Arc Fault Detection Device

Abstract

For an arc fault detection device (1) having a first electrical wire (2) and at least one sensor (3), the sensor being adapted to monitor the current or voltage spectrum in the first electrical wire (2) and output an analog HF measurement signal, the arc fault detector (1) further comprising an input section (4) connected to the sensor (3), it is proposed that the input section (4) comprises: - an input band-pass filter (5) connected to the sensor (3) for filtering the analog HF measurement signal, - wherein the passband (18) of the input band-pass filter (5) comprises a predeterminable arc frequency range (7) for detecting an arc effect, - a sampling mixer (6) connected to the input band-pass filter (5), - wherein the sampling frequency (10) of the sampling mixer (6) is lower than twice the upper threshold frequency (9) of the arc frequency range (7).

Description

Technical Field

[0001] The present disclosure relates to an arc fault detection device. Background Art

[0002] Arc fault detection devices are known according to many different detection methods.

[0003] An arc generates high-frequency noise on an electric wire or in a circuit. An arc fault detector observes the electric wire by measuring current or voltage and analyzing the measurement signal. Known arc fault detectors detect an arc by analyzing the current or voltage frequency behavior of a specific pattern in the high-frequency components of the measurement signal.

[0004] Even though it may be easy to analyze signals in the high-frequency or radio frequency range of interest in a radio measurement laboratory, the required equipment is large and expensive. There is no possibility of implementing the corresponding measurement equipment of these technologies in a commercial arc fault detection device (AFDD) that can be sold at a reasonable price and is small enough to be arranged in a typical household and / or commercial fuse box.

[0005] Mixing RF frequency measurement signals into a lower frequency range is known. Even though it is easier to analyze signals with a lower frequency, downmixing usually causes a loss of signal level and requires additional amplifier circuits.

[0006] Combining a low-complexity, small and simple hardware design with low cost and a low false trip tendency is one of the major problems of all arc fault detection devices. Summary of the Invention

[0007] The object of the present invention is to overcome the disadvantages of the current state of the art by providing an arc fault detection device having a small and simple hardware design that is easy to implement and having a low false trip tendency.

[0008] According to the present invention, this object is solved by the following features.

[0009] An arc fault detection device having a first electric wire and at least one sensor adapted to monitor the current or voltage spectrum in the first electric wire and output an analog HF measurement signal, the arc fault detection device further comprising an input section connected to the sensor, the input section comprising:

[0010] - an input band-pass filter connected to the sensor for filtering the analog HF measurement signal,

[0011] - wherein the passband of the input band-pass filter has a predeterminable arc frequency range for detecting the arc effect,

[0012] - A sampling mixer, which is connected to the input band - pass filter,

[0013] - wherein the sampling frequency of the sampling mixer is lower than twice the upper - threshold frequency of the arc - frequency range.

[0014] The arc - fault detection device can be implemented using small and simple hardware. The sampling mixer can be realized with just two passive components, semiconductor switches, and a very simple signal generator. Therefore, a very simple and small PCB design is possible.

[0015] The sampling mixer deliberately violates the Nyquist - Shannon criterion. The resulting aliasing effect generates other signals with low frequencies and increases the signal level in the down - converted frequency band. Therefore, no other amplification stage is required. Due to the high signal level in the easily analyzable frequency band, the AFDD has a low false - tripping tendency. Description of the Drawings

[0016] The present invention is described with reference to the accompanying drawings. The drawings only show the preferred embodiments of the present invention. Thus shown

[0017] Figure 1 is a block diagram of a preferred embodiment of an actual arc - fault detection device;

[0018] Figure 2 is according to Figure 1 the functional block diagram of the sampling mixer of the arc - fault detection device;

[0019] Figure 3 is according to Figure 2 the circuit diagram of a preferred embodiment of the sampling mixer; and

[0020] Figure 4 is a frequency spectrum. Detailed Description of the Invention

[0021] Figure 1 Shows a preferred embodiment of an arc - fault detection device 1 having a first electric wire 2 and at least one sensor 3, the sensor 3 being adapted to monitor the current or voltage spectrum in the first electric wire 2 and output an analog HF measurement signal, the arc - fault detector 1 further comprising an input section 4 connected to the sensor 3, the input section 4 including:

[0022] - An input band - pass filter 5, which is connected to the sensor 3 for filtering the analog HF measurement signal,

[0023] - wherein the pass - band 18 of the input band - pass filter 5 has a predeterminable arc - frequency range 7 for detecting the arc effect,

[0024] - A sampling mixer 6, which is connected to the input band - pass filter 5,

[0025] - The sampling frequency 10 of the sampling mixer 6 is lower than twice the upper threshold frequency 9 of the arc frequency range 7.

[0026] A common abbreviation for the arc fault detection device 1 is AFDD 1. This abbreviation is also used in this article.

[0027] The arc fault detection device 1 can be implemented using small and simple hardware. The sampling mixer 6 can be implemented with just two passive components 22, 23, a semiconductor switch 24, and a very simple signal generator 13. Therefore, a very simple and small PCB design is possible.

[0028] The sampling mixer 6 consciously violates the Nyquist-Shannon criterion. The resulting aliasing effect generates other signals with low frequencies and increases the signal level in the down-converted frequency band. Therefore, no other amplification stage is required. Due to the high signal level in the easily analyzable frequency band, the AFDD 1 has a low false trip tendency.

[0029] The AFDD 1 includes at least one first wire 2 passing through the AFDD 1. The AFDD 1 can include other wires. The AFDD 1 can be an independent device or integrated into an arc fault circuit breaker, which includes a switch contact or a hybrid circuit arrangement or a solid-state arrangement for interrupting at least one wire 2.

[0030] The AFDD 1 includes at least one sensor 3 for monitoring the current or voltage spectrum in the first wire 2. The sensor 3 can be any type of sensor suitable for monitoring voltage and / or current in the high-frequency range. The sensor 3 is adapted to output an analog HF measurement signal. Typical current or voltage sensors 3 usually output analog signals. HF means high frequency. Another abbreviation for HF is RF, which stands for radio frequency. In the context of the present invention, HF or RF means signals in the range of several MHz.

[0031] Arcs generate frequency components in a typical frequency range. An arc can be determined by analyzing only a part of the spectrum. This part or bandwidth is called the arc frequency range 7. Since arcs usually generate signals with a certain bandwidth, different signal frequency bands can be used as the arc frequency range 7. According to the actual invention, it is intended to pre-determine the frequency range as the arc frequency range 7. According to a preferred embodiment, the arc frequency range 7 has a lower threshold frequency 8 in the range of 2 MHz to 4 MHz. According to a preferred embodiment, the arc frequency range 7 has an upper threshold frequency 9 in the range of 4 MHz to 6 MHz. Further preferably, the arc frequency range 7 has a bandwidth of at least 500 kHz. Studies have shown that arcs can be detected with a high degree of accuracy by analyzing this frequency range.

[0032] The AFDD 1 further includes an input section 4 connected to the sensor 3. The input section 4 is intended for editing the measurement signal provided by the sensor 3 before the measurement signal is analyzed in a control unit 16 connected to the input section 4.

[0033] The input section 4 includes an input band - pass filter 5 which is connected to the sensor 3 for filtering the analog HF measurement signal. The pass - band 18 of the input band - pass filter 5 must be selected such that a predetermined arc - frequency range 7 of interest for detecting arc effects is part of the pass - band 18. Figure 4 A spectrum showing the pass - band 18 of the input band - pass filter 5 is presented, which spectrum has an upper cut - off frequency 11 and a lower cut - off frequency 12. The spectrum also shows the arc - frequency range 7.

[0034] The output of the input band - pass filter 5 is connected to the sampling mixer 6 of the AFDD 1. The sampling mixer 6 transforms the measurement signal into a lower frequency band by mixing the band - pass - filtered measurement signal with a mixing signal having a sampling frequency 10. Figure 2 A block diagram showing a preferred embodiment of the sampling mixer 6 is presented. The sampling mixer 6 includes a local oscillator 13 for generating a mixing signal having a sampling frequency 10. According to the preferred embodiment, the mixing signal is a rectangular signal. The rectangular signal can be generated with a very simple generator which includes only two semiconductor switches and several passive components. The sampling frequency 10 is the fundamental frequency of the rectangular signal. However, the rectangular signal includes higher harmonics.

