EP4377984A1

EP4377984A1 - Circuit breaker and method

Info

Publication number: EP4377984A1
Application number: EP22777619.2A
Authority: EP
Inventors: Marvin TANNHÄUSER
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2021-09-28
Filing date: 2022-09-12
Publication date: 2024-06-05
Also published as: DE102021210833A1; CN118020129A; WO2023052105A1

Abstract

The invention relates to a circuit breaker for protecting an electric low-voltage circuit, comprising: - a housing with at least one grid-side connection and a load-side connection, and - a mechanical separating contact unit which is connected to an electronic interruption unit in series, wherein - the mechanical separating contact unit is paired with the load-side connection, and the electronic interruption unit is paired with the grid-side connection, - the level of the current in the low-voltage circuit, in particular between the grid-side phase conductor connection and the load-side phase conductor connection, is ascertained, - a process for preventing a current flow in the low-voltage circuit is initiated if current thresholds and/or current/time thresholds are exceeded, - a measurement impedance is provided between two conductors of the low-voltage circuit, said measurement impedance being connected to the connection between the mechanical separating contact unit and the electronic interruption unit (EU), and - while the contacts of the mechanical separating contact unit are open and the electronic interruption unit is switched to a high-ohmic state, the electronic interruption unit is switched to a low-ohmic state for a first duration in order to check the functionality of the circuit breaker.

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.e. 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. The rated currents can be scaled further, from 0.5 A to 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.

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 in the event of an overload and/or Switch off short circuit automatically. 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 for tripping (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 interruption 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 are connected in series with the electronic interrupting unit, ie the current of the low-voltage circuit to be protected is routed both via the mechanical isolating contact system and via the electronic interrupting unit.

The present invention relates in particular to low-voltage AC circuits with an AC voltage, usually with a time-dependent sinusoidal AC voltage with the frequency f. The time dependence of the instantaneous voltage value u(t) of the AC voltage is given by the equation: u(t) = U * sin ( 2n * f * t). Where: u(t) = instantaneous voltage value at time t

U = amplitude 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, i.e.:

M = 2n*f = 2n/T = angular frequency of the AC voltage (T = period of the oscillation)

The specification of the angular frequency (M) 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(ut)

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 AC voltage, which is in particular constant over time, the time-dependent value from the angular velocity M 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°. I.e. 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° ) .

Consequently, the instantaneous voltage value u(t) means the instantaneous value of the voltage at the time t, i.e. in the case of a sinusoidal (periodic) AC voltage, the value of the voltage at the phase angle cp (cp = 0...2n or <p = 0°. ..360°, the respective period) .

The object of the present invention is to improve a protective switching device of the type mentioned above, in particular to improve the safety of such a protective switching device or to achieve greater safety in the electrical low-voltage circuit to be protected by the protective switching device.

This object is achieved by a protective switching device having the features of patent claim 1 and by a method according to patent claim 16 .

According to the invention, a protective switching device for protecting an electrical low-voltage circuit, in particular a low-voltage alternating current circuit, is proposed, having: a housing with at least one mains-side connection and one load-side connection, - a mechanical isolating contact unit, which is connected in series with an electronic interrupting unit, the mechanical isolating contact unit being assigned to the load-side connection and the electronic interrupting unit to the mains-side connection,

- 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 to determine the magnitude of the current in the low-voltage circuit,

- A control unit, which is connected to the current sensor unit, the mechanical isolating contact unit and the electronic interrupter unit, wherein when current and/or current time limit values are exceeded, avoidance of a current flow in the low-voltage circuit is initiated.

According to the invention, a measuring impedance is provided between two conductors of the low-voltage circuit. On the one hand, the measuring impedance is connected to the connection between the mechanical isolating contact unit and the electronic interruption unit. On the other hand, the measurement impedance is connected to the other conductor. Especially with the other conductor on the mains-side connection.

The protective switching device is designed according to the invention such that the electronic interrupting unit (EU) is switched to a low-impedance state for a first period of time for functional testing of the protective switching device when the contacts of the mechanical isolating contact unit are open and the electronic interrupting unit is switched to high resistance. D. H . the electronic interruption unit is starting from the high-impedance state for a first period of time in the switched to the low-impedance state and is then again in the high-impedance state.

The first period of time can be in the range of 100 ps to 1 s. For example 100 ps , 200 ps , 1 ms , 2 ms , 10 ms , 11 ms , ..., 20 ms , 21 ms , ..., 100 ms , ..., 200 ms , ... 1 s .

With switching times in the range of 1 ms to 2 ms, a voltage change can be detected for a functional test. With periods of 20 ms to 100 ms or 1 second, it can be checked (repeatedly) whether there is a voltage of about 0 V (instantaneous or then also the effective value of the voltage) across the electronic interruption unit.

This has the particular advantage that the electronic interruption unit can be checked with regard to its “can be switched on and switched-on state”.

Advantageous refinements of the invention are specified in the dependent claims and in the exemplary embodiment.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that (for one conductor) the magnitude of the voltage across the electronic interruption unit can be determined.

This has the particular advantage that specifically the magnitude of the voltage between the grid-side connection point and the load-side connection point of the electronic interruption unit can be determined or is determined.

In an advantageous embodiment of the invention, the magnitude of the voltage across the electronic interruption unit is determined when the electronic interruption unit is switched (action) for the first period of time into the low-impedance state. If a second voltage threshold value is exceeded, a second error condition is present, so that another or subsequent low resistance of the electronic interruption unit is avoided and/or closing of the contacts is avoided. (Ie . if the voltage falls below the second threshold value, there is no error condition.) The first voltage threshold should preferably be less than 1

be v . The first voltage threshold can be between 0 volts (or greater than 0 volts) and smaller (e.g. 10% smaller) than the

Instantaneous value of the currently applied AC voltage (especially when monitoring or comparing instantaneous values).

This has the particular advantage that the electronic interrupting unit can be checked more precisely with regard to its “can be switched on” or the switched-on state.

