DE102017208851A1 - Störlichtbogenerkennungseinheit - Google Patents

Abstract

The invention relates to an arc fault detection unit for an electrical circuit, comprising: an inductance, a photodiode, both connected to a control unit and configured such that the voltage generated in the inductance and the photodiode is monitored so that when exceeded a first limit value of the voltage of the inductance at a first time or a first rise limit value of the time increase of the voltage of the inductance at the first time and on exceeding a second limit value of the voltage of the photodiode at a subsequent second time or a second rise limit value the voltage of the photodiode at the subsequent second time an arcing fault detection signal is emitted.

Description

The invention relates to an arc fault detection unit, an arc fault sensor and a method for arc fault detection, each for an electrical circuit.

By electrical circuit is meant in particular medium-voltage and / or low-voltage circuits.
Electrical low-voltage circuit in particular circuits are meant that have voltages up to 1000 volts AC or 1500 volts DC; in particular these voltages are usually greater than the low voltage, with values of 25 volts or 50 volts AC and 60 volts or 120 volts DC.
By circuit is meant in particular circuits with turn-off currents of 63 amperes to 6300 amps, more specifically of 63 or 125 amps to 630 amperes or 1600 amperes, and of 630 amperes or 1200 amperes to 6300 amps.
By turn-off currents is meant the current at which the electrical circuit is usually interrupted, for example by a protective device, such as a circuit breaker.
With circuit breaker particular compact circuit breaker respectively Molded Case Circuit Breaker, short MCCB, or open circuit breaker respectively Air Circuit Breaker, short ACB meant.

Circuit breakers are protective devices that function in a similar way to a fuse. Circuit breakers monitor the current flowing through them through a conductor and interrupt the electrical current to an energy sink, or consumer, which is referred to as tripping, when protection parameters such as current limits or current-time-out limits, i. if a current value exists for a certain period of time, be exceeded. The interruption occurs, for example, through contacts of the circuit breaker, which are opened.

With circuit breaker according to the invention, in particular circuit breaker with a control unit, such as an electronic trip unit, also referred to as Electronic Trip Unit, short ETU, meant. The control unit monitors the level of the electric current measured by sensors, such as Rogowski coils, or additionally in an analogous manner to the voltage or / and other parameters of the electrical circuit and causes an interruption of the electrical circuit.

One problem is so-called arcing faults in an electrical circuit, such as an electrical system. By arcs arcs are meant, as they occur in electrical circuits in the circuit or in the system. For example, these can be caused by short circuits or bad connections.

Switching arcs, as they occur during electrical switching, especially at the contacts, are not meant.

For the operation of an electrical system, it is very advantageous to detect such arcing faults (fast) and possibly interrupt the electrical circuit to prevent further damage.

These fault arcs based on faults or faults are produced by ionization of a gas (usually air) by means of an electrical discharge between electrodes of different potential or phase position, or between an electrode and earth or earth potential.

If a current flows in a "nearly interrupted" phase conductor, a so-called serial arc occurs at the point of interruption.

If a (fast) short circuit with another phase conductor occurs, it is referred to as a parallel arc fault.
Parallel arcing faults may be caused, for example, by aging of the insulating material or presence of conductive contamination between phase conductors. They can occur between two different phase conductors, between phase conductors (L) and ground conductors (PE), or between phase conductors and neutral conductors (N).

If an arc represents the characteristics of a parallel and a serial arc, this is called a combined arc fault. When talking about phase, ground or neutral conductors, this not only applies to the conductors, but also to all system components with the same potential as the phase, earth or neutral conductors.

Interruption arcs create a faulty connection between the system components (conductors) of different potential.

A fault arc gives off a great deal of energy to the environment, in particular heat and radiation of a very high intensity. In addition, macroscopic and physical effects such as dielectric loss, pressure wave, chemical reaction and high frequency wave occur.

Therefore, very large destructive effects and personal danger emanate from him (including fire hazard).
The early detection of an arc and, if possible, the erasure of a destruction phase is a challenge for condition monitoring and the protection system of electrical installations.

Individual arc fault detection solutions have been proposed, but there is still the problem of reliable detection of arcing faults. That the detection reliability (probability that it is actually an arc) of arcing faults, the avoidance of false tripping and an improvement in the detection time are still a problem.

