CN113671321B - Cable fault identification and positioning method based on lead code multipath iterative analysis - Google Patents

Cable fault identification and positioning method based on lead code multipath iterative analysis Download PDF

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CN113671321B
CN113671321B CN202111218560.0A CN202111218560A CN113671321B CN 113671321 B CN113671321 B CN 113671321B CN 202111218560 A CN202111218560 A CN 202111218560A CN 113671321 B CN113671321 B CN 113671321B
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cable
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multipath
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iterative
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CN113671321A (en
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张大兴
黄泽荣
尹星光
李贤靓
蔡冰子
袁昊宇
田明明
李泽基
王掬涵
袁英平
温振兴
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Huizhou Power Supply Bureau of Guangdong Power Grid Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/083—Locating faults in cables, transmission lines, or networks according to type of conductors in cables, e.g. underground
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing

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Abstract

The invention provides a cable fault identification and positioning method based on lead code multipath iterative analysis, which is characterized in that a lead code signal is injected into one end of a cable to be detected, simultaneously, a reflected signal is received and subjected to multipath iterative analysis, information such as the number of multipath, the polarity of a peak value, the strength, the arrival time and the like in the reflected signal is obtained, and the detection of a cable fault, the identification of a fault type, the judgment of a fault degree and the positioning of a fault point are realized through the information. The invention can not only judge whether the cable has faults, but also provide the fault type, the fault severity and the fault point position, is beneficial to comprehensively and comprehensively evaluating the cable state, and provides more reliable and accurate basis for monitoring and maintaining the cable.

Description

Cable fault identification and positioning method based on lead code multipath iterative analysis
Technical Field
The invention relates to the technical field of power secondary equipment, in particular to a cable fault identification and positioning method based on lead code multipath iterative analysis.
Background
With the rapid development of urban construction, the power cable gradually replaces overhead lines to become the main force of the urban power transmission and distribution network by virtue of the advantages of small floor space, environmental friendliness to cities and the like. However, in the manufacturing, transporting, installing and operating processes, the cable is affected by factors such as process, construction quality, operating environment and external force damage, and insulation defects are easily generated, so that insulation breakdown accidents are caused. In recent years, the cable of a power grid company is large in scale, fast in growth and long in running time, part of the cable is close to or even exceeds the design service life of the cable, and the failure rate is high for a long time. Therefore, how to reduce the failure rate of the power cable and ensure the power supply reliability of the cable line has become a problem that cannot be ignored.
At present, the commonly used cable fault detection methods include a pulse current method, a time domain reflection method, an impedance spectroscopy method and the like. The pulse current method can detect the high-resistance fault of the cable, but high voltage is needed to break down the fault point, and the test precision is easy to be interfered by the outside. The time domain reflection method is a nondestructive testing method, and the position of a cable fault point is judged by recording the time difference between a reflected pulse and a transmitted pulse. The time domain reflection method injects pulse signals, and the reflected pulses are easily deformed due to the influence of noise and attenuation in the transmission process, so that the fault positioning precision is influenced. The impedance spectroscopy extracts the running state information of the cable by measuring the curve of the input impedance of the head end of the cable along with the change of frequency, thereby judging the local defects of the cable. Impedance spectrum data is easy to measure, but how to extract and analyze the characteristic quantity of a local defect from the data is a difficult problem. In the prior art, the PLC-based modulation module is adopted, and the line impedance is monitored in a non-invasive mode to complete the diagnosis and positioning of the cable fault. However, the line impedance may vary periodically/non-periodically with the access of the equipment in the power grid, thereby causing misjudgment of the cable fault. Or a signal transmission function is extracted and analyzed by utilizing PLC channel estimation, so that the cable degradation phenomenon is judged, the degradation degree is quantized, and the degradation position is positioned. The acquisition of the signal transmission function is susceptible to signal attenuation and line noise, so that the cable state identification rate and the positioning accuracy are not high.
Disclosure of Invention
Aiming at the problems, the invention provides a cable fault identification and positioning method based on lead code multipath iterative analysis, which injects lead code signals into one end of a cable, receives reflected signals and carries out multipath iterative processing to obtain multipath information in the reflected signals and realize cable fault detection.
