Overvoltage protection switch, low-voltage circuit and method for serial fault arcs

Abstract

Fire protection switch for a low-voltage circuit having a mains frequency for detecting serial arc faults, comprising: - a first sensor (SR1) for determining the level of the current (I) of the low-voltage circuit, - a control unit (SE) connected to the first sensor (SR1) which is designed to detect serial arc faults in the low-voltage electrical circuit and to emit an arc fault detection signal (FS) upon detection of an arc fault, characterized by that if the current (I) falls below a first threshold value (G1), a determination is made with regard to serial arc faults, When an arc fault is detected, an interruption lock is activated, If the current level (I) subsequently exceeds the first threshold value (G1) and the interruption lock is activated, no arc fault detection signal (FS) is emitted.

Description

[0001] The invention relates to a fire protection switch for serial arc faults according to the preamble of patent claim 1, a low-voltage circuit and a method for detecting serial arc faults according to the preamble of patent claim 14.

[0002] Low voltage refers to voltages up to 1000 volts AC or up to 1500 volts DC. Low voltage refers in particular to voltages higher than extra-low voltage, with values ​​of 25 or 50 volts AC or 60 or 120 volts DC. Low-voltage circuits, networks, or systems refer to circuits with rated currents of up to 125 amperes, more specifically up to 63 amperes.

[0003] A low-voltage circuit with a mains frequency refers, in particular, to alternating current circuits. Mains frequency refers to frequencies in the range 10 Hz to 1 kHz, particularly frequencies of 50 Hz, 60 Hz, 400 Hz, or 16 2 / 3 Hz. Frequencies of 50 Hz are used specifically in European low-voltage circuits and networks; 60 Hz is used in (US) American networks.

[0004] Arc faults are arcs that occur in the event of a fault, i.e., caused by faults in the electrical circuit. For example, due to poorly clamped or faulty connections in the electrical circuit, such as poorly clamped or poorly conductive contacts, e.g., in junction boxes, switches, or sockets in the low-voltage circuit.

[0005] This does not include (interference) arcs such as those that occur during regular operation of a network, e.g. when switching or on the brushes of a motor.

[0006] Serial arc faults refer to arcs that occur in the current path of the circuit, meaning that the current that also flows through a load, for example, flows through the arc. This means that if a current flows in a "nearly interrupted" conductor, a so-called serial arc fault occurs at the point of interruption.

[0007] In contrast, parallel arcs are not meant, ie arcs that occur between two conductors of an electrical circuit, ie when a (near) short circuit occurs with another conductor.

[0008] Arc fault devices are relatively new protective devices for electrical circuits or power grids and are used to detect arc faults. Such arc faults can be caused by poorly clamped electrical connections in distribution boxes or sockets, or by poor insulation and contacts. Arc fault devices can be used, in particular, in domestic installations such as fuse boxes to detect such faults. Upon detection of a fault, i.e., upon detection of an arc fault, e.g., due to an arc fault threshold being exceeded, they can initiate an interruption of the electrical circuit, interrupt the circuit themselves, or emit an arc fault detection signal.

[0009] In low-voltage circuit installations, AFDs are often installed for each feeder used to a consumer, often at the point of the feeder, such as in a fuse box. Typically, one AFD is used per feeder.

[0010] Fire protection devices operate using a variety of detection principles, methods, and techniques. The spectrum or noise generated by an arc fault, particularly in the high-frequency range, is often determined and evaluated. This often involves highly complex analyses.

[0011] In practice, the problem with parallel branches or parallel lines that are protected by different fire protection devices is that if there is a fault in one branch, the parallel line or the parallel branch also receives or is impressed with a fault arc spectrum (e.g. the high-frequency noise of the fault arc) due to crosstalk, which is detected by the parallel fire protection device and leads to the shutdown of an otherwise fault-free branch by the fire protection device.