In order to avoid the destructive effects of arcing faults, suitable components are selected, as well as a clean installation and regular checks of the entire system. In particular, corresponding standards have been adopted in the areas of protection technology and safety of electrical installations. These standards are regularly adjusted by committees. Furthermore, appropriate test procedures are prescribed.

The object of the present invention is to improve the detection of arcing faults, in particular to achieve high detection reliability and fast detection time.

This object is achieved by an arc fault detection unit having the features of patent claim 1, an arc fault sensor according to claim 11 and a method having the features of patent claim 12.

• - eine Induktivität,
• - eine Photodiode,

die beide mit einer Steuereinheit verbunden sind und die derart ausgestaltet ist, dass
die in der Induktivität und der Photodiode erzeugte Spannung dahingehend überwacht wird, dass bei Überschreitung:

1. a) eines ersten Grenzwertes der Spannung der Induktivität zu einem ersten Zeitpunkt oder eines ersten Anstiegs-Grenzwertes des zeitlichen Anstieges der Spannung der Induktivität zum ersten Zeitpunkt, und bei Überschreitung
2. b) eines zweiten Grenzwertes der Spannung der Photodiode zu einem nachfolgenden zweiten Zeitpunkt oder eines zweiten Anstiegs-Grenzwertes der Spannung der Photodiode zum nachfolgenden zweiten Zeitpunkt ein Störlichtbogenerkennungssignal abgegeben wird.

Die Induktivität, die beispielsweise vorteilhaft als Spule, Luftspule oder Spule in SMD-Ausführung ausgeführt sein kann, und die Photodiode sind hierbei im Bereich des elektrischen Stromkreises, insbesondere der elektrischen Leiter angeordnet.
Die Induktivität und die Photodiode erfassen erfindungsgemäß einerseits das elektrische Feld eines Störlichtbogens (Induktivität) und andererseits die, gegebenenfalls kurzzeitige, Lichtstrahlung des Störlichtbogens (Photodiode).
Nur wenn beide nacheinander auftreten und deren Werte bzw. deren Äquivalente, wie beispielsweise die erzeugte elektrische Spannung, gewisse Grenzwerte überschreiten, wird ein Störlichtbogenerkennungssignal abgegeben.
Der Vorteil liegt in einer genauen und sicheren Erkennung von Störlichtbögen, wobei Fehlauslösungen durch die Kombination mehrere Kriterien (zwei unterschiedliche physikalische Größen, zeitlich nacheinander, zwei Grenzwerte überschritten) vermieden werden.According to the invention, a novel combination of optical detection and electrical field measurement is proposed, as well as the evaluation of the signal characteristics. For this purpose, an arc fault detection unit for an electrical circuit is proposed, comprising:

• an inductance,
• a photodiode,

both connected to a control unit and configured such that
the voltage generated in the inductor and the photodiode is monitored so that when exceeded:

1. a) a first limit value of the voltage of the inductance at a first time or a first rise limit value of the time increase of the voltage of the inductance at the first time, and when exceeded
2. b) a second threshold value of the voltage of the photodiode at a subsequent second time or a second increase threshold value of the voltage of the photodiode at the subsequent second time an arcing fault detection signal is emitted.

The inductance, which can be advantageously embodied, for example, as a coil, air coil or coil in SMD design, and the photodiode are arranged in the region of the electrical circuit, in particular the electrical conductor.
According to the invention, the inductance and the photodiode detect, on the one hand, the electric field of an arc fault (inductance) and, on the other hand, the, possibly short-term, light radiation of the arc fault (photodiode).
Only when both occur in succession and their values or their equivalents, such as the generated electrical voltage, exceed certain limits, a Störlichtbogenerkennungssignal is emitted.
The advantage lies in an accurate and reliable detection of arcs, whereby false tripping by the combination of several criteria (two different physical quantities, one after the other, two limits exceeded) are avoided.

Advantageous embodiments are specified in the subclaims.

1. a) des ersten Grenzwertes oder ersten Anstiegs-Grenzwertes und
2. b) des zweiten Grenzwertes oder zweiten Anstiegs-Grenzwertes überwacht.

