CN110686626B - OPGW (optical fiber composite overhead ground wire) icing monitoring system and method based on phase-sensitive optical time domain reflection system - Google Patents
OPGW (optical fiber composite overhead ground wire) icing monitoring system and method based on phase-sensitive optical time domain reflection system Download PDFInfo
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
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- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
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- G01D5/35354—Sensor working in reflection
- G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
- G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
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- G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
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Abstract
The invention discloses an OPGW icing monitoring method based on a phase-sensitive optical time domain reflection system. Obtaining the distribution of Rayleigh backscattering signals in the composite optical cable of the overhead ground wire on time and space through a phase sensitive optical time domain reflection system; fourier transform is carried out on the phase demodulation result of the Rayleigh backscattering signal, and useless high-frequency information is removed through low-pass filtering; obtaining the peak frequency of the first resonance peak on each distance column according to the frequency spectrum information; splicing the peak frequencies of the resonance peaks of each distance row into a one-dimensional array and carrying out median filtering; carrying out probability statistics after long-time measurement, recording the frequency of the highest peak of a statistical result as the resonance frequency of a corresponding position, and obtaining a confidence interval and an untrusted interval according to the variance of the resonance frequency; and obtaining a calibration resonant frequency and an actual resonant frequency through multiple measurements, and calculating the actual icing thickness according to the calibration resonant frequency and the actual resonant frequency, thereby realizing the distributed and intelligent icing thickness monitoring method.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to an OPGW (optical fiber composite overhead ground wire) icing monitoring system and method based on a phase-sensitive optical time domain reflection system.
Background
In the process of power transmission, due to the fact that the terrain and the ground conditions are quite complex, the probability that the power transmission line is subjected to line icing is quite high, and particularly in areas with high humidity or prone to snow, the phenomenon of line icing is prone to occurring. The ice coating of the transmission line seriously threatens the safe operation of a power grid, and can cause serious accidents such as line tripping, power failure, galloping damage, line breakage, tower collapse and the like. Therefore, the effective monitoring technology is adopted to monitor the state of the long-distance power transmission line equipment, so that the running state of the equipment can be timely and accurately mastered, the safe, reliable and economic running of the equipment is ensured, the disaster loss is reduced when sudden natural disasters are met, and the safe and stable running of the power transmission line and the power system is ensured.
In early icing monitoring, a method for establishing an icing station is generally adopted at home and abroad to study and observe the icing condition of a power transmission line, and the method has the disadvantages of large investment, long construction period, high operation cost and limited quantity, and cannot realize real-time monitoring of the icing condition of the whole power grid. In recent years, the technology for monitoring the icing of the power transmission line and the microclimate on line is rapidly developed and gradually becomes a main means for sensing the icing state of the power grid and preventing large-area icing and snow disasters. Currently, the ice coating monitoring methods are mainly developed as follows: weighing method, wire inclination angle method, image monitoring method, icing rate meter method, simulation wire method, quasi-distributed optical fiber sensing method and the like. Among them, the weighing method and the wire inclination method are widely applied in China. However, these monitoring methods are all point-type monitoring methods, and only certain specific lines on the transmission line are subjected to icing state monitoring, and line distributed real-time monitoring in the true sense cannot be realized.
At present, optical fiber sensing is gradually favored by the power industry due to the advantages of insulation, electromagnetic interference resistance, high temperature resistance, corrosion resistance, water resistance, easiness in implantation, convenience in networking and the like, and becomes the best choice in many application fields in smart grid construction. The distributed optical fiber sensing fully utilizes the idle optical fiber resources in the electric power optical fiber communication network, and has obvious application effect and wide development prospect in the aspects of temperature, strain, vibration, icing, partial discharge and the like of the power transmission line.
Among a plurality of distributed optical fiber sensing technologies, a phase-sensitive optical time domain reflectometry (phi-OTDR) system has extremely high sensitivity, high corresponding measurement speed and electromagnetic interference resistance, and can realize long-distance fully distributed sensing. The phi-OTDR system is used in the power system, the running state of the tested overhead ground wire composite optical cable (OPGW) can be evaluated from the vibration angle, the on-line safety monitoring of the running state of the tested line is realized, the accident potential can be timely eliminated, and the major economic loss is avoided. However, the Φ -OTDR system has not been widely applied in the power industry, and a monitoring method for the icing condition of the power transmission line is relatively lacking at present.
Disclosure of Invention
The purpose of the invention is as follows: in order to solve the technical problems in the background art, the invention aims to provide an OPGW (optical fiber composite overhead ground wire) icing monitoring method based on a phase-sensitive optical time domain reflection system, which has the characteristics of high degree of intelligence, convenience for a computer to automatically analyze and judge the icing degree and important economic and social values.