[0012] This should be done by Fig. 1 and Fig. 2 will be explained in more detail. Fig. Figure 1 shows a low-voltage circuit with two conductors L, N, e.g., a phase conductor L and a neutral conductor N. It has a first branch with a first load LOAD1, to which the two conductors are connected, and a second branch with a second load LOAD2, to which the two conductors are also connected. An AFDD (fire protection device) is connected upstream or between the first load LOAD1. A MCB (circuit breaker) is connected upstream or between the second load LOAD2.

[0013] If a serial arc fault occurs in one of the two conductors to the first load LOAD1, this is detected by the fire protection device AFDD and can lead to a direct or indirect interruption of the electrical low-voltage circuit of this branch.

[0014] In the example, a single-phase alternating current network with two conductors is shown as the low-voltage circuit; the same applies to a three-phase alternating current network with 3 (phase) conductors or 3 (phase) conductors plus neutral conductor or other network types.

[0015] Fig. 2 shows an arrangement according to Fig. 1, with the difference that there is no (serial) arc fault in the conductors to the first load LOAD1; however, there is a (serial) arc fault in the conductors to the second load LOAD2. The lines of the two feeders are parallel, adjacent, or close to each other. Crosstalk couples the spectrum of the arc fault in the lines from the second load LOAD2 to the (fault-free) lines of the first load LOAD1. This is detected by the AFDD and leads to the interruption of the fault-free feeder to the first load LOAD1.

[0016] If the AFDD fire protection device is not yet switched on, but an arc fault is present in the second branch, this will be detected after the AFDD fire protection device is switched on and will trigger or issue an arc fault detection signal. This means that the first branch cannot be continuously supplied with power, even though it is essentially fault-free.

[0017] Chinese Patent Application Laid-Open CN 1 05 629 112 A discloses an arc fault detection device and method. The arc fault detection device consists of a dual-bus circuit, a Rogowski coil, a sensing resistor, a signal processing circuit, a microprocessor, a test circuit, an acousto-optic alarm circuit, and a key. The dual-bus circuit supplies power to the device. The Rogowski coil detects a current signal from the protected line and converts the current signal into a voltage signal via the sensing resistor. The signal processing circuit separates the voltage signal into a high-frequency signal and a power frequency signal. Finally, an envelope and a power frequency current waveform of a high-frequency signal are output to a microprocessor. The arc fault detection is performed by the microprocessor processing.If the microprocessor determines that the arc fault is an arc fault, the sound-light alarm circuit generates a sound-light alarm and uploads the alarm status via the dual bus circuit. The key is connected to the microprocessor, and the test circuit is connected between the Rogowski coil and the microprocessor.

[0018] German patent application DE 10 2016 209 445 A1 discloses an arc fault detection unit. The application relates to an arc fault detection unit for a low-voltage electrical circuit, comprising at least one voltage sensor for periodically determining electrical voltage values ​​(u(n), u(k)) of the electrical circuit. The sensor is connected to an evaluation unit configured to continuously sum a first half of a first number of voltage values ​​(u(n), u(k)) to a first partial sum (TS1) and the second half of voltage values ​​(u(n), u(k)) to a second partial sum (TS2), and to determine a difference (DU) between the two partial sums.Either the difference (DU) or the amount of the difference (DU) is compared with a first threshold value (SW1) and an arc fault detection signal (SLES) is emitted if this threshold value is exceeded, or the difference (DU) is compared with a second threshold value (SW2) and an arc fault detection signal (SLES) is emitted if this threshold value is undershot.

[0019] The American patent application US 2009 / 0 171 603 A1 discloses methods for detecting serial arcs in electrical signals. A method for detecting a serial arc fault in an AC signal is provided.A method for detecting a series arcing fault in an AC signal comprises: a) calculating discrete wavelet coefficients using a current signal as input for calculating the discrete wavelet coefficients and outputting an output signal filtered for the discrete wavelet coefficients; b) subsampling the output signal filtered for the discrete wavelet coefficients and outputting a subsampled output signal; c) calculating critical variables from the subsampled output signal; d) determining, based on the critical variables, whether a series arcing fault is present in the current signal; and e) outputting a signal indicating the presence of a series arcing fault in the current signal when substantially all critical variables satisfy a predetermined criterion.

