Protection switching device and method

Abstract

The invention relates to a protective switching device (SG) for protecting a three-phase low-voltage alternating current circuit having a neutral conductor, comprising:-series circuits of mechanical phase contacts (K1, K2, K3) and electronic switches (S1, S2, S3), each of which electrically connects a network-side phase connection (LG1, LG2, LG3) to a load-side phase connection (LL1, LL2, LL3), the network-side neutral conductor connection (NG) is connected to the load-side neutral conductor connection (NL) by means of mechanical neutral conductor contacts (KN), and the mechanical contacts (K1, K2, K3, KN) can be switched to open together to avoid a current flow or to close together for a current flow, the electronic switches (S1, S2, S3) can be switched by means of the semiconductor-based switching element into a high-resistance state of the switching element in order to avoid a current flow or into a low-resistance state of the switching element in order to avoid a current flow, the electronic switches can be switched independently of one another into the high-resistance state or into the low-resistance state, in order to avoid or enable current flow depending on the phase conductor.

Description

Technical Field

[0001] The present invention relates to the technical field of protective switching devices for low-voltage circuits having an electronic switch and a method for a protective switching device for a low-voltage circuit having an electronic switch. Background Art

[0002] Low voltage refers to an alternating voltage up to 1000 volts or a direct voltage up to 1500 volts. Low voltage especially refers to a voltage greater than a small voltage, the value of the small voltage being 50 volts alternating voltage or 120 volts direct voltage.

[0003] A low-voltage circuit or a low-voltage power grid or a low-voltage system refers to a circuit with a rated current or a nominal current up to 125 amperes, more particularly up to 63 amperes. A low-voltage circuit especially refers to a circuit with a rated current or a nominal current up to 50 amperes, 40 amperes, 32 amperes, 25 amperes, 16 amperes or 10 amperes. The mentioned current values especially refer to the rated current, the nominal current or / and the breaking current, i.e., the maximum current that is conducted through the circuit under normal circumstances, or the current at which the circuit is usually interrupted, for example, interrupted by a protection device such as a protective switching device or a line protection switch or a circuit breaker. The rated current can be further classified, from 0.5 A through 1 A, 2 A, 3 A, 4 A, 5 A, 6 A, 7 A, 8 A, 9 A, 10 A, etc. up to 16 A.

[0004] A line protection switch is an overcurrent protection device that has been known for a long time and is used in low-voltage circuits in electrical installation technology. The line protection switch protects the line from damage caused by overheating due to excessive current and / or short circuit. The line protection switch can automatically turn off the circuit in case of overload and / or short circuit. The line protection switch is a non-automatic reset fuse element.

[0005] Different from the line protection switch, the current of a circuit breaker is set to be greater than 125 amperes and, in some cases, also starts from 63 amperes. Therefore, the structure of the line protection switch is simpler and more delicate. The line protection switch usually has a fixing possibility for fixing on a so-called top-hat rail (support rail, DIN rail, TH35).

[0006] The line protection switch adopts an electromechanical structure. In the housing, they have mechanical switch contacts or working current triggers for interrupting (triggering) the current. Usually, a bimetallic protection element or a bimetallic element is used to trigger (interrupt) in case of long-term overcurrent (overcurrent protection) or thermal overload (overload protection). An electromagnetic trigger with a coil is used to trigger briefly in case of exceeding the overcurrent limit value or in case of a short circuit (short-circuit protection). One or more arc extinguishing chambers or devices for extinguishing arcs are provided. In addition, connection elements for the conductors of the circuit to be protected are provided.

[0007] Protective switching devices with an electronic interrupt unit or an electronic switch are a relatively recent development. The protective switching device has a semiconductor-based electronic interrupt unit / electronic switch. That is, the current in the low-voltage circuit is conducted through a semiconductor device or a semiconductor switch, which can interrupt the current or switch to a conductive state. The protective switching device with an electronic interrupt unit / electronic switch also typically has a mechanical separating contact system, which has separating characteristics, in particular according to the relevant standards of the low-voltage circuit, where the contacts of the mechanical separating contact system are connected in series to the electronic interrupt unit / electronic switch, i.e., the current in the low-voltage circuit to be protected is conducted both through the mechanical separating contact unit and through the electronic interrupt unit.

[0008] The present invention particularly relates to a low-voltage alternating current circuit, which has an alternating voltage, which typically has a time-dependent sinusoidal alternating voltage with a frequency f. The time dependence of the instantaneous voltage value u(t) of the alternating voltage is described by the following equation:

[0009] u(t) = U * sin(2π * f * t)

[0010] where:

[0011] u(t) = the instantaneous voltage value at time t

[0012] U = the amplitude of the voltage

[0013] The harmonic alternating voltage can be represented by the rotation of a pointer, the length of which corresponds to the amplitude (U) of the voltage. Here, the instantaneous deflection is the projection of the pointer on the coordinate system. The oscillation period corresponds to a full rotation of the pointer, and its full angle is 2π (2Pi) or 360°. The angular frequency is the rate of change of the phase angle of this rotating pointer. The angular frequency of a harmonic oscillation is always 2π times its frequency, i.e.:

[0014] ω = 2π * f = 2π / T = the angular frequency of the alternating voltage (T = the period duration of the oscillation)

[0015] The description of the angular frequency (ω) is usually preferred over the frequency (f) because many vibration theory formulas can be represented more compactly with the help of the angular frequency due to the appearance of trigonometric functions, which, by definition, have a period of 2π:

[0016] u(t) = U * sin(ωt)

[0017] In the case of an angular frequency that is not constant in time, the term instantaneous angular frequency is also used.

[0018] In the case of a sinusoidal, especially time-constant alternating voltage, the time-dependent value according to the angular velocity ω and the time t corresponds to the time-dependent angle This angle is also called the phase angle

[0019] That is, the phase angle periodically passes through the range of 0...2π or 0°...360°. That is, the phase angle periodically assumes values between 0 and 2π or 0° and 360° ( or due to periodicity; abbreviated as: or ).

[0020] Therefore, the instantaneous voltage value u(t) refers to the instantaneous value of the voltage at the time point t, that is, in the case of a sinusoidal (periodic) alternating voltage, it refers to the voltage value with respect to the phase angle ( or for the corresponding period). The same applies to the instantaneous current value i(t), etc. SUMMARY OF THE INVENTION

[0021] The technical problem to be solved by the present invention is to improve the protection switch device of the type mentioned above, in particular to present a new concept for a multi-phase protection switch device and to enable greater flexibility of the multi-phase protection switch device.