The technical scheme is as follows: in order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a phase sensitive optical time domain reflection system comprises a narrow linewidth laser 1, a 1 x 2 optical fiber coupler 2, an acousto-optic modulator 3, an erbium-doped optical fiber amplifier 4, an optical fiber circulator 5, a sensing optical fiber 6, an arbitrary waveform generator 7, a 2 x 2 optical fiber coupler 8, a balanced optical detector 9, a data acquisition card 10 and a computer 11. The components of the system are explained as follows:
the narrow linewidth laser 1 is used for generating laser output to the 1 multiplied by 2 optical fiber coupler 2;
and the 1 x 2 optical fiber coupler 2 is used for dividing the laser into two paths, one path is used as sensing probe light and input to the acousto-optic modulator 3, the other path is used as local reference light and input to the 2 x 2 optical fiber coupler 8, the instantaneous optical power of the sensing probe light is greater than that of the local reference light, and the coupling splitting ratio can be selected to be 90: 10.
And the acousto-optic modulator 3 is used for modulating the light of the sensing probe into light pulses and transmitting the light pulses to the erbium-doped fiber amplifier 4, wherein the acousto-optic modulator 3 is used for modulating the laser into the light pulses and simultaneously enabling the laser pulses to obtain frequency shift with fixed frequency, and the frequency shift can be 200 MHz.
The erbium-doped fiber amplifier 4 amplifies the power of the optical pulse signal output by the acousto-optic modulator 3, and inputs the amplified optical pulse signal to the first port of the fiber circulator 5.
The fiber is used for amplifying the laser pulse power and improving the Rayleigh scattering light intensity excited in the sensing fiber 6 so as to improve the sensing range of the system, and the maximum gain of the fiber can be 20 dBm.
And the optical fiber circulator 5 receives the optical pulse signal from the first port and outputs the optical pulse signal to the sensing optical fiber 6 from the second port, and the Rayleigh back scattering light generated by the sensing optical fiber 6 is input from the second port and output to the 2 x 2 optical fiber coupler 8 from the third port.
The optical fiber circulator 5 is a three-port optical fiber circulator, and is optically characterized in that light input from the first port can be output only from the second port, light input from the second port can be output only from the third port, and the sensing fiber 6 is a single-mode fiber for standard communication.
The arbitrary waveform generator 7 generates a pulse sequence with adjustable frequency, outputs the pulse sequence with repetition frequency of 1kHz and optical pulse width, namely the duration of optical pulse of 100ns, controls the acousto-optic modulator 3 to realize optical pulse output, and the pulse sequence is simultaneously used as an acquisition trigger source of the data acquisition card 10.
The 2 x 2 optical fiber coupler 8 is used for sensing the wave combination of the back scattering light of the optical fiber and the local reference light, and the coupling splitting ratio is 50: 50.
the balanced optical detector 9 is used for converting optical signals input by the 2 multiplied by 2 optical fiber coupler 8 into electric signals, and the electric signals are output to the data acquisition card 10;
and the data acquisition card 10 is used for realizing signal analog-to-digital conversion, acquiring the electric signal output by the balanced optical detector 9, converting the electric signal into a digital signal and transmitting the digital signal to the computer 11.
And the computer 11 is used for processing the digital signals acquired by the data acquisition card 10.
Laser generated by the narrow linewidth laser 1 is divided into two paths of optical signals through a 1 x 2 optical fiber coupler 2, one path of optical signals is a sensing probe optical signal and is modulated into optical pulses through an acoustic optical modulator 3, the optical pulses are subjected to optical power amplification through an erbium-doped optical fiber amplifier 4, the amplified optical pulses are input into a first port of an optical fiber circulator 5 and are output to a sensing optical fiber 6 through a second port, and sensing optical signals which are scattered in a backward direction in the sensing optical fiber 6 are transmitted back to a second port of the optical fiber circulator 5 and are output through a third port; the other path output by the 1 × 2 optical fiber coupler 2 is a local reference optical signal, the local reference optical signal and a sensing optical signal output by the third port of the optical fiber circulator 5 enter the 2 × 2 optical fiber coupler 8 for wave combination, and two output ports of the 2 × 2 optical fiber coupler 8 are connected with the balanced optical detector 9.