Dies hat den besonderen Vorteil, dass zum einen nur zwei Leitungen für die Übertragung der Meßsignale / Spannungen erforderlich sind. Zum anderen, dass nur die Auswertung eines Signal- bzw. Spannungsverlaufs in der Steuereinheit erfolgen muss, wodurch die Übertragung und Auswertung vereinfacht wird.In an advantageous embodiment of the invention, the inductor and the photodiode are electrically connected in parallel. The sum voltage of the inductance and the photodiode becomes excessive

1. a) the first limit or first rise limit and
2. b) of the second limit or second rise limit.

This has the particular advantage that on the one hand only two lines for the transmission of the measuring signals / voltages are required. On the other hand, that only the evaluation of a signal or voltage curve in the control unit must be made, whereby the transmission and evaluation is simplified.

In an advantageous embodiment of the invention, an arcing fault detection signal is emitted only if, between the first and second times, the voltage of the inductance or the sum voltage falls below a third limit value.
This has the particular advantage that a further criterion for the detection of arcing faults is used, a higher detection reliability achieved and the probability of false triggering is reduced.

In an advantageous embodiment of the invention, the inductor and / or the photodiode, a resistor is connected in parallel.
This has the particular advantage that the current caused by the photodiode (current source) can be measured directly as a voltage (in the range of a few hundred millivolts).

In an advantageous embodiment of the invention, the electrical current is determined in the electrical circuit and a Störlichtbogenerkennungssignal only delivered when also the current or the temporal change in current exceeds a fourth limit.

This has the particular advantage that a further criterion for the detection of arcing faults is used, whereby a higher detection reliability is achieved and the probability of false triggering is reduced.

In an advantageous embodiment of the invention, the first and second times have a time interval of less than 5, in particular less than 4, microseconds. This has the particular advantage that
This has the particular advantage that the arc detection is narrowed down more accurately, resulting in faster detection, higher detection reliability and reduces the likelihood of false triggering.

In an advantageous embodiment of the invention, the inductance is designed as a coil. In particular, as a planar coil, flat coil or air coil, for example, in a printed circuit board integrated form or as an SMD component.
This has the particular advantage that a simple realization of an inductance is given.

In an advantageous embodiment of the invention, the electrical circuit is a low-voltage circuit.
This has the particular advantage that, in particular for low-voltage circuits, a safer possibility for arc fault detection is provided.

In an advantageous embodiment of the invention, the fault arc detection signal is supplied to a circuit breaker of the electrical circuit.
This has the particular advantage that a quick shutdown of the electrical circuit can be done. Furthermore, that a circuit breaker is extended by a functionality.

In an advantageous embodiment of the invention, the fault arc detection signal is fed to a short circuit of the electrical circuit.
This has the particular advantage that a particularly fast shutdown of the electrical circuit can take place, ie a shutdown, which is usually faster than a circuit breaker.
The primary goal can be the immediate shutdown of a developing arc. A short circuit with a short circuiter can occur in less than a microsecond.

As a result of other protective devices, the much less critical short circuit is detected and disconnected.

According to the invention, the inductance and the photodiode can be combined as a unit in a separate housing. The control unit is arranged spatially separated. Both can be connected to each other via an electrical line, such as a two-wire or coaxial line. The control unit may be arranged on or in a circuit breaker.
This has the particular advantage that a sensor according to the invention is given, which can be arranged in a small design in the vicinity of the electrical circuit or in the system, with an arc detection can be realized even in confined spaces.

1. a) eine elektrische oder magnetische Feldkomponente erfasst wird, insbesondere in eine, beispielsweise proportionale, erste Spannung umgewandelt wird,
2. b) eine optische Komponente erfasst wird, insbesondere in eine, beispielsweise proportionale, zweite Spannung umgewandelt wird, die Spannungen einzeln oder als Summenspannung dahingehend überwacht werden, dass bei Überschreitung:
3. c) eines ersten Grenzwertes der ersten Spannung zu einem ersten Zeitpunkt oder eines ersten Anstiegs-Grenzwertes des zeitlichen Anstieges der ersten Spannung zum ersten Zeitpunkt und bei Überschreitung
4. d) eines zweiten Grenzwertes der zweiten Spannung zu einem nachfolgenden zweiten Zeitpunkt oder eines zweiten Anstiegs-Grenzwertes der zweiten Spannung zum nachfolgenden zweiten Zeitpunkt ein Störlichtbogenerkennungssignal (SLES) abgegeben wird.