[0022] The above technical problem is solved by a protection switch device having the features of claim 1 and by a method according to claim 17.

[0023] According to the present invention, there is provided a protection switch device for protecting a multi-phase low-voltage alternating current circuit having a neutral conductor, in particular a three-phase low-voltage alternating current circuit having a neutral conductor, having:

[0024] - a housing having first, second, and third grid-side phase connectors and first, second, and third load-side phase connectors for the first, second, and third phase conductors of the three-phase low-voltage alternating current circuit,

[0025] a grid-side neutral conductor connector and a load-side neutral conductor connector for the neutral conductor of the low-voltage alternating current circuit,

[0026] - a first series circuit of a first mechanical phase contact and a first electronic switch, a second series circuit of a second mechanical phase contact and a second electronic switch, and a third series circuit of a third mechanical phase contact and a third electronic switch, wherein the first series circuit electrically connects the first grid-side phase connector to the first load-side phase connector, the second series circuit electrically connects the second grid-side phase connector to the second load-side phase connector, and the third series circuit electrically connects the third grid-side phase connector to the third load-side phase connector,

[0027] - the grid-side neutral conductor connector is connected to the load-side neutral conductor connector through a mechanical neutral conductor contact,

[0028] - The mechanical phase contact and the mechanical neutral conductor contact can be switched to open together to avoid current flow or switched to closed together for current flow.

[0029] - The electronic switch can be switched by means of a semiconductor-based switching element into a high-resistance state of the switching element to avoid current flow, or into a low-resistance state of the switching element for current flow.

[0030] - The protective switching device is designed such that the first, second, and third electronic switches can be switched into the high-resistance state or the low-resistance state independently of one another.

[0031] This has the advantage that the phase conductors can be switched into the high-resistance state or the low-resistance state independently of one another. Previous protective switching devices, especially the widely used classical electromechanical protective switching devices (line protective switches, circuit breakers, residual current protective switches), do not have this possibility because there the mechanical separating contact units open or close all contacts simultaneously (multipole devices).

[0032] This gives the protective switching device greater flexibility and more flexible switching characteristics.

[0033] Further advantageous embodiments of the invention are given in the dependent claims and the embodiments.

[0034] In an advantageous embodiment of the invention, a current sensor unit is provided for each series circuit respectively, for correspondingly determining the magnitude of the current in the corresponding phase conductor. In particular, an instantaneous current value exists (and is determined). This means that first, second, and third current sensor units are provided. The first current sensor unit is arranged in the first series circuit, the second current sensor unit is arranged in the second series circuit, and the third current sensor unit is arranged in the third series circuit, respectively for determining the magnitude of the current in the first, second, and third phase conductors, in particular such that an instantaneous current value exists.

[0035] In an advantageous expansion thereof, a control unit is provided, which is connected to the current sensor unit, the mechanical contacts, and the electronic switches. The protective switching device is designed such that when at least one first current threshold in the phase conductor is exceeded, the avoidance of the current flow in the involved phase conductor is initiated by the involved electronic switch, in particular for a first time period.

[0036] This has the particular advantage that when a specified current threshold or current-time threshold is exceeded (i.e., when the current threshold is exceeded within a defined time period), only the involved conductor (or the involved conductors) is selectively interrupted. In addition, current flow can still be achieved in the other conductors (uninvolved conductors) in a polyphase low-voltage AC circuit.

[0037] By avoiding the duration of the first time period and advantageously reconnecting or becoming low-resistance again after the first time period, the power supply safety can be further ensured or it can be further checked whether the current threshold is exceeded. Advantageously, this can be performed, in particular, by evaluating the instantaneous value of the current magnitude.

[0038] In an advantageous design of the present invention, the first time period is less than 20 ms, in particular less than 10 ms.

[0039] This has the particular advantage that for a half-wave or full-wave of the voltage or current in an AC circuit, in this example (20 ms, 10 ms) with respect to the 50 Hz mains frequency, an interruption is made, so that the power supply safety is provided again using the next full-wave or half-wave. In particular, it can become low-resistance in the region of the next zero-crossing (in the zero-crossing or in the region 1 ms before or after it) after the interruption.

[0040] In an advantageous design of the present invention, the protective switching device is designed such that when at least one second current threshold, in particular the effective value, in at least one phase conductor (or two phase conductors, in particular three phase conductors) is exceeded for at least one first time period, the avoidance of current flow is initiated by opening the contact. The second current threshold can advantageously be numerically higher than the first current threshold.

[0041] The first time period can be less than 100 ms, 20 ms, in particular less than 10 ms.

[0042] This has the particular advantage that if one or more electronic switches remain in a faulty low-resistance state and thus exceed the second current threshold, the avoidance of current flow in the low-voltage AC circuit is initiated, and thus the safety of the circuit is improved.

[0043] In an advantageous design of the present invention, the mechanical neutral conductor contact can be opened or closed together with the phase contact. In particular, the neutral conductor contact is closed before the phase contact is closed or ( / and) the neutral conductor contact is opened after the phase contact is opened.

[0044] This has the particular advantage that the neutral conductor contact is always opened and closed without current. This reduces the contact wear and extends the service life. In addition, this can avoid the occurrence of an arc when the neutral conductor contact is opened.

[0045] In an advantageous design of the present invention, the mechanical phase contact is part of a mechanical separating contact unit that opens or closes the contacts together. In particular, the mechanical separating contact unit has a handle that is accessible on the protective switching device for manually (user-operably) opening or closing the phase contact (of the mechanical separating contact unit).

[0046] This has the particular advantage that, contrary to the high-impedance state of avoiding current flow associated with the AND phase of the electronic switch, complete current isolation of all phase conductors is achieved simultaneously. Compatibility characteristics according to classical electromechanical protection switchgear can be achieved via the handle.

[0047] In an advantageous embodiment of the invention, the protection switchgear is designed such that the mechanical disconnecting contact unit can be opened by the control unit, but cannot be closed. In particular, the mechanical disconnecting contact unit can be closed via the handle only after being released by the control unit.

[0048] This has the particular advantage that the safety of the protection switchgear is increased because the control unit does not accidentally (erroneously) close the contacts.

[0049] In an advantageous embodiment of the invention, the electronic switch is part of an electronic interruption unit, where the electronic switches can be switched independently of one another.

[0050] This has the particular advantage that a compact electronic interruption unit is provided which combines the electronic switches, enabling a space-saving design and utilization of the synergistic effects of the components.

[0051] In an advantageous embodiment of the invention, the electronic interruption unit / electronic switch has a bidirectional voltage withstand strength. In particular, overvoltage protection is provided for semiconductor-based switching elements.

