AC-DC arc fault detection method based on Rogowski coil magnetic coupling resonance

Abstract

The invention provides an AC-DC arc fault detection method based on Rogowski coil magnetic coupling resonance, and the method comprises the steps: enabling a to-be-detected line to pass through a uniformly wound Rogowski coil, and obtaining a specified resonant frequency through adjusting the size of a skeleton structure, the number of turns of a winding, and the capacitance value of a parallel inductor; when the circuit to be detected has an arc fault, the Rogowski coil amplifies the characteristic frequency band signal corresponding to the resonant frequency through magnetic coupling resonance so as to detect the arc fault state.

Description

Technical Field

[0001] The invention belongs to the technical field of AC and DC arc fault detection, and in particular relates to an AC and DC arc fault detection method based on magnetic coupling resonance of a Rogowski coil. Background Art

[0002] In recent years, with the development and progress of technology in the low-voltage power distribution industry, the system scale and voltage and current levels have gradually increased, the cable structure has become increasingly complex, and the potential line safety risks have also increased. Fault arc is a gas ionization discharge phenomenon caused by air breakdown due to aging and damage of insulation in electrical lines or equipment, loose electrical connections, humid air, and a sharp increase in voltage and current. It is an important cause of electrical fires. Usually, the series arc fault is connected in series in the electrical line, and its impedance reduces the load working current. Therefore, the traditional overcurrent protection device will not produce an action to cut off the fault circuit. For parallel arc faults, the fault current is related to the fault circuit impedance. If the line impedance is high, the fault current is small, and the traditional circuit protection device will not respond to it. Since the continuous burning of the arc fault will produce a higher temperature, when the arc continues to burn, it often causes electrical fires. Therefore, designing a low-cost and high-efficiency arc fault detection device is of great significance for preventing electrical fires and protecting the safety of life and property.

[0003] At present, arc fault detection methods are mainly based on detection methods such as electromagnetic wave signals, sound signals, light signals, heat signals, and high-frequency current associated with arcs. Due to the diversity, randomness, and uncertainty of the occurrence location of arc faults, the detection of sound, light, heat, and other signals requires an increase in the number of sensors and detection locations, resulting in increased detection and system maintenance costs. Voltage and current are electrical quantities that are easy to obtain in traditional distribution line protection systems. Therefore, existing arc fault detection methods mainly detect fault characteristics in current or voltage. From the perspective of current characteristics, existing detection methods mostly use current zero-point singularity, waveform similarity, harmonic content, high-frequency content, and rise rate to construct fault judgment criteria; due to the obvious difference in high-frequency signal characteristics during normal and fault conditions, the use of signal high-frequency characteristics to distinguish arc faults is currently widely used. However, traditional current transformers are not only prone to core saturation under high currents, resulting in increased measurement errors, but also have significant bandwidth limitations in high-frequency current environments. Due to its design principle and the characteristics of the core material, the response frequency range of the transformer is usually limited, and it is impossible to accurately capture subtle changes in high-frequency signals. The rapid change of high-frequency current may cause signal distortion or attenuation, affecting the accuracy and reliability of fault detection, especially when it is necessary to monitor high-frequency arc faults. At the same time, affected by nonlinear loads, it is usually difficult to meet the multi-type requirements of loads during fault detection using a single feature. Therefore, multi-feature fusion technology based on machine learning and deep learning technology has attracted the attention of many scholars in recent years. However, the deployment of complex algorithms to embedded hardware devices faces challenges such as computing power, storage space, energy consumption, and real-time performance. Hardware usually has limited resources, and complex algorithms may exceed its tolerance. In addition, the energy consumption and execution time of the algorithm also need to be considered to ensure the efficiency and real-time performance of the system. Summary of the invention