Specifically, the invention provides a cable fault identification and positioning method based on lead code multipath iterative analysis, which comprises the following steps:
s1: the fault detection equipment sends a lead code test signal and injects the lead code test signal into a cable to be tested through a coupler;
s2: the fault detection equipment simultaneously collects lead code reflection signals in the cable to be detected through the coupler;
s3: performing multipath signal iterative processing on the lead code reflection signal;
s4: judging whether the cable to be tested has a fault or not by using an output result of the multi-path signal iterative processing obtained after signal processing, and if so, switching to S5; otherwise, ending the detection;
s5: and judging the fault type of the cable to be tested, calculating the fault degree of the cable to be tested, and calculating the fault position of the cable to be tested.
Wherein, the iterative processing of the multipath signal further comprises the following steps:
carrying out correlation operation on the input signal and the locally stored lead code, wherein the formula is as follows:
Figure GDA0003438087380000021
Figure GDA0003438087380000022
wherein m (k) is the kth element in an autocorrelation measurement sequence obtained by carrying out correlation calculation on an input signal and a locally stored lead code, k is the sequence number of the sequence, and N is the length of the lead code; b (k) is the kth element in the autocorrelation calculation module input sequence, b (k + n) is the kth element in the autocorrelation calculation module input sequence; s (n) is the nth element in the conjugate sequence of preamble s; r (k) is the collected reflected signal; (k) is the multipath filtering processing module output; n is a radical ofiterRepresenting the number of iterations; s denotes the conjugate of the preamble s.
Further, the iterative processing of the multipath signal further includes the following steps:
comparing | m (k) | with a threshold value T, and if the amplitude of no element in | m (k) | is larger than T, stopping iteration and ending the signal processing flow; otherwise, finding the first element with amplitude larger than the threshold value T, and respectively recording the amplitude P of the elementNiterAnd serial number
Figure GDA0003438087380000023
Expressed as:
Figure GDA0003438087380000024
Figure GDA0003438087380000025
respectively recording the magnitude P of the amplitude of L times of iterative computationNiterAnd serial number
Figure GDA0003438087380000031
Obtaining a vector
Figure GDA0003438087380000032
And
Figure GDA0003438087380000033
as an output result of the iterative processing of the multipath signal.
Further, the iterative processing of the multipath signal further includes the following steps:
if the iteration times reach the preset upper limit, stopping the iteration and ending the signal processing flow, otherwise, P is usedNiterThe collected reflection signal is processed by multipath filtering as input, and the formula is as follows:
Figure GDA0003438087380000034
where s is a locally stored preamble and fNiterIs the NthiterSub-iterative multipath filteringOutputting by a module; r (k) is the kth element in the multipath filtering processing module input sequence, and k is the sequence number; s (k) is the kth element in the locally stored preamble sequence; s (n) is the nth element in the locally stored preamble sequence; f. ofNiter-1(k) After the Niter-1 iteration, the multipath filtering processing module outputs the kth element in the sequence.
Further, the determining whether the cable to be tested has a fault further includes:
s401: if the output result L of the multi-path signal iterative processing is larger than 1, judging that the cable has a fault, otherwise, switching to S402 for further judgment;
s402: if the vector is
Figure GDA0003438087380000035
The first element p in (1)1<0, judging that the cable has a fault, otherwise, turning to S403 for further judgment;
s403: if the position of the fault point is at a distance L from the head end of the cablefLess than the length L of the cable to be measuredcAnd if not, judging that the cable has no fault, and finishing the cable fault identification.
Wherein, judge the fault type of the cable that awaits measuring, still include:
if the cable to be tested judges that a fault exists, further judging the fault type:
Figure GDA0003438087380000036
h represents a fault type, and when L is 1 and the first element p1 in the fault type is less than 0, the fault type is determined to be a short-circuit fault; if L is 1 and the first element p1 in L is >0, then the circuit-breaking fault is determined; if L is larger than 1 and the first element p1 in the L is less than 0, determining that the fault is low-resistance fault; if L is greater than 1 and the first element p1 in the set is <0, then a high-resistance fault is determined.