[0052] This has the particular advantage that overvoltage robustness is provided and inductive line loops can be switched off.

[0053] In an advantageous embodiment of the invention, the mechanical phase contacts are associated with the load-side phase connections, and the electronic switches are associated with the grid-side phase connections.

[0054] This has the particular advantage that a favorable design is provided which supports phase-related switching of the electronic switches and enables self-testing (in particular, self-testing of the electronic switches and the electronic interruption unit) even when the contacts are open. In addition, the energy supply of the protection switchgear is ensured even when the contacts are open.

[0055] In an advantageous embodiment of the invention, voltage sensor units are respectively arranged between each phase conductor and the neutral conductor for determining the voltage magnitude between the corresponding phase conductor and the neutral conductor, in particular the instantaneous voltage value. The voltage sensor units are connected to the control unit.

[0056] In an advantageous expansion of this design, the protective switching device is designed such that, when it is activated by the control unit to become low-resistance (especially in the absence of an overcurrent event, that is, if the first or second current threshold is not exceeded; for example, when it is activated by the user side to become low-resistance), (all) the electronic switches become low-resistance in sequence at the corresponding zero-crossing of the voltage (or when the voltage is less than 50V, 25V, especially less than 10V).

[0057] This has the particular advantage that the turn-off load in the electronic switches (and thus the wear) is reduced. In addition, this reduces the grid feedback effect.

[0058] In an advantageous design of the present invention, the protective switching device is designed such that, when it is activated by the control unit to become high-resistance (especially in the absence of an overcurrent event, that is, if the first or second current threshold is not exceeded; for example, when it is activated by the user side to become high-resistance), (all) the electronic switches become high-resistance in sequence at the corresponding zero-crossing of the voltage (or when the voltage is less than 50V, 25V, especially less than 10V).

[0059] This has the particular advantage that the grid feedback effect is reduced and the turn-off load in the switches is reduced.

[0060] In an advantageous design of the present invention, one or the control unit is provided, which is connected to a current sensor unit, a voltage sensor unit, a mechanical phase contact, and an electronic switch. The protective switching device is designed such that, when the (at least) first current threshold in the conductor is exceeded, the flow of current in the involved conductor is avoided by activating the involved electronic switch. When the voltage crosses zero for the next time or the next-next time, the electronic switch becomes low-resistance again to enable the flow of current.

[0061] This has the particular advantage that enhanced robustness against false triggering is achieved, and thus enhanced power supply security is achieved.

[0062] In an advantageous design of the present invention for a three-phase low-voltage AC circuit, a solution for a classical three-phase grid is advantageously provided, and the protective switching device has at least the following switching states:

[0063] - All mechanical phase contacts are open, and all electronic switches are high-resistance.

[0064] - All mechanical phase contacts are closed, and all electronic switches are low-resistance.

[0065] - All mechanical phase contacts are closed, and all electronic switches are high-resistance.

[0066] - All mechanical phase contacts are closed, the first electronic switch is low-resistance, and the second and third electronic switches are high-resistance.

[0067] - All mechanical phase contacts are closed, the second electronic switch is of low resistance, and the first and third electronic switches are of high resistance.

[0068] - All mechanical phase contacts are closed, the third electronic switch is of low resistance, and the first and second electronic switches are of high resistance.

[0069] In another advantageous design of the present invention for a three-phase low-voltage AC circuit, the protective switching device has at least the following switching states:

[0070] - All mechanical phase contacts are open, and all electronic switches are of high resistance.

[0071] - All mechanical phase contacts are closed, and all electronic switches are of low resistance.

[0072] - All mechanical phase contacts are closed, and all electronic switches are of high resistance.

[0073] - All mechanical phase contacts are closed, the first and second electronic switches are of low resistance, and the third electronic switch is of high resistance.

[0074] - All mechanical phase contacts are closed, the first and third electronic switches are of low resistance, and the second electronic switch is of high resistance.

[0075] - All mechanical phase contacts are closed, the second and third electronic switches are of low resistance, and the first electronic switch is of high resistance.

[0076] These two advantageous designs or a combination of both have the particular advantage that new switching states of the protective switching device are provided in order to respond individually and more flexibly to overcurrent conditions (short-circuit current conditions). Thus, it does not respond to the interruption of all phases, but can act phase-related, thereby enabling a higher power supply security in the low-voltage circuit.

[0077] In another advantageous design of the present invention, the protective switching device has at least the following switching states:

[0078] - All mechanical phase contacts are open, a part of the electronic switches is of low resistance, and another part of the electronic switches is of high resistance.

[0079] In particular, one electronic switch is of low resistance while the other electronic switches are of high resistance.

[0080] Alternatively or additionally, in particular, two electronic switches are of low resistance while the other electronic switches are of high resistance.

[0081] Alternatively or additionally, the protective switching device may have the following switching states:

[0082] - All mechanical phase contacts are open, and all electronic switches are of low resistance.

[0083] In particular, these switching states are provided when measuring resistors are respectively arranged between the phase conductors and the neutral conductor. For this purpose, in one design, a first measuring resistor is arranged between the first phase conductor L1 and the neutral conductor N, a second measuring resistor is arranged between the second phase conductor L2 and the neutral conductor N, and a third measuring resistor is arranged between the third phase conductor L3 and the neutral conductor N.

[0084] These switching states are advantageously intended to check whether the electronic switch can be turned on or off. This means that when the mechanical phase contact is open, the electronic switch is briefly turned on in order to check the functionality (with respect to the turn-on ability or ( / and) turn-off ability). Here, the measuring current flows through the corresponding measuring resistor.

[0085] According to the invention, a corresponding method (method claim) for a protective switching device for a low-voltage circuit with an electronic (semiconductor-based) switch / switching element is claimed, which has the same and other advantages.

[0086] The method for a protective switching device (SG) for protecting a three-phase low-voltage AC circuit with a neutral conductor has:

[0087] - A series circuit of a mechanical phase contact and an electronic switch,

[0088] wherein each series circuit respectively electrically connects the grid-side phase connection to the load-side phase connection,

[0089] - The grid-side neutral conductor connection is electrically connected to the load-side neutral conductor connection through a mechanical neutral conductor contact,

[0090] - The mechanical contacts can be switched to open together to avoid current flow or switched to close together for current flow,

[0091] - The electronic switch can be switched into the high-resistance state of the switching element by means of a semiconductor-based switching element to avoid current flow, or switched into the low-resistance state of the switching element for current flow,

[0092] The electronic switches can be switched into the high-resistance state or the low-resistance state independently of each other in order to (advantageously) avoid or enable current flow depending on the phase conductors.

