Method for testing and locating distribution network line faults based on optical fiber pulse transmission

Abstract

The present invention provides a method for testing and locating faults in a distribution network line based on optical fiber pulse transmission, which relates to the technical field of distribution networks. The method includes obtaining the phase voltage signal, phase current signal and optical fiber transmission signal of the distribution network line, and judging faults through wavelet transform. When a fault exists, a narrow linewidth laser is used to generate a probe light, and a scattered signal is obtained after modulation by a Bragg grating array. The scattered signal is subjected to gain adjustment and coherent demodulation to determine the mutation point. Based on the mutation point, a bidirectional reflection measurement is adopted to obtain a reflection signal, and the fault location is determined by combining the group velocity dispersion equation and adaptive multi-stage dispersion compensation. Through optoelectronic joint detection and multi-stage signal processing, the present invention improves the accuracy of fault location, realizes the fast and accurate location of distribution network faults, and has strong anti-interference ability and environmental adaptability.

Description

Technical Field

[0001] The present invention relates to the technology of distribution networks, and particularly to a method for testing and locating faults in distribution network lines based on optical fiber pulse transmission. Background Art

[0002] Distribution network lines are an important part of the power system, and their safe and stable operation is directly related to the reliable power supply to users. With the continuous expansion of the scale and the increase in complexity of distribution networks, the rapid and accurate location of line faults has become a key link in ensuring power supply reliability. At present, the fault location in distribution networks mainly relies on traditional electrical quantity measurement methods, including impedance measurement methods, traveling wave ranging methods, etc. At the same time, with the development of optical fiber sensing technology, fault detection methods based on optical fibers have gradually been applied, and this method has the advantages of anti-electromagnetic interference and high accuracy.

[0003] Traditional electrical quantity measurement methods are easily affected by factors such as system impedance changes and load fluctuations. In complex distribution networks, the location accuracy often fails to meet the actual requirements. Especially in multi-branch lines, it is more difficult to accurately locate the fault point.

[0004] Existing optical fiber fault detection systems do not fully consider the influence of optical fiber dispersion effects during signal processing, resulting in a significant reduction in measurement accuracy during long-distance transmission. At the same time, due to the attenuation of optical signals during transmission, the detection sensitivity will also be affected.

[0005] Current fault location methods generally lack real-time adaptability and cannot dynamically adjust measurement parameters according to the actual transmission environment, which makes it difficult to ensure the location accuracy and reliability under different working conditions, especially in harsh environments or complex fault conditions. Summary of the Invention

[0006] The embodiments of the present invention provide a method for testing and locating faults in distribution network lines based on optical fiber pulse transmission, which can solve the problems in the prior art.

[0007] In the first aspect of the embodiments of the present invention, a method for testing and locating faults in distribution network lines based on optical fiber pulse transmission is provided, including:

[0008] Obtain the phase voltage signal and phase current signal of the distribution network line, and at the same time obtain the transmission signal of the optical fiber in the distribution network line; according to the phase voltage signal and the phase current signal, judge whether there is a fault in the distribution network line through wavelet transform;

[0009] When it is confirmed that there is a fault in the distribution network line, a detection light is generated by a narrow linewidth laser, and the detection light is frequency - modulated by a Bragg grating array to obtain the scattered signal generated by the acousto - optic interaction; the gain coefficient of the photodetector is adjusted in real - time according to the scattered signal intensity; the scattered signal is coherently demodulated to extract the signal amplitude and phase information, and the signal mutation point is determined;

[0010] Based on the time information of the mutation point, using the bidirectional reflection measurement method, detection light pulses are respectively emitted at both ends of the optical fiber to obtain the bidirectional reflection signal; by calculating the time delay difference and attenuation characteristics of the bidirectional reflection signal, a group velocity dispersion equation including the zero - dispersion coefficient and dispersion slope is established, and combined with the adaptive multi - stage dispersion compensation algorithm, the specific position of the fault point is obtained;

[0011] Generate a fault location report containing the fault point location information and send the fault location report to the distribution network monitoring center.

[0012] Judging whether there is a fault in the distribution network line according to the phase voltage signal and the phase current signal through wavelet transform includes:

[0013] Perform wavelet transform on the phase voltage signal and the phase current signal to obtain the high - frequency components and low - frequency components of the phase voltage signal and the phase current signal, determine the energy eigenvalue of the high - frequency components according to the energy of each frequency band in the high - frequency components, and when the energy eigenvalue exceeds the preset energy threshold, it is determined that a fault has occurred;

[0014] According to the polarity relationship and phase sequence relationship of the high - frequency components, determine the fault type, where the fault phase is determined according to the polarity of the first wave of the high - frequency components, and the fault nature is determined according to the phase sequence relationship between different phases.

[0015] Adjusting the gain coefficient of the photodetector in real - time according to the scattered signal intensity; coherently demodulating the scattered signal, extracting the signal amplitude and phase information, and determining the signal mutation point includes:

[0016] Determine the signal power of the scattered signal intensity, and determine the signal - to - noise ratio according to the ratio of the signal power to the rated power of the photodetector;

[0017] According to the deviation between the signal power and the preset target power, calculate the gain coefficient of the photodetector through an exponential function, the base of the exponential function is the natural constant, and the exponent is the opposite of the product of the deviation and the signal - to - noise ratio, and apply a time - response constraint to the gain coefficient, so that the ratio of the change rate of the gain coefficient to the current gain value is equal to the difference between the target value and the current value of the gain coefficient, and perform a time - domain response constraint on the gain coefficient;

[0018] Coherently mix the scattered signal with the local oscillation signal to obtain an in-phase component signal and a quadrature component signal, and reconstruct the in-phase component signal and the quadrature component signal to obtain a complex-domain signal;

[0019] Normalize the complex-domain signal and extract the signal envelope through Hilbert transform. At the same time, calculate the instantaneous phase of the complex-domain signal and perform phase unwrapping to construct a multi-dimensional feature vector including the amplitude change rate and the phase change rate; determine the signal mutation point according to the comparison result between the weighted cumulative sum of the multi-dimensional feature vector and the preset dynamic threshold.

[0020] Based on the time information of the mutation point, adopt the bidirectional reflection measurement method, and respectively transmit detection optical pulses at both ends of the optical fiber to obtain the bidirectional reflection signal, including:

[0021] Transmit the first optical pulse at both ends of the optical fiber according to the time sequence of the reference time plus the cycle time, and transmit the second optical pulse according to the time sequence of the reference time plus the cycle time and the rated delay compensation time;

[0022] Respectively collect the bidirectional reflection signals generated by the transmission of the first optical pulse and the second optical pulse in the optical fiber, and calculate the first transmission delay and the second transmission delay of the bidirectional reflection signal, where the first transmission delay is the sum of the round-trip time of the first reflection signal from the transmitting end to the fault point and the system delay of the transmitting end, and the second transmission delay is the sum of the round-trip time of the second reflection signal from the transmitting end to the fault point and the system delay of the transmitting end; calculate the initial value of the fault point position according to the difference between the first transmission delay and the second transmission delay and the total length of the optical fiber.

[0023] By calculating the delay difference and attenuation characteristics of the bidirectional reflection signal, establish a group velocity dispersion equation including the zero dispersion coefficient and the dispersion slope, and combine with the adaptive multi-stage dispersion compensation algorithm to obtain the specific position of the fault point, including:

[0024] Obtain the power value of the bidirectional reflection signal, establish a bidirectional power equation including the attenuation coefficient and the reflection coefficient, calculate the differential attenuation of the optical fiber link according to the bidirectional power equation, and correct the initial value of the fault point position according to the differential attenuation;

[0025] Establish a group velocity dispersion equation including the zero dispersion coefficient and the dispersion slope, calculate the frequency-domain compensation function according to the group velocity dispersion equation, perform convolution operation on the bidirectional reflection signal and the frequency-domain compensation function, and perform inverse Fourier transform to obtain the compensated time-domain waveform;

[0026] Perform a weighted iterative operation on the first transmission delay, the second transmission delay, the differential attenuation, and the compensated time-domain waveform to obtain the final value of the fault point location, and stop the iteration when the position difference between two adjacent iterations is less than a preset error threshold.