The invention further provides a method for detecting an arc fault in an electrical circuit, in which

1. a) an electrical or magnetic field component is detected, in particular converted into an, for example, proportional, first voltage,
2. b) an optical component is detected, in particular in a, for example, proportional, second voltage is converted, the voltages are monitored individually or as a sum voltage to the effect that when exceeded:
3. c) a first limit value of the first voltage at a first time or a first rise limit value of the time increase of the first voltage at the first time and when exceeded
4. d) a second threshold value of the second voltage at a subsequent second time or a second increase threshold value of the second voltage at the subsequent second time an arc fault detection signal (SLES) is delivered.

• - des ersten Grenzwertes der ersten Spannung zu einem ersten Zeitpunkt oder des ersten Anstiegs-Grenzwertes des zeitlichen Anstieges der ersten Spannung zum ersten Zeitpunkt und bei Überschreitung
• - eines zweiten Grenzwertes der zweiten Spannung zu einem nachfolgenden zweiten Zeitpunkt oder eines zweiten Anstiegs-Grenzwertes der zweiten Spannung zum nachfolgenden zweiten Zeitpunkt ermittelt,

so dass das Vorhandensein eines Störlichtbogens in seiner Wahrscheinlichkeit berechnet wird, und nur bei Vorliegen einer Mindestwahrscheinlichkeit ein Störlichtbogenerkennungssignal (SLES) abgegeben wird. In an advantageous embodiment of the method, an evaluation unit, such as a microcontroller, FPGA or DSP, is provided, which has a classifier, ie a classification is implemented or realized therein which, in a multi-dimensional feature space, exceeds the following:

• - The first limit value of the first voltage at a first time or the first increase threshold value of the temporal increase of the first voltage at the first time and when exceeded
• a second limit value of the second voltage is determined at a subsequent second time point or a second rise limit value of the second voltage at the subsequent second time point,

so that the presence of an arc is calculated in its probability, and only in the presence of a minimum probability, an arc fault detection signal (SLES) is delivered.

• - dem Vorliegen eines Mindeststromwertes oder der Änderung eines Stromwertes, die einen Änderungsstromwert überschreitet, geprüft werden.

Alternatively or additionally, with regard to

• - be checked for the presence of a minimum current value or the change of a current value exceeding a change current value.

• - des ersten Grenzwertes der ersten Spannung zum ersten Zeitpunkt oder des ersten Anstiegs-Grenzwertes des zeitlichen Anstieges der ersten Spannung zum ersten Zeitpunkt und bei Überschreitung
• - des zweiten Grenzwertes der zweiten Spannung zum nachfolgenden zweiten Zeitpunkt oder des zweiten Anstiegs-Grenzwertes der zweiten Spannung zum nachfolgenden zweiten Zeitpunkt oder/und dem Vorliegen eines Mindeststromwertes oder/und der Änderung eines Stromwertes, das Vorhandensein eines Störlichtbogens in seiner Wahrscheinlichkeit berechnet wird und bei Vorliegen einer Mindestwahrscheinlichkeit das Störlichtbogenerkennungssignal (SLES) abgegeben wird.

This method may for example be characterized in that the electrical or magnetic field component is converted into the first voltage,
the optical component is converted to the second voltage,
the voltages and the time intervals or / and temporal changes are monitored such that a fast classifier implements the transgression in a cost-effective evaluation unit (microcontroller, FPGA, DSP) in a multi-dimensional feature space:

• - The first limit value of the first voltage at the first time or the first increase threshold value of the temporal increase of the first voltage at the first time and when exceeded
• the second limit value of the second voltage at the subsequent second time point or the second limit voltage limit value at the subsequent second time point and / or the presence of a minimum current value or / and the change of a current value, the probability of the presence of an arc fault being calculated and at There is a minimum probability that the fault arc detection signal (SLES) is emitted.

All embodiments, both dependent on dependent on the patent claim 1, as well as referring back only to individual features or combinations of features of claims, cause an improvement in the detection of arcs.

The described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which will be explained in connection with the drawing.

• 1a ein erstes Schaltbild,
• 1b ein zweites Schaltbild,
• 2 eine erstes Ausführungsbeispiel,
• 3 ein erstes Prinzipschaltbild einer Anlage,
• 4 ein erstes Diagramm,
• 5, 6, 7 erste, zweite und dritte Entscheidungsbäume.