[0020] The object of the present invention is to improve a fire protection switch, in particular to enable a supply of a circuit when arc fault crosstalk could occur due to lines lying in parallel.

[0021] This object is achieved by a fire protection switch having the features of patent claim 1, a low-voltage circuit according to patent claim 13 or a method having the features of patent claim 14.

[0022] According to the invention, a fire protection switch for a low-voltage circuit having a mains frequency for detecting serial arc faults comprises: - a first sensor for determining the current level of the low-voltage circuit, - a control unit connected to the first sensor, which is designed such that serial arc faults in the low-voltage electrical circuit are detected and an arc fault detection signal is emitted upon detection of an arc fault.

[0023] If the current falls below a first threshold value, a determination is made regarding serial arc faults, When an arc fault is detected, an interruption lock is activated, If the first current threshold is subsequently exceeded and the interruption lock is activated, no arc fault detection signal is emitted.

[0024] This advantageously prevents arc fault signals present in the low-voltage circuit of the fire protection switch from being detected by crosstalk before the fire protection switch is switched on or before a current flows in the low-voltage circuit of the fire protection switch, and also prevents the circuit from being interrupted by the fire protection switch after it has been switched on or a consumer has been connected due to false detections caused by crosstalk.

[0025] Advantageous embodiments of the invention are specified in the subclaims.

[0026] In an advantageous embodiment of the invention, if the first threshold value of the current level is exceeded, the interruption lock is deactivated if an arc fault is not detected for a first period of time.

[0027] This has the particular advantage that once the crosstalk has been eliminated, the interruption lock is deactivated and the fire protection switch is again available with its full monitoring function.

[0028] In an advantageous embodiment of the invention, the mains frequency range is defined by a frequency in the range 10 Hz to 1 kHz, in particular by a mains frequency of 50 or 60 Hz.

[0029] This has the particular advantage of enabling improved detection of arc faults, particularly in alternating current networks.

[0030] In an advantageous embodiment of the invention, the first sensor determines the level of the current in the range of the mains frequency.

[0031] This has the particular advantage of enabling particularly precise determination of the current level in the relevant range, for example by using a filter.

[0032] In an advantageous embodiment of the invention, a second sensor is provided for determining the level of levels in a high-frequency range of the low-voltage circuit, which is connected to the control unit. The second sensor (SR2) determines, in particular, a voltage, current, or power as a level in the high-frequency range.

[0033] This has the particular advantage that the use of two or a second sensor enables a more precise detection of arc faults.

[0034] In an advantageous embodiment of the invention, the high-frequency range is defined by a range from 10 kHz to 50 MHz, in particular by a range from 30 kHz to 30 MHz, and more specifically by frequencies in the range around 2 MHz. This has the particular advantage of enabling particularly good detection of arc faults.

[0035] In an advantageous embodiment of the invention, an arc fault event is defined by: 1. the exceeding of a first threshold value of the current level in the mains frequency range; 2. the exceeding of a second threshold value of the level in the high frequency range and 3. the exceeding of a third threshold value of the derivative of the level in the high frequency range with respect to time.

[0036] This has the particular advantage of enabling simple and reliable detection of arc fault events or arc faults.

[0037] In an advantageous embodiment of the invention, a third sensor is provided for determining the voltage level, particularly in the mains frequency range, of the low-voltage circuit, which is connected to the control unit. This has the particular advantage of enabling precise determination of the voltage level.

[0038] In an advantageous embodiment of the invention, if the current falls below the first threshold value, an arc fault event is defined by: 1. the exceeding of a voltage threshold of the level of the voltage in the range of the network frequency; 2. the exceeding of the second threshold value of the level in the high frequency range and 3. the exceeding of the third threshold value of the derivative of the level in the high frequency range with respect to time.