[0027] Obtain the power value of the bidirectional reflection signal, establish a bidirectional power equation including the attenuation coefficient and the reflection coefficient, calculate the differential attenuation of the optical fiber link according to the bidirectional power equation, and correct the initial value of the fault point location according to the differential attenuation; establish a group velocity dispersion equation including the zero dispersion coefficient and the dispersion slope, and calculate the frequency-domain compensation function according to the group velocity dispersion equation, including:

[0028] Establish a bidirectional power equation including the attenuation coefficient and the reflection coefficient, where the bidirectional power equation includes a forward transmission equation and a reverse transmission equation. The forward transmission equation describes the power attenuation characteristic from one end of the optical fiber to the fault point, and the reverse transmission equation describes the power attenuation characteristic from the other end of the optical fiber to the fault point; calculate the differential attenuation coefficient according to the ratio of the forward transmission equation to the reverse transmission equation.

[0029] Based on the differential attenuation coefficient, establish a non-linear correction equation between power and temperature. The non-linear correction equation includes the first-order coefficient and the second-order coefficient of power, and introduces a temperature correction term. Correct the differential attenuation coefficient according to the non-linear correction equation, and correct the initial value of the fault point location according to the corrected differential attenuation coefficient.

[0030] Establish a group velocity dispersion equation including the zero dispersion coefficient, the dispersion slope, and the second-order dispersion slope. Decompose the group velocity dispersion equation into a material dispersion term and a waveguide dispersion term, where the material dispersion term is determined by the second-order wavelength derivative of the refractive index, and the waveguide dispersion term is determined by the normalized frequency and the relative refractive index difference.

[0031] Construct a frequency-domain compensation function according to the group velocity dispersion equation, calculate the derivative of the phase of the frequency-domain compensation function with respect to the angular frequency to obtain the group delay response; apply the frequency-domain compensation function to the bidirectional reflection signal to obtain the compensated dispersion amount.

[0032] In the second aspect of the embodiments of the present invention,

[0033] Provide an electronic device, including:

[0034] A processor;

[0035] A memory for storing instructions executable by the processor;

[0036] Wherein, the processor is configured to call the instructions stored in the memory to execute the method described above.

[0037] In the third aspect of the embodiments of the present invention,

[0038] a computer-readable storage medium is provided, on which computer program instructions are stored, and when the computer program instructions are executed by a processor, the foregoing method is implemented.

[0039] The beneficial effects of the present application are as follows:

[0040] 1. The present invention analyzes the phase voltage signal and phase current signal of the distribution network line through wavelet transform, and combines the optical fiber transmission signal to realize the rapid detection of faults, improving the accuracy and reliability of fault detection.

[0041] 2. The present invention uses a narrow linewidth laser and a Bragg grating array for frequency modulation, optimizes the scattered signal quality by adjusting the gain coefficient of the photodetector in real time, and uses coherent demodulation technology to extract signal features, which can accurately identify signal mutation points and effectively improve the accuracy of fault location.

[0042] 3. Based on the bidirectional reflection measurement method and the group velocity dispersion equation, and combined with the adaptive multi-stage dispersion compensation algorithm, the present invention can effectively eliminate the dispersion influence in the optical fiber transmission process, realize the accurate location of the fault point, and at the same time realize the timely transmission of fault information by generating a fault location report, providing a reliable basis for fault handling. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a schematic flow chart of a method for testing and locating faults in a distribution network line based on optical fiber pulse transmission according to an embodiment of the present invention;

[0044] Figure 2 is a schematic diagram of a distribution network fault detection system according to an embodiment of the present invention;

[0045] Figure 3 is a schematic diagram of statistics of fault location accuracy according to an embodiment of the present invention;

[0046] Figure 4 is a schematic diagram for comparing compensation effects in different stages according to an embodiment of the present invention;

[0047] Figure 5 is a schematic diagram of bidirectional power attenuation characteristic analysis according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0049] The technical solutions of the present invention will be described in detail below with specific embodiments. These specific embodiments may be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments.

[0050] Figure 1 The flowchart of the method for testing and locating faults in a distribution network line based on optical fiber pulse transmission according to an embodiment of the present invention is shown as Figure 1 shown, and the method includes:

[0051] Obtain the phase voltage signal and phase current signal of the distribution network line, and at the same time obtain the transmission signal of the optical fiber in the distribution network line; judge whether there is a fault in the distribution network line through wavelet transform according to the phase voltage signal and the phase current signal;

[0052] When it is confirmed that there is a fault in the distribution network line, use a narrow linewidth laser to generate a probe light, frequency modulate the probe light through a Bragg grating array, and obtain the scattered signal generated by the acousto-optic interaction; adjust the gain coefficient of the photodetector in real time according to the scattered signal intensity; perform coherent demodulation on the scattered signal, extract the signal amplitude and phase information, and determine the signal mutation point;

[0053] Based on the time information of the mutation point, adopt the bidirectional reflection measurement method, emit probe light pulses at both ends of the optical fiber respectively, and obtain the bidirectional reflection signal; establish a group velocity dispersion equation including the zero dispersion coefficient and dispersion slope by calculating the time delay difference and attenuation characteristics of the bidirectional reflection signal, and combine it with the adaptive multi-stage dispersion compensation algorithm to obtain the specific position of the fault point;

[0054] Generate a fault location report including the fault point location information, and send the fault location report to the distribution network monitoring center.

[0055] In an optional implementation manner, judging whether there is a fault in the distribution network line through wavelet transform according to the phase voltage signal and the phase current signal includes:

[0056] Perform wavelet transform on the phase voltage signal and the phase current signal to obtain the high-frequency components and low-frequency components of the phase voltage signal and the phase current signal. Determine the energy eigenvalue of the high-frequency components according to the energy of each frequency band in the high-frequency components. When the energy eigenvalue exceeds the preset energy threshold, it is determined that a fault has occurred;

[0057] Determine the fault type according to the polarity relationship and phase sequence relationship of the high-frequency components, where the fault phase is determined according to the polarity of the first wave of the high-frequency components, and the fault nature is determined according to the phase sequence relationship between different phases.

[0058] First, perform wavelet decomposition on the phase voltage signal and the phase current signal of the distribution network line. Use the db4 wavelet basis function and set the decomposition level to 4 layers to obtain the high-frequency components d1, d2, d3, d4 and the low-frequency component a4 respectively. The high-frequency components contain fault transient characteristic information, and the low-frequency components reflect the basic trend of the signal. To improve the analysis accuracy, preprocess the original signal, use a 50Hz sampling frequency, and set the number of sampling points to 1024 points.

[0059] Conduct energy characteristic analysis on the obtained high-frequency components and calculate the energy values of each frequency band. Taking phase A as an example, when operating normally, the energy values of the d1-d4 frequency bands are 0.15, 0.21, 0.28, and 0.32 respectively. When a single-phase grounding fault occurs, the energy values increase significantly to 1.85, 2.31, 2.68, and 2.92. Set the energy threshold to 5 times the maximum energy value in the normal state, that is, 1.60. When the energy of any frequency band exceeds the threshold, it is determined that a fault has occurred in the line.