[0035] It is desirable that the sampling frequency 10 of the sampling mixer 6 is lower than twice the upper threshold frequency 9 of the arc - frequency range 7. This means that the Nyquist - Shannon criterion is violated and aliasing occurs during mixing. As mentioned before, aliasing generates additional frequency components in the same frequency band as the band into which the measurement signal is transformed. These additional frequency components are added to the components generated in the absence of aliasing.

[0036] The sampling frequency 10 depends on the frequency range 7 which is considered relevant for arc detection. The preferred frequency range is as described above. According to a special embodiment, the upper cut - off frequency 11 of the input band - pass filter 5 is higher than the upper threshold frequency 9 of the arc - frequency range 7, and the sampling frequency 10 of the sampling mixer 6 is lower than twice the upper cut - off frequency 11 of the band - pass filter 5.

[0037] According to a particularly preferred embodiment, the sampling frequency 10 is at least 1 MHz. This enables the ADFF to identify relevant signal changes within 1 μs.

[0038] Preferably, the sampling frequency 10 is within the range of the most interesting frequencies of the arc frequency range 7. Due to the mixing effect of the sampling mixer 6, the frequencies around the sampling frequency 10 are down-converted to baseband signals. Mixing a 5.001 MHz signal with a 5 MHz square wave will be transformed into 1 kHz and some other mixing products. Due to the aliasing effect caused by sampling, the aliasing frequencies are transformed back to 1 kHz (4.999 MHz, 5.001 MHz, 9.999 MHz, 10.001 MHz, 14.999 MHz, …). Some of the mixing products are located at these aliasing frequencies. This means that these signals are transformed to the 1 kHz fundamental frequency.

[0039] When the arc frequency range 7 is shifted to the baseband, preferably, the lower cut-off frequency 12 of the input band-pass filter 5 is higher than half of the bandwidth of the arc frequency range 7.

[0040] Figure 3 A circuit diagram showing a preferred embodiment of the sampling mixer 6. This embodiment includes: an ohmic resistor 22; a switching element 24, especially a semiconductor such as an FET; and a capacitor 23. This embodiment of the sampling mixer 6 is a switchable passive RC low-pass filter that has a local oscillator 13 for controlling the switching element 24. This embodiment combines all three blocks according to Figure 2 of all three blocks.

[0041] The duty cycle of the rectangular signal will control the effective value of the resistor 22. The value of the resistor affects the upper threshold frequency of the sampling mixer 6. Using a 50% duty cycle will double the resistor. The resistor multiplication factor is equal to the reciprocal of the duty cycle. Such a mixer is also called a switched RC filter. According to the preferred embodiment, the duty cycle of the rectangular signal can be controlled to be in the range of 20% to 80%, especially 50%. By increasing the duty cycle, the amplitude within the baseband can be increased. However, this brings an important drawback of different harmonic filtering.

[0042] The output of the sampling mixer 6 is connected to an intermediate band-pass filter 14 for removing unnecessary frequency components. According to the preferred embodiment, the upper cut-off frequency 17 of the intermediate band-pass filter 14 is lower than the upper cut-off frequency 12 of the input band-pass filter 5.

[0043] An envelope detector 15 is connected to the output of the intermediate filter 14. The envelope detector should be configured to detect signal changes within 10 μs. The envelope detector 15 is a standard component in many AFDDs.

[0044] The output of the envelope detector 15 is connected to the control unit 16 of the arc-fault detection device 1. The control unit 16 is embodied to compare the signal delivered by the envelope detector 15 with at least one arc criterion and to output a trigger signal if the signal matches the arc criterion. The trigger output is not shown in the figures.

[0045] The following are the principles for understanding and interpreting the actual disclosure.

[0046] Features are usually introduced with the numeral "a". Thus, unless stated otherwise in the context, "a" should not be construed as a numerical term.