The arbitrary waveform generator 7 generates a pulse sequence with adjustable frequency, the acousto-optic modulator 3 is modulated to enable the acousto-optic modulator 3 to output light pulses, and the pulse sequence generated by the arbitrary waveform generator 7 simultaneously triggers the data acquisition card 10 to enable the data acquisition card 10 to acquire electric signals output by the balance light detector 9. The balanced optical detector 9 converts the optical signal input by the 2 × 2 optical fiber coupler 8 into an electrical signal, and the electrical signal is subjected to analog-to-digital conversion by the data acquisition card 10 and transmitted to the computer 11 for signal processing.
The invention also provides an OPGW icing monitoring method based on the phase-sensitive optical time domain reflection system, which specifically comprises the following steps:
step 1: connecting sensing optical fibers in a phase-sensitive optical time domain reflectometry (phi-OTDR) system with optical fibers in an overhead ground wire composite optical cable (OPGW) by using jumper optical fibers, setting a plurality of sampling points on an optical fiber length axis, and collecting different sampling points for multiple times in a preset time period by using a computer in the phi-OTDR system to obtain the distribution of Rayleigh Backscattering (RBS) signals in the optical fibers of the overhead ground wire composite optical cable between two towers on a measurement time axis and the optical fiber length axis;
step 2: carrying out phase demodulation on RBS signals of each sampling point acquired for multiple times within the preset time in the step 1, carrying out Fourier transform on phase values of the phase signals after the phase demodulation, which correspond to each sampling point on the optical fiber length axis, along a time axis in a fixed time window, and obtaining frequency spectrums of the phase signals through low-pass filtering;
and step 3: the phase signal frequency spectrum finally obtained in the step 2 is a two-dimensional array, the row of the two-dimensional array represents the intensity distribution information of a certain frequency component on all sampling points of the optical fiber length axis, the column of the two-dimensional array represents the intensity distribution information of a certain sampling point of the optical fiber length axis on all frequency components, each column of the two-dimensional array is subjected to numerical processing, and the peak frequency of the first resonance peak at the position where each sampling point on the optical fiber length axis represents is obtained;
and 4, step 4: splicing the peak frequency of the first resonance peak at the representation position of each sampling point on the optical fiber length axis into a one-dimensional array, carrying out median filtering on the one-dimensional array by using the set window width to obtain a frequency information one-dimensional array after smoothing treatment, wherein each element in the one-dimensional array is the peak frequency of the first resonance peak at the representation position of each sampling point on the optical fiber length axis in a preset time period, and the element index is the position represented by each sampling point on the optical fiber length axis;
and 5: acquiring a preset time period of the step 1 for multiple times by a phi-OTDR system in continuous time, processing the acquired RBS signals in the steps 2 to 4, counting the frequency of each peak frequency of the processed frequency information one-dimensional arrays at the same element index, recording the peak frequency with the highest frequency as the resonant frequency of the sampling point representing the position of the optical fiber, and finally obtaining the resonant frequency of each sampling point representing the position in the continuous time on the optical fiber length axis in the composite optical cable of the overhead ground wire;
step 6: under the condition that the overhead ground wire composite optical cable is not coated with ice, the phi-OTDR system is processed in the steps 1 to 5 to obtain the overhead ground wire composite optical cableThe resonant frequency of the ground wire composite optical cable without ice coating is recorded as a calibration resonant frequency f01And under the condition that the overhead ground wire composite optical cable is iced, carrying out the processing from the step 1 to the step 5 on the phi-OTDR system to obtain the resonance frequency under the condition that the overhead ground wire composite optical cable is not iced, and recording the resonance frequency as the actual resonance frequency f02According to measured f01And f02The actual icing thickness can be calculated, and a distributed and intelligent icing thickness monitoring method is realized.
As a further preferable scheme of the overhead ground wire composite optical cable ice-coating monitoring method of the phase-sensitive optical time domain reflection system, in the step 3, each column of the two-dimensional array of the phase signal frequency spectrum is subjected to numerical processing, specifically as follows:
each column of the two-dimensional array of the spectrum of the phase signal can be regarded as a one-dimensional array with the frequency component f as an element index, and the following processing is performed for each element in the array,
wherein,
is the value of the one-dimensional array element after processing, IN(f) The method comprises the following steps that the phase signal spectrum is a one-dimensional array element, N is the serial number of each row of a two-dimensional array of the phase signal spectrum, f is the index of the one-dimensional array element, f belongs to N, and f is larger than or equal to 1.
And (3) performing the above formula processing on each element of the one-dimensional array to obtain a new one-dimensional array, and taking an element index f corresponding to a first peak value in the elements of the one-dimensional array, namely the peak frequency of a first resonance peak at the position represented by each sampling point on the optical fiber length axis.