[0060] Analyze the polarity characteristics of the high-frequency components and identify the fault phase through the polarity of the first wave. Taking the ABC three-phase system as an example, when a single-phase grounding fault occurs in phase A, the high-frequency component of phase A shows a positive polarity mutation, with an amplitude reaching 2.5pu, while the high-frequency components of phases B and C show negative polarity mutations, with an amplitude of about -1.2pu. Combine the phase sequence relationship to further judge the fault type: during an interphase short circuit, the phase sequence deviation between the fault phases increases significantly, exceeding the normal interval of 120°; during a grounding fault, the phase sequence deviation between the fault phase and the ground potential decreases significantly, approaching 0°.

[0061] Further verify the fault judgment result by analyzing the correlation of the phase current envelopes of each phase. When operating normally, the correlation coefficient of the three-phase current envelopes is greater than 0.95. When a fault occurs, the correlation coefficient between the fault phase and the non-fault phase drops below 0.3. Based on the comprehensive analysis of multi-dimensional characteristics, finally determine the fault type and the fault phase.

[0062] Figure 2 This is a schematic diagram of the distribution network fault detection system according to the embodiment of the present invention:

[0063] This figure shows the results of wavelet transform analysis for a single-phase ground fault on phase A of a distribution network line. In the figure, the db4 wavelet basis function is used for 4-layer decomposition, the sampling frequency is 50 Hz, and the number of sampling points is 1024. From the waveform characteristics, after the fault occurs, the high-frequency component d1 of phase A (represented by circular markers) shows an obvious positive polarity mutation, with a maximum amplitude reaching 2.5 pu and located at about 3 pu above the chart, showing typical single-phase ground fault characteristics. The corresponding high-frequency component d1 of phase B (represented by square markers) and the high-frequency component d1 of phase C (represented by triangular markers) both show negative polarity mutation characteristics, with amplitudes of about -1.2 pu, located at 0 pu in the middle of the chart and -3 pu below the chart respectively. This polarity relationship and amplitude distribution among the three phases clearly reflect the characteristics of the ground fault on phase A. In terms of the time scale, within the observation window of 0 - 7 ms, the waveforms of each phase show obvious exponential decay characteristics. Among them, the decay time constant of the fault phase A is about 5 ms, while the decay time constants of the non-fault phases B and C are about 4 ms. The periodic oscillation characteristics of the waveforms indicate that there is an inherent frequency response in the system, and the oscillation frequency is about 1 Hz. By observing the propagation characteristics and phase relationships of the waveforms, the fault point location and fault nature can be accurately judged, providing a reliable technical basis for fault location.

[0064] Through multi-layer wavelet decomposition and energy feature analysis, instantaneous faults can be detected quickly and accurately, with the detection time less than 10 ms, greatly improving the real-time performance of fault detection; the fault type is identified by combining the polarity of the first wave and the phase sequence relationship, avoiding the problem that traditional methods are easily interfered by transient processes, and the accuracy rate of fault type identification is increased to more than 98%; the current envelope correlation analysis is introduced as an auxiliary verification means to construct a multi-dimensional feature criterion system, significantly improving the reliability of fault diagnosis and reducing the misjudgment rate to less than 0.1%.

[0065] In an optional implementation, the gain coefficient of the photodetector is adjusted in real time according to the scattered signal intensity; the scattered signal is coherently demodulated to extract the signal amplitude and phase information, and determining the signal mutation point includes:

[0066] Determine the signal power of the scattered signal intensity, and determine the signal-to-noise ratio according to the ratio of the signal power to the rated power of the photodetector;

[0067] According to the deviation between the signal power and the preset target power, calculate the gain coefficient of the photodetector through an exponential function, where the base of the exponential function is the natural constant and the exponent is the opposite of the product of the deviation and the signal-to-noise ratio, and apply a time response constraint to the gain coefficient, so that the ratio of the change rate of the gain coefficient to the current gain value is equal to the difference between the target value and the current value of the gain coefficient, and apply a time-domain response constraint to the gain coefficient;

[0068] Coherently mix the scattered signal with the local oscillation signal to obtain the in-phase component signal and the quadrature component signal, and reconstruct the in-phase component signal and the quadrature component signal to obtain a complex-domain signal;

[0069] Perform normalization processing on the complex-domain signal and extract the signal envelope through Hilbert transform. At the same time, calculate the instantaneous phase of the complex-domain signal and perform phase unwrapping to construct a multi-dimensional feature vector including the amplitude change rate and the phase change rate; Determine the signal mutation point according to the comparison result between the weighted cumulative sum of the multi-dimensional feature vector and the preset dynamic threshold.

[0070] First, obtain the power characteristics of the scattered signal. Measure the instantaneous power value of the scattered signal using an optical power meter, and obtain 1000 data points through continuous sampling. Calculate the average power value as the signal power of the scattered signal. For example, in practical applications, the average power of the scattered signal obtained in a certain measurement is -25 dBm. At the same time, obtain the rated power parameter of the used photodetector. Taking the InGaAs PIN-type detector as an example, its rated power is -10 dBm. Calculate the signal-to-noise ratio by the ratio of the signal power to the rated power. In this case, the signal-to-noise ratio is 0.316.

[0071] When determining the target power, comprehensively consider the dynamic range and detection sensitivity requirements of the system, and set the target power to -20 dBm. Calculate the deviation between the actual signal power and the target power. In this example, the deviation is -5 dB. Combine the signal-to-noise ratio obtained above, multiply the deviation value by the signal-to-noise ratio and take the opposite number to get -1.58. Calculate the initial gain coefficient as 0.206 with the natural constant as the base and -1.58 as the exponent.

[0072] To ensure the smoothness of gain adjustment, impose a time response constraint on the gain coefficient. First, determine the target value of the gain coefficient, which is set to 0.8 in this example. In the time domain, obtain the current gain value every 1 ms, and calculate the difference between the target value and the current value. Assume that the current gain value at a certain moment is 0.3, then the difference is 0.5. Set the ratio of the change rate of the gain coefficient to the current gain value as this difference, so as to achieve smooth gain adjustment. Specifically, if the current gain is 0.3 and the target gain is 0.8, then in the next 1 ms time window, the gain change rate is limited to 0.15 / ms.

[0073] Through experimental verification, after adopting this scheme, when 10 random failures occur, the average error of signal detection is reduced from 15% of the traditional scheme to less than 5%. At the same time, the convergence time of gain adjustment is shortened from the traditional 50 ms to 20 ms, significantly improving the system response speed. In an environment with a temperature fluctuation of ±20 °C, the system can still maintain stable detection performance, and the signal amplitude fluctuation is always controlled within ±2%.

[0074] For different types of photodetectors, this solution also has good adaptability. When using an APD detector, the rated power is set to -30 dBm and the target power is set to -25 dBm, and the system can still achieve accurate gain adjustment. Field tests show that at three different distances of 5 km, 10 km, and 20 km, the accuracy rate of signal detection remains above 95%, which is better than the 80% detection accuracy of the existing technology.

[0075] When there are multiple fault points in the optical fiber link, this solution can adaptively adjust the detection gain of each section of the optical fiber. Experimental verification shows that in the case of 3 fault points and a total optical fiber length of 30 km, the positioning error of the most remote fault point is controlled within the range of ±50 m, which is a significant improvement compared to the ±200 m error of the traditional solution. The dynamic range of the system is extended to 40 dB, a 10 dB increase compared to the existing technology, effectively solving the problem of insufficient sensitivity in detecting remote faults.

[0076] A local oscillator light source with a frequency of 193.1 THz is used, and the continuous optical signal output by it is mixed with the scattered signal to be measured in a 90-degree optical mixer. The in-phase component signal and the quadrature component signal are obtained through a balanced detector, and the signal sampling rate is set to 1 GS / s. In actual tests, the amplitude range of the in-phase component signal is ±100 mV, and the amplitude range of the quadrature component signal is ±95 mV.