[0093] Advantageously, the magnitude of the current in the corresponding series circuit is determined, and when at least one first current threshold in the series circuit is exceeded, the avoidance of the current flow in the involved series circuit is initiated by the involved electronic switch, in particular for a first time period.

[0094] All design solutions, not only in the form of dependent claims referring to claim 1 or 17, but also referring to individual features or combinations of features of the claims alone, especially the reference of the device claims to be processed to the independent method claims, have achieved improvements in protecting switchgear, especially improving the safety of the circuit, and have provided a new solution for protecting switchgear. Description of the Drawings

[0095] The characteristics, features and advantages of the present invention described and the implementation manner thereof will become clearer and easier to understand in conjunction with the following description of the embodiments. The embodiments are described in detail with reference to the drawings.

[0096] Here, in the drawings:

[0097] Figure 1 A first illustration of a protective switchgear is shown.

[0098] Figure 2 A second illustration of a protective switchgear is shown.

[0099] Figure 3 A third illustration of a protective switchgear is shown. Detailed Description of the Embodiments

[0100] Figure 1 An exemplary illustration of a protective switchgear SG for protecting a three-phase low-voltage AC circuit with a neutral conductor is shown. The protective switchgear SG is 4-pole in the example, i.e., for example, for three-phase conductors and a neutral conductor, and includes:

[0101] - A housing GEH having first, second and third grid-side phase connectors LG1, LG2, LG3 and first, second and third load-side phase connectors LL1, LL2, LL3 for the first, second and third phase conductors L1, L2, L3 of the low-voltage AC circuit.

[0102] A grid-side neutral conductor connector NG and a load-side neutral conductor connector NL for the neutral conductor N of the low-voltage AC circuit.

[0103] An energy source is usually connected on the grid side Grid.

[0104] An electrical appliance is usually connected on the load side Load.

[0105] In the housing GEH:

[0106] - A first series circuit SS1 of a first mechanical phase contact K1 and a first electronic switch S1.

[0107] A second series circuit SS2 of a second mechanical phase contact K2 and a second electronic switch S2.

[0108] The third series circuit SS3 of the third mechanical phase contact K3 and the third electronic switch S3,

[0109] wherein (in the housing):

[0110] The first series circuit SS1 electrically connects the first grid-side phase connection LG1 to the first load-side phase connection LL1,

[0111] The second series circuit SS2 electrically connects the second grid-side phase connection LG2 to the second load-side phase connection LL2, and

[0112] The third series circuit SS3 electrically connects the third grid-side phase connection LG3 to the third load-side phase connection LL3,

[0113] - The grid-side neutral conductor connection (NG) is connected to the load-side neutral conductor connection (NL) through the mechanical neutral conductor contact (KN),

[0114] - The mechanical phase contacts K1, K2, K3 and the mechanical neutral conductor contact KN can be switched together, i.e., they are opened together to avoid current flow or closed together for current flow, i.e., the mechanical contacts are connected to each other through mechanical coupling (such as a switch shaft).

[0115] - The electronic switches S1, S2, S3 can be switched to the high-resistance state of the switching element to avoid current flow or to the low-resistance state of the switching element for current flow by means of semiconductor-based switching elements.

[0116] According to the present invention, the protective switching device is designed such that the first, second and third electronic switches can be switched to the high-resistance state or the low-resistance state independently of each other. This means that the first, second and third electronic switches are switched to the high-resistance state or the low-resistance state independently of each other. In particular, the current flow depending on the phase conductors is avoided or can be achieved.

[0117] According to Figure 1 , the first, second and third current sensor units SI1, SI2, SI3 are provided. The first current sensor unit SI1 is arranged or disposed in the first series circuit SS1, the second current sensor unit SI2 is arranged or disposed in the second series circuit SS2, and the third current sensor unit SI3 is arranged or disposed in the third series circuit SS3 for respectively determining the magnitudes of the currents in the first, second and third phase conductors L1, L2, L3, especially the instantaneous current values.

[0118] According to Figure 1, the first mechanical phase contact K1, the second mechanical phase contact K2, the third mechanical phase contact K3, and the mechanical neutral contact KN are part of a mechanical disconnect contact unit MK, which disconnects or closes the phase contacts K1, K2, K3 and the neutral contact KN together. The mechanical disconnect contact unit MK can have a handle HH accessible on the protective switchgear for manually (operated by a person) disconnecting or closing the contacts. The mechanical disconnect contact unit MK corresponds to a classical unit known, for example, from electromechanical protective switchgear (line protection switch, circuit breaker), (however, according to the present invention, there are no elements for overcurrent or short-circuit recognition, such as a bimetallic release, etc.).

[0119] The protective switchgear is designed in particular such that the mechanical disconnect contact unit MK can be disconnected by the control unit SE but not closed. In particular, the mechanical disconnect contact unit MK can only be closed by the handle HH after being released by the control unit SE. For this purpose, a release unit LC can be provided. This means that the handle HH can only close the contacts when a release signal (from the control unit) is present or released. In the absence of a release or release signal, the handle HH can be operated, but the contacts cannot be closed ("Dauerrutscher, continuous slip").

[0120] The release unit LC can also be designed such that the contacts K1, K2, K3, KN of the mechanical disconnect contact unit MK can be disconnected by a control signal from the control unit SE, as Figure 1 shown by the arrow from the control unit SE to the release unit LC in

[0121] According to Figure 1 , the mechanical contacts K1, K2, K3, KN are associated with the load-side phase connection / load-side Load, and the electronic switches S1, S2, S3 are associated with the grid-side phase connection / grid-side Grid.

[0122] The grid-side neutral conductor connection NG is connected to the load-side neutral conductor connection NL via the neutral conductor contact KN. In this example, no electronic interruption unit is provided in the neutral conductor path in the housing of the protective switchgear. This means that there is no electronic switch in the neutral conductor connection between the grid-side neutral conductor connection NG and the load-side neutral conductor connection NL (no electronic switch).

[0123] In particular, the mechanical disconnect contact unit MK can be designed such that the neutral conductor contact KN closes before the phase contacts K1, K2, K3 close. Similarly, the neutral conductor contact KN can be disconnected after the phase contacts K1, K2, K3 are disconnected.

[0124] The first electronic switch S1, the second electronic switch S2, and the third electronic switch S3 can be part of an electronic interruption unit EU, where the electronic switches S1, S2, and S3 can be switched independently of each other.