As a further preferable scheme of the ice-coating monitoring method for the overhead ground wire composite optical cable of the phase-sensitive optical time domain reflection system, in the step 6, according to f01And f02To calculate overheadThe concrete steps of the actual ice coating thickness of the ground wire composite optical cable are as follows:
step 1: according to a nominal resonant frequency f01Horizontal tension T of overhead ground wire composite optical cable under condition of no ice coating01：T01＝4m0l2f01 2Wherein l is the horizontal distance between the suspension points of the composite optical cable of the overhead ground wires of two adjacent towers, and m is0The unit length mass of the composite optical cable of the overhead ground wire under the condition of no ice coating and the horizontal stress sigma of the composite optical cable of the overhead ground wire under the condition of no ice coating01：
Wherein A is the sectional area of the overhead ground wire composite optical cable.
Step 2: unit length mass m of overhead ground wire composite optical cable under ice coating condition02The relationship with the ice coating thickness b is: m is02＝m0+0.9πb(d+b)×10-3And d is the diameter of the composite optical cable of the overhead ground wire. According to the actual resonance frequency f02Horizontal stress sigma of overhead ground wire composite optical cable under icing condition02：
And step 3: the basic form of the overhead ground wire composite optical cable state equation is as follows:
wherein E is the Young modulus of the composite optical cable of the overhead ground wire, beta is the horizontal distance height difference angle between the suspension points of the composite optical cable of the overhead ground wire of two adjacent towers, alpha is the thermal expansion coefficient of the composite optical cable of the overhead ground wire, and t1And t2The temperature of the composite optical cable of the overhead ground wire under the condition of no ice coating and the temperature of the composite optical cable under the condition of ice coating are respectively shown, gamma 'and gamma are respectively the comprehensive specific load under the condition of ice coating and the condition of no ice coating, and the mass relationship of the gamma' and the gamma and the unit length is as follows:
where g is the acceleration of gravity, the above relation may in practice ignore the term α Ecos β (t)2-t1) And (6) performing calculation.
The relational expression obtained from the step 1 to the step 2 is
And
substituting the state equation of the overhead ground wire composite optical cable to obtain the equation:
in the above equation, the known quantity comprises the mass m per unit length of the overhead ground wire composite optical cable without ice coating0The diameter d of the composite optical cable of the overhead ground wire, the horizontal distance l between suspension points of the composite optical cable of the overhead ground wires of two adjacent towers and the calibration resonant frequency f01True resonant frequency f02The calculated sectional area A of the composite optical cable of the overhead ground wire, the Young modulus E of the composite optical cable of the overhead ground wire, the height difference angle beta of the horizontal distance between suspension points of the composite optical cable of the overhead ground wires of two adjacent towers and the gravity acceleration g; the unknown quantity comprises the icing thickness b, and the actual equivalent icing thickness b of the composite optical cable of the overhead ground wire can be obtained through calculation.
Has the advantages that: compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:
the invention adopts the phase sensitive optical time domain reflection system to obtain the vibration data of the power transmission line, has the advantages of high response speed, high positioning precision, electromagnetic interference resistance and the like, can realize long-distance fully-distributed sensing, uses an OPGW optical cable to construct a large-scale optical fiber sensing network with strong anti-interference capability, and saves the cost for arranging other sensors;
the distributed icing monitoring of the power transmission line can be realized by monitoring the resonant frequency information of each span of the power transmission line and combining the material parameters and the geographic information of the power transmission line, and the confidence interval and the non-confidence interval of the icing monitoring of the power transmission line are provided for reference and judgment. The invention has the characteristics of high intelligent degree of the monitoring method, convenience for automatic analysis and judgment of the icing degree by a computer, and important economic value and social value.
Drawings
FIG. 1 is a general schematic diagram of the hardware system architecture of the present invention;
FIG. 2 is a schematic diagram of a phase-sensitive optical time domain reflectometry system according to the present invention;
FIG. 3 is a flow chart of the present invention;
FIG. 4 is a graph of Rayleigh backscattered light intensity;
FIG. 5 is a graph of the spectrum of the phase demodulation result after Fourier transform;
figure 6 is a graph of the frequency of the first resonance peak within the OPGW time window;
FIG. 7 is a plot of the OPGW harmonic peak frequency versus the fluctuation within one hour;
FIG. 8 is a graph of the average OPGW resonant peak frequency over one hour;
FIG. 9 is a comparison graph before and after the harmonic peak frequency median filtering at the same position of OPGW;
FIG. 10 is a frequency probability statistics chart of the resonance peak of the OPGW;
fig. 11 is a statistical diagram of the frequency variance of the resonance peak of OPGW.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments. Because the scheme can be expanded or deformed in various ways, the related devices can be replaced by devices with similar functions and different models, and the protection scope of the patent is not limited by the scheme.
