A method and apparatus for optical cable icing monitoring

Abstract

The present application relates to the field of optical fiber sensing, in particular to a kind of optical cable icing monitoring method and device.Mainly include: obtaining the first sensing data sequence in each sensing period, according to the first sensing data sequence, obtain the phase data sequence in each period;According to the phase data sequence, obtain the frequency spectrum data of the corresponding position phase change, according to the average value of the frequency spectrum data in multiple sensing periods, obtain the characteristic frequency, and estimate the icing thickness of the optical cable according to the change of the characteristic frequency.The present application reduces the interference fading of signal and environmental random noise, improves the single-span distance of icing monitoring, and can improve the icing monitoring accuracy.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing, and in particular to a method and apparatus for monitoring icing on optical cables. Background Technology

[0002] Optical Fiber Composite Overhead Ground Wire (OPGW) cables have optical fibers placed within the ground wires of overhead high-voltage transmission lines to form an optical fiber communication network for the power grid. This provides communication channels for protection, dispatching, administrative liaison, office automation, and dispatch automation. Located at the top of power lines, OPGW cables are difficult to inspect, maintain, and repair due to their location and the potential for power outages and safety concerns. Therefore, effective maintenance, inspection, and testing of OPGW cables, proactive fault prevention, and timely fault detection are crucial for improving the safe and reliable operation of the communication network and providing stronger communication support for the safe, reliable, and stable operation of the power grid. Common causes of OPGW cable faults include icing, lightning strikes, tower collapse, wind damage, electrical discharges, gunfire, explosions, and theft. Among the various icing phenomena, ice accumulation caused by freezing rain, rime, hoarfrost, and snow condensing around OPGW cables, and the resulting galloping, is the most common and harmful. Therefore, the need for ice detection on power grid lines to identify and address potential faults and ensure the safe and stable operation of the power grid is extremely urgent. Traditional electronic ice detection technologies, such as those based on tensile sensors (weighing) and cameras (image monitoring), suffer from drawbacks including difficulties in power grid setup, poor electromagnetic interference resistance, weak environmental adaptability, high cost, and difficulty in high-density deployment.

[0003] In recent years, some OPGW optical cables have been equipped with fully distributed fiber optic sensors to achieve online monitoring of the cables. These sensors use the entire optical fiber as the sensing element for external parameters and the signal transmission medium, offering advantages such as high sensitivity, strong resistance to electromagnetic interference, continuous measurement without blind spots, and the ability to measure a wide range of parameters. In particular, the sensing fiber can reuse idle fiber core resources in the OPGW cable, overcoming the shortcomings of traditional icing detection technologies. However, distributed fiber optic vibration sensors, such as Phase Sensitive Optical Time-Domain Reflectometry (Φ-OTDR), can only detect galloping phenomena and cannot determine whether icing has occurred or the degree of icing.

[0004] On the other hand, traditional Φ-OTDR sensing systems suffer from inherent phase fading. While Φ-OTDR coherent detection distributed fiber optic sensing systems using single-mode fiber as the sensing medium can improve the measurement accuracy of physical quantities in phase demodulation to some extent, their inherent low backscattering Rayleigh coefficient and susceptibility to signal attenuation limit the system's signal-to-noise ratio, making them unsuitable for long-distance Φ-OTDR sensing. Compared to traditional discrete fiber optic sensors based on reflection points, they exhibit a significant performance gap. Furthermore, OPGW optical cables are often laid over distances exceeding 50 kilometers, making it difficult to correctly demodulate the phase at the signal fading locations in traditional single-mode fiber, further impacting the reliability of Φ-OTDR distributed fiber optic sensing systems.

[0005] Therefore, how to improve the signal-to-noise ratio of the sensing signal of the Φ-OTDR distributed optical fiber sensing system when estimating icing thickness, thereby improving the accuracy of the Φ-OTDR distributed optical fiber sensing system in icing estimation, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of existing technologies, the present invention solves the problem that current distributed fiber optic vibration sensors cannot calculate ice thickness.

