Arc fault detection device with wideband sensor

Abstract

An arc fault detection device for detecting an arc fault in an electric line includes a first terminal and a second terminal for connecting the arc fault detection device to a conductor of the electric line. A sensor is adapted for generating a sensor signal from a current through the electric line; and a controller is adapted for detecting the arc fault from the sensor signal. The sensor includes an inductor connected to the first terminal and the second terminal and a capacitor connected in parallel with the inductor. The inductor and the capacitor form a resonant circuit with a resonance frequency, the resonance frequency determining an impedance behavior of the resonant circuit; wherein the inductor and the capacitor are chosen such that the impedance behavior of the resonant circuit corresponds to a desired impedance behavior over a relevant frequency range of the current through the electric line.

Claims

1. An arc fault detection device for detecting an arc fault in an electric line, the arc fault detection device comprising: a first terminal and a second terminal configured to connect the arc fault detection device to a conductor of the electric line; a sensor configured to generate a sensor signal from a current through the electric line; a circuit breaker configured to interrupt the electric line; and a controller configured to detect the arc fault from the sensor signal; wherein the sensor comprises an inductor connected to the first terminal and the second terminal and a capacitor connected in parallel with the inductor, wherein the inductor and the capacitor form a resonant circuit with a resonance frequency, the resonance frequency determining an impedance behavior of the resonant circuit, wherein the inductor and a capacitance of the capacitor are chosen such that the impedance behavior of the resonant circuit corresponds to a desired impedance behavior over a relevant frequency range of the current through the electric line, and wherein the inductor is a magnetic actuator configured to operate the circuit breaker.

2. The arc fault detection device of claim 1, wherein one end of the inductor is used as a reference point for at least one of the sensor and the controller.

3. The arc fault detection device of claim 1, wherein the sensor further comprises a resistor connected in parallel with the capacitor.

4. The arc fault detection device of claim 1, wherein the sensor further comprises a protection circuit configured to limit an output current and/or output voltage of the sensor; wherein an input of the controller is connected via the protection circuit to the resonant circuit.

5. The arc fault detection device of claim 4, wherein the sensor further comprises a resistor connected in parallel with the capacitor, and wherein the protection circuit comprises a protection capacitor connected in series with the resistor.

6. The arc fault detection device of claim 4, wherein the protection circuit comprises a transient blocking unit connected between the capacitor and the controller and adapted for blocking currents higher than a predefined current threshold; and/or wherein the protection circuit comprises a transient voltage suppressor.

7. The arc fault detection device of claim 6, wherein the transient voltage suppressor comprises at least one pair of antiparallel diodes connected in parallel with the capacitor; and/or wherein the transient voltage suppressor comprises at least two pairs of antiparallel diodes connected in parallel with the capacitor, the diodes of one of the two pairs being Schottky diodes.

8. The arc fault detection device of claim 7, wherein a protection resistor is connected between the capacitor and the at least one pair of antiparallel diodes; and/or wherein a first protection resistor is connected between the capacitor and a first pair of antiparallel diodes and a second protection resistor is connected between the first pair of antiparallel diodes and a second pair of antiparallel diodes.

9. The arc fault detection device of claim 1, wherein the sensor further comprises a filter circuit adapted for providing at least one filtered signal from the sensor signal; wherein the controller is adapted for detecting the arc fault from the at least one filtered signal.

10. The arc fault detection device of claim 9, wherein the sensor further comprises a protection circuit configured to limit an output current and/or output voltage of the sensor; wherein an input of the controller is connected via the protection circuit to the resonant circuit; and wherein the filter circuit is connected via the protection circuit to the resonant circuit.

11. A method for operating an arc fault detection device including a first terminal and a second terminal configured to connect the arc fault detection device to a conductor of an electric line; a sensor configured to generate a sensor signal from a current through the electric line; a circuit breaker configured to interrupt the electric line; and a controller configured to detect the arc fault from the sensor signal; wherein the sensor comprises an inductor connected to the first terminal and the second terminal and a capacitor connected in parallel with the inductor, wherein the inductor and the capacitor form a resonant circuit with a resonance frequency, the resonance frequency determining an impedance behavior of the resonant circuit, wherein the inductor and a capacitance of the capacitor are chosen such that the impedance behavior of the resonant circuit corresponds to a desired impedance behavior over a relevant frequency range of the current through the electric line, and wherein the inductor is a magnetic actuator configured to operate the circuit breaker, the method comprising: receiving the sensor signal from the sensor; determining from the sensor signal whether the electric line has an arc fault or not; when the arc fault is detected: generating a trip signal for interrupting the electric line.