Further, the fault degree of the cable to be tested is calculated by adopting a formula:
Figure GDA0003438087380000041
wherein Lvl denotes the severity of the cable fault, p1Representing a vector
Figure GDA0003438087380000042
The 1 st element in (1).
Further, calculating the fault position of the cable to be tested further includes:
calculating the distance between the fault point and the cable head end by using the arrival time of the first path:
Figure GDA0003438087380000043
wherein d is1Is composed of
Figure GDA0003438087380000044
V is the transmission speed of electromagnetic wave signal in cable, fsIs the sampling frequency.
Further, the calculating the fault location of the cable to be tested preferably includes: calculating the distance between the fault point and the cable head end by using the arrival time of the first path and the second path, wherein the formula is as follows:
Figure GDA0003438087380000045
wherein d is1And d2Are respectively as
Figure GDA0003438087380000046
Of the first and second elements, LcIs the known length of cable to be tested.
In summary, the present invention provides a cable fault identifying and positioning method based on lead code multipath iterative analysis, which injects a lead code signal into one end of a cable to be detected, receives a reflected signal and performs multipath iterative analysis, so as to obtain information such as multipath number, peak polarity, strength, arrival time, and the like in the reflected signal, and implement detection of cable fault, identification of fault type, judgment of fault degree, and positioning of fault point through the information.
The invention can not only judge whether the cable has faults, but also provide the fault type, the fault severity and the fault point position, is beneficial to comprehensively and comprehensively evaluating the cable state, and provides more reliable and accurate basis for monitoring and maintaining the cable. Meanwhile, the method can still ensure higher fault identification rate and fault positioning accuracy under the condition of low signal-to-noise ratio by utilizing the strong autocorrelation of the lead code, and is suitable for practical application scenes such as cable live detection, online monitoring and the like. In addition, the algorithm provided by the invention can be realized in the existing power line carrier equipment through simple firmware upgrade. A large amount of power line carrier networks in the medium-low voltage distribution network are utilized, extra hardware equipment is not needed to be added, cables in the medium-low voltage distribution network can be monitored on line, and the medium-low voltage distribution network cable monitoring system has the advantages of being simple in principle, economical, practical and convenient to use.
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Fig. 1 is a schematic view of a cable insulation state monitoring system employed in the present invention.
Fig. 2 is a flow chart of the cable insulation state detection according to the present invention.
Fig. 3 is a block diagram of multipath iterative processing of a reflected signal according to the present invention.
Fig. 4 is a cable fault identification process according to the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a cable fault identification and positioning method based on lead code multipath iterative analysis, which adopts a cable insulation state monitoring system as shown in figure 1 and comprises a cable fault detection device and a coupler. The fault detection equipment is used for injecting a lead code signal, receiving and collecting a reflected signal, extracting information such as multipath quantity, polarity, strength, arrival time and the like through multipath iterative signal processing, and realizing cable fault detection and positioning; the coupler couples the high-frequency test signal into the cable to be tested at the sending end and extracts the signal in the cable to be tested for the receiving end equipment.
Further, the present invention also provides a cable fault identification and positioning method based on preamble multipath iterative analysis, as shown in fig. 2, including the following steps:
s1: the fault detection equipment sends a lead code test signal and injects the lead code test signal into a cable to be tested through a coupler;
s2: the fault detection equipment simultaneously collects lead code reflection signals in the cable to be detected through the coupler;
s3: performing multipath signal iterative processing on the lead code reflection signal;
s4: judging whether the cable to be tested has a fault or not by using an output result of the multi-path signal iterative processing obtained after signal processing, and if so, switching to S5; otherwise, ending the detection;
s5: and judging the fault type of the cable to be tested, calculating the fault degree of the cable to be tested, and calculating the fault position of the cable to be tested.
Specifically, the multipath iterative processing process is as follows:
after the lead code is injected into the head end of the cable, the reflected signal is collected and processed by digital signal processing, as shown in fig. 3, including modules of autocorrelation calculation, threshold comparison, peak storage, multipath iterative processing, and the like.