[0077] The in-phase component and quadrature component signals collected are complex-reconstructed. Specifically, the in-phase component is used as the real part and the quadrature component is used as the imaginary part to construct a signal in the complex domain. To eliminate the influence of signal amplitude fluctuations, the signal in the complex domain is normalized so that the signal amplitude is restricted within the unit circle.

[0078] The Hilbert transform is performed on the normalized signal in the complex domain to extract the signal envelope. A 1024-point transformation window is used, and the window overlap rate is set to 50%. The analytical form of the signal is obtained through the Hilbert transform, and then the envelope information is extracted. Field tests show that this method can effectively capture the mutation characteristics of the signal amplitude and can accurately identify mutations with an amplitude change rate greater than 5%.

[0079] While extracting the signal envelope, the instantaneous phase of the signal in the complex domain is calculated. First, the phase information is unwrapped to eliminate the influence of phase jumps. The phase unwrapping uses an adaptive threshold method, and phase correction is performed when the phase difference between adjacent sampling points exceeds the preset threshold. In field tests, the phase difference threshold is set to π / 2, achieving continuous phase unwrapping. Based on the unwrapped phase information, the rate of change of the phase with time is calculated.

[0080] Construct a multi-dimensional feature vector that includes the rate of change of amplitude and the rate of change of phase. In the feature vector, set the weight coefficient of the rate of change of amplitude to 0.6 and the weight coefficient of the rate of change of phase to 0.4. Calculate the comprehensive index of the feature vector through weighted accumulation. At the same time, establish a dynamic threshold judgment mechanism to determine the threshold level based on the local statistical characteristics of the signal. In actual measurement, set the statistical window to 100 sampling points and set the dynamic threshold to 1.5 times the local mean.

[0081] When the weighted cumulative sum of the feature vector exceeds the dynamic threshold, it is determined as a signal mutation point. In practical applications, this scheme detects the fault signals on a 20-km optical fiber link and successfully identifies the position of the mutation point with a distance error less than 10 m. Compared with the traditional single-amplitude detection method, the positioning accuracy is improved by 65%. Under the condition of a signal-to-noise ratio of 10 dB, the false alarm rate of mutation point detection is reduced to less than 0.1%, showing a significant improvement compared with 1% of the existing technology.

[0082] This scheme shows good adaptability in different types of optical fiber fault scenarios. For fiber breakage faults, the detection accuracy of mutation points reaches 99.5%; for bending loss faults, the detection accuracy is 95%; for stress damage faults, the detection accuracy is 92%. These data are all better than the 80%-85% detection accuracy of the existing technology.

[0083] In an optional implementation manner, based on the time information of the mutation point, adopt the bidirectional reflectometry method, and respectively emit detection optical pulses at both ends of the optical fiber to obtain the bidirectional reflection signals, including:

[0084] Emit the first optical pulse at both ends of the optical fiber according to the timing sequence of the reference time plus the cycle time, and emit the second optical pulse according to the timing sequence of the reference time plus the cycle time and the rated delay compensation time;

[0085] Respectively collect the bidirectional reflection signals generated by the transmission of the first optical pulse and the second optical pulse in the optical fiber, and calculate the first transmission delay and the second transmission delay of the bidirectional reflection signals, where the first transmission delay is the sum of the round-trip time of the first reflection signal from the transmitting end to the fault point and the system delay of the transmitting end, and the second transmission delay is the sum of the round-trip time of the second reflection signal from the transmitting end to the fault point and the system delay of the transmitting end; calculate the initial value of the fault point position according to the difference between the first transmission delay and the second transmission delay and the total length of the optical fiber.

[0086] When performing optical fiber fault location by adopting the bidirectional reflectometry method based on the time information of the mutation point, first set an optical pulse transmitting device and a signal collecting device at both ends of the optical fiber respectively. The optical pulse transmitting device includes a laser, a pulse modulator and an optical switch, and the signal collecting device includes a photodetector and a data acquisition card.

[0087] Exemplarily, in a fiber optic bidirectional reflection measurement system, first configure the optical pulse emission device. A narrow linewidth laser with a central wavelength of 1550 nm is selected as the light source, and its linewidth is less than 100 kHz. The pulse modulator uses an acousto-optic modulator to generate optical pulses with a pulse width of 100 ns, and the repetition frequency is set to 10 kHz. The optical switch uses a semiconductor optical amplifier, with a switching time less than 5 ns and an extinction ratio greater than 45 dB.

[0088] The signal acquisition device uses an InGaAs APD photodetector with a bandwidth of 1 GHz, a responsivity of 0.9 A / W, and a dark current less than 2 nA. The sampling rate of the data acquisition card is set to 1 GS / s, and the resolution is 12 bit. Through the clock synchronization module, the timing synchronization of the devices at both ends of the fiber is ensured, and the clock accuracy is better than 50 ps.

[0089] Before starting the measurement, perform time calibration on the system. Determine the reference time through an external clock signal and set the reference time to T0. Set the optical pulse emission period to 100 μs, which ensures that the reflected signals of adjacent pulses do not overlap. Estimate the transmission delay based on the fiber length and set the rated delay compensation time to 50 μs.

[0090] At the A end of the fiber, emit the first optical pulse according to the timing of T0 plus 100 μs, and at the same time, emit the second optical pulse at the B end according to the timing of T0 plus 150 μs. In practical applications, when the total fiber length is 20 km, the one-way transmission delay of the optical signal in the fiber is about 100 μs. By precisely controlling the emission timing, the mutual interference of the bidirectional reflection signals is avoided.

[0091] For the first optical pulse, collect its reflection signal at the A end. Assuming that the fault point is located 8 km away from the A end, the round-trip time of the first reflection signal from emission to return to the A end is about 80 μs. Considering that the system delay introduced by devices such as optical switches and fiber connectors in the emission optical path is 2 μs, the actually measured first transmission delay is 82 μs.

[0092] Similarly, for the second optical pulse, collect its reflection signal at the B end. Since the fault point is 12 km away from the B end, the round-trip time of the second reflection signal is about 120 μs. The system delay at the B end is 2.1 μs, and the measured second transmission delay is 122.1 μs. By calculating the difference between the two transmission delays and combining the total fiber length of 20 km, the fault point position is initially determined to be 8.02 km.

[0093] This bidirectional measurement scheme significantly improves the accuracy of fault location. In 50 repeated tests, the standard deviation of the positioning error is less than 5 m, showing a significant improvement compared to the 20 m error of the traditional unidirectional measurement method. The measurement results are not affected by the fiber attenuation characteristics and can maintain stable positioning accuracy on fibers with different loss coefficients.

[0094] Figure 3 Schematic diagram for statistics of fault location accuracy in the embodiments of the present invention:

[0095] This figure comprehensively compares the accuracy performance of different fault location schemes. The circular marker curve represents the technical solution of the present invention (adopting an innovative two-way reflection and time delay difference analysis location algorithm), which shows excellent location accuracy at 20 evenly distributed test points. The average location error is only 0.05m, and the fluctuation range is strictly controlled within ±0.01m, reflecting the high stability of the system. The square marker curve represents the prior art solution 1 (using the traditional one-way reflection measurement method), with an average location error reaching 0.12m and the fluctuation range expanding to ±0.02m, showing an obvious decrease in accuracy under temperature fluctuations and uneven optical fiber losses. The diamond marker curve represents the prior art solution 2 (locating based on a simple power detection method), with the average error further increasing to 0.18m and the fluctuation range reaching ±0.03m, indicating the limitations of this method in complex environments. Through the analysis of the long-term monitoring data of the three schemes, it is found that the technical solution of the present invention not only has significant advantages in absolute accuracy, but also shows obvious technological progress in measurement stability and environmental adaptability. Especially in the case of a long optical fiber link or large changes in environmental conditions, this scheme can still maintain a high location accuracy, which is of great significance for practical engineering applications.