In an advantageous embodiment of the invention, the protective switching device is designed in such a way that when the contacts of the mechanical isolating contact unit are open, the magnitude of the voltage across the electronic interruption unit is determined when the electronic interruption unit is switched to high resistance. If the voltage falls below a first threshold value, a first fault condition is present, so that the electronic interrupter unit is prevented from becoming low-impedance (possibly again or for the first time) and/or the contacts are prevented from closing. (i.e. if the first voltage threshold is exceeded, there is no error condition.)

The first voltage threshold could be an rms/mean/rms value of the AC voltage. The first voltage threshold could be an instantaneous value of the voltage. The comparison can be made using effective values or instantaneous values over time.

This is used to check the electronic interruption unit with regard to its "disconnectability or the switched-off state", i.e. the high-impedance or high-impedance of the semiconductor-based switching elements.

The first voltage threshold is, for example, advantageously 5-15% of the nominal or applied voltage of the low-voltage circuit, for example 10%. This applies both to effective values and to instantaneous values of the AC voltage, depending on the type of comparison selected. For example, at specific points in time of the instantaneous value of the AC voltage can be measured. Z. B. at the moment when the instantaneous value of the AC voltage is +300 V or -300 V.

This has the particular advantage that it is easy to check the switch-off behavior of the electronic interruption unit.

In an advantageous embodiment of the invention, closing of the contacts of the mechanical isolating contact unit is avoided when one (of the two) error condition is present. In particular, no release signal (enable) is sent to the mechanical isolating contact unit. D. H . it is not possible to close the contacts of the mechanical isolating contact unit using a handle.

Furthermore, the electronic interruption unit can be prevented from becoming low-impedance.

Other error conditions may exist.

This has the particular advantage that only a functioning protective switching device with a functioning electronic interruption unit can be switched on. This increases operational reliability in the low-voltage circuit. This ensures that the ability to switch the electronic interrupter unit on and off works.

In an advantageous embodiment of the invention, the protective switching device can also be designed in such a way that further refinements are provided:

- a housing with a line-side neutral conductor connection, a line-side phase conductor connection, a load-side neutral conductor connection, a load-side phase conductor connection of the low-voltage circuit,

- A, in particular two-pole (especially in a single-phase circuit), mechanical isolating contact unit with load-side connection points and mains-side connection points, the load-side connection points being connected to the load-side neutral and phase conductor connections, so that an opening of contacts to avoid a current flow or a closing of the contacts for a current flow in the low-voltage circuit can be switched,

- An, in particular single-pole, electronic interruption unit, with a network-side connection point which is electrically connected to the network-side phase conductor connection, and a load-side connection point which is connected to a network-side connection point of the mechanical isolating contact unit, the electronic interruption unit being in a high-impedance state due to semiconductor-based switching elements has the switching elements to avoid current flow or a low-impedance state of the switching elements for current flow in the low-voltage circuit,

- a current sensor unit, for determining the magnitude of the current of the low-voltage circuit,

According to the invention, the magnitude of the voltage between the network-side connection point and the load-side connection point of the electronic interruption unit can be determined or is determined .

At least one voltage sensor unit connected to the control unit can be provided for this purpose. If there are several voltage sensor units, these are connected to the control unit.

According to the invention, the functional capability of the electronic interruption unit can be determined by determining the magnitude of the voltage across the electronic interruption unit. According to the invention, increased operational reliability of a protective switching device is thus achieved. Further will a new architecture or Structural design of a protective switching device proposed.

In an advantageous embodiment of the invention, a first voltage sensor unit connected to the control unit is provided, which determines the magnitude of a/the first voltage across the electronic interruption unit, in particular between the grid-side connection point and the load-side connection point of the electronic interruption unit.

This has the particular advantage that there is a simple solution with only one voltage sensor unit.

In an advantageous embodiment of the invention, a second voltage sensor unit connected to the control unit is alternatively provided, which determines the level of a second voltage between the network-side neutral conductor connection and the network-side phase conductor connection. Furthermore, a third voltage sensor unit connected to the control unit is provided, which determines the magnitude of a third voltage between the neutral conductor connection on the network side and the connection point of the electronic interruption unit on the load side. The protective switching device is designed in such a way that the level of a/the first voltage between the network-side connection point and the load-side connection point of the electronic interruption unit is determined from the difference between the second and third voltage.

This has the particular advantage that there is another solution based on classic voltage measurements. In addition, a more extensive testing of the protective switching device is made possible.

In an advantageous embodiment of the invention, the current sensor unit is provided on the circuit side between the line-side phase conductor connection and the load-side phase conductor connection.

This has the particular advantage that the device is compactly divided into two, with an electronic Interruption unit in the phase conductor together with a current sensor unit on the one hand and a continuous neutral conductor on the other. Furthermore, with a current sensor unit in the phase conductor, more extensive monitoring of currents is achieved both in the circuit itself and in the case of ground fault currents.

In an advantageous embodiment of the invention, a measuring impedance is connected in particular between the mains-side connection points of the mechanical isolating contact unit. In particular, the measuring impedance is an electrical resistance and/or capacitor, i. H . a single element or a series or Parallel connection of two elements .

In particular, the measuring impedance should have a high resistance value or Have an impedance value in order to keep the losses low. In particular, resistance values of more than 100 KOhm, better 1 MOhm, 2 MOhm, 3 MOhm, 4 MOhm or 5 MOhm, should be provided, especially more than 5 MOhm. In a 230 volt low-voltage circuit, the use of a measuring resistor of e.g. B. 1 MOhm to about 50 mW losses.

This has the particular advantage that the functionality of the electronic interruption unit can be checked more effectively, in particular when the isolating contacts are open, specifically in the case of the circuit breaker architecture according to the invention.