The autocorrelation calculation module performs correlation operation on the input signal and the locally stored lead code:
equation 1:
Figure GDA0003438087380000051
equation 2:
Figure GDA0003438087380000061
wherein m (k) is the kth element in an autocorrelation measurement sequence obtained by carrying out correlation calculation on an input signal and a locally stored lead code, k is the sequence number of the sequence, and N is the length of the lead code; b (k) is the kth element in the autocorrelation calculation module input sequence, b (k + n) is the kth element in the autocorrelation calculation module input sequence; s (n) is the nth element in the conjugate sequence of preamble s; r (k) is the collected reflected signal; (k) is the multipath filtering processing module output; n is a radical ofiterRepresenting the number of iterations; s denotes the conjugate of the preamble s.
Due to the good auto-and cross-correlation properties of the preamble, m (k) has sharp correlation peaks. Comparing | m (k) | with a threshold value T, and if no element exists in the sequence and the amplitude of the element is greater than T, stopping iteration and ending the signal processing flow; otherwise, finding the first element with the amplitude larger than the threshold value T, and recording the amplitude and the sequence number of the element, namely the formula 3-4: respectively recording the magnitude P of the amplitude of L times of iterative computationNiterAnd serial number
Figure GDA0003438087380000062
Obtaining a vector
Figure GDA0003438087380000063
And
Figure GDA0003438087380000064
as an output result of the iterative processing of the multipath signal.
Figure GDA0003438087380000065
Figure GDA0003438087380000066
Where T is a threshold value and | x | represents the absolute value of x. After recording the amplitude and the serial number, if the iteration times reach the set upper limit, stopping the iteration and ending the signal processing flow, otherwise, PNiterThe acquired reflected signal is input for multipath filtering as shown in equation 5:
Figure GDA0003438087380000067
where s is a locally stored preamble and fNiterIs the NthiterOutputting the multi-path filtering module of the secondary iteration; r (k) is the kth element in the multipath filtering processing module input sequence, and k is the sequence number; s (k) is the kth element in the locally stored preamble sequence; s (n) is the nth element in the locally stored preamble sequence; f. ofNiter-1(k) After the Niter-1 iteration, the multipath filtering processing module outputs the kth element in the sequence.
Outputting two vectors by signal processing of received data
Figure GDA0003438087380000071
And
Figure GDA0003438087380000072
the values in equations (3) and (4) are recorded for L iterations, respectively, where L represents the final iteration number and also represents the number of detected multipaths.
Further, the fault identification process is as follows:
the method comprises the following steps of identifying cable faults by utilizing multipath information such as multipath quantity, polarity, arrival time and the like extracted by multipath iterative processing of reflected signals, wherein the identification process is shown in figure 4, and the specific judgment steps are as follows:
s401: if the output result L of the multi-path signal iterative processing is larger than 1, judging that the cable has a fault, otherwise, switching to S402 for further judgment;
s402: if the vector is
Figure GDA0003438087380000073
The first element p in (1)1<0, judging that the cable has a fault, otherwise, turning to S403 for further judgment;
s403: if the position of the fault point is at a distance L from the head end of the cablefLess than the length L of the cable to be measuredcAnd if not, judging that the cable has no fault, and finishing the cable fault identification.
Further, the fault type is judged as follows:
if the cable to be tested judges that a fault exists, further judging the fault type by adopting a formula 6:
Figure GDA0003438087380000074
wherein H represents a fault type when the number of multipaths is 1, and
Figure GDA0003438087380000075
the first element p in (1)1<0, judging as a short-circuit fault; if the number of multipaths is 1, and
Figure GDA0003438087380000076
the first element p in (1)1>0, judging as open circuit fault; if the number of multipaths is greater than 1, and
Figure GDA0003438087380000077
the first element p in (1)1<0, judging as a low-resistance fault; if the number of multipaths is greater than 1, and
Figure GDA0003438087380000078
the first element p in (1)1<0, high impedance fault is determined.
Further, the degree of failure is calculated as:
if the cable to be tested has a degradation phenomenon, further calculating the severity of the fault, as shown in formula 7:
Figure GDA0003438087380000079
wherein Lvl denotes the severity of the cable fault, p1Representing a vector
Figure GDA0003438087380000081
The 1 st element in (1).