[0007] The embodiments of the present invention adopt the following technical solutions:

[0008] In a first aspect, the present invention provides a method for monitoring icing on optical cables, specifically comprising: acquiring a first sensing data sequence in each sensing cycle; acquiring a phase data sequence in each cycle based on the first sensing data sequence; acquiring spectral data of phase changes at corresponding positions based on the phase data sequence; obtaining a characteristic frequency based on the average value of the spectral data in multiple sensing cycles; and estimating the icing thickness of the optical cable based on the change in the characteristic frequency.

[0009] Preferably, the step of acquiring the first sensing data sequence in each sensing cycle specifically includes: generating a cyclically encoded probe light signal and a local oscillator light signal, receiving the backscattered Rayleigh light signal corresponding to the probe light signal; acquiring the beat signal between the local oscillator light signal and the backscattered Rayleigh light signal, and demodulating the first sensing data sequence from the beat signal.

[0010] Preferably, the generation of the cyclically encoded probe light signal and local oscillator light signal specifically includes: generating a periodically changing cyclic code, the change period being consistent with the sensing period, and the value of the cyclic code being between 1 and -1.

[0011] Preferably, the step of demodulating the first sensing data sequence from the beat signal specifically includes: performing correlation operations on the beat signal and cyclic code at each time point, using the result of the correlation operation as the sensing data at that time point, and using the collection of sensing data from all time points as the first sensing data sequence for that period.

[0012] Preferably, the step of obtaining the phase data sequence in each cycle based on the first sensing data sequence specifically includes: performing at least three cyclic shifts on the first sensing data sequence in each cycle to obtain a corresponding number of compensation data sequences; merging the multiple compensation data sequences of each cycle with the first sensing data sequence by vector summation to form the second sensing data sequence of that cycle; calculating the phase of each second sensing data in the second sensing data sequence of each cycle by arctangent calculation, and taking the phase of all time points in each cycle as the phase data sequence of that cycle.

[0013] Preferably, the step of performing at least three cyclic shifts on the first sensing data sequence for each cycle to obtain a corresponding number of compensation data sequences specifically includes: each time a cyclic shift is performed, based on the previous cyclic shift, all sensing data in the first sensing data sequence are cyclically shifted in a specified direction by a specified offset, and the data sequence obtained after each cyclic shift is taken as a compensation data sequence.

[0014] Preferably, the step of merging multiple compensation data sequences of each period with the first sensing data sequence into a second sensing data sequence of that period by vector summation specifically includes: performing vector summation on the compensation data corresponding to the same time point in all compensation data sequences of each period and the sensing data corresponding to the same time point in the first sensing data sequence to obtain the second sensing data corresponding to each time point, and merging the second sensing data of all time points into a second sensing data sequence.

[0015] Preferably, the step of calculating the phase of each second sensing data in each period of the second sensing data sequence by arctangent specifically includes: taking the arctangent of the ratio of the real part to the imaginary part of each second sensing data, and using the value of the arctangent as the phase of the second sensing data.

[0016] Preferably, obtaining the characteristic frequency based on the average value of spectral data in multiple sensing cycles specifically includes: averaging the spectral data at all time points in all phase data sequences, and obtaining the characteristic frequency from the average value of the spectral data.

[0017] On the other hand, the present invention provides a device for monitoring optical cable icing, specifically comprising: a laser, a polarization-maintaining coupler, an encoding generator, an electro-optic modulator, an erbium-doped fiber amplifier, a filter, a circulator, a sensing fiber, an integrated coherent receiver, a data acquisition card, and a processor. Specifically, the laser and the polarization-maintaining coupler, the polarization-maintaining coupler and the electro-optic modulator, and the polarization-maintaining fiber coupler and the coherent receiver are all connected by polarization-maintaining fibers; the encoding generator and the electro-optic modulator are connected by cables; the electro-optic modulator and the erbium-doped amplifier, the erbium-doped amplifier and the filter, the filter and the first port of the circulator, and the third port of the circulator and the coherent receiver are connected by single-mode fibers; wherein, the polarization-maintaining fiber coupler is used to generate sensing light and local oscillator light, the electro-optic modulator generates a specified cyclic encoded pulse light signal under the modulation of the encoding generator, and the processor performs optical cable icing monitoring according to the method provided in the first aspect.