In an advantageous embodiment of the invention, the low-voltage circuit is a three-phase alternating current circuit. The protective switching device has several or further line-side and load-side phase conductor connections to protect the phases of the electrical circuit. Between each of the line-side and load-side phase conductor connections, there is in each case an electronic interruption unit with voltage determination according to the invention, in particular first voltage sensor units. In addition, a contact of the mechanical isolating contact unit is provided between each of the line-side and load-side phase conductor connections. This has the particular advantage of providing protection for three phase AC circuits. In an advantageous embodiment of the invention, the protective switching device is designed in such a way that the contacts of the mechanical isolating contact unit can be opened by the control unit, but cannot be closed.

This has the particular advantage that increased operational reliability is achieved, since the contacts cannot be accidentally closed by the control unit.

In an advantageous embodiment of the invention, the mechanical isolating contact unit can be operated by a mechanical handle in order to switch an opening of contacts or a closing of the contacts.

This has the particular advantage that it has the functionality of a classic circuit breaker.

In an advantageous embodiment of the invention, the mechanical isolating contact unit is designed in such a way that the contacts can only be closed by the mechanical handle after a release (enable), in particular a release signal.

This has the particular advantage that there is increased protection and increased operational reliability, since switching on a defective circuit breaker is avoided.

In an advantageous embodiment of the invention, an energy supply is provided, in particular for the control unit, which is connected to the grid-side neutral conductor connection and the grid-side phase conductor connection. In particular, a fuse, in particular a fuse, is provided in the connection to the network-side neutral conductor connection. In particular, the measurement impedance can advantageously be connected to the line-side neutral conductor connection via the fuse.

This has the particular advantage that a compact electronic assembly is made possible. Furthermore, there is only one cross-connection between the phase conductor and the neutral conductor in the protective switching device. A fault in the protective switching device, the one Causes a short circuit between the phase conductor and the neutral conductor and can thus be easily protected, secured or being found .

In an advantageous embodiment of the invention, with closed contacts of the mechanical isolating contact unit and a low-impedance interrupting unit and

- When a current is determined that exceeds a first current value, in particular that the first current value is exceeded for a first time limit, the electronic interruption unit becomes highly resistive and the mechanical isolating contact unit remains closed,

- When a current is determined which exceeds a (higher) second current value, in particular for a second time limit, the electronic interruption unit becomes highly resistive and the mechanical isolating contact unit is opened,

- When a current is determined which exceeds a (even higher) third current value, the electronic interruption unit becomes highly resistive and the mechanical isolating contact unit is opened.

This has the particular advantage that there is a graded shutdown concept for increased currents for a protective switching device according to the invention.

In an advantageous embodiment of the invention, the control unit has a microcontroller.

This has the particular advantage that the functions according to the invention for increasing the safety of a protective switching device or of the low voltage electrical circuit to be protected can be realized by a (customizable) computer program product. In addition, changes and improvements to the function can thus be loaded individually onto a protective switching device.

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. The method for a circuit breaker protecting a low voltage electrical circuit comprising:

- a housing with at least one mains-side connection and one load-side connection,

- a mechanical isolating contact unit, which is connected in series with an electronic interrupting unit, the mechanical isolating contact unit being assigned to the load-side connection and the electronic interrupting unit to the mains-side connection,

- that the magnitude of the current in the low-voltage circuit, in particular between the line-side phase conductor connection and the load-side phase conductor connection, is determined, that when current and/or current-time limit values are exceeded, current flow in the low-voltage circuit is avoided,

- That a measuring impedance is provided between two conductors of the low-voltage circuit, the measuring impedance being connected on the one hand to the connection between the mechanical isolating contact unit and the electronic interruption unit.

To test the function of the protective switching device, when the contacts of the mechanical isolating contact unit are open and the electronic interruption unit is switched to high resistance, the electronic interruption unit is switched to a low resistance state for a first period of time.

With the polarity of the applied instantaneous value of the AC voltage, i . H . the measurement time, it can be determined whether a first semiconductor-based switching element (for a first voltage polarity) or a second semiconductor-based switching element (for a second voltage polarity) is tested.

When the electronic interruption unit is switched to the low-impedance state for the first period of time, the magnitude of the voltage across the electronic interruption unit is determined. If a/the second voltage threshold value is exceeded, a second error condition is present, so that the electronic interruption unit is prevented from becoming further low-impedance and/or the contacts are prevented from closing.

When the contacts of the mechanical isolating contact unit are open and the electronic interruption unit (EU) is switched to high resistance, the magnitude of the voltage across the electronic interruption unit can also be determined. If the voltage falls below a/the first threshold value, a first fault condition is present, so that the electronic interruption unit is prevented from becoming low-impedance and/or the contacts are prevented from closing.

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, cause the microcontroller to improve or increase the safety of such a protective switching device. to achieve greater safety in the electrical low-voltage circuit to be protected by the protective switching device.

The microcontroller 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 16, as well as referring only to individual features or combinations of features of patent claims, in particular also a referencing of the pending arrangement claims to the independent method claim and vice versa, bring about an improvement in a protective switching device, in particular an improvement in the safety of a protective switching device or of the electrical circuit , and provide a new concept for a protective switching device .

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,

FIG. 3 shows a third representation of a protective switching device with first voltage curves,

FIG. 4 shows a fourth representation of a protective switching device with second voltage curves,

FIG. 5 shows a fifth representation of a protective switching device.