[0125] The electronic interruption unit / electronic switch can have a bidirectional breakdown voltage strength. In particular, overvoltage protection is provided for semiconductor-based switching elements in order to limit the voltage and thus provide protection for semiconductor-based switching elements.

[0126] A control unit SE (as already partially mentioned) is provided, which is connected to current sensor units SI1, SI2, SI3, mechanical contacts K1, K2, K3, KN, or a mechanical disconnect contact unit MK (as Figure 1 shown) and the electronic switches S1, S2, and S3.

[0127] The current sensor units SI1, SI2, and SI3 respectively determine the magnitude of the current in their respective conductors, such that in particular the instantaneous value of the current exists.

[0128] When at least one first current threshold in the conductor, in particular the instantaneous value of the current, is exceeded, the avoidance of current flow in the involved conductor is initiated by making the electronic switch highly resistive.

[0129] The high resistance can in particular persist for a first time period. After the first time period, the involved electronic switch can become low resistive again.

[0130] The first time period can in particular be less than 20 ms, in particular less than 10 ms (especially with reference to a 50 Hz low-voltage AC circuit).

[0131] The change to low resistance can alternatively or additionally take place in particular at the next zero crossing of the voltage or before or after the zero crossing. (All 3 options: at the zero crossing, before the zero crossing, or after the zero crossing (e.g., within one millisecond / 1 ms) are possible, or when numerically below a voltage threshold, in particular 50 V, 25 V, or 10 V.

[0132] The protective switching device can be designed such that when a second current threshold (which can in particular be the effective value) in at least one phase conductor (or two phase conductors, especially in three phase conductors) is exceeded for at least a first time period, the avoidance of current flow is initiated by opening the contacts. The first time period is less than 100 ms, 10 ms, or in particular less than 1 ms.

[0133] Advantageously, the second current threshold can be numerically greater than or less than the first current threshold.

[0134] As Figure 1As shown, a differential current sensor unit ZCT can be provided for collecting the differential current of a low-voltage AC circuit, such as those known from fault current protection switches. The differential current sensor unit ZCT is connected to a control unit SE.

[0135] In the example according to Figure 1 , the current sensor units SI1, SI2, SI3 are arranged between the grid-side connectors LG1, LG2, LG3 of the series circuit of the electronic switches S1, S2, S3 and the mechanical phase contacts K1, K2, K3. Specifically, they are arranged between the grid-side connectors LG1, LG2, LG3 and the electronic switches S1, S2, S3. The current sensor units SI1, SI2, SI3 can also be arranged in other ways. For example, they can be arranged between the electronic switches S1, S2, S3 and the mechanical phase contacts K1, K2, K3.

[0136] Figure 2 The illustration according to Figure 1 is shown, with the following differences.

[0137] On the one hand, an energy supply device NT, such as a power supply, is provided for supplying energy to the protection switch device SG, especially to the control unit SE. In this example, the energy supply device NT is connected to the phase conductors L1, L2, L3 and the neutral conductor N on the one hand. It can also be connected to only a part of the conductors (at least two) to supply energy. In this example, the energy supply device NT is connected to the control unit SE on the other hand to supply energy to it.

[0138] On the other hand, the control unit SE is combined with the electronic switches S1, S2, S3 and the current sensor units SI1, SI2, SI3, as Figure 2 shown.

[0139] In addition, voltage sensor units are respectively provided between each phase conductor and the neutral conductor. The first voltage sensor unit SU1 is provided between the first phase conductor L1 and the neutral conductor N, the second voltage sensor unit SU2 is provided between the second phase conductor L2 and the neutral conductor N, and the third voltage sensor unit SU3 is provided between the third phase conductor L3 and the neutral conductor N for determining the voltage magnitude between the corresponding phase conductor and the neutral conductor, especially the instantaneous voltage value present. The voltage sensor units SU1, SU2, SU3 are connected to the control unit SE.

[0140] In the case of starting to become low-resistance by the control unit SE, the electronic switches S1, S2, S3, for example:

[0141] - when starting to become low-resistance on the user side, or

[0142] - In the case of activation to low resistance via the protection switchgear, especially in the absence of an overcurrent event (i.e., if neither the first nor the second current threshold is exceeded), for example if the internal inspection function (for internal inspection) of the protection switchgear activates to low resistance,

[0143] => The electronic switches can advantageously become low resistance in sequence at the corresponding zero crossings of the voltage (e.g., near the voltage zero crossing, defined by a voltage numerically lower than, for example, 50 V, 25 V, or 10 V).

[0144] In the case of activation to high resistance via the control unit SE, the electronic switches S1, S2, S3, for example:

[0145] - When activated to high resistance on the user side, or

[0146] - In the case of activation to high resistance via the protection switchgear, especially in the absence of an overcurrent event (i.e., if neither the first nor the second current threshold is exceeded), for example if the internal inspection function (for internal inspection) of the protection switchgear activates to high resistance,

[0147] => The electronic switches can advantageously become high resistance in sequence at the corresponding zero crossings of the voltage (e.g., near the voltage zero crossing, defined by a voltage numerically lower than, for example, 50 V, 25 V, or 10 V).

[0148] For this purpose, as already mentioned, the voltage sensor units SU1, SU2, SU3 are connected to the control unit SE, which is also connected to the current sensor units SI1, SI2, SI3, the mechanical phase contacts K1, K2, K3 (or the mechanical disconnect contact unit MK) and the electronic switches (S1, S2, S3). The protection switchgear can also advantageously be designed such that when at least the first current threshold in the conductor (especially the instantaneous value of the current) is exceeded, the flow of current in the involved conductor is avoided by activating the involved electronic switches. When the voltage next or once again crosses zero, the electronic switches become low resistance again so that current flow can be achieved.

[0149] This can be done multiple times until the first repetition count is exceeded. Then it is possible to:

[0150] a) All electronic switches become high resistance, or ( / and)

[0151] b) The contacts are opened (current isolation).

[0152] Figure 3 It shows according to Figure 2In the illustration, the difference is that measuring resistors are respectively arranged between the phase conductors and the neutral conductor. For this purpose, a first measuring resistor R1 (or measuring impedance) is arranged between the first phase conductor L1 and the neutral conductor N, a second measuring resistor R2 (or measuring impedance) is arranged between the second phase conductor L2 and the neutral conductor N, and a third measuring resistor R3 (or measuring impedance) is arranged between the third phase conductor L3 and the neutral conductor N.