[0018] Compared with existing technologies, the beneficial effects of the embodiments of the present invention are as follows: averaging multiple spectral data reduces the error in estimating icing thickness. Furthermore, in a preferred embodiment, a combination of cyclic coding and correlation calculation is used to reduce signal interference fading and environmental random noise, and vector summation is used to reduce single-cycle fading, thereby increasing the single-span distance for icing monitoring and improving the accuracy of icing monitoring. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0020] Figure 1 A flowchart of a method for monitoring icing of optical cables provided in an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of a device for monitoring optical cable icing, provided in an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] This invention is an architecture of a specific functional system. Therefore, the specific embodiments mainly describe the functional logic relationship of each structural module, and do not limit the specific software and hardware implementation methods.

[0024] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] Example 1:

[0026] To improve the accuracy of existing Φ-OTDR distributed optical fiber sensing systems in judging icing conditions and estimating icing thickness, this embodiment provides a method for monitoring optical cable icing.

[0027] like Figure 1 As shown, the specific steps of the optical cable icing monitoring method provided in this embodiment of the invention are as follows:

[0028] Step 101: Obtain the first sensing data sequence in each sensing cycle, and obtain the phase data sequence in each cycle based on the first sensing data sequence.

[0029] In the method provided in this embodiment, an Φ-OTDR distributed optical fiber sensing system is used to detect icing on the optical cable. The raw data used for calculation is the sensing data obtained from the sensing system. Multiple sensing data are acquired in each sensing cycle, and the sensing data, ordered by acquisition time, constitutes the first sensing data sequence for that cycle. By calculating the corresponding phase data for each sensing data in the first sensing data sequence, the corresponding phase data sequence for that cycle can be obtained.

[0030] The method for acquiring the first sensing data sequence in each sensing cycle specifically includes: generating a cyclically encoded probe light signal and a local oscillator light signal, and receiving the backscattered Rayleigh light signal corresponding to the probe light signal. The backscattered Rayleigh light signal of the cyclically encoded light signal transmitted back from the sensing fiber is received, and the beat signal between the local oscillator light signal and the backscattered Rayleigh light signal is acquired. The sensing data is then demodulated from the beat signal.

[0031] Step 102: Obtain the spectral data of the phase change at the corresponding position based on the phase data sequence, obtain the characteristic frequency based on the average value of the spectral data in multiple sensing cycles, and estimate the icing thickness of the optical cable based on the change of the characteristic frequency.

[0032] In typical implementation scenarios, the waveform of environmental noise is usually jagged, so the impact of low environmental noise on data accuracy can be mitigated by averaging data over multiple periods. Therefore, it is necessary to obtain and use a phase data sequence of M periods.

[0033] The phase data at each position of the sensing fiber for M sensing cycles are Fourier transformed to obtain the phase change spectrum data at the corresponding position. The characteristic frequency is then calculated by averaging the spectrum data at all time points in the entire phase data sequence. After obtaining the characteristic frequency, the icing thickness can be estimated based on the changes in the characteristic frequency.

[0034] After steps 101-102 provided in this embodiment, higher-precision icing monitoring data can be obtained.

[0035] Furthermore, in order to improve the signal-to-noise ratio, the method provided in this embodiment can also use a combination of cyclic coding and correlation calculation.

[0036] A periodically varying cyclic code is generated to modulate the probe optical signal and the local oscillator optical signal. The variation period of the cyclic code is consistent with the sensing period, and the value of the cyclic code is between 1 and -1.

