value)

The instantaneous current threshold values SWI can be transmitted synchronously to the instantaneous current value DI to the current comparator CIE due to the presence of the phase angle cp (t) of the voltage in the threshold value unit SWE, so that a phase-related (phase-angle-related) comparison between the instantaneous current value DI and the instantaneous current threshold value SWI can be done.

FIG. 5 shows, on the one hand, the profile of the magnitude of a mains-side voltage Vgrid in volts [V], on the left vertical axis, a period of a sinusoidal alternating voltage over time t in s[s], on the horizontal axis. For example, a sinusoidal AC voltage in the low-voltage AC circuit. The instantaneous voltage values of the voltage are given over time, with the time being proportional to the phase angle (f=50 Hz).

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

The time profile of the instantaneous current threshold value (threshold) is based on the absolute value profile of the voltage, d . H . the curve in the area of the positive voltage half-wave is the same as the curve in the area of the negative voltage half-wave.

The time (scaled) progression of the instantaneous current threshold values threshold is set or selected using the setting element. fixed predetermined limit value tes/maximum value for the current threshold value scaled according to the invention. Z. B. the amplitude (scaling 1) is set to 100 A set, or eg 5 times the nominal current. With a nominal current of eg 16 A to eg

5 * 16A * 1.414 (root 2) = 113 A (root 2 => peak value of the instantaneous value of the current) .

In general, the course of the instantaneous current threshold values corresponds to the course of the voltage in the circuit, as shown in FIG. That means, for example, in the case of a triangular voltage curve, a triangular current threshold value curve would be used. The background is that the level of the voltage determines the level of the (short-circuit) current. According to the invention, low threshold values are consequently used at low voltage and high threshold values at high voltage, in order to enable fast, phase-angle-independent, short-circuit detection.

According to FIG. 5, the (periodic) instantaneous current threshold values SWI have a minimum value. I.e. the sine curve is not ideal (only approximately or approximately sinusoidal). The minimum value is greater than zero. The minimum value is in the range 5 to 20% of the maximum value, for example (at) 10% or 15%, i.e. the amplitude of the current threshold curve threshold.

The minimum value takes the place of or in the area of the zero crossing of the (sine) curve for the current threshold values.

In the case of a sinusoidal voltage curve over time in the low-voltage AC circuit, the voltage and current threshold values over time are phase-synchronized in such a way that the point in time of the amplitude (maximum value) of the voltage corresponds to the point in time of the amplitude (maximum value) of the current threshold value, as shown in Figure 5.

The range of the zero crossing of the voltage also corresponds to the range of the minimum value of the current threshold value. The phase angle resolution determines the speed of calculating the threshold values. With a phase angle resolution of 1°, ie there is a threshold value for each full phase angle of the voltage, ie there is an instantaneous threshold value approximately every 55.5 ps. Switching off takes place preferably via an analog comparator, ie continuously, and is therefore significantly faster (eg in the nanosecond range) than the phase angle resolution.

Alternatively, in the case of fully digital processing, the following time profile applies. The phase angle resolution determines the speed of detection. With a phase angle resolution of 1°, i.e. there is a threshold value for each full phase angle of the voltage, i.e. there is an instantaneous threshold value approximately every 55.5 ps, this means that a switch-off can take place after a minimum of approximately 60 ps. With higher phase angle resolutions, shorter switch-off times can be achieved.

In this example, the values are then processed with at least 18 kHz.

The current threshold values can also be stored (scaled) in a table, with the value then being adjusted if necessary.

The current threshold values can, for example, be calculated generally or based on tables as follows:

The level of the voltage is converted into a digital voltage value.

The level of the voltage is converted into a digital voltage value, the digital voltage value is normalized to its amplitude value, then the amount is formed, then the amount is multiplied by a first factor (kl) and then a minimum value (k2) is added, the resulting result results in a scaling factor (FM(t) ) for the at least one current threshold, which multiplies by the at least one current threshold to obtain a (time-varying) adjusted current threshold.

The equation for the scaling factor for this is:

FM(t) - scaling factor u_Grid(t) - instantaneous voltage value

U_amplitude - amplitude of the voltage (or maximum instantaneous value of the voltage)

FM(t) = kl * ( abs (u_Grid ( t ) / U_amplitude) ) + k2

Current threshold (new) FM(t) * current threshold (old)

Alternatively, the absolute value of the voltage value is subtracted from the amplitude of the voltage value, then the result is multiplied by a factor (k3), the resulting result gives a correction value that is subtracted from the at least one current threshold value in order to obtain a (time-varying) adjusted current threshold value receive.

The equation for the correction value FK(t) is:

FK(t) - correction value

FK(t) = k3 * (U_amplitude - abs (u_Grid ( t ) ) )

Although the invention has been illustrated and described in more detail by the exemplary embodiment, the invention is not limited by the disclosed examples and other variations can be derived therefrom by a person skilled in the art without departing from the protective scope of the invention.