12. The method of claim 11, wherein at least one of a low-frequency component and a high-frequency component is extracted from the sensor signal and is analyzed to determine whether the electric line has an arc fault or not.

13. A computer program comprising instructions which, when the computer program is executed by a computer, cause the computer to carry out the method of claim 11.

14. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of claim 11.

15. An arc fault detection device for detecting an arc fault in an electric line, the arc fault detection device comprising: a first terminal and a second terminal configured to connect the arc fault detection device to a conductor of the electric line; a sensor configured to generate a sensor signal from a current through the electric line; and a controller configured to detect the arc fault from the sensor signal, wherein the sensor comprises an inductor connected to the first terminal and the second terminal and a capacitor connected in parallel with the inductor, wherein the inductor and the capacitor form a resonant circuit with a resonance frequency, the resonance frequency determining an impedance behavior of the resonant circuit, wherein the inductor and the capacitor are chosen such that the impedance behavior of the resonant circuit corresponds to a desired impedance behavior over a relevant frequency range of the current through the electric line, wherein the sensor further comprises a protection circuit configured to limit an output current and/or output voltage of the sensor, and wherein an input of the controller is connected via the protection circuit to the resonant circuit.

16. The arc fault detection device of claim 15, wherein the sensor further comprises a resistor connected in parallel with the capacitor, and wherein the protection circuit comprises a protection capacitor connected in series with the resistor.

17. The arc fault detection device of claim 15, wherein the protection circuit comprises a transient blocking unit connected between the capacitor and the controller and adapted for blocking currents higher than a predefined current threshold; and/or wherein the protection circuit comprises a transient voltage suppressor.

18. The arc fault detection device of claim 17, wherein the transient voltage suppressor comprises at least one pair of antiparallel diodes connected in parallel with the capacitor; and/or wherein the transient voltage suppressor comprises at least two pairs of antiparallel diodes connected in parallel with the capacitor, the diodes of one of the two pairs being Schottky diodes.

19. The arc fault detection device of claim 18, wherein a protection resistor is connected between the capacitor and the at least one pair of antiparallel diodes; and/or wherein a first protection resistor is connected between the capacitor and a first pair of antiparallel diodes and a second protection resistor is connected between the first pair of antiparallel diodes and a second pair of antiparallel diodes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject-matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

(2) FIG. 1 schematically shows an arc fault detection device according to an embodiment of the invention.

(3) FIG. 2 schematically shows a sensor of an arc fault detection device according to an embodiment of the invention.

(4) FIG. 3 schematically shows an arc fault detection device according to a further embodiment of the invention.

(5) FIG. 4 shows a diagram illustrating a transfer impedance behavior of a resonant circuit of an arc fault detection device according to an embodiment of the invention.

(6) FIG. 5 shows a diagram illustrating a transfer impedance behavior of a sensor of an arc fault detection device according to an embodiment of the invention.

(7) FIG. 6 shows a flow diagram illustrating a method for operating an arc fault detection device according to an embodiment of the invention.

(8) The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(9) FIG. 1 schematically shows an arc fault detection device 100 adapted for detecting an arc fault in an electric line 102, such as a series or parallel arc or an arc to ground. The electric line 102 may comprise one or more conductors, e.g. a phase conductor 104 and a neutral conductor 106, which connect a load 108 to an electric power source 110, e.g. a power grid or a battery. In this example, the arc fault detection device 100 is electrically connected to the phase conductor 104 via a first phase terminal 112 and a second phase terminal 114 and to the neutral conductor 106 via a first neutral terminal 116 and a second neutral terminal 118.

(10) Generally, the arc fault detection device 100 may be adapted for interrupting the electric line 102, i.e. for disconnecting the load 108 from the electric power source 110, when an arc fault is detected in at least one of the conductors 104, 106 and/or between the two conductors 104, 106 and/or between one of the two conductors 104, 106 and ground. In this example, the arc fault detection device 100 comprises a circuit breaker 120 with a circuit breaker switch 121 arranged in the phase conductor 104. Additionally, the arc fault detection device 100 may comprise a bimetal 122 for protecting the electric line 102 against an overload and a magnetic actuator 124 for protecting the electric line 102 against short circuits. The bimetal 122 and the magnetic actuator 124 may be connected in series with the circuit breaker switch 121.