[0004] In view of the many defects and shortcomings of the existing technical solutions, the present invention utilizes the principle of magnetic coupling resonance, combines the advantages of the Rogowski coil sensor with large bandwidth and no magnetic saturation, and connects inductors and capacitors of different values ​​in parallel by impedance matching, thereby increasing the frequency adjustable range, realizing resonant amplification of the characteristic frequency band signal of the arc fault, and effectively extracting the specific high-frequency components in the line current. Unlike the traditional Rogowski coil sensor combined with an integrator for line current measurement, this combination not only enhances the response of the high-frequency signal, but also effectively filters out low-frequency noise, further expanding the bandwidth and improving the signal-to-noise ratio. In the monitoring of arc faults or other high-frequency currents, the synergistic effect of magnetic coupling resonance and Rogowski coils helps to improve the sensitivity and reliability of the detection system and realize the detection of AC and DC arc faults.

[0005] The technical solution specifically adopted by the present invention to solve the technical problem is: A method for detecting AC and DC arc faults based on the magnetic coupling resonance of Rogowski coils. The line to be measured passes through a uniformly wound Rogowski coil. By adjusting the skeleton structure size, the number of winding turns, and the parallel inductance and capacitance values, a specified resonance frequency is obtained. When an arc fault occurs in the line to be measured, the Rogowski coil amplifies the signal in the characteristic frequency band corresponding to the resonance frequency through magnetic coupling resonance to detect the arc fault state.

[0006] Further, according to the comparison between the set threshold and the collected signal in the characteristic frequency band, it is judged whether an arc fault occurs.

[0007] Further, when the detected signal exceeds the threshold, after waiting for a first time period, if a signal exceeding the threshold is detected again within the next second time period, an arc fault may occur in the line, and the zero-crossing rate calculation is entered: starting from the signal that first exceeds the threshold, the zero-crossing rate of the signal within a third time period is calculated; and only the zero-crossing rate ZCR of the signal with an amplitude exceeding a given value is calculated. If 0.002 < ZCR < 0.02, it is judged that an arc fault occurs in the line to be measured; if it is not within this range, if a signal exceeds the threshold within the next fourth time period, the zero-crossing rate of the signal within the third time period is calculated again and the arc fault is judged; if no signal exceeds the threshold within the fourth time period, it is judged that there is no arc fault in the line.

[0008] The formula for calculating the zero-crossing rate ZCR is; Wherein, s is a signal with a length of T, and the function is 1 when the parameter A is true, otherwise it is 0.

[0009] And, a sensor for detecting AC and DC arc faults based on the magnetic coupling resonance of Rogowski coils, including: a uniformly wound Rogowski coil and an inductor and / or capacitor connected in parallel at both ends of the Rogowski coil; by adjusting the skeleton structure size, the number of winding turns, and the parallel inductance and capacitance values, a specified resonance frequency is obtained; the line to be measured passes through the Rogowski coil. When an arc fault occurs in the line to be measured, the Rogowski coil amplifies the signal in the characteristic frequency band corresponding to the resonance frequency through magnetic coupling resonance; used to detect the arc fault state.

[0010] Further, different inductors and / or capacitors are connected in parallel in an impedance matching manner to increase the frequency adjustable range.

[0011] And, a device for detecting AC and DC arc faults based on the magnetic coupling resonance of Rogowski coils, including: the above-mentioned sensor, and the sensor is connected to a single-chip microcomputer; the single-chip microcomputer judges whether an arc fault occurs according to the set threshold and the signal in the characteristic frequency band collected by the sensor.

[0012] Further, when the signal detected by the single-chip microcomputer exceeds the threshold, after waiting for the first duration, if a signal exceeding the threshold is detected again within the next second duration, an arc fault may occur in the circuit, and the zero-crossing rate calculation is entered: starting from the signal that first exceeds the threshold, calculate the zero-crossing rate of the signal within the third duration; and only calculate the zero-crossing rate ZCR of the signal whose amplitude exceeds the given value. If 0.002 < ZCR < 0.02, it is determined that an arc fault has occurred in the circuit under test; if it is not within this range, if a signal exceeds the threshold within the next fourth duration, calculate the zero-crossing rate of the signal within the third duration again and perform an arc fault judgment; if no signal exceeds the threshold within the fourth duration, it is determined that there is no arc fault in the circuit.