[0037] In a specific implementation scenario, the method for generating the cyclic code Enc(x) is as follows:

[0038]

[0039] Where x is an input with a value greater than 1, and Enc(x) has a value range of {1, -1}. In actual implementation, the optional pulse duty cycle of the cyclic encoding is 50%, and the effective pulse width of the optional symbol is 100ns.

[0040] For the corresponding cyclic encoding, it is also necessary to perform correlation operations on the beat signal and cyclic encoding at each time point, and use the result of the correlation operation as the sensing data at that time point. The collection of sensing data at all time points is used as the first sensing data sequence of that cycle.

[0041] In a specific implementation scenario, the relevant calculation result r at position l xy The specific calculation method for (1) is as follows:

[0042]

[0043] Where x(n) is the nth code value in the cyclic encoding, y(nl) is the beat signal at position n+l, and the total length of the sampled data is N.

[0044] By combining the above-mentioned cyclic coding and related calculations, the sidelobe suppression ratio of the sensing signal can be improved, thereby increasing the signal-to-noise ratio and improving the accuracy of icing monitoring.

[0045] Furthermore, to reduce the impact of single-cycle fading on monitoring accuracy, vector summation can be used when acquiring the phase data sequence for each cycle. The first sensor data sequence for each cycle is cyclically shifted at least three times to obtain a corresponding number of compensated data sequences. These compensated data sequences are then combined with the first sensor data sequence using vector summation to form the second sensor data sequence for that cycle. For example, in a certain implementation scenario, K cyclic shifts are performed on the first sensor data sequence within a single cycle to obtain K sets of compensated data sequences. These K sets are then combined using vector summation to form a new first sensor data sequence for that single cycle, which is the second sensor data sequence for that cycle. Then, the phase of each second sensor data in the second sensor data sequence for each cycle is calculated using arctangent, and the phases at all time points within each cycle are used as the phase data sequence for that cycle.

[0046] Each time a cyclic shift is performed, based on the previous cyclic shift, all sensor data in the first sensor data sequence are cyclically shifted in a specified direction by a specified offset. The data sequence after each cyclic shift is used as a compensation data sequence. For example: shifting the first sensor data sequence 1 position to the right generates the K0th compensation data sequence; shifting the first sensor data sequence 2 positions to the right generates the K1th compensation data sequence; and so on, until the first sensor data sequence is shifted K positions to the right, generating the (K-1)th compensation data sequence. In practice, theoretically, a larger K value results in a higher compensation effect, but a larger K value increases the computational load and gradually reduces the algorithm's gain on signal-to-noise ratio improvement. Therefore, K is usually greater than or equal to 3, and preferably 6.

[0047] The specific method for vector summation is as follows: the compensation data corresponding to the same time point in all compensation data sequences of each cycle and the sensing data corresponding to the same time point in the first sensing data sequence are vector summed to obtain the second sensing data corresponding to each time point, and the second sensing data of all time points are combined into the second sensing data sequence.

[0048] In a specific implementation scenario, the method for vector summation is as follows.

[0049]

[0050] Among them, R t Let r be the vector sum at time t within the sampling period. t , where k is the compensation data at time t in the k-th compensation data sequence.

[0051] After acquiring the compensation data, the phase of each second sensor data in each cycle's second sensor data sequence needs to be calculated using the arctangent. Specifically: the arctangent of the ratio of the real part to the imaginary part of each second sensor data is calculated, and the value of the arctangent is used as the phase of that second sensor data.

[0052] In a specific implementation scenario, the phase φ of the sensing data at each location in the new sensing data sequence is calculated using the arctangent. t Specifically:

[0053]

[0054] Among them, a t Let b be the real part of the new sensing data at position t. t Let t be the imaginary part of the new sensing data at position t.

[0055] In the scenario of monitoring icing on overhead transmission lines, the icing thickness is related to the characteristic frequency of the sensing optical fiber. The specific calculation method for icing thickness is as follows:

[0056]

[0057] Where f is the characteristic frequency of the sensing fiber under this operating condition, in Hz, and n is the ice thickness index.

