Cable defect identification and positioning method and device based on time-varying matched filtering

Abstract

The invention discloses a cable defect identification and positioning method and device based on time-varying matched filtering. Relates to the power equipment state detection technology and the application field thereof. The method comprises the following steps: connecting a measured cable to measuring equipment through a connecting line; disconnecting the measured cable and the connecting line, injecting a pulse signal by the measuring equipment, and measuring a reflected signal vos (t) generated when the tail end of the connecting line is short-circuited; the measured cable and the connecting line are connected, the measurement equipment keeps setting parameters unchanged, and a reflection signal in the measured cable is obtained; designing a time-varying matched filter based on a reflection signal generated when the tail end of the connecting line is short-circuited, filtering the reflection signal in the tested cable to obtain a filtered reflection signal curve, and determining reflection time through an extreme point on the filtered reflection signal curve; and calculating the position lf of the cable defect according to the reflection time. According to the invention, the detection capability of the time domain reflection technology on small defects in the cable and in a noise environment is improved, and the method has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment status detection and its application technologies, and more specifically, to a method and device for cable defect identification and location based on time-varying matched filtering. Background Art

[0002] With the development of production technologies and friendly power supply methods, cables are widely used in power transmission and distribution networks. At the same time, cable detection technologies are also constantly evolving. In existing cable detection technologies, time-domain reflectometry (TDR) is a fast and effective defect detection and location technology and is also the basis for many other detections.

[0003] The key in TDR is the identification and location of the reflected signal. In existing reflected signal identification, a simple threshold method is mostly used to determine the presence or absence of the signal, lock the interval where the reflected signal is located, and further calculate the arrival time of the reflected signal through other methods such as the energy method, threshold method, and phase method. In this process, if the intensity of the reflected signal in the measurement result is low or there is a large amount of noise in the measurement result, causing the reflected signal to be submerged in the noise, it is very easy to lead to missed detections. Matched filtering is an effective technology for detecting target signals in a noisy environment. However, existing matched filtering does not consider the attenuation and dispersion characteristics of the cable, resulting in an unclear filtering result and poor location accuracy.

[0004] Therefore, it is an urgent problem for those skilled in the art to design a method and device for cable defect identification and location based on time-varying matched filtering to improve the detection and location capabilities of reflected signals in complex environments. Summary of the Invention

[0005] In view of this, the present invention provides a method and device for cable defect identification and location based on time-varying matched filtering. The present invention improves the detection capabilities of time-domain reflectometry for minute defects in cables and in a noisy environment, and has broad application prospects.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for cable defect identification and location based on time-varying matched filtering, comprising:

[0008] Step 1: Connect the cable under test to the measurement device through a connecting wire;

[0009] Step 2: Disconnect the cable under test and the connecting wire, and the measurement device injects a pulse signal to measure the reflected signal v os (t) generated when the end of the connecting wire is short-circuited;

[0010] Step 3: Connect the cable under test to the connecting wire, and keep the set parameters of the measuring device unchanged to obtain the reflection signal inside the cable under test;

[0011] Step 4: Design a time-varying matching filter based on the reflection signal generated when the end of the connecting wire is short-circuited, and filter the reflection signal inside the cable under test to obtain the filtered reflection signal curve, and determine the reflection time through the extreme points on the filtered reflection signal curve;

[0012] Step 5: Calculate the position l of the cable defect according to the reflection time f 。

[0013] Preferably, the construction equation of the time-varying matching filter is as follows:

[0014] H(ω,t)=Ke -jωT S * (ω,t);

[0015] where K is a constant, T is the time length of the pulse signal injected into the cable, * represents the conjugate operation; S(ω, t) is the frequency-domain expression of the pulse after propagating in the cable for t time.

[0016] Preferably, the law of the time-varying filter transformation is based on the attenuation and dispersion characteristics of the cable under test, and the attenuation and dispersion characteristics of the cable are represented by the attenuation coefficient γ of the cable c ; the frequency-domain expression of the pulse after propagating in the cable for t time is as follows:

[0017]

[0018] In the formula, S(ω) is the frequency-domain expression of the pulse signal injected into the cable; γ c =α c +jβ c , α c is the attenuation coefficient of the cable, β c is the phase coefficient of the cable.