[0013] The formula for calculating the zero-crossing rate ZCR is; Wherein, s is a signal with a length of T, and the function is 1 when the parameter A is true, otherwise it is 0.

[0014] Compared with the prior art, the present invention and its preferred solutions utilize the principle of magnetic coupling resonance, combine the advantages of large bandwidth and no magnetic saturation of the Rogowski coil sensor, and connect inductors and capacitors with different values in parallel through impedance matching, increasing the frequency adjustable range, realizing the resonant amplification of the signal in the arc fault characteristic frequency band, and effectively extracting specific high-frequency components in the line current. Different from the traditional Rogowski coil sensor combined with an integrator for measuring the line current, this combination not only enhances the response to high-frequency signals, but also can effectively filter out low-frequency noise, further expanding the bandwidth and improving the signal-to-noise ratio. In the monitoring of arc faults or other high-frequency currents, the synergistic effect of magnetic coupling resonance and the Rogowski coil helps to improve the sensitivity and reliability of the detection system, and realizes the detection of AC and DC arc faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described in detail below with reference to the drawings and specific embodiments: Figure 1 Schematic diagram of the Rogowski coil structure and the principle of the present invention; Figure 2 Schematic diagram of the connection between the Rogowski coil and the circuit in the embodiment of the present invention; Figure 3 Flowchart of the arc fault algorithm in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] In order to make the features and advantages of this patent more obvious and understandable, specific embodiments are hereby given and described in detail as follows: It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0017] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0018] The present invention is specifically described below by an embodiment: Rogowski coil structure Figure 1 As shown. The Rogowski coil has no iron core, and the induced signal is very weak at low frequencies. Its output is proportional to the rate of change of current. The slow change of low-frequency current causes the signal amplitude to be very small. At high frequencies, the Rogowski coil exhibits better response performance, can sense larger voltage signals, and accurately capture subtle changes in high-frequency current. In addition, since the Rogowski coil has a coreless structure, magnetic saturation is avoided, and it has a wide bandwidth and high signal accuracy in high-frequency applications, making it suitable for detection scenarios such as high-frequency arc faults. Magnetic coupling resonance amplifies the current signal at the resonant frequency, allowing the Rogowski coil to more effectively sense current changes at a specific frequency, acting like a bandpass filter.

[0019] Traditional Rogowski coil sensors must be used in conjunction with an integrator and are mainly used to sense and measure current signals within a wide frequency band. They lack frequency selectivity and require subsequent algorithm processing to extract current characteristic signals.

[0020] In the scheme designed by the present invention, the Rogowski coil sensor no longer needs to be used in conjunction with an integrator, but uses magnetic coupling resonance to realize the function of a bandpass filter, specifically extracting and amplifying signals in a specific frequency band of the fault current. According to the characteristic frequency bands of DC and AC arc faults, by adjusting the number of turns and frame size of the Rogowski coil, and connecting a specific value of inductance or capacitance in parallel at both ends of the coil, and changing the internal parameters of the coil by impedance matching, the resonant frequency of the coil can be adjusted to the fault characteristic frequency band, thereby directly and effectively extracting the current component of the frequency band, and realizing efficient detection and amplification of arc fault characteristic signals.

[0021] Due to the limitation of its working principle, the traditional Rogowski coil sensor needs to be combined with an integrator to process the signal, so it can only be used in AC scenarios and cannot detect DC faults. The present invention uses the principle of magnetic coupling resonance to amplify signals in a specific frequency band. Even when a fault arc occurs in a DC scenario, the fault signal of the corresponding frequency band can be accurately captured. Therefore, it is not only suitable for the detection of AC faults, but also can realize the effective monitoring of DC faults, making the present invention widely applicable and adaptable in AC and DC arc fault detection.