[0096] In the prior art, two main fault location methods are adopted: one is the traditional one-way reflection measurement method, which only uses the reflection signal in a single direction for location and cannot effectively eliminate system errors and environmental impacts; the other is the location method based on power detection, which estimates the fault location by detecting the power attenuation of the reflected light, but this method is easily affected by the unevenness of optical fiber losses and temperature fluctuations, resulting in low location accuracy. These prior arts have problems such as low location accuracy, unstable measurement results, and poor environmental adaptability in practical applications. Especially in the case of a long optical fiber link or large changes in environmental conditions, the location error will further increase.

[0097] To solve the above problems, the present application proposes a fault location method based on two-way reflection and time delay difference analysis. The innovation of this method lies in: firstly, adopting the two-way reflection measurement principle, detecting light pulses are emitted at both ends of the optical fiber respectively, and by comparing the transmission characteristics of the two-way reflection signals, the influence of system errors is effectively eliminated; secondly, the time delay difference analysis technology is innovatively introduced, and by precisely controlling the emission timing of the two light pulses, high-precision time delay measurement is achieved; finally, through the comprehensive analysis of the two-way reflection signals, an accurate fault point location model is established.

[0098] This technical solution brings remarkable technical effects: First, through the principle of bidirectional reflection measurement, the systematic error in the unidirectional measurement method is effectively overcome, and the positioning accuracy is greatly improved; Second, the time delay difference analysis technology is adopted to significantly reduce the influence of environmental factors on the measurement results and enhance the measurement stability of the system; Third, by comprehensively analyzing the bidirectional reflection signals, the adaptability of the system to complex environments is enhanced, so that even when the optical fiber link is long or the environmental conditions change greatly, a high positioning accuracy can still be maintained.

[0099] In an alternative embodiment, by calculating the time delay difference and attenuation characteristics of the bidirectional reflection signal, establishing a group velocity dispersion equation including zero dispersion coefficient and dispersion slope, and combining with an adaptive multi-stage dispersion compensation algorithm, obtaining the specific position of the fault point includes:

[0100] Obtain the power value of the bidirectional reflection signal, establish a bidirectional power equation including attenuation coefficient and reflection coefficient, calculate the differential attenuation of the optical fiber link according to the bidirectional power equation, and correct the initial value of the fault point position according to the differential attenuation;

[0101] Establish a group velocity dispersion equation including zero dispersion coefficient and dispersion slope, calculate the frequency domain compensation function according to the group velocity dispersion equation, perform convolution operation on the bidirectional reflection signal and the frequency domain compensation function, and perform inverse Fourier transform to obtain the compensated time domain waveform;

[0102] Perform weighted iterative operation on the first transmission time delay, the second transmission time delay, the differential attenuation, and the compensated time domain waveform to obtain the final value of the fault point position, and stop the iteration when the position difference obtained in two adjacent iterations is less than a preset error threshold.

[0103] In the power analysis of the bidirectional reflection signal, the power data of forward and reverse transmissions are respectively obtained. Taking a certain type of optical fiber as an example, when the incident optical power is 10 mW, the reflection signal power is measured at the transmitting end and the receiving end respectively. During forward transmission, the power attenuates to 7.2 mW at a distance of 5 km from the transmitting end, and attenuates to 7.5 mW during reverse transmission. By comparing the bidirectional power differences, the differential attenuation characteristics of the optical fiber are calculated. Actual tests show that the average attenuation coefficient of this optical fiber is 0.22 dB / km, and the reflection coefficient is about -45 dB. The initial position of the fault point is corrected according to the differential attenuation, and it is preliminarily determined that the fault point is located 5.2 km from the transmitting end.

[0104] In the group velocity dispersion compensation stage, first measure the dispersion coefficient when the zero-dispersion wavelength is 1550 nm. The zero-dispersion coefficient of this optical fiber is 16 ps / nm / km, and the dispersion slope is 0.08 ps / nm² / km. Based on these parameters, establish the group velocity dispersion equation, and calculate the frequency-domain compensation function through this equation. The adaptive multi-stage dispersion compensation algorithm is used for optimization. This algorithm adopts a progressive compensation strategy, which is divided into two stages: coarse adjustment and fine adjustment. In the coarse adjustment stage, divide the dispersion compensation range into multiple sub-intervals, scan with a step size of 2 ps / nm / km, and the compensation coefficient gradually increases from 8 ps / nm / km to 24 ps / nm / km. Conduct pulse response analysis for each compensation value. When the pulse waveform is the narrowest and has the best symmetry, record the current compensation value as the result of the coarse adjustment. The test data shows that the best coarse adjustment compensation value is 16.4 ps / nm / km.

[0105] After entering the fine adjustment stage, perform local optimization with a fine step size of 0.2 ps / nm / km near the coarse adjustment compensation value. At the same time, introduce an adaptive weight mechanism to dynamically adjust the compensation parameters according to the distortion degree of the pulse waveform. When the waveform distortion is large, increase the compensation step size to 0.4 ps / nm / km to accelerate convergence; when the waveform approaches the ideal state, reduce the compensation step size to 0.1 ps / nm / km to improve accuracy. Evaluate the compensation effect by calculating the skewness and kurtosis indexes of the pulse waveform. When the absolute value of the skewness is less than 0.1 and the kurtosis is close to 3, it is considered to reach the best compensation state.

[0106] To further improve the compensation accuracy, the algorithm also considers the influence of higher-order dispersion. In each iteration, adjust the zero-dispersion coefficient and the dispersion slope simultaneously. The adjustment range of the dispersion slope is: 0.05 - 0.12 ps / nm² / km. The actual measurement shows that when the zero-dispersion coefficient is 16.35 ps / nm / km and the dispersion slope is 0.078 ps / nm² / km, the best compensation effect is obtained. After dispersion compensation, perform a fast Fourier transform on the acquired bidirectional reflection signal, convert the signal to the frequency domain and perform a convolution operation with the compensation function. Then perform an inverse Fourier transform to obtain the time-domain waveform eliminating the influence of dispersion. The compensated waveform shows that the pulse width at the fault point position is reduced from the original 85 ps to 42 ps, and the waveform symmetry index is improved to 0.96, significantly improving the positioning accuracy.

[0107] Finally, weighted iterative calculations are performed to comprehensively analyze the first transmission delay of 5.21 km, the second transmission delay of 5.18 km, the differential attenuation correction value of 5.2 km, and the compensated time-domain waveform positioning value of 5.19 km. The iterative weights are set to 0.3, 0.3, 0.2, and 0.2 respectively, and the position error threshold is set to 0.01 km. After three rounds of iterative operations, the position difference between two adjacent calculations decreases from 0.03 km to 0.008 km, which is less than the preset threshold, and the final position of the fault point is determined to be 5.195 km.

[0108] Figure 4 Schematic diagram for comparing the compensation effects at different stages of the embodiment of the present invention:

[0109] This figure comparatively shows the improvement of the system performance at each compensation stage during the fault location process. The technical solution of the present invention (slant-filled column) represents the adoption of a progressive multi-stage compensation strategy, including temperature dynamic compensation and adaptive dispersion compensation algorithms. As can be seen from the figure, the system performance is improved from 85% in the initial state to 88% after temperature compensation, further increased to 91% through dispersion compensation, and finally reaches a high-performance state of 94%. The prior art solution (dot-filled column) represents the conventional fixed-step compensation method, and its performance improvement is relatively slow: 85% in the initial state, 86% after temperature compensation, 88% after dispersion compensation, and finally only reaches 89%. The comparison between the two solutions clearly shows that the technical solution of the present invention achieves more significant performance improvement at each processing stage through a refined multi-stage compensation strategy, and finally realizes a comprehensive performance advantage of 5 percentage points.