[0019] Preferably, construct the time-varying matching filter equation according to the measurement result of the reflection signal generated when the end of the measuring connecting wire is short-circuited, and the expression is as follows:

[0020]

[0021] In the formula, V oD is the frequency-domain expression of v oD (t), and v oD (t) is the reflection signal generated by the connector D between the connecting wire and the cable; V os is the frequency-domain expression of v os (t).

[0022] Preferably, the reflected signal inside the cable under test is filtered to obtain the measurement result, and the expression is as follows:

[0023] y(t) = F -1 (X(ω)·H(ω,t)).

[0024] where F -1 represents the inverse Fourier transform, X(ω) is the frequency-domain expression of the measurement result, and H(ω,t) is the frequency-domain expression of the time-varying matched filter.

[0025] Preferably, it further includes a cable defect identification and location device based on time-varying matched filtering, including: a host computer, a pulse source, a T-type connector, a data acquisition card, and a connecting wire;

[0026] The host computer sends a control signal to the pulse source to control the pulse source to generate an injection signal;

[0027] The signal output by the pulse source is transmitted to the connecting wire through the T-type connector;

[0028] The T-type connector splits the signal. One connecting wire transmits the signal to the cable under test, and the other is connected to the data acquisition card, and the data acquisition card is used to collect signal data in real time;

[0029] The data acquisition card transmits the collected signal data back to the host computer;

[0030] The end of the connecting wire is connected to the cable under test. The cable under test includes a connector D and a defect location, and is used to receive the injection signal and generate a reflected signal.

[0031] Preferably, the length of the connecting wire is greater than 1 / 2v2t td , where v2 is the wave velocity of the connecting wire; t td is the arrival time difference between the injection signal and the reflected signal of the connector D.

[0032] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a cable defect identification and location method and device based on time-varying matched filtering, which improves the time-domain reflection device. A time-varying matched filter is constructed through the short-circuit calibration result and the measurement result, and the measurement signal is further processed by time-varying matched filtering. In the processing result, if an extreme value appears, it indicates that there is a reflected signal at that position, and the time point corresponding to the extreme value is the arrival time of the reflected signal. This method can effectively improve the detection and location ability of reflected signals in the presence of defects and strong noise environments, significantly improve the level of cable time-domain reflection detection technology, and has important industrial practical value. Brief Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained according to the provided accompanying drawings.

[0034] Figure 1 It is a measurement result diagram of short - circuit calibration in the embodiment of the present invention;

[0035] Figure 2 It is a measurement result diagram of the cable reflection signal in the embodiment of the present invention;

[0036] Figure 3 It is the time - varying matched - filtering result of the measurement result in the embodiment of the present invention;

[0037] Figure 4 It is a device model diagram of the present invention. Specific embodiments

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0039] The embodiment of the present invention discloses a method for identifying and locating cable defects based on time - varying matched filtering, including:

[0040] Step 1: Connect the cable under test to the measurement device through a connecting wire;

[0041] Step 2: Disconnect the cable under test and the connecting wire, the measurement device injects a pulse signal, and measures the reflection signal v os (t) generated when the end of the connecting wire is short - circuited;

[0042] Step 3: Connect the cable under test and the connecting wire, the measurement device keeps the set parameters unchanged, and obtains the reflection signal inside the cable under test;

[0043] Step 4: Design a time - varying matched filter based on the reflection signal generated when the end of the connecting wire is short - circuited, and filter the reflection signal inside the cable under test to obtain the filtered reflection signal curve, and determine the reflection time through the extreme points on the filtered reflection signal curve;

[0044] Step 5: Calculate the position l of the cable defect according to the reflection time f .

[0045] Furthermore, the reflected signal v generated when the end of the connection line is short-circuited os (t) is as shown Figure 1 .