[0058] The optical cable icing monitoring method provided in this embodiment reduces the estimation of icing thickness by averaging multiple spectral data. It also reduces signal interference fading and environmental random noise by combining cyclic coding and correlation calculation, and reduces single-cycle fading by vector summation, thereby increasing the single-span distance for icing monitoring and improving the accuracy of icing monitoring.

[0059] Example 2:

[0060] Based on the optical cable icing monitoring method provided in Embodiment 1 above, the present invention also provides an apparatus for implementing the above method for optical cable icing monitoring, such as... Figure 2 The diagram shown is a schematic diagram of the device architecture according to an embodiment of the present invention.

[0061] The device provided in this embodiment includes a laser, a polarization-maintaining coupler, a code generator, an electro-optic modulator, an erbium-doped fiber amplifier (EFDA), a filter, a circulator, a sensing fiber, an integrated coherent receiver (ICR), a data acquisition card, and a processor. Specifically:

[0062] The laser is connected to the polarization-maintaining coupler, the polarization-maintaining coupler to the electro-optic modulator, and the polarization-maintaining fiber coupler to the coherent receiver via polarization-maintaining fiber. The encoder generator and the electro-optic modulator are connected by a cable. The electro-optic modulator and the erbium-doped amplifier, the erbium-doped amplifier and the filter, the filter and the first port of the circulator, and the third port of the circulator and the coherent receiver are connected by single-mode fiber. The polarization-maintaining fiber coupler is used to generate the sensing light and the local oscillator light. The electro-optic modulator generates a specified cyclic coded pulse light signal under the modulation of the encoder generator.

[0063] In practical implementation, the types and parameters of each component can be selected according to actual needs. A set of reference types and parameters is provided below. The sensing fiber is specifically an idle fiber core in an OPGW optical cable. The laser output wavelength is 1550nm. Driven by the encoder generator, the electro-optic modulator generates a cyclic coded pulse optical signal with a duty cycle of 50% and an effective symbol pulse width of 100ns. The filter is specifically a fiber Bragg grating. The splitting ratio of the fiber coupler is 50:50. The integrated coherent receiver model is a 4-channel ICR. In practical implementation, other types of components or other parameters can also be used as needed, as long as the relevant data can be obtained and processed according to the principle of the method in Example 1.

[0064] The backscattered Rayleigh light signal from the sensing fiber enters the signal port of the ICR. After polarization diversity and 90° mixing, the beat signal between the local oscillator light and the Rayleigh backscattered wave (RBS) is converted into an electrical signal with four polarization channels by the integrated coherent receiver. At the integrated coherent receiver, a 4-channel oscilloscope is used as a data acquisition card for data acquisition. The digital signal processing required in Example 1 is performed offline on the processor. In the scenario of the 4-channel integrated coherent receiver and 4-channel data acquisition card in this example, the received 4-polarization channel electrical signals are reassembled into two complex signals, corresponding to X and Y polarizations respectively.

[0065] Furthermore, in the above-mentioned device, the encoding generator is specifically an Arbitrary Function Generator (AFG). The AFG is used to generate encoded electrical pulses and modulate an electro-optic modulator with a high extinction ratio (>40dB) to generate intensity-modulated optical pulses. The extinction ratio of the electro-optic modulator is greater than 40dB.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for monitoring icing on optical cables, characterized in that, Specifically, it includes: Obtain the first sensing data sequence in each sensing cycle, and obtain the phase data sequence in each cycle based on the first sensing data sequence; The acquisition of the first sensing data sequence in each sensing cycle specifically includes: generating a cyclically encoded probe light signal and a local oscillator light signal; receiving the backscattered Rayleigh light signal corresponding to the probe light signal; acquiring the beat signal between the local oscillator light signal and the backscattered Rayleigh light signal; and demodulating the first sensing data sequence from the beat signal. The acquisition of the phase data sequence in each cycle based on the first sensing data sequence specifically includes: performing at least three cyclic shifts on the first sensing data sequence in each cycle to obtain a corresponding number of compensation data sequences; and merging multiple compensation data sequences of each cycle with the first sensing data sequence to form the second sensing data sequence of that cycle through vector summation. The vector summation method is as follows: ； in, The vector sum at time t within the sampling period. The compensation data at time t in the k-th compensation data sequence is calculated by arctangent; the phase of each second sensing data in the second sensing data sequence of each cycle is calculated, and the phase of all time points in each cycle is taken as the phase data sequence of that cycle. The spectral data of phase change at the corresponding position is obtained from the phase data sequence. The characteristic frequency is obtained from the average value of the spectral data in multiple sensing cycles. The icing thickness of the optical cable is estimated based on the change of the characteristic frequency.