Referring to fig. 1 and fig. 2, the invention provides a phase sensitive optical time domain reflectometry system, which includes a narrow linewidth laser 1, a 1 × 2 fiber coupler 2, an acousto-optic modulator 3, an erbium-doped fiber amplifier 4, a fiber circulator 5, a sensing fiber 6, an arbitrary waveform generator 7, a 2 × 2 fiber coupler 8, a balanced optical detector 9, a data acquisition card 10, and a computer 11. The components of the system are explained as follows:
the narrow linewidth laser 1 is used for generating laser output to the 1 multiplied by 2 optical fiber coupler 2;
and the 1 x 2 optical fiber coupler 2 is used for dividing the laser into two paths, one path is used as sensing probe light and input to the acousto-optic modulator 3, the other path is used as local reference light and input to the 2 x 2 optical fiber coupler 8, the instantaneous optical power of the sensing probe light is greater than that of the local reference light, and the coupling splitting ratio can be selected to be 90: 10.
And the acousto-optic modulator 3 is used for modulating the light of the sensing probe into light pulses and transmitting the light pulses to the erbium-doped fiber amplifier 4, wherein the acousto-optic modulator 3 is used for modulating the laser into the light pulses and simultaneously enabling the laser pulses to obtain frequency shift with fixed frequency, and the frequency shift can be 200 MHz.
The erbium-doped fiber amplifier 4 amplifies the power of the optical pulse signal output by the acousto-optic modulator 3, and inputs the amplified optical pulse signal to the first port of the fiber circulator 5.
The fiber is used for amplifying the laser pulse power and improving the Rayleigh scattering light intensity excited in the sensing fiber 6 so as to improve the sensing range of the system, and the maximum gain of the fiber can be 20 dBm.
And the optical fiber circulator 5 receives the optical pulse signal from the first port and outputs the optical pulse signal to the sensing optical fiber 6 from the second port, and the Rayleigh back scattering light generated by the sensing optical fiber 6 is input from the second port and output to the 2 x 2 optical fiber coupler 8 from the third port.
The optical fiber circulator 5 is a three-port optical fiber circulator, and is optically characterized in that light input from the first port can be output only from the second port, light input from the second port can be output only from the third port, and the sensing fiber 6 is a single-mode fiber for standard communication.
The arbitrary waveform generator 7 generates a pulse sequence with adjustable frequency, outputs the pulse sequence with repetition frequency of 1kHz and optical pulse width, namely the duration of optical pulse of 100ns, controls the acousto-optic modulator 3 to realize optical pulse output, and the pulse sequence is simultaneously used as an acquisition trigger source of the data acquisition card 10.
The 2 x 2 optical fiber coupler 8 is used for sensing the wave combination of the back scattering light of the optical fiber and the local reference light, and the coupling splitting ratio is 50: 50.
the balanced optical detector 9 is used for converting optical signals input by the 2 multiplied by 2 optical fiber coupler 8 into electric signals, and the electric signals are output to the data acquisition card 10;
and the data acquisition card 10 is used for realizing signal analog-to-digital conversion, acquiring the electric signal output by the balanced optical detector 9, converting the electric signal into a digital signal and transmitting the digital signal to the computer 11.
And the computer 11 is used for processing the digital signals acquired by the data acquisition card 10.
Laser generated by the narrow linewidth laser 1 is divided into two paths of optical signals through a 1 x 2 optical fiber coupler 2, one path of optical signals is a sensing probe optical signal and is modulated into optical pulses through an acoustic optical modulator 3, the optical pulses are subjected to optical power amplification through an erbium-doped optical fiber amplifier 4, the amplified optical pulses are input into a first port of an optical fiber circulator 5 and are output to a sensing optical fiber 6 through a second port, and sensing optical signals which are scattered in a backward direction in the sensing optical fiber 6 are transmitted back to a second port of the optical fiber circulator 5 and are output through a third port; the other path output by the 1 × 2 optical fiber coupler 2 is a local reference optical signal, the local reference optical signal and a sensing optical signal output by the third port of the optical fiber circulator 5 enter the 2 × 2 optical fiber coupler 8 for wave combination, and two output ports of the 2 × 2 optical fiber coupler 8 are connected with the balanced optical detector 9.
The arbitrary waveform generator 7 generates a pulse sequence with adjustable frequency, the acousto-optic modulator 3 is modulated to enable the acousto-optic modulator 3 to output light pulses, and the pulse sequence generated by the arbitrary waveform generator 7 simultaneously triggers the data acquisition card 10 to enable the data acquisition card 10 to acquire electric signals output by the balance light detector 9. The balanced optical detector 9 converts the optical signal input by the 2 × 2 optical fiber coupler 8 into an electrical signal, and the electrical signal is subjected to analog-to-digital conversion by the data acquisition card 10 and transmitted to the computer 11 for signal processing.