The drawing shows:

• 1a a first circuit diagram,
• 1b a second circuit diagram,
• 2 a first embodiment,
• 3 a first block diagram of a plant,
• 4 a first diagram,
• 5 . 6 . 7 first, second and third decision trees.

FIG. 1a shows a parallel connection of an inductance in the upper part of the figure L, a photodiode PD and a resistance R , This parallel connection can be the electrical voltage U provide.

In the lower part of the figure la is only the parallel connection of the photodiode PD drawn with the resistor R, where the voltage U can be provided.

This circuit can, for example, in the arc fault detection unit SLEE be arranged, as well as in a separate arc fault sensor SLS , In this case, the sensor, the inductance L and the photodiode PD at least have. The sensor can also have at least one resistor R exhibit. The sensor SLS can by a sensor line SL, such as a two-wire or coaxial line, with the arc fault detection unit SLEE or / and a control unit SE be connected.

Figure lb shows an alternative embodiment according to Figure la, with the difference that the inductance L with the photodiode PD connected in series. Parallel to the series connection, the resistor R is connected to which the electrical voltage U can be tapped. This circuit is functional analogous to Figure la.

2 shows a practical embodiment of a Störlichtbogensensors SLS , Here are an inductance L , a photodiode PD and a resistor R on a printed circuit board LP arranged. The circuit board LP has connections for a sensor cable SL on, such as according to 2 a (twisted) two-wire cable.

3 shows an inventive application of the invention in a (low voltage) circuit or a (low voltage) system. This has an energy source or energy supply NSE on, such as a low voltage feed. The energy feed NSE follows a first protective element LSE as a (low voltage) circuit breaker. At this one or more electrical lines LT are connected, is transmitted via the electrical energy to not subscribed energy sinks or consumers. The wires LT may be designed to transfer energy from single-phase or alternating current as well as for three-phase alternating current or similar.

The cables to the consumers can be further protective elements LS1 . LS2 . LS3 , such as circuit breakers, be associated with a consumer or a group of consumers by a respective protective element LS1 . LS2 or LS3 is secured.

In each case an arc fault detection unit SLEE can be arranged in the region of the lines LT. Alternatively, one or more arc fault sensors SLS1 . SLS2 . SLS3 be arranged to detect any occurring arc fault, as in the example in 3 shown.

The arc fault sensors SLS1 . SLS2 . SLS3 are over first, second and third sensor lines SL1 . SL2 . SL3 with the fault arc detection unit SLEE or control unit SE connected. As a result, multiple line sections or areas can be detected by one (or possibly several) arc fault detection unit SLEE / Control unit SE be monitored.

If an arc in the arc fault detection unit SLEE or control unit SE detected, may be an arcing fault detection signal SLES be transmitted to a protective element, whereby this interrupts the electrical circuit or line section in a row.
In the example, a first, second or third arc fault detection signal SLES1 . SLES2 . SLES3 about in 3 dashed lines shown connecting lines to the first, second and third protection element LS1 . LS2 . LS3 be transmitted.

The fault arc detection unit SLEE or control unit SE can also be in the protection element, in the example circuit breaker LS1 . LS2 or and LS3 be self-integrated or assigned to it.

4 shows a first diagram of the course of the sum voltage of the inductance L and the photodiode PD over time. The time t is given in μs / microseconds on the horizontal X axis. On the vertical Y-axis, the voltage U in mV / millivolt.

The course of the sum voltage of the inductance L and the photodiode PD shows a first voltage swing A1 , followed by a second voltage rise A2 ,

According to the invention, it has been recognized that the first voltage swing A1 by a field component, such as the E or H field, so depending on the type of arc, a pulse of the electric field leads to the discharge or the pulse of the incipient current flow associated magnetic field or direct coupling of an electromagnetic wave ie e and H - Field, the arc of arc caused by the inductance L , in the example by a coil, is detected, is caused. The coupling can also be detected by the connecting line of the photodiode, wherein the amount of detection is determined by the length of the connecting line of the photodiode.
The second increase in voltage A2 is caused by the subsequent optical component of the arc fault, by the photodiode PD is detected.
The temporal distance of both events A1 . A2 is typically in the single-digit microsecond range.