Further, the fault location is calculated as:
after detecting that a cable fault exists and judging the fault type, calculating the distance between the fault point and the cable head end by using the arrival time of the first path, as shown in formula 8:
Figure GDA0003438087380000082
wherein d is1Is composed of
Figure GDA0003438087380000083
V is the transmission speed of the electromagnetic wave signal in the cable, fsIs the sampling frequency.
Due to d in the formula (8)1Is a positive integer, thus LfThe calculation error of (2 f) is influenced by the sampling frequency and is v/(2 f)s). The transmission speed v of the electromagnetic wave signal in the cable is related to the cable material, for a specific power cable, the fault location precision is related to the sampling rate, and the higher the sampling rate is, the higher the location precision is, and otherwise, the lower the location precision is.
For low and high resistance faults, there are multiple reflection paths, over the length (L) of the cable to be testedc) Under the known condition, the distance between the fault point and the cable head end is calculated by using the arrival time of the first path and the second path, so that the fault positioning accuracy can be prevented from being influenced by the sampling rate, as shown in formula 9:
Figure GDA0003438087380000084
wherein d is1And d2Are respectively as
Figure GDA0003438087380000085
Of the first and second elements, LcIs the known length of cable to be tested.
The invention can not only judge whether the cable has faults, but also provide the fault type, the fault severity and the fault point position, is beneficial to comprehensively and comprehensively evaluating the cable state, and provides more reliable and accurate basis for monitoring and maintaining the cable; the high fault identification rate and the high fault positioning precision can be still ensured under the condition of low signal to noise ratio by utilizing the strong autocorrelation of the lead code, and the method is suitable for practical application scenes such as cable live detection, online monitoring and the like; in addition, when the low-resistance and high-resistance faults are detected, the fault location is calculated by using the arrival time of the first path and the second path, so that the fault location error can be prevented from being influenced by the sampling rate, and the location precision is further improved;
the algorithm provided by the invention can be realized in the existing power line carrier equipment through simple firmware upgrade. A large amount of power line carrier networks in the medium-low voltage distribution network are utilized, extra hardware equipment is not needed to be added, cables in the medium-low voltage distribution network can be monitored on line, and the medium-low voltage distribution network cable monitoring system has the advantages of being simple in principle, economical, practical and convenient to use.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (9)

1. A cable fault identification and positioning method based on lead code multipath iterative analysis is characterized by comprising the following steps:
s1: the fault detection equipment sends a lead code test signal and injects the lead code test signal into a cable to be tested through a coupler;
s2: the fault detection equipment simultaneously collects lead code reflection signals in the cable to be detected through the coupler;
s3: performing multipath signal iterative processing on the lead code reflection signal;
s4: judging whether the cable to be tested has a fault or not by using an output result of the multi-path signal iterative processing obtained after signal processing, and if so, switching to S5; otherwise, ending the detection;
s5: and judging the fault type of the cable to be tested, calculating the fault degree of the cable to be tested, and calculating the fault position of the cable to be tested.
2. The cable fault identification and location method based on preamble multipath iterative analysis as claimed in claim 1, wherein the multipath signal iterative process further comprises the following steps:
carrying out correlation operation on the input signal and the locally stored lead code, wherein the formula is as follows:
Figure FDA0003438087370000011
Figure FDA0003438087370000012
wherein m (k) is the kth element in an autocorrelation measurement sequence obtained by carrying out correlation calculation on an input signal and a locally stored lead code, k is the sequence number of the sequence, and N is the length of the lead code; b (k) is the kth element in the autocorrelation calculation module input sequence, b (k + n) is the kth element in the autocorrelation calculation module input sequence; s (n) is the nth element in the conjugate sequence of preamble s; r (k) is the collected reflected signal; (k) is the multipath filtering processing module output; n is a radical ofiterRepresenting the number of iterations; s denotes the conjugate of the preamble s.