The invention also provides an OPGW icing monitoring method based on the phase-sensitive optical time domain reflection system, which specifically comprises the following steps:
step 1: connecting sensing optical fibers in a phase-sensitive optical time domain reflectometry (phi-OTDR) system with optical fibers in an overhead ground wire composite optical cable (OPGW) by using jumper optical fibers, setting a plurality of sampling points on an optical fiber length axis, and collecting different sampling points for multiple times in a preset time period by using a computer in the phi-OTDR system to obtain the distribution of Rayleigh Backscattering (RBS) signals in the optical fibers of the overhead ground wire composite optical cable between two towers on a measurement time axis and the optical fiber length axis;
step 2: carrying out phase demodulation on RBS signals of each sampling point acquired for multiple times within the preset time in the step 1, carrying out Fourier transform on phase values of the phase signals after the phase demodulation, which correspond to each sampling point on the optical fiber length axis, along a time axis in a fixed time window, and obtaining frequency spectrums of the phase signals through low-pass filtering;
and step 3: the phase signal frequency spectrum finally obtained in the step 2 is a two-dimensional array, the row of the two-dimensional array represents the intensity distribution information of a certain frequency component on all sampling points of the optical fiber length axis, the column of the two-dimensional array represents the intensity distribution information of a certain sampling point of the optical fiber length axis on all frequency components, each column of the two-dimensional array is subjected to numerical processing, and the peak frequency of the first resonance peak at the position where each sampling point on the optical fiber length axis represents is obtained;
and 4, step 4: splicing the peak frequency of the first resonance peak at the representation position of each sampling point on the optical fiber length axis into a one-dimensional array, carrying out median filtering on the one-dimensional array by using the set window width to obtain a frequency information one-dimensional array after smoothing treatment, wherein each element in the one-dimensional array is the peak frequency of the first resonance peak at the representation position of each sampling point on the optical fiber length axis in a preset time period, and the element index is the position represented by each sampling point on the optical fiber length axis;
and 5: acquiring a preset time period of the step 1 for multiple times by a phi-OTDR system in continuous time, processing the acquired RBS signals in the steps 2 to 4, counting the frequency of each peak frequency of the processed frequency information one-dimensional arrays at the same element index, recording the peak frequency with the highest frequency as the resonant frequency of the sampling point representing the position of the optical fiber, and finally obtaining the resonant frequency of each sampling point representing the position in the continuous time on the optical fiber length axis in the composite optical cable of the overhead ground wire;
step 6: under the condition that the overhead ground wire composite optical cable is not iced, the phi-OTDR system is processed in the steps 1 to 5 to obtain the resonant frequency under the condition that the overhead ground wire composite optical cable is not iced, and the resonant frequency is recorded as a calibrated resonant frequency f01And under the condition that the overhead ground wire composite optical cable is iced, carrying out the processing from the step 1 to the step 5 on the phi-OTDR system to obtain the resonance frequency under the condition that the overhead ground wire composite optical cable is not iced, and recording the resonance frequency as the actual resonance frequency f02According to measured f01And f02The actual icing thickness can be calculated, and a distributed and intelligent icing thickness monitoring method is realized.
As a further preferable scheme of the overhead ground wire composite optical cable ice-coating monitoring method of the phase-sensitive optical time domain reflection system, in the step 3, each column of the two-dimensional array of the phase signal frequency spectrum is subjected to numerical processing, specifically as follows:
each column of the two-dimensional array of the spectrum of the phase signal can be regarded as a one-dimensional array with the frequency component f as an element index, and the following processing is performed for each element in the array,
wherein,
is the value of the one-dimensional array element after processing, IN(f) The method comprises the following steps that the phase signal spectrum is a one-dimensional array element, N is the serial number of each row of a two-dimensional array of the phase signal spectrum, f is the index of the one-dimensional array element, f belongs to N, and f is larger than or equal to 1.
And (3) performing the above formula processing on each element of the one-dimensional array to obtain a new one-dimensional array, and taking an element index f corresponding to a first peak value in the elements of the one-dimensional array, namely the peak frequency of a first resonance peak at the position represented by each sampling point on the optical fiber length axis.