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:

- a line-side neutral conductor connection NG, a line-side phase conductor connection LG, a load-side neutral conductor connection NL, a load-side phase conductor connection LL of the low-voltage circuit; an energy source is usually connected to the grid side GRID, and a consumer is usually connected to the load side LOAD;

- a (two-pole) mechanical isolating contact unit MK with load-side connection points APLL, APNL and line-side connection points APLG, APNG, with a load-side connection point APNL for the neutral conductor, a load-side connection point APLL for the phase conductor, a line-side connection point APNG for the neutral conductor, and a line-side connection point for the phase conductor network-side connection point APLG is provided. The load-side connection points APNL, APLL are connected to the load-side neutral and phase conductor connections NL, LL, so that opening of contacts KKN, KKL to avoid current flow or closing of the contacts for current flow in the low-voltage circuit can be switched,

- A, in particular single-pole, electronic interruption unit EU (which is arranged in particular in the phase conductor in the case of a single-pole design) with a grid-side connection point EUG, which is electrically connected to the grid-side phase conductor connection LG, and a load-side connection point EUL, which is connected to the grid-side Connection point APLG of the mechanical isolating contact unit MK is electrically connected or. is connected, wherein the electronic interruption unit has or has a high-impedance state of the switching elements to avoid a current flow or a low-impedance state of the switching elements to current flow in the low-voltage circuit by semiconductor-based switching elements. is switchable,

- A current sensor unit S I, for determining the level of the current of the low-voltage circuit, which is arranged in particular in the phase conductor,

- A control unit SE, which is connected to the current sensor unit SI, the mechanical isolating contact unit MK and the electronic interruption unit EU is connected, wherein when current and / or current time limit values are exceeded, avoidance of a current flow in the low-voltage circuit is initiated.

According to the invention, the protective switching device is designed in such a way that the magnitude of the voltage across the electronic interruption unit can be determined. D. H . the level of a first voltage between the grid-side connection point EUG and the load-side connection point EUL of the electronic interruption unit EU can be determined or is determined .

For this purpose, a first voltage sensor unit SUI connected to the control unit SE is provided in the example according to FIG.

In the voltage measurement by the first voltage sensor unit SUI, the voltage across the series connection of electronic interruption unit EU and current sensor S I can alternatively also be determined, as shown in FIG. The current sensor unit S I has a very low internal resistance, so that the determination of the level of the voltage is not affected or is only negligibly affected.

According to the invention, a measuring impedance ZM is also connected between the network-side connection points APLG, APNG of the mechanical isolating contact unit MK. The measuring impedance ZM can be an electrical resistor and/or capacitor, for example. The measuring impedance can also be an inductance. In particular, the measurement impedance can be a series connection or parallel connection of a resistor and/or capacitor and/or inductance.

Advantageously, a second voltage sensor unit SU2 can be provided, which determines the magnitude of the voltage between the line-side neutral conductor connection NG and the line-side phase conductor connection LG. The first voltage sensor unit can also be replaced by using two voltage measurements (before the electronic interrupting unit and after the electronic interrupting unit). The voltage across the electronic interruption unit is determined by forming a difference.

A/the second voltage sensor unit SU2 connected to the control unit SE can be provided, which determines the level of a second voltage between the network-side neutral conductor connection (NG) and the network-side phase conductor connection (LG). Furthermore, a third voltage sensor unit SU3 (not shown) connected to the control unit can be provided, which determines the level of a third voltage between the network-side neutral conductor connection NG and the load-side connection point EUL of the electronic interruption unit EU. The protective switching device is designed in such a way that the level of a/the first voltage between the grid-side connection point EUG and the load-side connection point EUL of the electronic interruption unit EU is determined from the difference between the second and third voltage.

In the example according to FIG. 1, the electronic interruption unit EU has a single-pole design, in the example in the phase conductor. In this case, the line-side connection point APNG for the neutral conductor of the mechanical isolating contact unit MK is connected to the line-side neutral conductor connection NG of the housing GEH.

The protective switching device SG is advantageously designed in such a way that the contacts of the mechanical isolating contact unit MK can be opened by the control unit SE but not closed, which is indicated by an arrow from the control unit SE to the mechanical isolating contact unit MK.

The mechanical isolating contact unit MK can be operated by a mechanical handle HH on the protective switching device SG in order to open or close the contacts manually KKL, KKN to switch. The mechanical handle HH indicates the switching status (open or closed) of the contacts of the mechanical isolating contact unit MK.

Furthermore, the contact position (or the position of the handle, closed or open) can be transmitted to the control unit SE. The contact position (or the position of the handle) can be determined, for example, using a sensor.

The mechanical isolating contact unit MK is advantageously designed in such a way that a (manual) closing of the contacts by the mechanical handle is only possible after a release (enable), in particular an enable signal. This is also indicated by the arrow from the control unit SE to the mechanical isolating contact unit MK. i.e. The contacts KKL, KKN of the mechanical isolating contact unit MK can only be closed by the handle HH when the release or the release signal (from the control unit) is present. Although the handle HH can be actuated without the release or the release signal, the contacts cannot be closed ("permanent slipping").

The protective switching device SG has an energy supply NT, for example a power pack. In particular, the power supply NT is provided for the control unit SE, which is indicated in FIG. 1 by a connection between the power supply NT and the control unit SE. The power supply NT is (on the other hand) connected to the line-side neutral conductor connection NG and the line-side phase conductor connection LG. A fuse SS, in particular a fuse, can advantageously be provided in the connection to the network-side neutral conductor connection NG (or/and phase conductor connection LG).

Alternatively, the measuring impedance ZM can be connected to the line-side neutral conductor connection NG via the fuse SS. A three-pole electronic unit EE (FIG. 5) can thus advantageously be implemented, for example as a module, the three Having connection points, a neutral connection point and two phase connection points. The electronics unit EE has, for example, the electronic interruption unit EU, the control unit SE, the power supply NT (particularly including fuse SS), the current sensor unit SI, the first voltage sensor unit SUI and optionally the second voltage sensor unit SU2.

The low-voltage circuit can be a three-phase AC circuit, with a neutral conductor and three phase conductors. For this purpose, the protective switching device can be designed as a three-phase variant and can have, for example, further line-side and load-side phase conductor connections. In an analogous manner, inventive electronic interruption units and voltage determination devices (e.g. by means of first voltage sensor units) are provided between the further line-side and load-side phase conductor connections. Likewise contacts of the mechanical isolating contacts unit.

The measuring impedance ZM should have a very high value (resistance or impedance value) in order to keep losses low. For example, with a resistor with a value of z. B. 1 MOhm . A value of 1 MOhm results in losses of about 50 mW in a 230 V low voltage circuit.