2. The method for monitoring optical cable icing according to claim 1, characterized in that, The generation of the cyclically encoded probe optical signal and local oscillator optical signal specifically includes: A periodically changing cyclic code is generated, with the change period matching the sensing period, and the value of the cyclic code is between 1 and -1.

3. The method for monitoring optical cable icing according to claim 2, characterized in that, The demodulation of the first sensing data sequence from the beat signal specifically includes: Correlation operations are performed on the beat signal and cyclic code at each time point, and the result of the correlation operation is used as the sensor data at that time point. The collection of sensor data at all time points is used as the first sensor data sequence of that period.

4. The method for monitoring optical cable icing according to claim 1, characterized in that, The step of performing at least three cyclic shifts on the first sensing data sequence for each cycle to obtain a corresponding number of compensation data sequences specifically includes: Each time a cyclic displacement is performed, based on the previous cyclic displacement, all the sensor data in the first sensor data sequence are cyclically moved in the specified direction by a specified offset, and the data sequence after each cyclic displacement is used as a compensation data sequence.

5. The method for monitoring optical cable icing according to claim 1, characterized in that, The step of merging multiple compensated data sequences of each period with the first sensing data sequence to form the second sensing data sequence of that period through vector summation specifically includes: In each cycle, the compensation data corresponding to the same time point in all compensation data sequences and the sensing data corresponding to the same time point in the first sensing data sequence are vector-summed to obtain the second sensing data corresponding to each time point. The second sensing data of all time points are combined into the second sensing data sequence.

6. The method for monitoring optical cable icing according to claim 1, characterized in that, The step of calculating the phase of each second sensing data in each period of the second sensing data sequence by arctangent specifically includes: Calculate the arctangent of the ratio of the real part to the imaginary part of each second sensing data, and use the value of the arctangent as the phase of that second sensing data.

7. The method for monitoring optical cable icing according to claim 1, characterized in that, The step of obtaining the characteristic frequency based on the average value of spectral data over multiple sensing cycles specifically includes: The characteristic frequency is obtained by averaging the spectral data at all time points in all phase data sequences.

8. A device for monitoring icing on optical cables, characterized in that, This includes lasers, polarization-maintaining couplers, encoders, electro-optic modulators, erbium-doped fiber amplifiers, filters, circulators, sensing fibers, integrated coherent receivers, data acquisition cards, and processors. Specifically: The laser and the polarization-maintaining coupler, the polarization-maintaining coupler and the electro-optic modulator, and the polarization-maintaining fiber coupler and the coherent receiver are all connected by polarization-maintaining fibers. The encoder generator and the electro-optic modulator are connected by a cable. The electro-optic modulator and the erbium-doped amplifier, the erbium-doped amplifier and the filter, the filter and the first port of the circulator, and the third port of the circulator and the coherent receiver are connected by single-mode fibers. The polarization-maintaining fiber coupler is used to generate sensing light and local oscillator light. The electro-optic modulator generates a specified cyclic coded pulse light signal under the modulation of the encoder generator. The processor performs optical cable icing monitoring according to any one of claims 1-7.

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