[0047] The conjunction "or" should be interpreted inclusively rather than exclusively. Unless otherwise specified in the context, "A or B" also includes "A and B", where "A" and "B" represent any features.

[0048] Unless the disclosure of the present invention is otherwise limited, in several embodiments, ordinal numeral terms such as "first", "second", or "third" are used to distinguish, in particular, feature X or object Y. In particular, a feature X or an object Y having an ordinal numeral term in the claims does not mean that the embodiments of the present invention covered by the claims must have another feature X or another object Y.

[0049] Unless otherwise specified in the context, the combination of "substantially" with a numerical value includes a tolerance of ±10% around the given numerical value.

[0050] Unless otherwise specified in the context, for a range of values, the endpoints are included.

Claims

1. An arc fault detection device (1) having a first electrical wire (2) and at least one sensor (3), the sensor being adapted to monitor the current or voltage spectrum in the first electrical wire (2) and output an analog HF measurement signal, the arc fault detection device (1) further comprising an input section (4) connected to the sensor (3), the input section (4) comprising: - An input bandpass filter (5) connected to the sensor (3) for filtering the analog HF measurement signal, - wherein the passband (18) of the input bandpass filter (5) has a predeterminable arc frequency range (7) for detecting arc effects, - A sampling mixer (6) connected to the input bandpass filter (5), wherein the sampling mixer (6) comprises an ohmic resistor (22), a switching element (24), a capacitor (23), and a local oscillator (13) for controlling the switching element (24); - wherein the sampling frequency (10) of the sampling mixer (6) is lower than twice the upper threshold frequency (9) of the arc frequency range (7).

2. The arc fault detection device (1) according to claim 1, characterized in that, The upper cut-off frequency (11) of the input bandpass filter (5) is higher than the upper threshold frequency (9) of the arc frequency range (7), and the sampling frequency (10) of the sampling mixer (6) is lower than twice the upper cut-off frequency (11) of the bandpass filter (5).

3. The arc fault detection device (1) according to claim 1 or 2, characterized in that, The sampling mixer (6) comprises a local oscillator (13) for generating a mixing signal having the sampling frequency, and the mixing signal generated by the local oscillator (13) is a rectangular signal.

4. The arc fault detection device (1) according to claim 3, characterized in that, The duty cycle of the rectangular signal can be controlled to be in the range of 20% to 80%.

5. The arc fault detection device (1) according to claim 3, characterized in that, The duty cycle of the rectangular signal is 50%.

6. The arc fault detection device (1) according to any one of claims 1 or 2, characterized in that, The arc frequency range (7) has a lower threshold frequency (8) in the range of 2 MHz to 4 MHz.

7. The arc fault detection device (1) according to any one of claims 1 or 2, characterized in that, The arc frequency range (7) has an upper threshold frequency (9) in the range of 4 MHz to 6 MHz.

8. The arc fault detection device (1) according to any one of claims 1 or 2, characterized in that, The sampling frequency (10) is at least 1 MHz.

9. The arc fault detection device (1) according to any one of claims 1 or 2, characterized in that, The lower cut-off frequency (12) of the input bandpass filter (5) is higher than half of the bandwidth of the arc frequency range (7).

10. The arc fault detection device (1) according to any one of claims 1 or 2, characterized in that, An intermediate bandpass filter (14) is connected to the output of the sampling mixer (6).

11. The arc fault detection device (1) according to claim 10, characterized in that, The upper cut-off frequency (17) of the intermediate bandpass filter (14) is lower than the lower cut-off frequency (12) of the input bandpass filter (5).

12. The arc fault detection device (1) according to claim 10, characterized in that, An envelope detector (15) is connected to the output of the intermediate bandpass filter (14).

13. The arc fault detection device (1) according to claim 12, characterized in that, The output of the envelope detector (15) is connected to the control unit (16) of the arc fault detection device (1), and the control unit (16) is embodied to compare the signal delivered by the envelope detector (15) with at least one arc criterion and output a trigger signal if the signal matches the arc criterion.

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