The measuring impedance should advantageously be greater than 100 KOhm.

High resistance means a state in which only a negligible current flows. In particular, by high resistance is meant resistance values greater than 1 kilohm, more preferably greater than 10 kilohms, 100 kilohms, 1 megohm, 10 megohms, 100 megohms, 1 gigaohm, or greater.

Low-impedance means a condition in which the current value specified on the protective switching device could flow. In particular, low-impedance means resistance values that are less than 10 ohms, better less than 1 ohm, 100 milliohms, 10 milliohms, 1 milliohm or less. FIG. 2 shows an illustration according to FIG. 1, with the difference that an energy source EQ with a nominal voltage U _N of the low-voltage circuit is connected to the network side GRID. Furthermore, on the load side LOAD a consumer or Energy sink ES is connected.

Furthermore, a release signal enable is drawn in at the connection of the control unit SE to the mechanical isolating contact unit MK.

The mechanical isolating contact unit MK is shown in an open state OFF, i. H . with open contacts KKN, KKL to avoid current flow.

The protective switching device SG works, for example, in principle such that when the contacts of the mechanical isolating contact unit and low-impedance interrupting unit and

- When a current is determined that exceeds a first current value, in particular that the first current value is exceeded for a first time limit, the electronic interruption unit EU becomes highly resistive and the mechanical isolating contact unit MK remains closed,

- When a current is determined which exceeds a higher second current value, in particular for a second time limit, the electronic interruption unit EU becomes highly resistive and the mechanical isolating contact unit MK is opened,

- When a current is determined that exceeds an even higher third current value, the electronic interruption unit becomes highly resistive and the mechanical isolating contact unit MK is opened.

FIG. 3 shows a representation according to FIG. 2, with various differences. The voltages on and in the protective switching device are shown in more detail:

- the nominal voltage U _N of the energy source EQ of the low-voltage circuit,

- between the line-side neutral conductor connection NG and mains-side phase conductor connection LG applied mains voltage U _L u

- the second voltage U2 or U _N , _G ND measured in the protective switching device by the second voltage sensor unit SU2 _?

- The first voltage Ul or U _S measured with the first voltage sensor unit SUI across the electronic interruption unit EU.

In this variant according to FIG. 3, the first voltage Ul (or U _sw ) is measured directly across the electronic interruption unit (ie without a current sensor unit SI). The second voltage U2 (or U _N , _GND ) corresponds to the mains voltage U _L N minus the (minimum) voltage drop across the current sensor unit SI and the ohmic losses.

A detail of the electronic interruption unit EU is also shown, with the (single-pole) electronic interruption unit EU having semiconductor-based switching elements TI, T2. In the example according to FIG. 3, two series-connected semiconductor-based switching elements TI, T2 are provided. An overvoltage protection device TVS is advantageously provided above the series connection of the two semiconductor-based switching elements TI, T2.

In the embodiment according to FIG. 3, two unidirectional electronic switching elements (anti-serial) are connected in series. The first unidirectional switching element is arranged so that it can be switched in a first current direction and the second unidirectional switching element is arranged so that it can be switched in the opposite current direction, with the unidirectional switching elements being conductive in the opposite direction to their current switching direction (directly or indirectly, e.g. through internal or external diodes connected in parallel). In particular, the protective switching device is designed in such a way that the first and the second switching element can be switched independently of one another.

The following situation is considered below:

- There is nominal voltage or mains voltage (e.g. 230 V AC) at the mains-side connection LG, NG or mains side GRID or mains connection of the protective switching device, - A consumer or energy sink ES or load is connected to the load side LOAD of the protective switching device,

In the first step, the check in the OFF state of the electronic protection device should be considered.

Is to:

- The mechanical isolating contact unit is open (contacts open)

- The electronic interruption unit is switched off (semiconductor-based switching elements have high resistance)

- The control unit (incl. controller unit) is active

The electrical potential between the electronic interruption unit and the mechanical isolating contact unit is defined by the measuring impedance ZM and the impedance of the electronic interruption unit when switched off (voltage divider).

The control unit can now switch on the semiconductor-based switching elements (which of the two semiconductors is active?) at any point in time (and thus at a specific voltage distribution (depending on the instantaneous value of the voltage, half-wave of the voltage). Taking into account the polarity of the AC voltage or AC voltage the switching elements of the electronic interruption unit EU can be tested with this.

The electronic interruption unit EU (or the electronic switch) is thus switched on for a very short time (in the millisecond range), for example. If the electronic interruption unit is functional, this can be determined by the (simultaneous) voltage measurement (e.g. first voltage sensor unit, second voltage sensor unit) and (subsequent) evaluation. For example, in the case of a defective semiconductor-based switching element, it can be determined whether it always remains switched on (fault pattern: "alloyed through") or always off (fault pattern: "burned out").

This covers two typical and frequent error patterns. If the check is error-free, a (first) enable condition for switching on the protective switching device, specifically the electronic interrupting unit or the mechanical isolating contact unit .

If the check is not error-free, there will be no release to switch on the protective switching device, there is an error condition so that the outgoing feeder or consumer / load can not be switched on and thus a dangerous state is prevented .

The protective switching device is designed in such a way that when the contacts of the mechanical isolating contact unit MK are open and the electronic interruption unit EU is switched to high resistance, the magnitude of the voltage across the electronic interruption unit, i. H . the first voltage Ul is determined. If the voltage falls below a first threshold value, a first fault condition is present, so that the electronic interruption unit is prevented from becoming low-impedance and/or the contacts are prevented from closing. With regard to the mechanical isolating contact unit MK, for example, a release signal enable is not emitted by the control unit SE to the mechanical isolating contact unit MK.

On the right-hand side of FIG. 3, three corresponding voltage curves are shown over time. The level of the voltage in volts is plotted on the vertical y-axis and the time in milliseconds (ms) is plotted on the horizontal x-axis. In each case, the course of the level of the first voltage U1 and the level of the second voltage U2 is shown over time.