[0039] This has the particular advantage of enabling detection of an arc fault event when no current or only a very low current is flowing. In this case, the invention uses the presence of a voltage instead of the current for arc fault detection.

[0040] Thus, if the fire protection switch has not yet been switched on or, for example, there is no consumer, it can be concluded that there are arc fault signals on the - actually inactive - line that were coupled in by crosstalk, and switching off the fire protection switch after it has been switched on or, for example, the consumer has been connected can be avoided.

[0041] In an advantageous embodiment of the invention, each arc fault event, particularly one that occurs consecutively, is integrated or summed (over time) to form an arc fault sum. If an arc fault limit is exceeded, an arc fault detection signal is emitted.

[0042] This has the particular advantage that an arc fault detection signal is only emitted when several consecutive arc fault events occur, thus avoiding false tripping due to a random arc fault event.

[0043] In an advantageous embodiment of the invention, the integration speed during integration depends on the level of the current in the mains frequency range, in particular that integration is faster at higher currents.

[0044] This has the particular advantage that a faster interruption of the electrical circuit is initiated, especially at higher currents, which have a higher potential for damage.

[0045] In an advantageous embodiment of the invention, an interruption unit is provided which interrupts the current flow in the low-voltage circuit when an arc fault detection signal is present.

[0046] This has the particular advantage that if an arc fault detection signal is present, the low-voltage circuit is interrupted.

[0047] In an advantageous embodiment of the invention, the fire protection switch has a housing.

[0048] The interruption unit can be arranged within the housing, so that a compact switch is advantageously provided.

[0049] The interruption unit can be located outside the housing of the fire protection switch. It can, for example, be part of another switch, such as a miniature circuit breaker or residual current device, allowing an existing network to be retrofitted with a fire protection switch function without wasting unnecessary installation space. The arc fault detection signal can be transmitted to the interruption unit or is transmitted to the interruption unit.

[0050] In an advantageous embodiment of the invention, the fire protection switch is arranged in a first branch of the low-voltage circuit. In an advantageous embodiment of the invention, lines of a second branch of the low-voltage circuit are arranged at least partially parallel to the first branch.

[0051] This has the particular advantage that it enables reliable detection of arc faults, particularly when there are multiple branches, and thus cables can be laid close together.

[0052] According to the invention, a low-voltage circuit comprising a fire protection switch according to the invention is also claimed.

[0053] According to the invention, a method is also claimed in parallel, in which serial arc faults are detected in an electrical low-voltage circuit and an arc fault detection signal is emitted upon detection of an arc fault.

[0054] If the current in the low-voltage circuit falls below a first threshold, a detection for serial arc faults is performed. If an arc fault is detected, an interruption lockout is activated. If the current subsequently exceeds the first threshold and the interruption lockout is activated, no arc fault detection signal is emitted.

[0055] All embodiments, both in dependent form referring back to the independent patent claims and referring back only to individual features or combinations of features of patent claims, result in an improvement of a fire protection switch.

[0056] The described properties, features and advantages of this invention and the manner in which they are achieved will become clearer and more clearly understandable in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0057] The drawing shows: Fig. 1 a first representation of a low-voltage circuit to explain the invention, Fig. 2 a second representation of a low-voltage circuit to explain the invention, Fig. 3 a first representation of signal curves, Fig. 4 a second representation of signal curves, Fig. 5 a third representation of signal curves, Fig. 6 a fourth representation of signal curves, Fig. 7 a fifth representation of signal curves, Fig. 8 a first block diagram of a fire protection switch, Fig. 9 a second block diagram of a fire protection switch, Fig. 10 a third block diagram of a fire protection switch, Fig. 11 a fourth block diagram of a fire protection switch.

[0058] Fig. 1 and Fig. 2 shows a schematic diagram of a low-voltage circuit with two branches, as explained above.