(11) Furthermore, the arc fault detection device 100 comprises a sensor 126 for detecting a current through the electric line 102, here through the phase conductor 104. The sensor 126 is adapted for providing a sensor signal 128, e.g. a voltage signal, in dependence of the detected current.

(12) A controller 130 of the arc fault detection device 100 receives the sensor signal 128 from the sensor 126 and analyzes it using a specific detection algorithm to detect an arc fault. The controller 130 may comprise at least a processor and a memory (not shown) to perform such an algorithm. The algorithm may be implemented as hardware and/or software. The controller 130 may be adapted for analyzing the sensor signal 128 in one or more specific frequency bands. The controller 130 may further be adapted for generating a trip signal 132 when an arc fault is detected.

(13) It may be that an auxiliary switch (not shown), e.g. an electronic switch, is operated by means of the trip signal 132, which, when operated, causes the circuit breaker switch 121 to interrupt the phase conductor 104.

(14) For example, at least one of the magnetic actuator 124, the bimetal 122 and the auxiliary switch may be coupled to the circuit breaker switch 121 via a trip mechanism (not shown) of the arc fault detection device 100. The trip mechanism may also be operable manually by a user.

(15) In order to convert the current through the electric line 102 to the sensor signal 128, the sensor 126 comprises an inductor 134, which is connected to the terminals of one of the conductors 104, 106. In this example, the inductor 134 is connected at a line side to the first phase terminal 112 (via the circuit breaker switch 121 and the bimetal 122) and at a load side to the second phase terminal 114. Alternatively, the inductor 134 may be connected to the second phase terminal 114 via the circuit breaker switch 121 and the bimetal 122.

(16) For example, the inductor 134 may be the magnetic actuator 124. Alternatively, the inductor 134 may be realized as a separate inductive element arranged in the electric line 102.

(17) The sensor 126 further comprises a capacitor 136 connected in parallel with the inductor 134. The inductor 134 and the capacitor 136 form a resonant circuit 138 with a resonance frequency that is adapted to a desired impedance behavior of the resonant circuit 138 over a frequency range of interest. In other words, the resonance frequency is adjusted such that the resonant circuit 138 has a certain impedance behavior over the frequency range of interest (see also FIG. 4 and FIG. 5). For a given inductor, here in the form of the magnetic actuator 124, the resonance frequency may be adjusted based on a capacitance of the capacitor 136 and/or a resistance of a parallel-connected resistor (not shown in FIG. 1). For example, the resonance frequency may be adjusted to around 10 MHz or more. A sensor signal input of the controller 130 may be connected to the inductor 134 via the capacitor 136.

(18) With the resonant circuit 138, the impedance behavior of the sensor 126 can be precisely adapted to the signal strength at the frequencies of interest. In that way, a very high sensitivity of the sensor 126 can be achieved. For example, the cost and size constraint can be met by choosing a relatively small inductive element and then adapting its impedance accordingly. As mentioned above, an additional inductive element is not necessarily required to implement the sensor 126. Instead, an existing component inside the arc fault detection device 100, such as the magnetic actuator 124 or any other suitable inductive component, can be used as the inductor 134. The magnetic actuator 124 behaves like an inductor and may be used to trip the arc fault detection device 100 in case of a short circuit. By adjusting its impedance in a suitable manner, the magnetic actuator 124 may, for example, be used to sense an arc fault current in a frequency range from 50 Hz to 20 MHz.

(19) It may be that all electric and/or electronic components of the sensor 126 and/or the controller 130 are connected to a common reference point 140, which may be arranged at a load side of the inductor 134, as shown in FIG. 1, or, alternatively, at a line side of the inductor 134, i.e., the reference point 140 may be at either of two ends of the inductor 134. The reference point 140 may be connected to ground.

(20) Additionally to the resonant circuit 138, which acts as an impedance matching stage of the sensor 126, the sensor 126 may comprise at least one of a protection stage for protecting the controller 130 against an overcurrent and/or overvoltage and a filter stage for filtering the sensor signal 128, as described in more detail below.