The voltage curves for a fault-free state of the electronic interruption unit EU are shown in the first upper graphic NORM. In this case, the difference in the amplitude between the first voltage U1 and the second voltage U2 is due to the voltage drop across the measuring impedance ZM. The first voltage threshold should be based on the size of the measuring impedance. The first For example, the voltage threshold should be slightly smaller than the nominal voltage minus the voltage drop across the measuring impedance. If the first voltage Ul is greater than the first voltage threshold value, then there is a fault-free electronic interruption unit EU. The evaluation can be based on the instantaneous values of the voltage as well as on the effective values of the voltage. If the first voltage U1 is greater than the first voltage threshold value, there is consequently a first release condition, as a result of which the electronic interruption unit may become low-resistance and/or the contacts of the mechanical isolating contacts unit may be closed. This is shown in FIG. 3 by an arrow labeled enable, from the control unit SE to the mechanical isolating contact unit MK, for releasing the closing of the contacts of the mechanical isolating contact unit MK by the handle HH. The connection or the arrow from the control unit SE to the electronic interruption unit EU shows a progression of the switching state of the electronic interruption unit over time, in which a switched-off/high-impedance state is off and a switched-on/low-impedance state of the electronic interruption unit EU is on is marked . In the example, the electronic interruption unit EU is in the switched-off state off, which is represented by a straight line next to 'off'.

In the second graphic in the middle, 'TI is "shorten"', the voltage curve for a defective electronic interruption unit EU is shown, in which in the example a semiconductor-based switching element, in the example the switching element TI, is constantly conductive (alloyed through/short-circuited). This causes a flow in a Half-wave of the electrical voltage, a current flows through the electronic interruption unit, although this is actually (should be) high-impedance.The conductivity in the current direction affected by the semiconductor-based switching element concerned prevents the build-up of a voltage across the semiconductor-based one concerned switching element . D. H . , the magnitude of the first voltage Ul cannot exceed the first voltage threshold value, which can be determined by means of the first voltage sensor unit SUI in conjunction with the control unit SE. This is indicated in FIG. 3 by the abbreviation DT.

In the third graphic below, 'T2 is "shorting"', the voltage curve for a defective electronic interruption unit EU is shown, in which the other semiconductor-based switching element, in the example the switching element T2, is constantly conductive (alloyed through/short-circuited). The same applies to the middle graphic said .

The second and third graphics show an error state of the electronic interruption unit EU, which according to the invention can be found when the contacts of the mechanical isolating contact unit and low-resistance interruption unit are closed before the contacts of the mechanical isolating contact unit are closed and which prevents manual closing of the contacts of the mechanical isolating contact unit.

This is explained again in other words. FIG. 3 shows an overview of the circuit diagram and voltage curves in the event that a switching element in the electronic interruption unit is defective, in this case alloyed through/short-circuited. Since unidirectionally blocking power semiconductors are typically used, the functionality of the semiconductor-based switching element TI or T2 can be tested depending on the applied voltage polarity. If an AC voltage is present at the terminals of a functional protective switching device, a voltage Ul or . Etc, which can be determined via a corresponding first voltage sensor unit SUI. This is illustrated in the NORM graph above. If one of the two switching elements is broken down, the voltage can no longer be picked up by the electronic interruption unit. The measured voltage becomes zero here for a certain period of time (approx. 5ms). This is shown in the two curves 'TI is "shorten"'' and 'T2 is "shorten"''. This enables the measurement the detection of a defective switching element. If both switching elements fail, the first voltage Ul or Etc always zero (not shown).

FIG. 4 shows an illustration according to FIG. 3 with the difference that the electronic interruption unit EU is briefly switched on and off. This is indicated by a square-wave signal with regard to the states off on at the connection between the control unit SE and the electronic interruption unit EU.

On the right-hand side of FIG. 4, three graphics according to FIG. 3 are again shown. Shown are voltage curves in the event that a switching element in the electronic interruption unit is defective, in this case it is burnt out/open. Since unidirectionally blocking power semiconductors are typically used, switching element TI or T2 can be tested for functionality depending on the voltage polarity applied.

If there is an AC voltage on the mains side of the functional protective switching device, a voltage Ul or . Etc, which can be measured via a corresponding voltage measurement (first voltage sensor unit SUI). This is illustrated in the "Health" histories above.

In order to check whether one of the two semiconductor-based switching elements has burned out, a short switch-on pulse is given, first period of time. If one of the two switching elements contained is burnt out, the switching element can no longer be switched on by the electronic interruption unit. The measured voltage then always remains the same as in the switched-off state, even when the device is switched on. This is shown in the middle graphic 'TI is "open"'' and the bottom graphic 'T2 is "open"'. This allows measuring and the detection of a defective switching element. D. H . The protective switching device is designed in such a way that when the contacts of the mechanical isolating contact unit MK are open and the electronic interruption unit EU is switched to high resistance, the electronic interruption unit EU is switched to a low resistance state for a first period of time, and the level of the voltage across the electronic interruption unit is determined.

If a second voltage threshold value is exceeded, a second fault condition is present, so that the electronic interruption unit is prevented from becoming low-impedance and/or the contacts are prevented from closing.

The protective switching device is advantageously designed in such a way that the contacts of the mechanical isolating contact unit MK are prevented from closing when a fault condition is present. In particular, no release signal (enable) is sent to the mechanical isolating contact unit MK.

FIG. 5 shows an illustration according to FIGS. 1 to 4, with the difference that the protective switching device is constructed in two parts. It contains an electronic first part EPART, for example on a printed circuit board. The first part EPART can have the control unit SE, the first voltage sensor unit SUI, the second voltage sensor unit SU2, the current sensor unit SI, the electronic interruption unit EU, the power supply NT. Furthermore, the first part can have the fuse SS, a switch SCH, the measuring impedance ZM, a temperature sensor TEM (in particular for the electronic interruption unit EU), a communication unit COM, a display unit DISP.