[0059] Fig. Figure 3 shows five signal curves over time. From top to bottom: 1. The course of the electric current I in a low-voltage circuit, for example in the first branch with the load LOAD1 according to Fig. 1.

[0060] The first section shows a fault-free case with a sinusoidal current I.

[0061] The second section shows a fault case with a series arc fault, which has an only approximately sinusoidal current I.

[0062] A first threshold value G1 is shown, each as a positive or negative threshold value of the same amount

[0063] In one embodiment of the invention, an arc fault is detected or an arc fault event occurs only when this (positive or negative) first threshold value G1 is exceeded. The first threshold value G1 can, for example, be 1 A, in the range around 1 A, or have a value in the range of 500 mA to 5 amperes.

[0064] 2. The RSSI level curve in the high-frequency range. The first section again shows the error-free case, with a low level. The second section again shows the error case, with a high level. A second threshold value G2 is shown.

[0065] In one embodiment of the invention, an arc fault detection or an arc fault event only occurs when this second threshold value G2 is exceeded.

[0066] The RSSI level can be a voltage, a current, a power, or an equivalent. It can be a direct level or a logarithmized level. For example, it can be the level at a specific frequency in the high-frequency range, or the level in a specific frequency range, i.e., a certain bandwidth at a frequency, in the high-frequency range.

[0067] For example, this could be the level at a frequency of 2 MHz with a bandwidth of 300 kHz. For example, the second threshold could be in the range of 300 mV to 1 volt.

[0068] The second threshold G2 can be a relative threshold, ie the height changes, for example depending on the noise or noise level on the line.

[0069] 3. The course of the first derivative of the level RSSI in the high frequency range over time dRSSI / dt.

[0070] The first section again shows the error-free case, where the time derivative has a value of zero. The second section again shows the error case, with peaks similar to a Dirac pulse at the edges of the RSSI level.

[0071] A third threshold G3 is shown, each as a positive or negative (-G3) threshold of the same amount.

[0072] In one embodiment of the invention, an arc fault detection or an arc fault event only occurs when this (positive or negative) third threshold value G3 is exceeded.

[0073] The third threshold value G3 can, for example, be 5000 volts / s.

[0074] 4. The course of an arc fault event Arc detector, which in this example is composed of the sum of the exceedance of the first threshold value G1 (the level of current I in the mains frequency range); the exceedance of the second threshold value G2 of the level RSSI in the high frequency range and the exceedance of the third threshold value G3 of the derivative of the level RSSI in the high frequency range with respect to time dRSSI / dt, for each half-wave of the electrical current I.

[0075] The first section again shows the fault-free case, where no pulses from an arc fault event are present. The second section again shows the fault case, with (continuous) pulses for an arc fault event.

[0076] 5. The arc fault sum curve (fault integrator), where, in the example, each arc fault event is integrated or summed to form an arc fault sum. An arc fault limit value G4 or fourth threshold value G4 is provided, which, if exceeded, triggers an arc fault detection signal.

[0077] In the example, an arc fault event must occur five times before the arc fault limit G4 or fourth threshold G4 is reached and an arc fault detection signal is issued.

[0078] The integration speed can depend on the magnitude of the current I. Alternatively, the arc fault limit G4 can depend dynamically on the magnitude of the current.

[0079] For example, an arc fault detection signal can be delivered within 800 ms (slow integration speed) at a current of 2.5 A. At a current of 16 A, it can be delivered within 100 ms (fast integration speed).

[0080] Fig. 4 shows a representation according to Fig. 3, with the difference that although an arc fault event is present or detected, it is caused by a level that results from crosstalk from another faulty line, for example according to Fig. 2, and is coupled into an undisturbed line.

[0081] Fig. 4 is identical to Fig. 3, with the difference that the current waveform I is sinusoidal in both sections.