[0046] Specifically, as shown Figure 2 , the reflected signals inside the cable under test are respectively the reflected signal v oD (t) of connector D, the reflected signal v of (t) at the defect, and the reflected signal v oE (t) generated at the open end of the cable under test

[0047] Specifically, the construction equation of the time-varying matched filter is as follows

[0048] H(ω,t) = Ke -jωT S * (ω,t);

[0049] where K is a constant, T is the time length of the pulse signal injected into the cable, * represents the conjugate operation; S(ω, t) is the frequency-domain expression of the pulse after propagating in the cable for t time

[0050] Specifically, the rule of the time-varying matched filter transformation is based on the attenuation and dispersion characteristics of the cable under test. The attenuation and dispersion characteristics of the cable are represented by the attenuation coefficient γ c of the cable; the frequency-domain expression of the pulse after propagating in the cable for t time is as follows

[0051]

[0052] In the formula, S(ω) is the frequency-domain expression of the pulse signal injected into the cable; γ c = α c + jβ c , α c is the attenuation coefficient of the cable, and β c is the phase coefficient of the cable

[0053] Specifically, the time-varying matched filter equation is constructed according to the measurement result of the reflected signal generated when the end of the measurement connection line is short-circuited, and the expression is as follows

[0054]

[0055] In the formula, V oD is the frequency-domain expression of v oD (t), and v oD (t) is the reflected signal generated by connector D between the connection line and the cable; V os is the frequency-domain expression of v os (t).

[0056] Specifically, the reflected signal inside the cable under test is filtered to obtain the measurement result, and the expression is as follows:

[0057] y(t) = F -1 (X(ω)·H(ω,t)).

[0058] Wherein, F -1 represents the inverse Fourier transform, X(ω) is the frequency-domain expression of the measurement result, and H(ω,t) is the frequency-domain expression of the time-varying matched filter.

[0059] Furthermore, if there is a reflected signal in the measurement result, extreme values will appear at certain moments on the y(t) curve, and the time corresponding to the extreme value is the arrival time of the reflected signal; the matched filtering method has excellent effects on the detection of target signals, and can also show good detection effects on signals interfered by white noise. Therefore, the time-varying matched filtering technology can effectively judge the presence or absence of reflected signals from the measurement results with noise interference.

[0060] Specifically, as Figure 4 shown, the present invention further includes a cable defect identification and positioning device based on time-varying matched filtering, including: a host computer, a pulse source, a T-type connector, a data acquisition card, and a connecting wire;

[0061] The host computer sends a control signal to the pulse source to control the pulse source to generate an injection signal;

[0062] The signal output by the pulse source is transmitted to the connecting wire through the T-type connector;

[0063] The T-type connector splits the signal. One connecting wire transmits the signal to the cable under test, and the other connects to the data acquisition card, and the data acquisition card is used to collect signal data in real time;

[0064] The data acquisition card transmits the collected signal data back to the host computer;

[0065] The end of the connecting wire is connected to the cable under test, and the cable under test includes a connector D and a defect location, and is used to receive the injection signal and generate a reflected signal.

[0066] Specifically, the length of the connecting wire is greater than 1 / 2v2t td , where v2 is the wave velocity of the connecting wire; t td is the arrival time difference between the injection signal and the reflected signal of the connector D.

[0067] Furthermore, the wiring model of the specific embodiment of the measurement device of the present invention is as Figure 4As shown in the figure, it includes: a measuring device and the cable under test. The measuring device consists of a pulse source, an acquisition card, a host computer, a T-type connector, and connecting cables. The pulse source generates a pulse signal with a 20 ns rise time and fall time, a 100 ns pulse width, and a signal amplitude of 5 V; the connecting cable is a coaxial cable with a length of 50 m and a model of SYV50; the cable under test is a single-core power cable with a length of 600 m and a model of 8.7 / 15 kV YJV35mm 2 , and the defect is assumed to be located at the 300 m position.

[0068] In the first step, the measurement system is calibrated. The connecting cable is disconnected from the cable under test, and the end of the connecting cable is short-circuited. The reflected pulse at the short-circuited end of the connecting cable is measured as shown in Figure 1 the figure, where v os (t) is the reflected signal at the short-circuited end.

[0069] In the second step, the reflected signal of the cable under test is measured. The connecting cable is connected to the cable under test, and the reflected signal of the cable under test is measured as shown in Figure 2 the figure. By analyzing the reflected pulse in Figure 2 , it can be known that v oD (t), v of (t), and v oE (t) are the reflected signals generated at connector D, the defect location, and the open end of the cable under test in Figure 4 respectively. From the measurement results in Figure 2 , it can be found that as the pulse propagates, the rise time of the pulse gradually becomes slower, and the starting time of the pulse is more difficult to determine. For the measurement results in Figure 2 , the time-varying matched filter is used to identify and locate the reflected pulse. The time-varying matched filter is constructed using the following formula:

[0070]

[0071] Then, the result after matched filtering is calculated using the following matched filtering formula:

[0072] y(t) = F -1 (X(ω)·H(ω,t)).