[0110] The prior art usually adopts a fixed-step compensation strategy and uses preset fixed parameters for processing during temperature compensation and dispersion compensation. Although this method is simple to implement, due to the lack of perception of the real-time state of the system and the ability of adaptive adjustment, the compensation effect is limited, and it is difficult to maintain stable system performance in a complex environment. Especially in the case of rapid temperature changes or uneven fiber dispersion characteristics, the fixed-step compensation method is difficult to respond to the changes in the system state in a timely manner, resulting in problems of insufficient compensation or over-compensation.

[0111] First, in the temperature compensation stage, a dynamic compensation algorithm is innovatively adopted. By real-time monitoring the influence of temperature changes on signal transmission characteristics and adaptively adjusting the compensation parameters, the degradation of system performance caused by temperature fluctuations is effectively suppressed. Second, in the dispersion compensation stage, an adaptive dispersion compensation algorithm is adopted. According to the degree of signal distortion, the compensation step size is dynamically adjusted. A larger step size is adopted for rapid approximation when the dispersion is large, and a fine step size is used for fine-tuning when approaching the optimal compensation state, which not only ensures the convergence speed but also improves the compensation accuracy.

[0112] Through the above technical improvements, significant performance enhancements have been achieved in each compensation stage in this embodiment. Compared with the prior art, this solution not only has obvious advantages in the final performance, but more importantly, it realizes a stepped and stable improvement in the system performance. During the temperature compensation stage, the influence of ambient temperature fluctuations is effectively overcome through dynamic compensation; during the dispersion compensation stage, the adaptive algorithm not only improves the compensation accuracy but also avoids signal distortion caused by over-compensation; in the final state, the system exhibits excellent stability and reliability.

[0113] The innovation of this technical solution lies in the combination of a progressive compensation strategy and an adaptive algorithm. Through multi-stage refined processing, the system performance is gradually optimized. The compensation effect of each stage provides a better processing basis for the next stage, forming a virtuous cycle of performance improvement. This method not only improves the overall performance of the system but also enhances the system's adaptability to environmental changes, providing a strong guarantee for the stable and reliable operation of the optical fiber fault location system.

[0114] In an alternative embodiment, the power value of the bidirectional reflection signal is obtained, a bidirectional power equation including an attenuation coefficient and a reflection coefficient is established, the differential attenuation of the optical fiber link is calculated according to the bidirectional power equation, and the initial value of the fault point position is corrected according to the differential attenuation; a group velocity dispersion equation including a zero dispersion coefficient and a dispersion slope is established, and calculating the frequency domain compensation function according to the group velocity dispersion equation includes:

[0115] A bidirectional power equation including an attenuation coefficient and a reflection coefficient is established. The bidirectional power equation includes a forward transmission equation and a reverse transmission equation. The forward transmission equation describes the power attenuation characteristics from one end of the optical fiber to the fault point, and the reverse transmission equation describes the power attenuation characteristics from the other end of the optical fiber to the fault point; the differential attenuation coefficient is calculated according to the ratio of the forward transmission equation to the reverse transmission equation;

[0116] A non-linear correction equation of power and temperature is established based on the differential attenuation coefficient. The non-linear correction equation includes the first-order coefficient and the second-order coefficient of power and introduces a temperature correction term. The differential attenuation coefficient is corrected according to the non-linear correction equation, and the initial value of the fault point position is corrected according to the corrected differential attenuation coefficient;

[0117] A group velocity dispersion equation including a zero dispersion coefficient, a dispersion slope and a second-order dispersion slope is established, and the group velocity dispersion equation is decomposed into a material dispersion term and a waveguide dispersion term. The material dispersion term is determined by the second-order wavelength derivative of the refractive index, and the waveguide dispersion term is determined by the normalized frequency and the relative refractive index difference;

[0118] Construct a frequency-domain compensation function according to the group velocity dispersion equation, calculate the derivative of the phase of the frequency-domain compensation function with respect to the angular frequency to obtain the group delay response; apply the frequency-domain compensation function to the bidirectional reflection signal to obtain the compensated dispersion amount.

[0119] Exemplarily, an optical power meter with a power resolution of 0.01 dB is selected and used in conjunction with a narrow-linewidth laser with a linewidth less than 100 kHz. The incident optical power is set to 13 dBm to ensure that the measurement dynamic range reaches 60 dB. In practical applications, a 20-km-long G.652D standard single-mode optical fiber is tested, and the operating wavelength is selected as 1550 nm.

[0120] When establishing the forward transmission equation, the continuous attenuation and local losses of the optical fiber are considered. Measured at end A, the average attenuation coefficient of the optical fiber is 0.185 dB / km. An optical fiber connector is set every 5 km, and the loss of a single connector is 0.2 dB. The measured data shows that a 10-dBm optical signal transmitted from end A has its power attenuated to -5 dBm after transmitting 8 km. At the same time, the reflection coefficient measured at the fault point is -42 dB, and the corresponding reflected optical power is -47 dBm.

[0121] The reverse transmission equation describes the optical transmission characteristics from end B to the fault point. An optical signal with the same power is transmitted from end B. After transmitting 12 km, the optical power at the fault point is measured to be -7.5 dBm. Due to the slight differences in the optical fiber material and structure, the average attenuation coefficient of the section from end B to the fault point is 0.195 dB / km, slightly higher than that of the section at end A. The connector loss remains at the 0.2-dB level.

[0122] By calculating the ratio of the forward transmission equation to the reverse transmission equation, the differential attenuation coefficient is obtained. Measurements are taken every 100 m within a range of 1 km before and after the fault point. The results show that the average differential attenuation coefficient before the fault point is 0.01 dB / km, and the standard deviation is 0.002 dB / km. The differential attenuation coefficient after the fault point increases to 0.02 dB / km, and the standard deviation is 0.003 dB / km.

[0123] This measurement scheme significantly improves the accuracy of the attenuation characteristic analysis. In 50 repeated tests, the measurement error of the differential attenuation coefficient is controlled within the range of ±0.005 dB / km. Compared with the error range of ±0.02 dB / km of the traditional unidirectional measurement method, the accuracy is improved by 75%. The repeatability of the measurement results is good. When continuously measuring for 24 hours, the data deviation does not exceed 3%.

[0124] When calculating the differential attenuation coefficient, the reference measurement interval is first determined. A 1-km range before and after the fault point is selected as the analysis window, which is divided into 20 measurement points with an interval of 50 m between each point. The forward and reverse transmission power values are recorded at each measurement point, and the ratio of the two is calculated. For example, at 500 m before the fault point, the forward power is -4.2 dBm, the reverse power is -6.8 dBm, and the power ratio is 2.6 dB.

[0125] The differential attenuation characteristics are analyzed through the changing trend of the power ratio. In the measurement interval before the fault point, the change rate of the power ratio remains at the level of 0.01 dB / 100 m. The closer to the fault point, the change rate of the power ratio gradually increases and reaches 0.03 dB / 100 m at 100 m before the fault point. This non-linear change characteristic reflects the local attenuation anomaly caused by optical fiber damage. In an optional way, the ratio of the first value corresponding to the forward transmission equation to the second value corresponding to the reverse transmission equation can be used as the differential attenuation coefficient.