[0082] Fig. 5 shows a representation according to Fig. 4, with the difference that a level RSSI in the high frequency range and consequently also the derivative of the level with respect to time RSSI / dt by crosstalk are present before the flow of an electric current in the mains frequency range of the low voltage circuit.

[0083] When the fire protection switch is switched on or a consumer is switched on, marked by the Switched load section, a current flows in the mains frequency range of the low-voltage circuit, consequently arc fault events are present from this point onwards, consequently an integration or summation of the arc fault events Arc detector takes place to form a fault arc sum Fault integrator, whereby when the arc fault limit value G4 is reached, an arc fault detection signal is emitted which, for example, leads to an interruption of the electrical circuit.

[0084] This would interrupt the low-voltage circuit shortly after switching on. Switching it on again would lead to the same result. A power supply would not be guaranteed.

[0085] Fig. 6 shows a representation according to Fig. 5, with the difference that the curve of the electrical voltage U over time is shown first. According to the invention, in order to detect an arc fault before switching on, ie before an electrical current flows or before the first threshold value G1 of the current I is exceeded in the range of the mains frequency, the voltage U or the exceeding of the voltage threshold value G5 or fifth threshold value G5, which is shown as a positive or negative (-G5) threshold value of the same amount, is used to detect an arc fault event instead of the current I.

[0086] This means that if the voltage threshold G5 or fifth threshold is exceeded, the second threshold G2 of the RSSI level in the high frequency range is exceeded and the third threshold G3 of the RSSI level derivative in the high frequency range is exceeded after the time dRSSI / dt, an arc fault event occurs (before switching on or before exceeding the first threshold of the current level).

[0087] In such a case, when the arc fault limit (G4) is reached, an arc fault detection signal is suppressed (SW-Trip) and an interruption lock (Trip disable) is activated. The history of the interruption lock value is shown in Fig. 6 shown at the bottom.

[0088] If the current is switched on or the first threshold value G1 is exceeded while the interruption lock is present, an arc fault detection signal is suppressed.

[0089] Cyclic checks can advantageously be performed to determine whether arcing faults are present or whether the arcing fault limit G4 is reached. In this case, the interruption lockout remains active.

[0090] Only when there are no more arc fault events or the arc fault limit value G4 is no longer reached or the arc fault limit value G4 is no longer reached after an initial time period t1, the integration or summation integrator reset is reset, and the interruption lock Trip disable is deactivated at the time Trip enabled.

[0091] This is in Fig. 7 shown. Fig. 7 shows a representation according to Fig. 6, with the difference that the voltage U and current I curves continue, but the RSSI level and, consequently, their derivative RSSI / dt are no longer available from a certain point in time. Consequently, from this point onward, arc fault events are no longer present, the arc fault limit is not reached, and after an initial time period t1, the integration or summation is reset (“Integrator reset”). In parallel, the Trip disable interlock is deactivated at the Trip enabled time. This means that from this point onward, the AFD operates in its normal mode.

[0092] Fig. 8 shows a first block diagram of a fire protection switch to explain the invention. Fig. 8 shows two conductors L, N of a low-voltage circuit passing through a fire protection switch AFD to the load LOAD1, analogous to Fig. 1. At least one of the two conductors L, N is assigned a first sensor SR1 for determining the level of current I in the mains frequency range of the low-voltage circuit, and a second sensor SR2 for determining the level of levels RSSI in a high-frequency range of the low-voltage circuit.

[0093] The two sensors SR1, SR2 are connected to a control unit SE, which determines the presence of serial arc faults and, if arc faults are present, outputs an arc fault detection signal FS at an output.

[0094] The control unit SE can have further components, such as a central computer unit MCU, analog-digital converters ADU1, ADU2, and / or filters FI1, FI2.

[0095] The filters FI1, FI2 can perform low-pass, high-pass, and / or band-pass filtering to limit or adapt the signals from the sensors SR1, SR2.

[0096] The sensor signals, which may have been filtered in this way, can be converted from analog to digital and are further processed / evaluated by the MCU computer unit.