[0153] Therefore, the switching characteristics of the electronic switches S1, S2, S3 can be checked by means of the measuring resistors R1, R2, R3 (which can also be designed as measuring impedances, i.e., can be implemented as a combination of resistors / capacitors and / or inductors, for example). For example, by briefly closing (in the μs, ms or smaller second range) the electronic switches when the contacts are open, and a measuring current corresponding to the measuring resistor (measuring impedance) is provided and can be checked (at the corresponding instantaneous value of the voltage). This can be done by briefly closing the electronic switches so as to generate a measuring current through the corresponding measuring resistors between the phase conductors and the neutral conductor. Alternatively or additionally, this can also be done by briefly closing two electronic switches so as to generate a measuring current through two phase conductors (two measuring resistors).

[0154] In this example, no (optional) differential current sensor unit ZCT is provided (but it can also be provided).

[0155] High impedance refers to a state in which only a negligibly small current flows. High impedance especially refers to a resistance value greater than 1 kΩ, preferably greater than 10 kΩ, 100 kΩ, 1 MΩ, 10 MΩ, 100 MΩ, 1 kΩ or greater.

[0156] Low impedance refers to a state in which the current value given on the protective switching device can flow. Low impedance especially refers to a resistance value less than 10 Ω, preferably less than 1 Ω, 100 mΩ, 10 mΩ, 1 mΩ or smaller.

[0157] The electronic switches S1, S2, S3 or the electronic interruption unit EU can have 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-commutating) power semiconductors. In particular, IGBTs and MOSFETs are particularly well-suited for electronic switches (as semiconductor-based switching elements) due to their low on-resistance, high breakdown resistance and good switching characteristics.

[0158] Thus, the protective switching device according to the invention comprises electronic and mechanical components. A reasonable arrangement of all components required for safe operation is a key point. In addition, various switching combinations can be achieved through the combination of an electronic switch and a mechanical contact.

[0159] In this example, the protective switching device has four grid-side connectors and four load-side connectors respectively. In this example, a 4-pole mechanical disconnect contact system is included in the device. The contacts are mechanically coupled to each other and can only be disconnected or closed together.

[0160] In the phase conductors, there are electronic switches connected in series with the mechanical contacts. Different from the mechanical contacts, these electronic switches are turned on or off independently of each other. In addition, a current sensor unit is arranged in the phase conductors (not in the neutral conductor N).

[0161] Traditional protective devices, such as three-pole or four-pole ones, basically only have two switching states nowadays: on or off.

[0162] According to the invention, additional switching states are proposed in the example of a four-pole (for example, for three-phase conductors and one neutral conductor) protective switching device, as shown in the following table.

[0163]

[0164] In addition to the now-known switching states off (OFF) and on (ON), there are other states, such as standby, hybrid 1, 2, 3, hybrid 12, 13, 23. In addition, there are test states (test 1, test 2, test 3, optional test 4) for the electronic switches.

[0165] With the new hybrid switching states, the protective switching device can respond to special load conditions or fault conditions in a different way from before. Therefore, the advantage is that in specific fault conditions, only one or two of the included electronic switches are put into a high-impedance (off) state. Even when turning on and off the load, it is also beneficial to execute the following switching sequence, in which only one or two of the included electronic switches are turned on twice.

[0166] Turning on can be carried out, for example, by turning on the electronic switches in sequence when the voltage passes through zero (i.e., not at the same time point, but at time-staggered time points, such as at the corresponding zero crossings of the voltage of the corresponding phase / corresponding phase conductor (which are, for example, phase-shifted by 120°)).

[0167] The turning-off process can be carried out similarly.

[0168] This makes it possible to reduce the grid feedback effect and reduce the turn-off load in the switching device (especially the electronic switch).

[0169] Overcurrent events (exceeding the current threshold) can be processed per phase / phase conductor. This can also protect the electronic switch against overload.

[0170] A phase can also be briefly turned off (become high impedance), for example for testing purposes.

[0171] The number of hybrid states or the number of hybrid states occurring per unit time can be counted, and if the limit number is exceeded, all electronic switches can become high impedance (or ( / and) the mechanical contacts can be opened).

[0172] For single-phase consumers, higher availability can be provided (only a fault on one phase, only that phase is turned off, and the other phases continue to operate).

[0173] Therefore, in one variant, the protective switching device has at least the following switching states:

[0174] -(1) All mechanical contacts are open, and all electronic switches are high impedance,

[0175] -(2) All mechanical contacts are closed, and all electronic switches are low impedance,

[0176] -(3) All mechanical contacts are closed, and all electronic switches are high impedance,

[0177] -(4) All mechanical contacts are closed, the first electronic switch is low impedance, and the second and third electronic switches are high impedance,

[0178] -(5) All mechanical contacts are closed, the second electronic switch is low impedance, and the first and third electronic switches are high impedance,

[0179] -(6) All mechanical contacts are closed, the third electronic switch is low impedance, and the first and second electronic switches are high impedance.

[0180] Therefore, in another variant, the protective switching device has at least the following switching states:

[0181] -(1) All mechanical contacts are open, and all electronic switches are high impedance,

[0182] -(2) All mechanical contacts are closed, and all electronic switches are low impedance,

[0183] -(3) All mechanical contacts are closed, and all electronic switches are high impedance,

[0184] -(7) All mechanical contacts are closed, the first and second electronic switches are low impedance, and the third electronic switch is high impedance,

[0185] -(8) All mechanical contacts are closed, the first and third electronic switches are low impedance, and the second electronic switch is high impedance,

[0186] -(9) All mechanical contacts are closed, the second and third electronic switches are of low resistance, and the first electronic switch is of high resistance.

[0187] Thus, in another variant, the protective switching device has the following switching states:

[0188] -(1) All mechanical contacts are open, and all electronic switches are of high resistance,

[0189] -(2) All mechanical contacts are closed, and all electronic switches are of low resistance,

[0190] -(3) All mechanical contacts are closed, and all electronic switches are of high resistance,

[0191] -(4) All mechanical contacts are closed, the first electronic switch is of low resistance, and the second and third electronic switches are of high resistance,

[0192] -(5) All mechanical contacts are closed, the second electronic switch is of low resistance, and the first and third electronic switches are of high resistance,

[0193] -(6) All mechanical contacts are closed, the third electronic switch is of low resistance, and the first and second electronic switches are of high resistance,

[0194] -(7) All mechanical contacts are closed, the first and second electronic switches are of low resistance, and the third electronic switch is of high resistance,

[0195] -(8) All mechanical contacts are closed, the first and third electronic switches are of low resistance, and the second electronic switch is of high resistance,

[0196] -(9) All mechanical contacts are closed, the second and third electronic switches are of low resistance, and the first electronic switch is of high resistance.