(21) FIG. 2 schematically shows the sensor 126 with the resonant circuit 138 and an optional protection circuit 200 for limiting a current through and/or a voltage across the sensor 126 and the controller 130. The protection circuit 200 interconnects the resonant circuit 138 with a sensor signal output 202 of the sensor 126, which may be connected to the sensor signal input of the controller 130 as shown in FIG. 1.

(22) In this example, the protection circuit 200 comprises a first pair of antiparallel Schottky diodes 204 and a second pair of antiparallel p-n junction diodes 206. Both pairs are connected in parallel with the inductor 134 and the capacitor 136. The antiparallel p-n junction diodes 206 may be arranged between the Schottky diodes 204 and the sensor signal output 202.

(23) It may be that the protection circuit 200 further comprises a first protection resistor 208 arranged between the capacitor 136 and the first pair and a second protection resistor 210 arranged between the first pair and the second pair. The protection resistors 208, 210 may have equal or different resistances.

(24) As already mentioned above with respect to FIG. 1, the resonant circuit 138 may comprise a resistor 212 connected in parallel with the inductor 134 and the capacitor 136. The resistor 212, depending on its resistance, limits the impedance of the resonant circuit 138 to a desired maximum.

(25) To protect the resistor 212 against an overcurrent and/or overvoltage, the protection circuit 200 may further comprise a protection capacitor 214, or blocking capacitor 214, connected in series with the resistor 212.

(26) The components of the resonant circuit 138 and the protection circuit 200 may each be connected to the reference point 140, e.g. at the load side of the inductor 134, i.e. of the magnetic actuator 124.

(27) As mentioned above, the sensor 126 may further comprise a filtering stage in the form of a filter circuit, as shown in FIG. 3.

(28) FIG. 3 shows the resonant circuit 138 of FIG. 2 in combination with the protection circuit 200 and a filter circuit 300. The filter circuit 300 may be arranged between the protection circuit 200 and the sensor signal output 202 of the sensor 126. In contrast to FIG. 2, the protection circuit 200 here comprises only one pair of antiparallel diodes 206, which are connected in parallel with the inductor 134 and the capacitor 136. The diodes 206 may be p-n junction diodes.

(29) A transient blocking unit (TBU) 302 adapted for blocking currents higher than a specific current threshold may be arranged between the capacitor 136 and the antiparallel diodes 206. The transient blocking unit 302 may be seen as a non-linear active resistor. By using the transient blocking unit 302 (instead of two pairs of diodes), a more compact version of the arc fault detection device 100 can be realized.

(30) The filter circuit 300 generates at least one filtered signal 304 from the sensor signal 128.

(31) For example, the filter circuit 300 may comprise a low-pass filter 306 adapted for outputting a low-frequency voltage u.sub.LF and a high-pass filter 308, e.g. a Sallen-Key high-pass filter with f.sub.0=100 kHz, adapted for outputting a high-frequency voltage u.sub.HF. Alternatively, the filter circuit 300 may be a bandpass filter.

(32) Accordingly, the controller 130 may be adapted for generating the trip signal 132 from the filtered signals 304, u.sub.LF, u.sub.HF by analyzing the filtered signals 304, u.sub.LF, u.sub.HF with an arc fault detection algorithm (see above).

(33) The requirements for the inductor 134 may be a high inductance and a high self-resonance frequency. The self-resonance frequency should be above a maximum frequency of interest. In general, it is required that the inductor 134 converts the current through the electric line 102 into a sensor signal 128 above the voltage noise of the amplifiers of the arc fault detection device 100 at all frequencies of interest. The matching stage may increase or decrease the impedance according to the signal level of an arc fault signal. The matching stage may be built using capacitors and resistors. Finally, the protection stage ensures that peak voltages, which may appear on an inductor, cannot propagate through the electronics of the arc fault detection device 100.

(34) An inductor is well-suited for sensing arc fault signals over a wide frequency range, because its impedance increases with the frequency of the arc fault signal, whereas the power spectral density of the arc fault signal decreases with its frequency. Ideally, the impedance should increase proportional to √{square root over (f)} to match the decrease in signal power of 1/f, i.e. the decrease of the signal amplitude proportional to 1/√{square root over (f)}. To compensate for that mismatch, amplifiers already present in the arc fault detection device 100 may be used.

(35) As indicated in FIG. 3 with a dotted line, the sensor 126 may, at least partially, be implemented on a power supplied main board 310 of the arc fault detection device 100. The controller 130 may also be a component of the main board 310 or may be implemented on a separate controller board (not shown).