The first part EPART has only three connections :

- the line-side phase conductor connection LG,

- a connection for the resp. to the line-side phase conductor connection point APLG of the mechanical isolating contact unit MK,

- a connection for a connection to the network side

Neutral conductor connection NG . The protective switching device contains a particularly mechanical second part MPART. The second part MPART can have the mechanical isolating contact unit MK, the handle HH, a release unit FG. Furthermore, the second part can have a position unit POS, for reporting the position of the contacts of the mechanical isolating contacts unit MK to the control unit, as well as the (neutral conductor) connection(s). Further units, not specified in detail, can be provided.

A compact protective switching device according to the invention can advantageously be implemented as a result of the division into two.

The release unit FG causes the actuation of the contacts of the mechanical isolating contact unit to be released by the handle HH when a release signal enable is present, see FIG

In the following, the invention is to be summarized again and explained in more detail.

An example of an electronic protection and switching device is proposed with:

- Housing with line-side and load-side connections

- Voltage sensor unit

- Current sensor unit for measuring the (load) current

- mechanical isolating contact unit incl. Handle (including display of the contact position, release by the electronics, isolating properties)

- Electronic interrupting unit with semiconductor-based switching elements

- control unit

- the functionality of the electronic interruption unit is checked,

- by continuously measuring the voltage across the electronic interrupting unit. Here z. B. can be determined in the switched-on state, whether e.g. B. a semiconductor component has burned out.

- by briefly (<10ms, preferably <lms, generally: <20ms, 50ms, 100ms, 200ms, 500ms or 1 s) switching on the electronic interruption unit when the contacts are open is switched off again, and at the same time measured voltage values and/or measured current values are recorded and these are analyzed in such a way that an alloyed or burned-out electronic interruption unit is recognized or alloyed or blown switching elements are detected.

It is advantageous to first measure, then switch and measure.

A first voltage sensor unit/voltage measuring unit across the electronic interrupting unit is proposed in order to determine the voltage across the electronic interrupting unit. Alternatively, a third voltage sensor unit can be provided in parallel with the second voltage sensor unit. H . between the electronic interruption unit and the mechanical isolating contact contact unit is provided, this being connected on the one hand to the phase conductor and on the other hand to the neutral conductor. The first voltage can be determined from the differential formation of the voltages between the second and third voltage sensor units. In this case, the first voltage sensor unit can be omitted.

An additional measurement impedance is proposed, which is attached between the two conductors/current paths (phase conductor L and neutral conductor N) in order to define the electrical potential between the electronic interruption unit EU and the mechanical isolating contact unit for measurement purposes (no "floating" potential.)

A computer program product or Algorithm that the electronic interrupt unit or switches the semiconductor-based switching elements on and off at suitable times (instantaneous values of the mains voltage) and at the same time evaluates the measured current and voltage values in order to recognize that the electronic interruption unit is functional or is not functional. The control unit SE can (for this purpose) have a microcontroller. The computer program product can be executed on the microcontroller. The computer program product includes instructions which, when the program is executed by the microcontroller, cause the microcontroller to control the protective switching device, in particular to support the method according to the invention, in particular to carry it out.

The computer program product can be stored on a computer-readable storage medium, such as a CD-ROM, a USB stick or the like.

Furthermore, a data carrier signal that transmits the computer program product can exist.

A mechanical isolating contact unit is proposed, which cannot be switched on as long as the control unit does not send an “enable” release signal.

The point in time for switching the semiconductor-based switching elements (for checking) depends on the polarity of the mains voltage that is currently present, so that individual switching elements can be checked in a targeted manner. Furthermore, the instantaneous value of the voltage can be taken into account when selecting the point in time.

In particular are:

- the first period of time: very short to short, 10 ps to 1 s,

- the first voltage threshold: 5-10% of the effective value / RMS value of the nominal voltage or . applied AC voltage or the instantaneous value of the AC voltage; e.g. B. 10-20V,

- the second voltage threshold: less than 1 volt,

Summarized :

-Voltage measurement across the electronic interrupting unit or . Determination of the voltage drop across the electronic interruption unit EU (e.g. via a simple voltage divider), - High-impedance measurement impedance (preferably R and/or C) to determine the electrical potential between the electronic interruption unit and the mechanical isolating contact unit

- Voltage detection across the electronic interrupting unit is used to : Detect an alloyed or burned out condition of a power semiconductor

- Enabling the possibility of switching on the mechanical isolating contact unit after error-free testing of the electronic see interruption unit

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

Claims

34 patent claims

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

- a housing (GEH) with at least one mains-side connection and one load-side connection,

- A mechanical isolating contact unit (MK), which is connected in series with an electronic interrupting unit (EU), the mechanical isolating contact unit being assigned to the load-side connection and the electronic interrupting unit (EU) being assigned to the network-side connection,

- 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 current flow or a low-impedance state of the switching elements to current flow in the low-voltage circuit,

- a current sensor unit (S I) to determine the magnitude of the current in the low-voltage circuit,

- A control unit (SE), which is connected to the current sensor unit (SI), the mechanical isolating contact unit (MK) and the electronic interrupting unit (EU), with current and/or current time limit values being exceeded avoiding a current flow of the low-voltage circuit is initiated,

- That a measuring impedance is provided between two conductors of the low-voltage circuit, the measuring impedance being connected on the one hand to the connection between the mechanical isolating contact unit (MK) and the electronic interruption unit (EU),

- That the protective switching device is designed such that the functional test of the protective switching device with geöf fneten contacts of the mechanical isolating contact unit (MK) and high-impedance switched electronic interruption unit (EU) the electronic interruption unit (EU) for a 35 first period of time is switched to a low-impedance state.

2 . Protective switching device (SG) according to Patent Claim 1, characterized in that the protective switching device is designed in such a way that the magnitude of the voltage across the electronic interruption unit can be determined for a conductor.