As a further preferable scheme of the ice-coating monitoring method for the overhead ground wire composite optical cable of the phase-sensitive optical time domain reflection system, in the step 6, according to f01And f02The concrete steps for calculating the actual ice coating thickness of the overhead ground wire composite optical cable are as follows:
step 1: according to a nominal resonant frequency f01Horizontal tension T of overhead ground wire composite optical cable under condition of no ice coating01：T01＝4m0l2f01 2Wherein l is the horizontal distance between the suspension points of the composite optical cable of the overhead ground wires of two adjacent towers, and m is0The unit length mass of the composite optical cable of the overhead ground wire under the condition of no ice coating and the horizontal stress sigma of the composite optical cable of the overhead ground wire under the condition of no ice coating01：
Wherein A is the sectional area of the overhead ground wire composite optical cable.
Step 2: unit length mass m of overhead ground wire composite optical cable under ice coating condition02The relationship with the ice coating thickness b is: m is02＝m0+0.9πb(d+b)×10-3And d is the diameter of the composite optical cable of the overhead ground wire. According to the actual resonance frequency f02Horizontal stress sigma of overhead ground wire composite optical cable under icing condition02：
And step 3: the basic form of the overhead ground wire composite optical cable state equation is as follows:
wherein E is the Young modulus of the composite optical cable of the overhead ground wire, beta is the horizontal distance height difference angle between the suspension points of the composite optical cable of the overhead ground wire of two adjacent towers, alpha is the thermal expansion coefficient of the composite optical cable of the overhead ground wire, and t1And t2The temperature of the composite optical cable of the overhead ground wire under the condition of no ice coating and the temperature of the composite optical cable under the condition of ice coating are respectively shown, gamma 'and gamma are respectively the comprehensive specific load under the condition of ice coating and the condition of no ice coating, and the mass relationship of the gamma' and the gamma and the unit length is as follows:
where g is the acceleration of gravity, the above relation may in practice ignore the term α Ecos β (t)2-t1) And (6) performing calculation.
The relational expression obtained from the step 1 to the step 2 is
And
substituting the state equation of the overhead ground wire composite optical cable to obtain the equation:
in the above equation, the known quantity comprises the mass m per unit length of the overhead ground wire composite optical cable without ice coating0The diameter d of the composite optical cable of the overhead ground wire, the horizontal distance l between suspension points of the composite optical cable of the overhead ground wires of two adjacent towers and the calibration resonant frequency f01True resonant frequency f02The calculated sectional area A of the composite optical cable of the overhead ground wire, the Young modulus E of the composite optical cable of the overhead ground wire, the height difference angle beta of the horizontal distance between suspension points of the composite optical cable of the overhead ground wires of two adjacent towers and the gravity acceleration g; the unknown quantity comprises the icing thickness b, and the actual equivalent icing thickness b of the composite optical cable of the overhead ground wire can be obtained through calculation.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. Numerous simplifications or substitutions made by those skilled in the art may be made without departing from the spirit of the invention, which should be construed to be within the scope of the invention.
Claims (3)
1. A method for monitoring ice coating of an overhead ground wire composite optical cable based on a phase-sensitive optical time domain reflection system is characterized by specifically comprising the following steps:
step 1: connecting a sensing optical fiber in a phase-sensitive optical time domain reflection system with an optical fiber in an overhead ground wire composite optical cable by using a jumper optical fiber, setting a plurality of sampling points on an optical fiber length axis, and collecting different sampling points for multiple times within a preset time period by using a computer in the phase-sensitive optical time domain reflection system to obtain the distribution of Rayleigh backscattering signals in the optical fiber of the overhead ground wire composite optical cable between two towers on a measurement time axis and the optical fiber length axis;
step 2: carrying out phase demodulation on the Rayleigh backscattering signals of each sampling point acquired for multiple times within the preset time in the step 1, carrying out Fourier transform on phase values of the phase signals after phase demodulation, which correspond to each sampling point on the optical fiber length axis, along a time axis in a fixed time window, and obtaining frequency spectrums of the phase signals through low-pass filtering;
and step 3: the phase signal frequency spectrum finally obtained in the step 2 is a two-dimensional array, the row of the two-dimensional array represents the intensity distribution information of a certain frequency component on all sampling points of the optical fiber length axis, the column of the two-dimensional array represents the intensity distribution information of a certain sampling point of the optical fiber length axis on all frequency components, each column of the two-dimensional array is subjected to numerical processing, and the peak frequency of the first resonance peak at the position where each sampling point on the optical fiber length axis represents is obtained;