[0022] When the line under test is operating normally, the frequency component of its current is usually below the MHz level, and no obvious high-frequency signal is generated. However, an arc fault will generate a significant high-frequency signal, and its frequency is usually much higher than the current frequency when the line is operating normally. Therefore, by adjusting the frame size and the value of the parallel inductor and capacitor, the resonant frequency of the Rogowski coil is adjusted so that it responds specifically to the high-frequency signal of the arc fault, which can effectively distinguish between the normal working state and the arc fault state.

[0023] The natural resonant frequency of the Rogowski coil is mainly determined by the frame size and the number of winding turns. For example, a Rogowski coil with Ra=8.5mm, Rb=24mm, h=15mm, 105 turns and uniform winding can reach a resonant frequency of 3MHz. Figure 2 The connection method shown can effectively filter out other frequency signals outside a specific frequency band (near the resonant frequency), effectively extract the high-frequency components of a specific frequency band in the line current, and can use a single-chip microcomputer to detect and identify the collected signals through a sampling circuit, thereby realizing the detection and judgment of arc faults.

[0024] The purpose of the present invention is to utilize the advantages of the Rogowski coil sensor, which has a large bandwidth and no magnetic saturation, and combine it with the principle of magnetic coupling resonance to extract specific high-frequency components in the line current signal to detect and identify whether an arc fault occurs in the line. The implementation of this solution mainly includes two modules: (1) Sensor detection module: Figure 1 The uniformly wound Rogowski coil shown in the figure can achieve different resonant frequencies by adjusting the frame structure size, winding turns, and parallel inductance and capacitance values ​​according to actual needs. Figure 2 As shown in the figure, the line to be tested passes through the coil. When the line to be tested is working normally, the Rogowski coil induction signal is very small, almost zero; however, when an arc fault occurs in the line to be tested, a large amount of high-frequency signals will appear in the line, and the coil amplifies the characteristic frequency band signal through magnetic coupling resonance. In this way, the sensor can effectively detect the arc fault state.

[0025] (2) Algorithm module: Since the high-frequency signals generated by arc faults have a very high frequency, due to the performance limitations of the microcontroller, the signal sampling rate cannot meet the precise capture and real-time processing of these high-frequency signals, and some key high-frequency signal features may not be detected in a timely or accurate manner. Therefore, to improve the detection reliability, on the basis of signal threshold judgment, the calculation of the signal zero-crossing rate can be added. The formula for the zero-crossing rate (zcr) is shown as follows.

[0026] Where s is a signal with a length T (number of sampling points), and the function is 1 when the parameter A is true and 0 otherwise.

[0027] The algorithm flow chart is as Figure 3 shown, taking a sampling rate of 100 kHz as an example (the thresholds in the figure are adjusted according to the actual situation). When the signal detected by the microcontroller exceeds the threshold, to avoid interference caused by factors such as the connection of electrical appliances or the operation of switches under normal working conditions, after waiting for 20 ms, if a signal exceeding the threshold is detected again within the next 60 ms, an arc fault may have occurred in the circuit, and the zero-crossing rate calculation is entered. Starting from the signal that first exceeds the threshold, the zero-crossing rate (ZCR) of the signal within 80 ms is calculated. To avoid interference, only the zero-crossing rate of signals with an amplitude exceeding 100 mV is calculated. If 0.002 < ZCR < 0.02, it is considered that an arc fault has occurred in the line to be measured; if it is not within this range, if a signal exceeds the threshold within the next 1 s, the zero-crossing rate of the signal within 80 ms is calculated again and an arc fault judgment is made; if no signal exceeds the threshold within 1 s, it is considered that there is no arc fault in the line.

[0028] It should be noted that unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those of ordinary skill in the field to which the present invention belongs. The "first", "second" and similar terms used in the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. Words such as "including" or "comprising" mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects. Words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right", etc. are only used to represent relative position relationships, and when the absolute position of the object being described changes, the relative position relationship may also change accordingly.