3 . Protective switching device (SG) according to Patent Claim 2, characterized in that the protective switching device is designed in such a way that when the contacts of the mechanical isolating contact unit (MK) are open, the magnitude of the voltage across the electronic interruption unit is determined when the electronic interruption unit (EU) is switched to high resistance, such that at If the voltage falls below a first threshold value, a first fault condition is present, so that the electronic interruption unit is prevented from becoming low-impedance and/or the contacts are prevented from closing.

4 . Protective switching device (SG) according to Patent Claim 2 or 3, characterized in that when the electronic interruption unit (EU) is switched to the low-impedance state for the first period of time, the level of the voltage across the electronic interruption unit is determined, that when a second voltage threshold value is exceeded, a second Error condition is present, so that a further low resistance of the electronic interruption unit is avoided and/or closing of the contacts is avoided.

5 . Protective switching device (SG) according to Patent Claims 3 and 4, characterized in that the contacts of the mechanical isolating contact unit (MK) are prevented from closing when a fault condition is present, in particular no release signal (enable) is issued to the mechanical isolating contact unit (MK).

6. Protective switching device (SG) according to one of the preceding claims, characterized in that a control unit (SE) connected to the first voltage sensor unit (SUI) is provided, which measures the level of a first voltage between a grid-side connection point (EUG) and a load-side connection point ( EUL) of the electronic interruption unit (EU).

7. Protective switching device (SG) according to one of the preceding claims 1 to 5, characterized in that a second voltage sensor unit (SU2) connected to the control unit (SE) is provided, which measures the level of a second voltage between the network-side neutral conductor connection (NG) and the network-side phase conductor connection (LG) determines that a third voltage sensor unit (SU3) connected to the control unit is provided, which determines the level of a third voltage between the network-side neutral conductor connection (NG) and the load-side connection point (EUL) of the electronic interrupter unit (EU) in such a way that the protective switching device is designed in such a way is that the level of a first voltage between the network-side connection point (EUG) and the load-side connection point (EUL) of the electronic interruption unit (EU) is determined from the difference between the second and third voltage.

8. Protective switching device (SG) according to one of the preceding claims, characterized in that the current sensor unit (SI) is provided on the circuit side between the line-side phase conductor connection and the load-side phase conductor connection.

9. Protective switching device (SG) according to any one of the preceding claims, characterized in that the measurement impedance is an electrical resistor and / or capacitor.

10. Protective switching device (SG) according to one of the preceding claims, characterized in that the low-voltage circuit is a three-phase alternating current circuit and the protective switching device has a plurality of mains-side and load-side phase conductor connections, between which a contact of the mechanical isolating contact unit and electronic interruption units are provided, as well as, in particular first, Voltage sensor units are provided, with which the level of voltage across the respective electronic interruption unit can be determined.

11. Protective switching device (SG) according to one of the preceding claims, characterized in that the protective switching device (SG) is designed such that the contacts of the mechanical isolating contact unit (MK) can be opened by the control unit (SE), but cannot be closed.

12. Protective switching device (SG) according to one of the preceding claims, characterized in that the mechanical isolating contact unit (MK) can be operated by a mechanical handle in order to switch an opening of contacts or a closing of the contacts.

13. Protective switching device (SG) according to claim 12, characterized in that the mechanical isolating contact unit (MK) is designed such that closing the contacts through the 38 mechanical handling only after a release (enable), in particular a release signal, is possible.

14 . Protective switching device (SG) according to any one of the preceding claims, characterized in that with closed contacts of the mechanical isolating contact unit and low-impedance interruption unit and

- When a current is determined that exceeds a first current value, in particular that the first current value is exceeded for a first time limit, the electronic interruption unit becomes highly resistive and the mechanical isolating contact unit (MK) remains closed,

- When a current is determined which exceeds a second current value, in particular for a second time limit, the electronic interruption unit becomes highly resistive and the mechanical isolating contact unit (MK) is opened,

- When a current is determined that exceeds a third current value, the electronic interruption unit becomes highly resistive and the mechanical isolating contact unit (MK) is opened.

15 . Protective switching device (SG) according to one of the preceding claims, characterized in that the control unit (SE) has a microcontroller.

16 . Method for a protective switching device (SG) for protecting a low-voltage electrical circuit with:

- That the mechanical isolating contact unit (MK) through a 39

opening of contacts to avoid a current flow or closing of the contacts for a current flow in the low-voltage circuit can be switched,

- That the electronic interruption unit (EU) is switched to a low-impedance state for a first period of time for the function test of the protective switching device when the contacts of the mechanical isolating contact unit (MK) are open and the electronic interruption unit (EU) is switched to high resistance.

17 . Method according to Patent Claim 16, characterized in that when the contacts of the mechanical isolating contact unit (MK) are open and the electronic interruption unit (EU) is switched to high resistance, the level of the voltage across the electronic interruption unit is determined, that when the voltage falls below a first threshold value, a first error condition is present, so that a low resistance of the electronic interruption unit is avoided and/or closing of the contacts is avoided. 40

18 . Method according to Patent Claim 16 or 17, characterized in that when the electronic interruption unit (EU) is switched to the low-impedance state for the first period of time, the magnitude of the voltage across the electronic interruption unit is determined, that if a second voltage threshold value is exceeded, a second fault condition is present, so that a further low resistance of the electronic interruption unit is avoided and/or closing of the contacts is avoided.

19 . Method according to Patent Claims 17 and 18, characterized in that when an error condition is present, manual closing of the contacts by manipulating the mechanical isolating contact unit (MK) is avoided.

20 . Computer program product comprising instructions which, when the program is executed by a microcontroller, cause the latter to support, in particular carry out, the method according to one of claims 16 to 19 with a protective switching device according to one of claims 1 to 15.

21 . Computer-readable storage medium on which the computer program product according to claim 20 is stored.

22 . Data carrier signal carrying the computer program product according to claim 20 .