[0073] The calculation result of the time-varying matched filtering is shown in Figure 3 the figure. Through Figure 3 , it can be determined that the arrival time t oD of the reflected pulse v D at connector D is 0.504 μs, and the arrival time t of of the reflected pulse v f at the defect is 4.04 μs. The wave velocity v p of the cable is generally 170 m / μs, so the location l fIt can be calculated by the following formula

[0074]

[0075] After calculation, the position of the defect is 300.56 meters, the error between the positioning result and the actual position is 0.56 m, and the relative error of the positioning result is 0.187%.

[0076] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section.

[0077] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cable defect identification and location method based on time-varying matched filtering, characterized in that: include: Step 1: Connect the cable under test to the measuring device through a connecting wire; Step 2: Disconnect the cable and connecting wires under test, inject a pulse signal into the measuring device, and measure the reflected signal v generated when the end of the connecting wire is short-circuited os (t); Step 3: Connect the cable under test to the connecting wire, keep the setting parameters of the measuring device unchanged, and obtain the reflected signal inside the cable under test; Step 4: Design a time-varying matched filter based on the reflection signal generated when the end of the connecting line is short-circuited, and filter the reflection signal inside the measured cable to obtain a filtered reflection signal curve, and determine the reflection time through the extreme value point on the filtered reflection signal curve; Step 5: Calculate the location of the cable defect l based on the reflection time f .

2. A cable defect identification and location method based on time-varying matched filtering according to claim 1, characterized in that: The construction equation of the time-varying matched filter is as follows: H(ω,t)=Ke -jωT S * (ω,t); Where K is a constant, T is the time length of the pulse signal injected into the cable, * represents the conjugate operation; S(ω, t) is the frequency domain expression of the pulse after it propagates inside the cable for t time.

3. A cable defect identification and location method based on time-varying matched filtering according to claim 2, characterized in that: The time-varying matched filter transformation rule is based on the attenuation and dispersion characteristics of the cable under test. The attenuation and dispersion characteristics of the cable are expressed by the attenuation coefficient γ of the cable. c The frequency domain expression of the pulse after propagating for time t inside the cable is as follows: Where S(ω) is the frequency domain expression of the pulse signal injected into the cable; γ c =α c +jβ c , α c is the attenuation coefficient of the cable, β c Phase coefficient of the cable.

4. A cable defect identification and location method based on time-varying matched filtering according to claim 3, characterized in that: The time-varying matched filter equation is constructed based on the measurement results of the reflected signal generated when the end of the connecting line is short-circuited. The expression is as follows: Where V oD v oD The frequency domain expression of (t), v oD (t) is the reflected signal generated by the connector D between the connecting wire and the cable; V os v os (t) is the frequency domain expression.

5. A cable defect identification and location method based on time-varying matched filtering according to claim 4, characterized in that: The reflected signal inside the measured cable is filtered to obtain the measurement result, which is expressed as follows: y(t)=F -1 (X(ω)·H(ω,t)). Among them, F -1 represents the inverse Fourier transform, X(ω) is the frequency domain expression of the measurement result, and H(ω,t) is the frequency domain expression of the time-varying matched filter.

6. A device applied to the cable defect identification and location method based on time-varying matched filtering as described in claims 1-5, characterized in that: include: Host computer, pulse source, T-connector, acquisition card, connecting wire; The host computer sends a control signal to the pulse source to control the pulse source to generate an injection signal; The signal output by the pulse source is transmitted to the connecting line through the T-type connector; The T-type connector splits the signal, one connection line is transmitted to the cable under test, and the other is connected to the acquisition card, which is used to collect signal data in real time; The acquisition card transmits the acquired signal data back to the host computer; The end of the connecting line is connected to the cable under test, and the cable under test includes a connector D and a defect position, which is used to receive an injected signal and generate a reflected signal.

7. The device according to claim 6, characterized in that The length of the connecting line is greater than 1 / 2v2t td , where v2 is the wave velocity of the connecting line; t td is the arrival time difference between the injected signal and the reflected signal at connector D.

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