Claims

35 patent claims

1 . Protective switching device (SG) for protecting an electrical low-voltage circuit having:

- a housing (GEH), with first (LI, NI) and second (L2, N2) terminals for conductors of the low-voltage circuit,

- A series circuit of a mechanical isolating contact unit (MK) and an electronic interruption unit (EU) electrically connecting the first and second terminals,

- That the mechanical isolating contact unit (MK) can be switched by opening contacts to avoid a current flow or by closing the contacts for a current flow in the low-voltage circuit,

- that the electronic interruption unit (EU) can be switched by semiconductor-based switching elements into a high-impedance state of the switching elements to avoid a current flow or a low-impedance state of the switching elements for current flow in the low-voltage circuit,

- A current sensor unit (S T ) to determine the level of the current of the low-voltage circuit, such that the instantaneous current values are available,

- A voltage sensor unit (SU) to determine the level of the voltage of the low-voltage circuit, such that the current voltage values are present,

- A control unit (SE), which is connected to the current sensor unit (ST), the voltage sensor unit (SU), the mechanical isolating contact unit (MK) and the electronic interrupter unit (EU), where at least one current threshold value is exceeded, avoiding current flow in the low-voltage circuit initiated becomes,

- that the protective switching device is designed in such a way that the at least one current threshold value is adjusted as a function of the magnitude of the voltage in the low-voltage circuit. 36

2 . Protective switching device (SG) according to Patent Claim 1, characterized in that the first connections (LI, NI) are mains-side connections and the second connections (L2, N2) are load-side connections, that the mechanical isolating contact unit (MK) is the load-side connections and the electronic interruption unit ( EU) is assigned to the grid-side connections,

3 . Protective switching device (SG) according to Patent Claim 1 or 2, characterized in that the at least one current threshold value is adjusted as a function of the level of the voltage in such a way that the at least one current threshold value is reduced as the voltage decreases and that the at least one current threshold value is increased as the voltage increases , is increased in particular up to a maximum value of the at least one current threshold value.

4 . Protective switching device (SG) according to claim 1, 2 or 3, characterized in that a continuous adjustment of the at least one current limit value takes place, in particular an adjustment that is carried out faster than 20 ms, more specifically faster than 10 ms or preferably faster than 1 ms.

5. Protective switching device (SG) according to Patent Claim 1, 2, 3 or 4, characterized in that the protective switching device is designed in such a way that the instantaneous current value of the determined magnitude of the current is compared with the at least one current threshold value by means of an analog comparator in such a way that at Exceeding the magnitude of the magnitude of the current above the magnitude of the at least one current threshold value avoiding the flow of current in the low-voltage circuit is initiated.

6. Protective switching device (SG) according to claim 5, characterized in that that the protective switching device is designed such that the at least one current threshold value is calculated digitally, the calculated digital current threshold value is converted into an analog current threshold value using a digital-to-analog converter (DAC), the analog current threshold value is fed to the comparator.

7. Protective switching device (SG) according to one of the preceding claims, characterized in that the protective switching device is designed in such a way that the level of the voltage is converted into a digital voltage value, the digital voltage value is normalized to its amplitude value, the amount is then formed, then the amount is multiplied by a first factor (kl) and then a minimum value (k2) is added, the resulting result gives a scaling factor (FM(t) ) for the at least one current threshold value, which is multiplied by the at least one current threshold value by an adjusted one to obtain the current threshold.

8. Protective switching device (SG) according to one of the preceding claims 1 to 6, characterized in that the protective switching device is designed in such a way that the level of the voltage is converted into a digital voltage value, the amount of the voltage value is subtracted from the amplitude of the voltage value, then the result is multiplied by a factor (k3), the resulting result yields a correction value which is subtracted from the at least one current threshold value in order to obtain an adjusted current threshold value.

9. Protective switching device (SG) according to one of the preceding claims, characterized in that dependent, in particular periodic, time profile of the current voltage values, in particular periodic see, instantaneous current threshold values (SWI) are present, that the instantaneous current values (DI) are compared phase-related with the instantaneous current threshold values (SWI), that when the amount of the instantaneous current threshold value (SWI) is exceeded, an interruption of the low-voltage circuit is initiated.

10 . Protective switching device (SG) according to Patent Claim 9, characterized in that the low-voltage circuit has a voltage curve that is sinusoidal over time, that the instantaneous current threshold values (SWI) have a current threshold value curve that is approximately sinusoidal in terms of time, in particular in terms of amount, with a minimum value that is greater than zero, in particular greater than 5 to 20% of the maximum value is that the time curves of voltage (DU) and current threshold values (SWI) are phase-related synchronized in such a way that the time of the amplitude of the voltage (DU) coincides with the time of the amplitude of the current threshold value (SWI) matches .

11 . Protective switching device (SG) according to Patent Claim 10, characterized in that the range of the zero crossing of the voltage (DU) corresponds to the range of the minimum value of the current threshold value (SWI).

12 . Method for protecting a low-voltage electrical circuit in a protective switching device with a mechanical isolating contact unit (MK) connected in series with an electronic interrupting unit (EU) that the mechanical isolating contact unit (MK) by opening contacts to prevent current flow or closing the contacts can be switched for a current flow in the low-voltage circuit, that the electronic interruption unit (EU) by semiconductor-based switching elements in a high-impedance state 39 of the switching elements can be switched to avoid current flow or a low-impedance state of the switching elements for current flow in the low-voltage circuit, that the level of the voltage of the low-voltage circuit is determined such that instantaneous voltage values are present, that the level of the current of the low-voltage circuit is determined such that the instantaneous Current values are present, that when the amount of the instantaneous current value is exceeded compared with at least one current threshold value, avoidance of the current flow in the low-voltage circuit is initiated, that the at least one current threshold value is adjusted depending on the level of the voltage of the protective switching device.

13 . Method according to Patent Claim 12, characterized in that the at least one current threshold value is adjusted as a function of the level of the voltage in such a way that the at least one current threshold value is reduced as the voltage decreases and that the at least one current threshold value is increased as the voltage increases, in particular up to a Maximum value of at least one current threshold value is increased.

14 . Computer program product comprising instructions which, when the program is executed by a microcontroller, cause this to support, in particular to carry out, the method according to one of claims 12 to 13 with a protective switching device according to one of claims 1 to 11.

15 . Computer-readable storage medium on which the computer program product according to claim 14 is stored.

16 . Data carrier signal carrying the computer program product according to claim 14 .