[0097] The sensors SR1, SR2 and the control unit SE can be arranged in a first housing GEH1. Similarly, a third sensor SR3 (not shown) can be provided for determining the voltage level, particularly in the mains frequency range of the low-voltage circuit, which is connected to the control unit SE.

[0098] Fig. 9 shows a block diagram according to Fig. 8, with the difference that conductors L and N have an interruption unit UE for interrupting the conductors of the circuit. The arc fault detection signal FS is transmitted from the control unit SE to the interruption unit UE, so that the circuit is interrupted in the event of an arc fault.

[0099] Furthermore, the sensors SR1, SR2, the control unit SE and the interruption unit UE are shown as separate components that are connected to each other by lines.

[0100] Fig. 10 shows a block diagram according to Fig. 9, with the difference that the sensors SR1, SR2, the control unit SE, and the interruption unit UE are housed in a housing GEH2. This creates a compact device in which all components are located. This device in the housing GEH2 could be the fire protection switch AFDD according to Fig. 1 or Fig. 2 be.

[0101] Fig. 11 shows an arrangement according to Fig. 10, with the difference that the interruption unit UE is arranged externally, ie outside the housing GEH2.

[0102] Only the sensors SR1, SR2 and the control unit SE are arranged in a housing GEH3.

[0103] The interruption unit UE can be a stand-alone component to which the arc fault detection signal FS is supplied. The interruption unit UE can also be part of another switch, switching device, or circuit breaker, such as a miniature circuit breaker or residual current device, which is triggered by the arc fault detection signal FS, i.e., interrupts the circuit.

[0104] In the following, the invention is explained in more detail in further embodiments in other words.

[0105] The current in the mains frequency range (50 or 60 Hz) must preferably exceed a first threshold G1. The RSSI level must preferably exceed a second threshold G2. It is assumed that an arc fault generates high levels. Furthermore, it is assumed that the arc fault rise occurs very quickly, typically less than 1 µs. This means that the level derivative must preferably be greater than a third threshold G3, both at the beginning and end of the arc fault. All of these criteria are met during an arc fault in one half-wave of the mains frequency.

[0106] To avoid nuisance tripping, these arc fault events can be integrated until an arc fault limit or fourth threshold is reached, i.e., the fault situation has persisted long enough. In this case, an arc fault detection signal is generated, which can be used directly or indirectly to interrupt the circuit.

[0107] In most electrical installations, cables from different branches are bundled together or are located in close proximity. This allows crosstalk or coupling of signals or interference from one cable to another, see Fig. 2.

[0108] If an arc fault is generated in another feeder, its level may be detected in the feeder protected by an AFD.

[0109] The fire protection switch may be triggered incorrectly.

[0110] A similar situation can occur with a consumer that generates (disturbing) high-frequency levels.

[0111] The invention is based on the idea of ​​checking whether there is a (high-frequency) disturbance that resembles an arc fault event, but where no load current is flowing. To detect this, the (mains) voltage is used instead of the current. The voltage is always present, and its shape is sinusoidal, so it can be used to simulate a current signal and enable the detection of arc faults.

[0112] In the positive case, this does not lead to the emission of an arc fault detection signal or interruption of the circuit, but to its suppression.

[0113] If this arc fault event no longer occurs, e.g. for a certain period of time, the fire protection device returns to its normal mode.

[0114] The controller can have a microprocessor or be microprocessor-controlled. The processes can be performed in the microprocessor or its peripheral components.

[0115] Although the invention has been illustrated and described in detail by the embodiment, the invention is not limited by the disclosed examples and other variations can be derived therefrom by a person skilled in the art without departing from the scope of the invention.