and 4, step 4: splicing the peak frequency of the first resonance peak at the representation position of each sampling point on the optical fiber length axis into a one-dimensional array, carrying out median filtering on the one-dimensional array by using the set window width to obtain a frequency information one-dimensional array after smoothing treatment, wherein each element in the one-dimensional array is the peak frequency of the first resonance peak at the representation position of each sampling point on the optical fiber length axis in a preset time period, and the element index is the position represented by each sampling point on the optical fiber length axis;
and 5: carrying out multiple times of collection of the preset time period in the step 1 on a phase-sensitive optical time domain reflection system in continuous time, carrying out the processing from the step 2 to the step 4 on a plurality of collected Rayleigh backscattering signals, carrying out statistics on a plurality of frequency information one-dimensional arrays obtained after the processing on the frequency information one-dimensional arrays, calculating the frequency of occurrence of each peak frequency of the frequency information one-dimensional arrays at the same element index, recording the peak frequency with the highest frequency of occurrence as the resonant frequency of the sampling point representing the position of the optical fiber, and finally obtaining the resonant frequency of each sampling point representing the position in the continuous time on the optical fiber length axis in the overhead ground wire composite optical cable;
step 6: under the condition that the overhead ground wire composite optical cable is not coated with ice, the phase-sensitive optical time domain reflection system is processed in the steps 1 to 5 to obtain the resonant frequency under the condition that the overhead ground wire composite optical cable is not coated with ice, and the resonant frequency is recorded as a calibrated resonant frequency f01And under the condition that the overhead ground wire composite optical cable is iced, performing the processing from the step 1 to the step 5 on the phase-sensitive optical time domain reflection system to obtain the resonance frequency under the condition that the overhead ground wire composite optical cable is not iced, and recording the resonance frequency as the actual resonance frequency f02According to measured f01And f02The actual ice coating thickness can be calculated.
2. The method for monitoring ice coating on the overhead ground wire composite optical cable according to claim 1, wherein in the step 3, each column of the two-dimensional array of the phase signal spectrum is numerically processed, specifically as follows:
each column of the two-dimensional array of the spectrum of the phase signal can be regarded as a one-dimensional array with the frequency component f as an element index, and the following processing is performed for each element in the array,
wherein,
is the value of the one-dimensional array element after processing, IN(f) Is a one-dimensional array element, N is the serial number of each row of the two-dimensional array of the phase signal frequency spectrum, f is the index of the one-dimensional array element and f belongs to N*And f is greater than or equal to 1;
and (3) performing the above formula processing on each element of the one-dimensional array to obtain a new one-dimensional array, and taking an element index f corresponding to a first peak value in the elements of the one-dimensional array, namely the peak frequency of a first resonance peak at the position represented by each sampling point on the optical fiber length axis.
3. Overhead ground wire composite optical cable icing monitoring method according to any of claims 1 or 2, characterized in that in step 6, according to f01And f02The concrete steps for calculating the actual ice coating thickness of the overhead ground wire composite optical cable are as follows:
step 1: according to a nominal resonant frequency f01Horizontal tension T of overhead ground wire composite optical cable under condition of no ice coating01：T01＝4m0l2f01 2Wherein l is the horizontal distance between the suspension points of the composite optical cable of the overhead ground wires of two adjacent towers, and m is0The unit length mass of the composite optical cable of the overhead ground wire under the condition of no ice coating and the horizontal stress sigma of the composite optical cable of the overhead ground wire under the condition of no ice coating01：
Wherein A is the sectional area of the overhead ground wire composite optical cable;
step 2: unit length mass m of overhead ground wire composite optical cable under ice coating condition02The relationship with the ice coating thickness b is: m is02＝m0+0.9πb(d+b)×10-3Wherein d is the diameter of the composite optical cable of the overhead ground wire according to the actual resonant frequency f02Horizontal stress sigma of overhead ground wire composite optical cable under icing condition02：
And step 3: the basic form of the overhead ground wire composite optical cable state equation is as follows:
wherein E is the Young modulus of the composite optical cable of the overhead ground wire, beta is the horizontal distance height difference angle between the suspension points of the composite optical cable of the overhead ground wire of two adjacent towers, alpha is the thermal expansion coefficient of the composite optical cable of the overhead ground wire, and t1And t2The temperature of the composite optical cable of the overhead ground wire under the condition of no ice coating and the temperature of the composite optical cable under the condition of ice coating are respectively shown, gamma 'and gamma are respectively the comprehensive specific load under the condition of ice coating and the condition of no ice coating, and the mass relationship of the gamma' and the gamma and the unit length is as follows:
where g is the acceleration of gravity, the above relation ignores the term α Ecos β (t) in practical cases2-t1) Calculating;
the relational expression obtained from the step 1 to the step 2 is
And
substituting the state equation of the overhead ground wire composite optical cable to obtain the equation:
and calculating to obtain the actual equivalent ice coating thickness b of the overhead ground wire composite optical cable.
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