[0029] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

[0030] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of AC and DC arc fault detection methods based on magnetic coupling resonance of Rogowski coils under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A method for detecting AC and DC arc faults based on magnetic coupling resonance of Rogowski coils, characterized in that: Pass the circuit under test through the uniformly wound Rogowski coil. By adjusting the skeleton structure size, the number of winding turns, and the parallel inductance and capacitance values, a specified resonant frequency is obtained. When an arc fault occurs in the circuit under test, the Rogowski coil magnetically couples and resonates to amplify the signal in the characteristic frequency band corresponding to the resonant frequency to detect the arc fault state.

2. The AC / DC arc fault detection method based on the magnetic coupling resonance of the Rogowski coil according to claim 1 is characterized in that: Judge whether an arc fault occurs based on the comparison between the set threshold and the collected signal in the characteristic frequency band.

3. The AC / DC arc fault detection method based on Rogowski coil magnetic coupling resonance according to claim 2, characterized in that: When the detected signal exceeds the threshold, after waiting for the first time period, if a signal exceeding the threshold is detected again within the next second time period, an arc fault may occur in the circuit, and the zero-crossing rate calculation is entered: starting from the signal that first exceeds the threshold, calculate the zero-crossing rate of the signal within the third time period; and only calculate the zero-crossing rate ZCR of the signal whose amplitude exceeds a given value. If 0.002 < ZCR < 0.02, it is judged that an arc fault occurs in the circuit under test; if it is not within this range, if a signal exceeds the threshold within the next fourth time period, calculate the zero-crossing rate of the signal within the third time period again and make an arc fault judgment; if no signal exceeds the threshold within the fourth time period, it is judged that there is no arc fault in the circuit.

4. The AC / DC arc fault detection method based on Rogowski coil magnetic coupling resonance according to claim 3, characterized in that: The zero-crossing rate ZCR calculation formula is; in, s is a signal of length T, function 1 if argument A is true, 0 otherwise.

5. An AC / DC arc fault detection sensor based on Rogowski coil magnetic coupling resonance, characterized in that: It includes: A uniformly wound Rogowski coil and an inductor and / or capacitor connected in parallel at both ends of the Rogowski coil; By adjusting the skeleton structure size, the number of winding turns, and the parallel inductance and capacitance values, a specified resonant frequency is obtained. Pass the circuit under test through the Rogowski coil. When an arc fault occurs in the circuit under test, the Rogowski coil magnetically couples and resonates to amplify the signal in the characteristic frequency band corresponding to the resonant frequency; for detecting the arc fault state.

6. The AC / DC arc fault detection sensor based on Rogowski coil magnetic coupling resonance according to claim 5, characterized in that: Connect different inductors and / or capacitors in parallel in an impedance matching manner to increase the frequency adjustable range.

7. An AC / DC arc fault detection device based on magnetic coupling resonance of Rogowski coils, characterized in that: It includes: The sensor according to claim 5 or 6, the sensor is connected to a single-chip microcomputer; the single-chip microcomputer judges whether an arc fault occurs according to the set threshold and the signal in the characteristic frequency band collected by the sensor.

8. The AC / DC arc fault detection device based on Rogowski coil magnetic coupling resonance according to claim 7, characterized in that: When the signal detected by the single-chip microcomputer exceeds the threshold, after waiting for the first time period, if a signal exceeding the threshold is detected again within the next second time period, an arc fault may occur in the circuit, and the zero-crossing rate calculation is entered: starting from the signal that first exceeds the threshold, calculate the zero-crossing rate of the signal within the third time period; and only calculate the zero-crossing rate ZCR of the signal whose amplitude exceeds a given value. If 0.002 < ZCR < 0.02, it is judged that an arc fault occurs in the circuit under test; if it is not within this range, if a signal exceeds the threshold within the next fourth time period, calculate the zero-crossing rate of the signal within the third time period again and make an arc fault judgment; if no signal exceeds the threshold within the fourth time period, it is judged that there is no arc fault in the circuit.

9. The AC / DC arc fault detection device based on Rogowski coil magnetic coupling resonance according to claim 8, characterized in that: The zero-crossing rate ZCR calculation formula is; in, s is a signal of length T, function 1 if argument A is true, 0 otherwise.

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