3. The cable fault identification and location method based on preamble multipath iterative analysis as claimed in claim 2, wherein the multipath signal iterative processing further comprises the following steps:
comparing | m (k) | with a threshold value T, and if the amplitude of no element in | m (k) | is larger than T, stopping iteration and ending the signal processing flow; otherwise, finding the first element with amplitude larger than the threshold value T, and respectively recording the amplitude P of the elementNiterAnd serial number
Figure FDA0003438087370000013
Expressed as:
Figure FDA0003438087370000014
Figure FDA0003438087370000021
respectively recording the magnitude P of the amplitude of L times of iterative computationNiterAnd serial number
Figure FDA0003438087370000022
Obtaining a vector
Figure FDA0003438087370000023
And
Figure FDA0003438087370000024
as an output result of the iterative processing of the multipath signal.
4. The cable fault identification and location method based on preamble multipath iterative analysis as claimed in claim 3, wherein the multipath signal iterative process further comprises the following steps:
if the iteration times reach the preset upper limit, stopping the iteration and ending the signal processing flow, otherwise, P is usedNiterThe collected reflection signal is processed by multipath filtering as input, and the formula is as follows:
Figure FDA0003438087370000025
respectively recording the magnitude P of the amplitude of L times of iterative computationNiterAnd serial number
Figure FDA0003438087370000026
Obtaining a vector
Figure FDA0003438087370000027
And
Figure FDA0003438087370000028
as an output result of the iterative processing of the multipath signal;
where s is a locally stored preamble and fNiterIs the NthiterOutputting the multi-path filtering module of the secondary iteration; r (k) is the kth element in the multipath filtering processing module input sequence, and k is the sequence number; s (k) is the kth element in the locally stored preamble sequence; s (n) is the nth element in the locally stored preamble sequence; f. ofNiter-1(k) After the Niter-1 iteration, the multipath filtering processing module outputs the kth element in the sequence.
5. The method for cable fault identification and location based on preamble multipath iterative analysis as claimed in claim 4, wherein said determining whether the cable to be tested has a fault further comprises:
s401: if the output result L of the multi-path signal iterative processing is larger than 1, judging that the cable has a fault, otherwise, switching to S402 for further judgment;
s402: if the vector is
Figure FDA0003438087370000029
The first element p in (1)1<0, judging that the cable has a fault, otherwise, turning to S403 for further judgment;
s403: if the position of the fault point is at a distance L from the head end of the cablefLess than the length L of the cable to be measuredcAnd if not, judging that the cable has no fault, and finishing the cable fault identification.
6. The cable fault identification and location method based on preamble multipath iterative analysis as recited in claim 5, further comprising:
if the cable to be tested judges that a fault exists, further judging the fault type:
Figure FDA0003438087370000031
h represents a fault type, and when L is 1 and the first element p1 in the fault type is less than 0, the fault type is determined to be a short-circuit fault; if L is 1 and the first element p1 in L is >0, then the circuit-breaking fault is determined; if L is larger than 1 and the first element p1 in the L is less than 0, determining that the fault is low-resistance fault; if L is greater than 1 and the first element p1 in the set is <0, then a high-resistance fault is determined.
7. The method for identifying and positioning the cable fault based on the lead code multipath iterative analysis as claimed in claim 6, wherein the degree of the cable fault to be measured is calculated by adopting a formula:
Figure FDA0003438087370000032
wherein Lvl denotes the severity of the cable fault, p1Representing a vector
Figure FDA0003438087370000033
The 1 st element in (1).
8. The method for cable fault identification and location based on preamble multipath iterative analysis as claimed in claim 7, wherein the calculating the cable fault location to be tested further comprises:
calculating the distance between the fault point and the cable head end by using the arrival time of the first path:
Figure FDA0003438087370000034
wherein d is1Is composed of
Figure FDA0003438087370000035
V is the transmission speed of electromagnetic wave signal in cable, fsIs the sampling frequency.
9. The cable fault identification and location method based on preamble multipath iterative analysis as recited in claim 8, further comprising:
calculating the distance between the fault point and the cable head end by using the arrival time of the first path and the second path, wherein the formula is as follows:
Figure FDA0003438087370000036
wherein d is1And d2Are respectively as
Figure FDA0003438087370000037
Of the first and second elements, LcIs the known length of cable to be tested.
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