(36) FIG. 4 and FIG. 5 show examples for desired impedance behaviors over a relevant frequency range of the current through the electric line 102, which, for example, may comprise frequencies up to at least 10 MHz.

(37) FIG. 4 shows the transfer impedance Z of the resonant circuit 138 for four different configurations of the arc fault detection device 100 in dependence of a frequency f. Each configuration is represented by a different impedance curve 400a to 400d, which indicate a magnitude of the transfer impedance Z. The maximum of each impedance curve 400a to 400d corresponds to the resonance frequency f.sub.0 of the respective resonant circuit 138 and is limited by the resistor 212 of the respective resonant circuit 138.

(38) In other words, the capacitor 136 may resonate with the inductor 134 at the resonance frequency f.sub.0, while the resistor 212 limits the peak impedance at resonance. If not limited, the impedance could become so large that it blocks the current at the resonance frequency f.sub.0. Depending on a given quality factor and a given inductance of the inductor 134, the impedance at resonance may vary. In general, the impedance may be seen as a measure for the sensitivity of the sensor 126 at a given frequency.

(39) Frequencies as low as 50 Hz are very important in view of arc fault detection because they contain information about arc faults as well as about other loads connected to the installations. In this low-frequency band, it is the ohmic resistance of the windings in the inductor 134 that mostly contributes to the impedance.

(40) FIG. 5 exemplarily shows a desired behavior of a transfer impedance Z.sub.T of the sensor 126, represented by a first transfer impedance curve 500a in comparison to the transfer impedance Z.sub.T of a conventional arc fault detection sensor with two current transformers, represented by a second transfer impedance curve 500b. Both curves 500a, 500b indicate a magnitude of the transfer impedance Z.sub.T. The transfer impedance Z.sub.T is indicative of the ability of a current sensor to convert a sensed current into voltage and may be measured in the sensor 126 between the output of the filter circuit 300 and the current injected into the magnetic actuator 124.

(41) As can be seen from FIG. 5, the transfer impedance Z.sub.T of the sensor 126 around the resonance frequency f.sub.0 is at least four times higher than the transfer impedance Z.sub.T of the conventional sensor and rapidly decreases around the resonance peak, which makes the sensor 126 more selective in the desired frequency band.

(42) FIG. 6 shows a flow diagram for a method for operating the arc fault detection device 100 of FIGS. 1 to 3.

(43) In step S10, the sensor signal 128, or the one or more filtered signals 304, u.sub.LF, u.sub.HF, is received at the sensor signal input of the controller 130 from the sensor signal output 202 of the sensor 126.

(44) In step S20, the controller 130 determines from the sensor signal 128, or from the one or more filtered signals 304, u.sub.LF, u.sub.HF, whether the electric line 102 has an arc fault or not, e.g. whether there is a series arc in at least one of the conductors 104, 106, a parallel arc between the two conductors 104, 106 or an arc between one of the two conductors 104, 106 and ground. The detection of the arc fault may be performed by analyzing the respective signal in different frequency bands using a specific algorithm (see above).

(45) In step S30, when the arc fault is detected, the trip signal 132 is output by the controller 130, which causes the circuit breaker switch 121 to interrupt the phase conductor 104.

(46) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or superordinate controller or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

LIST OF REFERENCE SYMBOLS

(47) 100 arc fault detection device 102 electric line 104 phase conductor 106 neutral conductor 108 load 110 electric power source 112 first terminal, first phase terminal 114 second terminal, second phase terminal 116 first neutral terminal 118 second neutral terminal 120 circuit breaker 121 circuit breaker switch 122 bimetal 124 magnetic actuator 126 sensor 128 sensor signal 130 controller 132 trip signal 134 inductor 136 capacitor 138 resonant circuit 140 reference point 200 protection circuit 202 sensor signal output 204 Schottky diode, transient voltage suppressor 206 p-n junction diode, transient voltage suppressor 208 first protection resistor 210 second protection resistor 212 resistor 214 protection capacitor 300 filter circuit 302 transient blocking unit 304 filtered signal 306 low-pass filter 308 high-pass filter 310 main board 400a-d impedance curves 500a first transfer impedance curve 500b second transfer impedance curve f.sub.0 resonance frequency u.sub.LF low-frequency voltage u.sub.HF high-frequency voltage