[0197] Thus, in one variant, the protective switching device also has at least some (or all) of the following switching states:

[0198] -(10) All mechanical contacts are open, the first electronic switch is of low resistance, and the second and third electronic switches are of high resistance,

[0199] -(11) All mechanical contacts are open, the second electronic switch is of low resistance, and the first and third electronic switches are of high resistance,

[0200] -(12) All mechanical contacts are open, the third electronic switch is of low resistance, and the first and second electronic switches are of high resistance,

[0201] -(13) All mechanical phase contacts are open, and the first, second, and third electronic switches are of low resistance.

[0202] As an example, in one variant, the protective switching device may also have at least one (or all) of the following switching states:

[0203] -(14) All mechanical contacts are open, the first electronic switch and the second electronic switch are of low resistance, and the third electronic switch is of high resistance.

[0204] -(15) All mechanical contacts are open, the second electronic switch and the third electronic switch are of low resistance, and the first electronic switch is of high resistance.

[0205] -(16) All mechanical contacts are open, the first electronic switch and the third electronic switch are of low resistance, and the second electronic switch is of high resistance.

[0206] Generally, the protection switch device is characterized, for example, by at least the following new switch states:

[0207] - All mechanical contacts are closed, a part of the electronic switches is of low resistance, and another part of the electronic switches is of high resistance.

[0208] The mechanical contact or the mechanical disconnect contact unit MK particularly refers to the (standard-compliant) disconnect function achieved by the disconnect contact unit MK. The disconnect function means the following key points:

[0209] - The minimum air distance according to the standard (the minimum distance between contacts),

[0210] - The contact position indication of the contacts of the mechanical disconnect contact unit,

[0211] - The operation / interruption of the contacts of the mechanical disconnect contact unit (by the control unit) is always possible (it is not possible to lock the contacts (continuously) in the closed state by the handle).

[0212] Regarding the minimum air distance between the contacts of the disconnect contact unit, this minimum air distance basically depends on the voltage. Other parameters include the degree of contamination, the type of field (uniform, non-uniform), and the air pressure or the height above the standard zero point.

[0213] There are corresponding regulations or standards for this minimum air distance or creepage distance. These regulations, for example, specify the minimum air distance for the impulse withstand voltage strength in air, which is used for non-uniform and uniform (ideal) electric fields depending on the degree of contamination. The impulse withstand voltage strength is the strength that can be withstood when the corresponding impulse voltage is applied. Only when this minimum length (minimum distance) exists does the disconnect contact unit or the protection switch device have the disconnect function (separator characteristic).

[0214] Here, in the sense of the present invention, the standard series DIN EN 60947 or IEC 60947 is relevant for the separator function and its characteristics, and is hereby incorporated by reference.

[0215] The characteristic of the separating contact unit advantageously lies in the minimum air distance of the open separating contacts in the off position (open position, open contacts), depending on the rated impulse withstand voltage and the degree of contamination. The minimum air distance is especially between (min) 0.01 mm and 14 mm. Particularly advantageously, the minimum air distance is between 0.01 mm at 0.33 kV and 14 mm at 12 kV, especially for degree of contamination 1 and especially for non-uniform fields.

[0216] Advantageously, the minimum air distance can have the following values:

[0217] E DIN EN 60947-1 (VDE 0660-100): 2018-06

[0218] Table 13 - Minimum air distance

[0219]

[0220] The degree of contamination and the field type correspond to the degree of contamination and the field type defined in the standard. Thereby, a standard-compliant protective switching device dimensioned according to the rated impulse withstand voltage can be advantageously achieved.

[0221] The mechanical separating contact unit specifically does not refer to relay contacts.

[0222] Although the present invention has been described in detail by way of examples in terms of details, the present invention is not limited to the disclosed examples and other variants can be derived therefrom by those skilled in the art without departing from the scope of protection of the present invention.

Claims

1. A protective switching device (SG) for protecting a three-phase low-voltage alternating current circuit having a neutral conductor, comprising: - a housing (GEH) having first, second, and third grid-side phase connections (LG1, LG2, LG3) for first, second, and third phase conductors (L1, L2, L3) of the low-voltage alternating current circuit and first, second, and third load-side phase connections (LL1, LL2, LL3), a grid-side neutral conductor connection (NG) and a load-side neutral conductor connection (NL) for the neutral conductor (N) of the low-voltage alternating current circuit, - a first series circuit (SS1) of a first mechanical phase contact (K1) and a first electronic switch (S1), a second series circuit (SS2) of a second mechanical phase contact (K2) and a second electronic switch (S2), a third series circuit (SS3) of a third mechanical phase contact (K3) and a third electronic switch (S3), wherein the first series circuit (SS1) electrically connects the first grid-side phase connection (LG1) to the first load-side phase connection (LL1), the second series circuit (SS2) electrically connects the second grid-side phase connection (LG2) to the second load-side phase connection (LL2), and the third series circuit (SS3) electrically connects the third grid-side phase connection (LG3) to the third load-side phase connection (LL3), - the grid-side neutral conductor connection (NG) is connected to the load-side neutral conductor connection (NL) by a mechanical neutral conductor contact (KN), - the mechanical phase contacts (K1, K2, K3) and the mechanical neutral conductor contact (KN) can be switched to open together to avoid current flow or switched to closed together for current flow, - the electronic switches (S1, S2, S3) can be switched by means of semiconductor-based switching elements into a high-resistance state of the switching elements to avoid current flow or into a low-resistance state of the switching elements for current flow, - the protective switching device is designed such that the first, second, and third electronic switches can be switched into the high-resistance state or the low-resistance state independently of one another.

2. The protective switching device (SG) according to claim 1, characterized in that first, second, and third current sensor units (SI1, SI2, SI3) are provided, the first current sensor unit (SI1) is provided in the first series circuit (SS1), the second current sensor unit (SI2) is provided in the second series circuit (SS2), and the third current sensor unit (SI3) is provided in the third series circuit (SS3), for respectively determining the magnitudes of the currents in the first, second, and third phase conductors, in particular such that there are instantaneous current values.

3. The protective switching device (SG) according to any one of the preceding claims, characterized in that The first mechanical phase contact (K1), the second mechanical phase contact (K2), the third mechanical phase contact (K3), and the mechanical neutral conductor contact (KN) are part of a mechanical disconnect contact unit (MK), which together open or close the phase contacts, in particular closing the neutral conductor contact (KN) before closing the phase contacts (K1, K2, K3), or opening the neutral conductor contact after opening the phase contacts (K1, K2, K3).