The exact time interval of both voltage increases or events A1 . A2 depends on various parameters of the arc generating system and depends mainly on the nature of the source. Specifically, when specifying the time interval, the electrical evaluation of the source is decisive (inductive or capacitive), as well as their potential difference to the counterelectrode of the arc. Thus, the time interval can be used as an application-specific measure for safe detection as a parameter.

The fault arc detection unit SLEE or control unit SE is designed such that it is checked for the occurrence of both events, as well as the chronological order and / or the time interval. In the presence of such Events an arc fault detection signal SLES is delivered.

For example, the detection can be made such that with regard to exceeding a first limit value U1 the voltage of the inductor at a first time t1 and exceeding a second limit U2 the voltage of the photodiode at a subsequent second time t2 an arc fault detection signal is emitted. Alternatively, even if a first increase limit value of the time increase of the voltage of the inductance is exceeded at a first time t1 and exceeding a second rise limit voltage of the photodiode at a subsequent second time t2 an arc fault detection signal is emitted.
It may also be with respect to a first rise limit value of the temporal increase of the voltage of the inductor at the first time t1 and exceeding a second limit U2 the voltage of the photodiode at a subsequent second time t2 being checked.
Respectively. with regard to the exceeding of a first limit value U1 the voltage of the inductor at a first time t1 and exceeding a second rise limit voltage of the photodiode at a subsequent second time t2 being checked.

This can be the first and second limit U1 . U2 be equal in magnitude to the voltage or / and first and second rise limit values of the voltage.

Furthermore, a further criterion can be introduced, according to which only an arcing fault detection signal ( SLES ) is given, if between the first and second time tl, t2 the voltage of the inductance L or sum voltage a third limit U3 below.

In the following the invention is explained in other words and further described. The invention proposes a novel, advantageous combination of optical detection and field measurement, as well as the evaluation of the waveforms.

In particular, it becomes an arc fault sensor SLS proposed, which is designed as a combination sensor. Through this is a detection and by means of the control unit SE an evaluation with early detection and increased detection security given.

As optical sensors photodiodes can be used as simple inexpensive sensor elements. According to the invention, the photodiodes are supplemented by inductors which can be realized by a coil, such as an inductor integrated in the printed circuit board, for example in the form of a printed circuit board integrated flat coil / planar coil, see 2 , As a result, an integrated solution is given, which is particularly small and therefore advantageous, since it can be inserted in hard to reach circuits / systems.

By parallel connection of both sensors, inductance L and photodiode PD, the combination of field generation and arc of the arc fault can be measured in a single signal path, scanned or evaluated.

In a control unit can be done by a microprocessor an evaluation in which, for example, an algorithm is implemented.

The photodiode PD can be used as a photodiode for near infrared ( NIR ), visible light ( VIS ) and / or ultraviolet light ( UV ).

Depending on the design of the fault arc sensor SLS / Combination sensors, the arc partial events "field" or "light" (optical) can be clearly separated and clearly identified, see 4 ,

If there is no inductance and the arc is only picked up by a photodiode, this is only the second event A2 determined. This can be done, for example, by using, for example, a photodiode in SMD design, if necessary. Shielded taps and short and / or shielded lines are used, which eliminates the influence of a field. As a result, however, only one component would be evaluated, whereby the detection security would be very low.

The fault arc sensor according to the invention SLS can also be used advantageously in the high and medium voltage, where high electric field strengths occur, which are well detected in the event of an arc fault.

According to the invention, it was recognized and proved by measurements that the proposed arc fault sensor SLS / Combined photodiode and coil sensor, the field effects of the arc arc are first visible, followed by a photocurrent that arises after a system-dependent, relatively constant time interval.

According to the invention, it is proposed as a protection criterion that, with regard to the presence of a pulse-like excitation followed by a rising photocurrent, a fault arc detection signal is tested SLES leave. Optionally, a decay of the through the inductor and circuit capacitance, which kept small should be waited, formed resonant circuit.

If only one event is detected, then it is another cause, there is no Störlichtbogenerkennungssignal SLES delivered.

A significant novelty according to the invention is the evaluation of the temporal behavior of a signal in which two physical modes of action are contained.

