A method and apparatus for cable defect identification and location based on time-varying matched filtering

Abstract

The application discloses a cable defect identification and positioning method and device based on time-varying matching filtering. It relates to the technical field of power equipment state detection and its application field. The method comprises the following steps: connecting the measured cable to the measuring device through a connecting line; disconnecting the measured cable and the connecting line, and measuring the reflected signal v os (t) generated when the end of the connecting line is short-circuited; connecting the measured cable and the connecting line, keeping the setting parameters of the measuring device unchanged, and obtaining the reflected signal inside the measured cable; designing a time-varying matching filter based on the reflected signal generated when the end of the connecting line is short-circuited, and filtering the reflected signal inside the measured cable to obtain a filtered reflected signal curve; determining the reflection time through the extreme points on the filtered reflected signal curve; and calculating the position l f of the cable defect according to the reflection time. The application improves the detection capability of the time-domain reflection technology for the small defects in the cable and in the noise environment, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power equipment state detection and its application, in particular to a cable defect identification and positioning method and device based on time-varying matched filtering. BACKGROUND

[0002] With the development of production technology and friendly power supply mode, cables are widely used in power transmission and distribution networks, and at the same time, cable detection technology is also developing. In the existing cable detection technology, time domain reflection detection is a fast and effective defect detection and positioning technology, and is also the basis of many other detections.

[0003] The identification and positioning of the reflected signal in the time domain reflection detection is the key. The existing reflected signal identification mostly uses a simple threshold method to judge the presence or absence of the signal, locks the interval where the reflected signal is located, and further calculates the arrival time of the reflected signal through other methods such as energy method, threshold method and phase method. In this process, if the reflected signal strength in the measurement result is low or there is a lot of noise signal in the measurement result, the reflected signal is easily submerged in the noise, which can easily lead to missed detection. Matched filtering is an effective technology for detecting target signals in a noisy environment. However, the existing matched filtering does not take into account the attenuation and dispersion characteristics of the cable, resulting in an unobvious filtering result and poor positioning accuracy.

[0004] Therefore, it is an urgent problem for those skilled in the art to design a cable defect identification and positioning method and device based on time-varying matched filtering to improve the detection and positioning ability of the reflected signal in a complex environment. SUMMARY

[0005] Therefore, the present application provides a cable defect identification and positioning method and device based on time-varying matched filtering, which improves the detection ability of the time domain reflection technology for small defects in the cable and in a noisy environment, and has a broad application prospect.

[0006] In order to achieve the above purpose, the present application adopts the following technical solutions:

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

[0008] Step 1: connecting the measured cable to the measuring device through a connecting line;

[0009] Step 2: disconnecting the measured cable and the connecting line, the measuring device injecting a pulse signal, and measuring the reflected signal v os (t) generated when the connecting line end is short-circuited;

[0010] Step 3: Connect the measured cable with the connecting line, and keep the setting parameters of the measuring device unchanged to obtain the reflection signal inside the measured cable;

[0011] 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 the filtered reflection signal curve, and determine the reflection time through the extreme point 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 matched filter is as follows:

[0014] H(ω,t)=Ke -jωT S * (ω,t);

[0015] Wherein, K is a constant, T is the time length of the pulse signal injected into the cable, and * 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 rule of the time-varying filter transformation is based on the attenuation and dispersion characteristics of the measured cable, and 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:

[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, and β c is the phase coefficient of the cable.

[0019] Preferably, the time-varying matched filter equation is constructed according to the measurement results of the reflection signal generated when the end of the connecting line 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 connecting head D between the connecting line and the cable; V os is the frequency domain expression of v os (t).

[0022] Preferably, the reflected signal inside the cable to be measured is filtered to obtain the measurement result, expressed as follows:

[0023] y(t)=F -1 (X(omega) * H(omega, t)).

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

[0025] Preferably, the cable defect identification and positioning device based on time-varying matched filtering further comprises a host computer, a pulse source, a T-shaped connector, a collection card and a connecting line.

[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 line through the T-shaped connector.

[0028] The T-shaped connector branches the signal, one branch being transmitted to the cable to be measured and the other branch being connected to the collection card, which is used to collect signal data in real time.

[0029] The collection card transmits the collected signal data back to the host computer.

[0030] The end of the connecting line is connected to the cable to be measured, which comprises a connector D and a defect position, and is used to receive the injection signal and generate a reflected signal.