4. The protective switching device (SG) according to claim 3, characterized in that the mechanical disconnect contact unit (MK) has a handle (HH) accessible on the protective switching device for manually opening or closing the contacts.

5. The protective switching device (SG) according to any one of the preceding claims, characterized in that the first electronic switch (S1), the second electronic switch (S2), and the third electronic switch (S3) are part of an electronic interruption unit (EU), where the electronic switches can be switched independently of each other.

6. The protective switching device (SG) according to any one of the preceding claims, characterized in that the mechanical phase contacts (K1, K2, K3) are associated with the load-side phase connections, and the electronic switches (S1, S2, S3) are associated with the grid-side phase connections.

7. The protective switching device (SG) according to any one of the preceding claims, characterized in that a control unit (SE) is provided, which is connected to the current sensor units (SI1, SI2, SI3), the mechanical contacts, and the electronic switches (S1, S2, S3), the protective switching device being designed such that when at least one first current threshold in a phase conductor is exceeded, the avoidance of current flow in the concerned phase conductor is initiated by the concerned electronic switch, in particular for a first time period.

8. The protective switching device (SG) according to claim 7, characterized in that the first time period is less than 20 ms, in particular less than 10 ms.

9. The protective switching device (SG) according to claim 7 or 8, characterized in that the protective switching device is designed such that when at least one second current threshold in at least one phase conductor is exceeded, in particular when at least one second current threshold is exceeded for at least a first duration, the avoidance of current flow is initiated by opening the contacts.

10. The protective switching device (SG) according to any one of claims 7 to 9, characterized in that voltage sensor units (SU1, SU2, SU3) are respectively provided between each phase conductor and the neutral conductor for determining the voltage magnitude between the respective phase conductor and the neutral conductor, in particular the presence of instantaneous voltage values, the voltage sensor units (SU1, SU2, SU3) being connected to the control unit (SE).

11. The protective switching device (SG) according to claim 10, characterized in that In the case of starting to become low - resistance by means of the control unit (SE), the electronic switches (S1, S2, S3) become low - resistance in sequence at the corresponding zero - crossings of the voltage.

12. The protective switching device (SG) according to claim 10 or 11, characterized in that in the case of starting to become high - resistance by means of the control unit (SE), the electronic switches (S1, S2, S3) become high - resistance in sequence at the zero - crossings of the voltage.

13. The protective switching device (SG) according to any one of claims 10 to 12, characterized in that a control unit (SE) is provided, which is connected to the current sensor unit (SI1, SI2, SI3), the voltage sensor unit, the mechanical phase contacts (K1, K2, K3) and the electronic switches (S1, S2, S3), the protective switching device is designed such that when at least a first current threshold in the conductor is exceeded, the avoidance of current flow in the concerned conductor is initiated by the concerned electronic switch, when the voltage crosses zero the next time or the next but one time, the electronic switch becomes low - resistance again to enable current flow.

14. The protective switching device (SG) according to any one of the above claims, characterized in that the protective switching device has at least the following switching states: - all mechanical contacts are open and all electronic switches are high - resistance, - all mechanical contacts are closed and all electronic switches are low - resistance, - all mechanical contacts are closed and all electronic switches are high - resistance, - all mechanical contacts are closed, the first electronic switch is low - resistance and the second and third electronic switches are high - resistance, - all mechanical contacts are closed, the second electronic switch is low - resistance and the first and third electronic switches are high - resistance, - all mechanical contacts are closed, the third electronic switch is low - resistance and the first and second electronic switches are high - resistance, In particular, the protective switching device has the following switching states: - all mechanical phase contacts are open and at least one electronic switch is low - resistance.

15. The protective switching device (SG) according to any one of the above claims, characterized in that the protective switching device has at least the following switching states: - all mechanical contacts are open and all electronic switches are high - resistance, - all mechanical contacts are closed and all electronic switches are low - resistance, - all mechanical contacts are closed and all electronic switches are high - resistance, - all mechanical contacts are closed, the first and second electronic switches are low - resistance and the third electronic switch is high - resistance, - all mechanical contacts are closed, the first and third electronic switches are low - resistance and the second electronic switch is high - resistance, - all mechanical contacts are closed, the second and third electronic switches are low - resistance and the first electronic switch is high - resistance.

16. The protective switching device (SG) according to any one of the above claims, characterized in that the protective switching device has the following switching states: - all mechanical contacts are open and all electronic switches are high - resistance, - all mechanical contacts are closed and all electronic switches are low - resistance, - all mechanical contacts are closed and all electronic switches are high - resistance, - all mechanical contacts are closed, the first electronic switch is low - resistance and the second and third electronic switches are high - resistance, - All mechanical contacts are closed, the second electronic switch is of low resistance, and the first and third electronic switches are of high resistance. - All mechanical contacts are closed, the third electronic switch is of low resistance, and the first and second electronic switches are of high resistance. - All mechanical contacts are closed, the first and second electronic switches are of low resistance, and the third electronic switch is of high resistance. - All mechanical contacts are closed, the first and third electronic switches are of low resistance, and the second electronic switch is of high resistance. - All mechanical contacts are closed, the second and third electronic switches are of low resistance, and the first electronic switch is of high resistance.

17. A method for a protective switching device (SG) for protecting a three-phase low-voltage alternating current circuit having a neutral conductor, comprising: - A series circuit of mechanical phase contacts (K1, K2, K3) and electronic switches (S1, S2, S3), wherein, each series circuit electrically connects the grid-side phase connectors (LG1, LG2, LG3) to the load-side phase connectors (LL1, LL2, LL3) respectively, - The grid-side neutral conductor connector (NG) is connected to the load-side neutral conductor connector (NL) through a mechanical neutral conductor contact (KN), - The mechanical contacts (K1, K2, K3, KN) can be opened together to avoid current flow, or can be closed together for current flow, - The electronic switches (S1, S2, S3) can be switched by means of semiconductor-based switching elements into a high-resistance state of the switching elements to avoid current flow or into a low-resistance state of the switching elements for current flow, The electronic switches can be switched independently of each other into a high-resistance state or a low-resistance state to avoid or enable current flow depending on the phase conductors.

18. The method according to claim 17, characterized in that the magnitude of the current in the corresponding series circuit is determined, and in the case of exceeding at least one first current threshold in the series circuit, the avoidance of current flow in the involved series circuit is initiated, in particular the avoidance of current flow lasts for a first time period, by the involved electronic switch.

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