The temporal sequence can be achieved, for example, by limiting values, threshold values or trigger thresholds, which are separated by a defined "dead time", time interval between the first and second time to be observed.
The time interval is typically in the single-digit microsecond range. Depending on the system, it is also possible, for example, to have a time interval of up to 500 ps.
The temporal behavior can be examined after the voltage increase of the inductive component to a minimum increase difference of the optical component / in the light signal time domain.

The waveform of the single or total voltage can be sampled after the field trigger and after the expiration of the expected time for a light signal by fast Fourier transform, more advantageous by constantly tracking algorithms, for example SFFT , to be recycled. The characteristic signals are then to be detected in the frequency domain, advantageously in phase.

Thus, variations in the amplitudes can have less influence on the decision regarding an arc fault.

5 . 6 and 7 show the evaluation of the course of the voltage of the inductor and the photodiode (individually or as a sum voltage) by means of so-called decision trees, respectively decision trees. These can be implemented as a form of machine learning, for example as an algorithm for decision.

1. 1.) erste Zeit H/E-Feld, t1;
2. 2.) Zeitabstand bis zum Spannungsanstieg Photodiode, zweite Zeit t2 bzw. Zeitabstand t2-t1;
3. 3.) Gradient Anstieg 1;
4. 4.) Gradient Anstieg 2;
5. 5.) Stromwert des zu überwachenden Stromes zum Zeitpunkt der der ersten oder/und zweiten Zeit t1, t2,

so kann mithilfe eines Klassifikationsverfahrens, z.B. eines Decision Trees, anhand mehrerer Merkmale des Zeitverlaufs der Spannung eine Identifikation im Merkmalsraum erfolgen. Nach der schnellen Klassifikation kann dann die Information „Störlichtbogen“ oder „Störimpuls“ mit hoher, und vor allem benennbarer Sicherheit angegeben werden. Dazu nachfolgend eine Klassifikation von (hier) 5 Klassen anhand zweier Merkmale bei modellhafter Verschränkung.Taking it according to 5 five decision criteria as classes, for example:

1. 1.) first time H / E field, t1 ;
2. 2.) Time interval until voltage rise photodiode, second time t2 or time interval t2 - t1 ;
3. 3.) Gradient increase 1 ;
4. 4.) Gradient increase 2 ;
5. 5.) Current value of the current to be monitored at the time of the first and / or second time t1 . t2 .

Thus, by means of a classification method, for example a decision tree, an identification in the feature space can take place on the basis of several features of the time profile of the voltage. After the rapid classification, the information "arc fault" or "glitch" with high, and above all namable security can be specified. Here is a classification of (here) 5 Classes based on two characteristics with model entanglement.

According to 5 An arcing fault detection signal will only occur if the decision is in the middle (dark pentagon). Otherwise, other disturbance variables, such as brush motor, old relay, switch, dimmer, powerline, may underlie.

According to the classification method / decision tree according to 6 a decision is made with two characteristics x1 . x2 that are not separable by simple thresholds. The decision tree is in 5 Shared classes. If the current voltage values are in or near the band RB, an arcing fault detection signal occurs.

7 shows the exemplary location of features in the decision tree.

The inventive idea can be combined with other criteria.
For example, the electrical circuit can be monitored for the magnitude or change in its current. An arc fault detection signal is issued only if the current or the time change of the current exceeds a fourth limit.

Furthermore, an acoustic sensor may be provided, wherein an acoustic measurement is performed, so that the acoustic component of an arc fault is detected. An arc fault detection signal is emitted only if there is also an acoustic component of an arc fault.

By combining these parameters, a clear criterion for a fault arc can be established, since, for example, the probability of accidental, simultaneous occurrence of a current change, a light pulse / light increase (optical) and a characteristic electromagnetic field is very low.

Another advantage of the invention results from the fact that the proposed arc fault sensor or the arc fault detection unit has a low maintenance requirement. In contrast to purely optical sensors, field sensors are insensitive to surface contamination by dust or the like.

For a clear fault determination, at least 2 prerequisites are necessary. By linking several criteria, it is possible to minimize the threshold values for the protection release.

For example, if a field strength increase is detected, which is accompanied by a light increase following a defined time and a large current change, then there is a clear arc of arc. A sole increase in field strength or light pulse, as well as a change in current (such as, for example, in typical switching operation), on the other hand, can be ruled out as an arcing fault.