[0126] Among them, when establishing the non-linear correction equation of power and temperature, a calibration experiment is first carried out. A 20-km long G.652D standard single-mode optical fiber is selected. At a wavelength of 1550 nm and at room temperature of 25 °C, the initial differential attenuation coefficient is measured to be 0.01 dB / km. The incident optical power is gradually increased from -10 dBm to 15 dBm, and the corresponding relationship between power and attenuation is recorded at intervals of 1 dBm.

[0127] The non-linear influence of power is characterized by the first-order coefficient and the second-order coefficient. Experimental data show that within the power range of -5 dBm to 10 dBm, the first-order coefficient is 0.002 dB / km / dBm, and the second-order coefficient is 0.0001 dB / km / dBm². When the incident power is 13 dBm, the attenuation increment caused by power is 0.043 dB / km. The non-linear correction equation can be expressed as:

[0128] ;

[0129] where α(P) represents the differential attenuation coefficient related to power; represents the reference attenuation coefficient; P represents the incident optical power.

[0130] The influence of temperature is compensated by introducing a temperature correction term. In the range of -20 °C to 60 °C, a set of data is measured at intervals of 10 °C. The temperature coefficient is measured to be 0.0002 dB / km / °C, and the temperature second-order coefficient is 0.00001 dB / km / °C². The complete non-linear correction equation is:

[0131] ;

[0132] Among them, T represents the actual environmental temperature, represents the reference temperature (room temperature).

[0133] Taking a certain actual measurement as an example, when the incident power is 13 dBm and the environmental temperature is 40 °C, the original differential attenuation coefficient is 0.01 dB / km. After power correction, it increases by 0.043 dB / km, and the temperature correction contributes 0.005 dB / km. The finally corrected differential attenuation coefficient is 0.058 dB / km.

[0134] Apply the corrected differential attenuation coefficient to fault point location. The original measurement shows that the fault point is located at 8.02 km. Considering the influence of power and temperature, the position correction value is 0.03 km, and the final determined fault point position is 8.05 km. Verified by actual measurement, the corrected positioning error is reduced to ±2 m, which is significantly improved compared with ±8 m before correction.

[0135] When establishing the group velocity dispersion equation, first consider the basic parameters of the G.652D standard single-mode fiber. At the operating wavelength of 1550 nm, the zero-dispersion coefficient D0 is 17 ps / nm / km, the dispersion slope S0 is 0.06 ps / nm² / km, and the second-order dispersion slope γ is 0.0002 ps / nm³ / km. The group velocity dispersion equation can be expressed as:

[0136] ;

[0137] Among them, λ0 is the zero-dispersion wavelength; represents the operating wavelength.

[0138] Decompose the group velocity dispersion equation into material dispersion and waveguide dispersion parts, where the material dispersion term is determined by the second-order wavelength derivative of the refractive index, and the waveguide dispersion term is determined by the normalized frequency and the relative refractive index difference.

[0139] Construct the frequency-domain compensation function according to the group velocity dispersion equation as shown in the following formula:

[0140] ;

[0141] Among them, B2 represents the group velocity dispersion coefficient, B3 represents the third-order dispersion coefficient, L represents the fiber length, and w represents the angular frequency.

[0142] Calculate the derivative of the phase of the frequency-domain compensation function with respect to the angular frequency as shown in the following formula:

[0143] .

[0144] Exemplarily, when decomposing the group velocity dispersion equation, the basic parameters of the optical fiber are first measured using a refractive index analyzer. The core refractive index is measured to be 1.4682, the cladding refractive index is 1.4628, the core diameter is 8.3 microns, and the cladding diameter is 125 microns. The material dispersion term is determined by the second-order wavelength derivative of the refractive index. The second-order derivative value is measured to be 0.0012 per square micron at 1550 nm, and the corresponding material dispersion contribution is -22 ps / nm / km. The waveguide dispersion term is determined by the structural parameters of the optical fiber. The relative refractive index difference is 0.36%, the normalized frequency is 2.4, and the calculated waveguide dispersion contribution is 39 ps / nm / km.

[0145] Based on the complete group velocity dispersion equation, the group velocity dispersion coefficient and the third-order dispersion coefficient are introduced when constructing the frequency-domain compensation function. A 20-kilometer-long optical fiber is tested. The group velocity dispersion coefficient is -20 ps² / km, the third-order dispersion coefficient is 0.1 ps³ / km, and the cumulative total dispersion reaches 340 ps / nm. The frequency-domain compensation function includes the effects of the second-order term and the third-order term and can effectively compensate for the dispersion effect during the optical fiber transmission process.

[0146] By calculating the phase derivative of the frequency-domain compensation function, the group delay response characteristics are obtained. The group delay is measured to be 680 picoseconds at the center frequency. The group delay fluctuation is controlled within ±5 picoseconds, and the compensation accuracy reaches 98%. This result indicates that the compensation function can accurately describe the time delay characteristics of the optical signal during the transmission process.

[0147] When applying the frequency-domain compensation function to the bidirectional reflection signal, the compensation for the forward reflection signal compresses the original 2-nanosecond pulse width to 0.5 nanoseconds, and the time resolution is improved by 75%. The compensation effect for the backward reflection signal is similar, and the 2.1-nanosecond pulse is compressed to 0.52 nanoseconds. The signal after bidirectional compensation has higher time resolution and spatial resolution.

[0148] This scheme shows excellent performance indicators in practical applications. The spatial resolution is improved from 0.4 meters in the traditional method to 0.1 meters, with a promotion rate of 75%. The measurement dynamic range is increased from 30 dB to 40 dB, with an increase of 33%. In terms of temperature adaptability, the operating temperature range covers -20 to 60 degrees Celsius, the compensation accuracy fluctuation is controlled within 5%, and the temperature sensitivity of the dispersion coefficient is 0.002 ps / nm / km / °C.

[0149] Figure 5 Schematic diagram for the analysis of the bidirectional power attenuation characteristics in the embodiments of the present invention:

[0150] Within the transmission distance range of 0 - 20 km, the system exhibits three different attenuation characteristic curves. The forward transmission curve (circular markers) shows a maximum attenuation of approximately -4 dB, an attenuation rate of 0.2 dB / km, and exhibits periodic fluctuations with an amplitude of approximately ±0.5 dB. The overall attenuation trend of the reverse transmission curve (square markers) is similar, but the attenuation rate is slightly lower, at 0.18 dB / km, with a maximum attenuation of approximately -3.6 dB. Its periodic fluctuations have a phase difference of approximately π compared to the forward transmission. The temperature compensation curve (diamond markers) lies between the two, with an attenuation rate of 0.19 dB / km and a maximum attenuation of approximately -3.8 dB. Its fluctuation characteristics show a phase difference of approximately π / 2 compared to the forward transmission. This compensation effect enables the system to maintain relatively stable transmission performance when the temperature changes. The fluctuation periods of the three curves are basically the same, approximately 10 km, indicating that the system has periodic power fluctuation characteristics during long-distance transmission.

[0151] By establishing a two-way power equation and introducing non-linear correction, the accuracy of fault point location is improved. The location error is reduced from the original 300 meters to within 50 meters, significantly enhancing the location accuracy. The group velocity dispersion equation is used to compensate for the dispersion of the signal, effectively eliminating the influence of dispersion on the location result, making the waveform of the fault point clearer and improving the reliability of fault identification. Combining temperature correction and non-linear correction, a complete fault location correction system is established, making the location result more stable and reliable, and applicable to fault location under different environmental conditions.

[0152] In the second aspect of the embodiments of the present invention,

[0153] A kind of electronic device is provided, including:

[0154] A processor;

[0155] A memory for storing instructions executable by the processor;

[0156] Wherein, the processor is configured to call the instructions stored in the memory to execute the method described above.

[0157] In the third aspect of the embodiments of the present invention,

[0158] A computer-readable storage medium is provided, on which computer program instructions are stored, and when the computer program instructions are executed by a processor, the method described above is implemented.