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

[0032] Compared with the prior art, the cable defect identification and positioning method and device based on time-varying matched filtering provided by the present application improve the time domain reflection device. The time-varying matched filter is constructed by the short-circuit calibration result and the measurement result, and the measurement signal is further processed by the time-varying matched filter. In the processing result, if an extreme value appears, it indicates that there is a reflected signal at this 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 positioning ability of the reflected signal in the presence of defects and strong noise environment, can significantly improve the level of cable time domain reflection detection technology, and has important industrial practical value. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute a part of the embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on the provided drawings.

[0034] Figure 1 is a measurement result graph of short circuit calibration in the embodiment of the present application;

[0035] Figure 2 is a measurement result graph of cable reflection signal in the embodiment of the present application;

[0036] Figure 3 is a time-varying matched filter result of measurement result in the embodiment of the present application;

[0037] Figure 4 is a device model graph of the present application. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments only constitute a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0039] The embodiment of the present application discloses a cable defect identification and positioning method based on time-varying matched filtering, comprising:

[0040] Step 1: connect the measured cable to the measuring device through the connecting line;

[0041] Step 2: disconnect the measured cable and the connecting line, the measuring device injects a pulse signal, and measures the reflection signal v os (t) generated when the end of the connecting line is short-circuited;

[0042] Step 3: connect the measured cable and the connecting line, and the measuring device keeps the setting parameters unchanged to obtain the reflection signal inside the measured cable;

[0043] 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 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 of the cable defect l f based on the reflection time.

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

[0046] Specifically, such as Figure 2 As shown, the reflected signals inside the cable under test are the reflected signals v from connector D. oD (t) The reflected signal v at the defect of (t) and the reflected signal v generated by the open-circuit end of the cable under test. oE (t).

[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 duration of the pulse signal injected into the cable, * indicates conjugate operation; S(ω, t) is the frequency domain expression of the pulse after propagating inside the cable for time t.

[0050] Specifically, the transformation law of the time-varying matched filter is based on the attenuation and dispersion characteristics of the cable under test, which are determined by the cable's attenuation coefficient γ. c The frequency domain expression of the pulse after propagating inside the cable for time t 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 β is the attenuation coefficient of the cable. c The phase coefficient of the cable.

[0053] Specifically, a time-varying matched filter equation is constructed based on the measurement results of the reflected signal generated when the end of the measuring connection line is short-circuited. The expression is as follows:

[0054]

[0055] In the formula, V oD For 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 For v os The frequency domain expression of (t).

[0056] Specifically, the reflection signal inside the cable to be measured is filtered to obtain a measurement result, and the expression is as follows:

[0057] y(t)=F -1 (X(omega) * H(omega, t)).

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

[0059] Further, if there is a reflection signal in the measurement result, there will be an extreme value at some time on the y(t) curve, and the time corresponding to the extreme value is the arrival time of the reflection signal; the matched filtering method has excellent effect on the detection of the target signal, and can also show good detection effect on the signal of white noise interference, so that the time-varying matched filtering technology can effectively judge whether there is a reflection signal in the measurement result with noise interference.

[0060] Specifically, as Figure 4 shown, the application also includes a cable defect identification and positioning device based on time-varying matched filtering, comprising: a host computer, a pulse source, a T-shaped connector, a collection card, a connection line;

[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 connection line through the T-shaped connector;

[0063] The T-shaped connector branches the signal, one connection line transmits to the cable to be measured, and the other connection line transmits to the collection card, and the collection card is used for real-time collection of signal data;

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

[0065] The end of the connection line is connected with the cable to be measured, which includes a connector D and a defect position, and is used for receiving the injection signal and generating a reflection signal.

[0066] Specifically, the length of the connection line is greater than 1 / 2v2t td , wherein v2 is the wave speed of the connection line; t td is the arrival time difference of the injection signal and the reflection signal of the connector D.

[0067] Further, the specific embodiment of the measurement device of the application is wired as shown in Figure 4As shown, this includes: a measuring device and a cable under test. The measuring device consists of a pulse source, a data acquisition card, a host computer, a T-connector, and a connecting cable. The pulse source generates a pulse signal with a rise and fall edge of 20ns and a pulse width of 100ns, with an amplitude of 5V; the connecting cable is a 50m long, SYV50 coaxial cable; the cable under test is a 600m long, 8.7 / 15kVYJV35mm² cable. 2 The defect in the single-core power cable is assumed to be at a distance of 300 meters.