Coil and diode are mounted in a circuit with a resistor on a circuit board. At the same time a current measurement with electrical procedures is running.

According to the invention, the combination of optical detection and field measurement with a novel combination sensor including evaluation of the sum voltage is proposed, which enables early and reliable detection. The signals of field and light measurement can be made via a signal line. That Two physically different causes can be recorded separately over a single channel.

The electric field is detected first. Then the reaction time of the diode is waited, which may be in the order of 3 to 4 microseconds. If, for example, 4μs no voltage increase or voltage change / edge occurs by the luminous flux, there is no Störlichtbogenerkennungssignal. However, this evaluation can be displayed or saved as a fault message.
Otherwise, an arc fault detection signal can be emitted after 4 to 5 μs.
Furthermore, a current evaluation can take place.

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

Claims (13)

Arc detection unit (SLEE) for an electrical circuit, comprising: an inductance (L), a photodiode (PD), both of which are connected to a control unit (SE) and which is designed such that the voltage generated in the inductance (L) and the photodiode (PD) is monitored so that when exceeded: a first limit value of the voltage of the inductance at a first time or a first rise limit value of the time increase of the voltage of the inductance at the first time and when exceeded - A second limit value of the voltage of the photodiode at a subsequent second time or a second increase threshold value of the voltage of the photodiode at the subsequent second time an arc fault detection signal (SLES) is issued. Arc fault detection unit (SLEE) after Claim 1 , characterized in that the inductance (L) and the photodiode (PD) are electrically connected in parallel or in series and the sum voltage is monitored for exceeding the first limit or first rise limit and second limit or second rise limit. Arc fault detection unit (SLEE) after Claim 1 or 2 , characterized in that only a Störlichtbogenerkennungssignal (SLES) is delivered when between the first and second time, the voltage of the inductance (L) or sum voltage falls below a third threshold. Arc fault detection unit (SLEE) after Claim 1 . 2 , or 3, characterized in that the inductance (L) and / or the photodiode (PD), a resistor (R) is connected in parallel. Arc fault detection unit (SLEE) according to one of the preceding claims, characterized in that in the electrical circuit of the electrical current is determined and a Störlichtbogenerkennungssignal is only issued when the current or the temporal change in current exceeds a fourth threshold. Arc fault detection unit (SLEE) according to one of the preceding claims, characterized in that the first and second time t1, t2 have a time interval of less than 500, more particularly less than 100, 50 or 10, in particular less than 5 or 4, microseconds. Arc fault detection unit (SLEE) according to one of the preceding claims, characterized in that the inductance (L) is designed as a coil. Arc fault detection unit (SLEE) according to one of the preceding claims, characterized in that the electrical circuit is a low voltage circuit. Arc fault detection unit (SLEE) according to one of the preceding claims, characterized in that the fault arc detection signal is supplied to a circuit breaker or a short circuit of the electrical circuit. Arc fault detection unit (SLEE) according to one of the preceding claims, characterized in that at least the inductance and the photodiode are combined as a unit in a separate housing and the control unit is arranged spatially separated. Arc fault sensor with an inductance (L) and a photodiode (PD) for an arc fault detection unit (SLES) according to one of Claims 1 to 10 , Method for detecting an arc in an electrical circuit, in which an electrical or magnetic field component is converted into a first voltage, converting an optical component into a second voltage, the voltages are monitored so that when they exceed: - A first limit value of the first voltage at a first time or a first increase threshold value of the temporal increase of the first voltage at the first time and when exceeded a second limit value of the second voltage at a subsequent second instant or a second increase threshold value of the second voltage at the subsequent second instant an arc fault detection signal (SLES) is issued. Method according to Claim 12 , characterized in that an evaluation unit is provided, which has a classifier and in a multi-dimensional feature space exceeding: - the first limit value of the first voltage at a first time or the first increase limit value of the time of rise of the first voltage at the first time and when exceeding a second limit value of the second voltage at a subsequent second time point or a second rising limit value of the second voltage at the subsequent second time point and / or the presence of a minimum current value or the change of a current value which exceeds a change current value, such that the probability of the presence of an arc is calculated, and an arc fault detection signal (SLES) is issued only if a minimum probability exists.

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