[0159] The present invention can be a method, device, system, and / or computer program product. The computer program product can include a computer-readable storage medium, on which computer-readable program instructions for executing various aspects of the present invention are uploaded.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing and locating distribution network line faults based on optical fiber pulse transmission, characterized in that: include: Acquire the phase voltage signal and phase current signal of the distribution network line, and simultaneously acquire the transmission signal of the optical fiber in the distribution network line; According to the phase voltage signal and the phase current signal, determining whether the power distribution network line has a fault by wavelet transform; When it is confirmed that there is a fault in the distribution network line, a narrow linewidth laser is used to generate detection light, and the detection light is frequency modulated through a Bragg grating array to obtain a scattered signal generated by the interaction of sound and light; the gain coefficient of the photodetector is adjusted in real time according to the intensity of the scattered signal; the scattered signal is coherently demodulated, the signal amplitude and phase information are extracted, and the signal mutation point is determined; Based on the time information of the mutation point, a bidirectional reflection measurement method is adopted to respectively transmit detection light pulses at both ends of the optical fiber to obtain a bidirectional reflection signal; by calculating the delay difference and attenuation characteristics of the bidirectional reflection signal, a group velocity dispersion equation including a zero dispersion coefficient and a dispersion slope is established, and combined with an adaptive multi-stage dispersion compensation algorithm, the specific location of the fault point is obtained; A fault location report including the location information of the fault point is generated, and the fault location report is sent to a distribution network monitoring center.

2. The method according to claim 1, characterized in that: Judging whether the power distribution network line has a fault by wavelet transform according to the phase voltage signal and the phase current signal includes: Performing wavelet transform on the phase voltage signal and the phase current signal to obtain high-frequency components and low-frequency components of the phase voltage signal and the phase current signal, determining energy characteristic values ​​of the high-frequency components according to the energy of each frequency band in the high-frequency components, and determining that a fault occurs when the energy characteristic value exceeds a preset energy threshold; The fault type is determined according to the polarity relationship and phase sequence relationship of the high-frequency components, wherein the fault phase is determined according to the polarity of the first wave of the high-frequency components, and the fault property is determined according to the phase sequence relationship between different phases.

3. The method according to claim 1, characterized in that The gain coefficient of the photodetector is adjusted in real time according to the intensity of the scattered signal; the scattered signal is coherently demodulated to extract the signal amplitude and phase information, and the signal mutation point is determined, including: Determining a signal power of the scattered signal intensity, and determining a signal-to-noise ratio based on a ratio of the signal power to a rated power of the photodetector; According to the deviation between the signal power and the preset target power, the gain coefficient of the photodetector is calculated by an exponential function, the base of the exponential function is a natural constant, and the exponent is the inverse of the product of the deviation and the signal-to-noise ratio, and a time response constraint is imposed on the gain coefficient so that the ratio of the rate of change of the gain coefficient to the current gain value is equal to the difference between the target value and the current value of the gain coefficient, and the gain coefficient is subjected to a time domain response constraint; Coherently mixing the scattered signal with a local oscillation signal to obtain an in-phase component signal and an orthogonal component signal, and reconstructing the in-phase component signal and the orthogonal component signal to obtain a complex domain signal; The complex domain signal is normalized and the signal envelope is extracted through Hilbert transform. At the same time, the instantaneous phase of the complex domain signal is calculated and phase unfolding is performed to construct a multidimensional feature vector including the amplitude change rate and the phase change rate. The signal mutation point is determined based on the comparison result of the weighted cumulative sum of the multidimensional feature vector and the preset dynamic threshold.

4. The method according to claim 1, characterized in that Based on the time information of the mutation point, a bidirectional reflection measurement method is adopted to respectively emit detection light pulses at both ends of the optical fiber to obtain a bidirectional reflection signal, which includes: A first optical pulse is emitted at one end of the optical fiber according to the timing sequence of the reference time plus the cycle time, and a second optical pulse is emitted at the other end according to the timing sequence of the reference time plus the cycle time and the rated delay compensation time; The bidirectional reflection signals generated by the transmission of the first optical pulse and the second optical pulse in the optical fiber are respectively collected, and a first transmission delay and a second transmission delay of the bidirectional reflection signal are calculated, wherein the first transmission delay is the sum of the round-trip time of the first reflection signal from the transmitting end to the fault point and the system delay of the transmitting end, and the second transmission delay is the sum of the round-trip time of the second reflection signal from the transmitting end to the fault point and the system delay of the transmitting end; the initial value of the fault point position is calculated according to the difference between the first transmission delay and the second transmission delay and the total length of the optical fiber.

5. The method according to claim 4, characterized in that By calculating the delay difference and attenuation characteristics of the bidirectional reflection signal, a group velocity dispersion equation including zero dispersion coefficient and dispersion slope is established, and combined with an adaptive multi-stage dispersion compensation algorithm, the specific location of the fault point is obtained, including: Obtaining the power value of the bidirectional reflection signal, establishing a bidirectional power equation including an attenuation coefficient and a reflection coefficient, calculating the differential attenuation of the optical fiber link according to the bidirectional power equation, and correcting the initial value of the fault point position according to the differential attenuation; Establishing a group velocity dispersion equation including a zero dispersion coefficient and a dispersion slope, calculating a frequency domain compensation function according to the group velocity dispersion equation, performing a convolution operation on the bidirectional reflection signal and the frequency domain compensation function and performing an inverse Fourier transform to obtain a compensated time domain waveform; The first transmission delay, the second transmission delay, the differential attenuation and the compensated time domain waveform are subjected to weighted iterative calculation to obtain a final value of the fault point position, wherein the iteration is stopped when the position difference obtained between two adjacent iterations is less than a preset error threshold.

6. The method according to claim 5, characterized in that Obtaining the power value of the bidirectional reflection signal, establishing a bidirectional power equation including an attenuation coefficient and a reflection coefficient, calculating the differential attenuation of the optical fiber link according to the bidirectional power equation, and correcting the initial value of the fault point position according to the differential attenuation; Establishing a group velocity dispersion equation including a zero dispersion coefficient and a dispersion slope, and calculating a frequency domain compensation function according to the group velocity dispersion equation comprises: Establishing a bidirectional power equation including an attenuation coefficient and a reflection coefficient, wherein the bidirectional power equation includes a forward transmission equation and a reverse transmission equation, wherein the forward transmission equation describes the power attenuation characteristics from one end of the optical fiber to the fault point, and the reverse transmission equation describes the power attenuation characteristics from the other end of the optical fiber to the fault point; calculating the differential attenuation coefficient according to the ratio of the forward transmission equation to the reverse transmission equation; A nonlinear correction equation of power and temperature is established based on the differential attenuation coefficient, wherein the nonlinear correction equation includes a first-order term coefficient and a second-order term coefficient of power, and a temperature correction term is introduced, the differential attenuation coefficient is corrected according to the nonlinear correction equation, and the initial value of the fault point position is corrected according to the corrected differential attenuation coefficient; Establishing a group velocity dispersion equation including a zero dispersion coefficient, a dispersion slope and a second-order dispersion slope, and decomposing the group velocity dispersion equation into a material dispersion term and a waveguide dispersion term, wherein the material dispersion term is determined by a second-order wavelength derivative of a refractive index, and the waveguide dispersion term is determined by a normalized frequency and a relative refractive index difference; A frequency domain compensation function is constructed according to the group velocity dispersion equation, and the derivative of the phase of the frequency domain compensation function with respect to the angular frequency is calculated to obtain the group delay response; and the frequency domain compensation function is applied to the bidirectional reflection signal to obtain the compensated dispersion amount.

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