[0068] The first step is to calibrate the measurement system by disconnecting the connecting wire from the cable under test and short-circuiting the end of the connecting wire. The reflected pulse at the short-circuited end of the connecting wire is then measured. Figure 1 As shown, v os (t) represents the reflected signal at the end of the short circuit.

[0069] The second step is to measure the reflected signal of the cable under test. Connect the connecting wire to the cable under test and measure the reflected signal of the cable under test, such as... Figure 2 As shown, analysis Figure 2 From the reflected pulse, we can know that v oD (t), v of (t) and v oE (t) are respectively Figure 4 The reflected signals generated at the connector D, the defect, and the open end of the cable under test. From Figure 2 The measurement results show that as the pulse propagates, the rising edge of the pulse gradually slows down, making the pulse start time more difficult to determine. Figure 2 The measurement results are used to identify and locate the reflected pulse using a time-varying matched filter. 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 results of time-varying matched filtering are as follows: Figure 3 As shown, through Figure 3 It can be determined that the connector D reflects the pulse v. oD The arrival time t of (t) D The defect reflection pulse is 0.504 μs. of The arrival time t of (t) f The wave velocity v of the cable is 4.04 μs. p The speed is typically 170 m / μs, so the location of the defect is l. fThe position of the defect can be calculated by the following formula

[0074]

[0075] The calculated position of the defect is 300.56 meters, the error of the positioning result with the actual position is 0.56 m, and the relative error of the positioning result is 0.187%.

[0076] The various embodiments described in this specification are presented by way of example, and each embodiment describes a specific feature of the application that is independently useful. Each embodiment can be used in combination with any other embodiment, and the various embodiments can be combined in any way. The various embodiments described in this specification are presented by way of example, and each embodiment describes a specific feature of the application that is independently useful. Each embodiment can be used in combination with any other embodiment, and the various embodiments can be combined in any way.

[0077] The above description of disclosed embodiments provides enough information to enable others skilled in the art to make and use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A time-varying matched filter based method for cable defect identification and location, characterized in that, Comprise: Step 1: the measured cable is connected to the measuring device through the connecting line; Step 2: disconnect the cable under test and the connecting line, measure the setup to inject the pulse signal, measure the reflection signal generated when the end of the connecting line is shorted ; Step 3: the measured cable is connected with the connecting line, and the measuring device keeps the setting parameters unchanged to obtain the reflection signal inside the measured cable; Step 4: a time-varying matched filter is designed based on the reflection signal generated when the end of the connecting line is short-circuited, and the reflection signal inside the measured cable is filtered to obtain the filtered reflection signal curve, and the reflection time is determined through the extreme point on the filtered reflection signal curve; Step 5: Calculate the location of the cable defect from the reflection time ; The construction equation of the time-varying matched filter is as follows: ； wherein K is a constant, T is the length of time of the pulse injected into the cable, denotes a conjugate operation; S (ω, t) is the frequency domain representation of the pulse after it has propagated t through the cable for a time The time-varying matched filter transform is based on the attenuation and dispersion characteristics of the cable under test, which are represented by the attenuation coefficient of the cable and the dispersion parameter of the cable t The frequency domain representation after the time transform is as follows: wherein is the frequency domain representation of the injected pulse signal into the cable; , is the attenuation coefficient of the cable, is the phase coefficient of the cable; The time-varying matched filter equation is constructed according to the measurement results of the reflection signal generated when the end of the connecting line is short-circuited, and the expression is as follows: wherein is the frequency domain expression of is a reflected signal generated by the connection head D between the connection line and the cable; is the frequency domain expression of The reflection signal inside the measured cable is filtered to obtain the measurement results, and the expression is as follows: wherein denotes the inverse Fourier transform, is a frequency domain representation of the measurement result, is a frequency domain representation of the time-varying matched filter.

2. An apparatus for use in a time-varying matched filter based cable defect identification and location method as claimed in claim 1, characterized in that, Comprise: Host computer, pulse source, T-shaped connector, acquisition card, connecting line; 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-shaped connector; The T-shaped connector divides the signal into two paths, one of which is transmitted to the measured cable, and the other of which is connected to the acquisition card, which is used to collect signal data in real time; The acquisition card transmits the collected signal data back to the host computer; The end of the connecting line is connected with the measured cable, which comprises a connecting head D and a defect position, and is used to receive the injection signal and generate a reflection signal.

3. The apparatus of claim 2, wherein, The length of the connection line is greater than wherein, is the wave velocity of the connection line; is the time difference of arrival of the injected signal and the connection head D reflected signal.

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