Claims

[1] Fire protection switch for a low-voltage circuit having a mains frequency for detecting serial arc faults, comprising: - a first sensor (SR1) for determining the level of the current (I) of the low-voltage circuit, - a control unit (SE) connected to the first sensor (SR1) which is designed to detect serial arc faults in the low-voltage electrical circuit and to emit an arc fault detection signal (FS) upon detection of an arc fault, characterized by , that if the current (I) falls below a first threshold value (G1), a determination is made with regard to serial arc faults, When an arc fault is detected, an interruption lock is activated, If the current level (I) subsequently exceeds the first threshold value (G1) and the interruption lock is activated, no arc fault detection signal (FS) is emitted. [2] Fire protection switch according to claim 1, characterized by that when the first threshold value (G1) of the current (I) is exceeded, the interruption lock is deactivated if an arc fault is not detected for a first time period (t1). [3] Fire protection switch according to one of the preceding claims, characterized by that the mains frequency range is defined by a frequency in the range 10 Hz to 1 kHz, in particular by a mains frequency of 50 or 60 Hz. [4] Fire protection switch according to one of the preceding claims, characterized by that the first sensor (SR1) determines the level of the current (I) in the range of the mains frequency. [5] Fire protection switch according to one of the preceding claims, characterized by , that a second sensor (SR2) is provided for determining the level (RSSI) in a high-frequency range of the low-voltage circuit, which is connected to the control unit (SE), that the second sensor (SR2) determines, in particular as a level, a voltage, a current or a power in the high-frequency range. [6] Fire protection switch according to claim 5, characterized by that an arc fault event is defined by:

1. the exceeding of a first threshold value (G1) of the current level (I) in the range of the mains frequency; 2. the exceeding of a second threshold value (G2) of the level (RSSI) in the high frequency range and 3. the exceeding of a third threshold value (G3) of the derivative of the level (RSSI) in the high frequency range with respect to time (dRSSI / dt). [7] Fire protection switch according to one of the preceding claims, characterized bythat a third sensor (SR3) is provided for determining the level of the voltage (U), in particular in the mains frequency range, of the low-voltage circuit which is connected to the control unit (SE). [8] Fire protection switch according to claim 7, characterized by that if the current (I) falls below the first threshold value (G1), an arc fault event is defined by:

1. the exceeding of a voltage threshold value (G5) of the voltage level (U) in the range of the mains frequency; 2. the exceeding of the second threshold value (G2) of the level (RSSI) in the high frequency range and 3. the exceeding of the third threshold (G3) of the derivative of the level (RSSI) in the high frequency range with respect to time (dRSSI / dt). [9] Fire protection switch according to claim 6 or 8, characterized bythat each arc fault event is integrated or summed to form a fault integrator, and if an arc fault limit (G4) is exceeded, an arc fault is detected. [10] Fire protection switch according to claim 9, characterized by that during integration the integration speed depends on the level of the current in the range of the mains frequency, in particular that integration is faster at higher currents. [11] Fire protection switch according to one of the preceding claims, characterized by that an interruption unit (UE) is provided which interrupts the current flow in the low-voltage circuit when an arc fault detection signal (FS) is present. [12] Fire protection switch according to claim 11, characterized bythat the fire protection switch has a housing and the interruption unit (UE) is arranged inside or outside the housing, in particular in the case of an external interruption unit, the arc fault detection signal (FS) can be transmitted to the interruption unit. [13] Low-voltage circuit comprising a fire protection switch according to one of claims 1 to 12. [14] Method in which serial arc faults are detected in a low-voltage electrical circuit and an arc fault detection signal (FS) is emitted when an arc fault is detected, characterized by , that if the current (I) in the low-voltage circuit falls below a first threshold value (G1), a determination is made with regard to serial arc faults, When an arc fault is detected, an interruption lock is activated, If the current level (I) subsequently exceeds the first threshold value (G1) and the interruption lock is activated, no arc fault detection signal (FS) is emitted. [15] Method according to claim 14, characterized by that when the first threshold value (G1) of the current (I) is exceeded, the interruption lock is deactivated if an arc fault is not detected for a first time period (t1).

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