Pulse reconstruction-based cable multi-defect measurement device and detection method

Abstract

The application discloses a kind of cable multiple defect measuring device and detection method based on pulse reconstruction, it is related to power equipment state detection technology and its application field.The application includes: host computer, pulse source, T-type connector, acquisition device and connecting line;The host computer is connected with the acquisition device, for receiving the result of data acquisition, while analyzing the measurement result;The pulse source is used to generate pulse signal and inject into cable inside;The T-type connector is used to connect the pulse source, the connecting line and the acquisition device;The acquisition device is used to collect injection pulse and reflected pulse from cable inside, and the acquisition result is transported to the host computer.The application measures cable internal defect using time domain reflection technology, estimates the equivalent parameter of cable defect according to reflection result, reconstructs the reflected pulse of defect, eliminates the interference pulse generated by secondary reflection, so as to realize the identification and positioning of multiple defects along cable.

Description

TECHNICAL FIELD

[0001] The present application relates to power equipment state detection technology and the application field thereof, and more particularly to a cable multi-defect detection device and method based on pulse reconstruction. BACKGROUND

[0002] Cable lines are inevitably affected by various factors when in operation and will inevitably produce defects. With the use of long-distance cable lines, the phenomenon of multiple defects existing simultaneously becomes more and more significant.

[0003] Time domain reflectometry is an effective cable defect detection and positioning technology. The existing time domain reflectometry technology locates the position of defects by calculating the time difference of arrival of the reflected pulses of the defects. However, when multiple defects are distributed along the cable, the pulse signal will be repeatedly reflected between the multiple defects, resulting in numerous secondary or even multiple reflected signals in the measured results. If the measured results are directly used to locate the defects along the cable, the defects will be misjudged, resulting in the number of detected defects being more than the actual defects, thereby causing erroneous maintenance. SUMMARY

[0004] Therefore, the present application provides a cable multi-defect detection device and method based on pulse reconstruction, which uses time domain reflectometry to measure the internal defects of the cable, estimates the equivalent parameters of the cable defects according to the reflection results, reconstructs the reflected pulses of the defects, and eliminates the interference pulses generated by the secondary reflections, thereby realizing the identification and positioning of multiple defects along the cable.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A cable multi-defect measurement device based on pulse reconstruction comprises an upper computer, a pulse source, a T-shaped connector, an acquisition device and a connecting line. The upper computer is connected to the acquisition device and is used to receive the results of data acquisition and analyze the measurement results. The pulse source is used to generate pulse signals and inject them into the cable. The T-shaped connector is used to connect the pulse source, the connecting line and the acquisition device. The acquisition device is used to collect the injected pulses and the reflected pulses from the cable and transmit the collected results to the upper computer.

[0007] Optionally, the output impedance of the pulse source, the input impedance of the acquisition device, the characteristic impedance of the T-shaped connector and the connecting line are equal. The length of the connecting line ensures that the injected pulse and the reflected pulse at the inlet end of the cable do not overlap in the measurement results.

[0008] A cable multi-defect detection method based on pulse reconstruction, which refers to any one of the cable multi-defect measurement devices based on pulse reconstruction, comprises the following steps:

[0009] Obtaining the measurement result of the measuring device, positioning the first defect on the cable, determining the type and equivalent resistance value of the first defect, establishing an equivalent model of the cable with the first defect, and reconstructing the first defect reflection pulse;

[0010] Removing the first defect reflection pulse from the measurement result to obtain a remaining measurement result;

[0011] The corresponding first reflection pulse in the remaining measurement result is caused by the next defect along the line of the cable, which is taken as a second defect, the position of the second defect is positioned, the type and equivalent resistance value of the second defect are determined, an equivalent model of the cable with all known defects including the second defect is established, and the reflection pulse of the current equivalent model is reconstructed.

[0012] The above steps are repeated until the positioning result of the defect is the full length of the measured cable, and the reconstruction process of the reflection pulse ends.

[0013] Optionally, the defects inside the cable are divided into first-type defects and second-type defects according to the characteristics of their reflection signals, the first-type defects are equivalent series resistance defects, and the polarity of the reflection pulse is the same as that of the injected pulse; the second-type defects are equivalent parallel resistance defects, and the polarity of the reflection pulse is opposite to that of the injected pulse.

[0014] Optionally, the first-type defects are equivalent series resistance defects, and the equivalent resistance R s of the defect is calculated according to the following formula:

[0015]

[0016] In the formula, Γ f is the reflection coefficient of the defect; and Z c is the characteristic impedance of the measured cable.

[0017] Optionally, the second-type defects are equivalent parallel defects, and the equivalent resistance R p of the defect is calculated according to the following formula:

[0018]

[0019] In the formula, Γ f is the reflection coefficient of the defect; and Z c is the characteristic impedance of the measured cable.

[0020] Optionally, for the reflection coefficient of the nth defect, the measurement result is used to obtain the reflection coefficient of the nth defect by using a recursive calculation method, and the recursive calculation formula of the reflection coefficient of the nth defect is as follows:

[0021]

[0022] In the formula, Γ nf is the reflection coefficient of the nth defect; and Vofn V represents the spectrum of the nth defect reflection pulse in the measurement results. oD V represents the spectrum of the reflected pulse at cable inlet D in the measurement results. os To calibrate the spectrum of the reflected pulse at the short-circuited end of the connecting wire during the test; γ c l is the propagation coefficient of the cable under test; fn Γ represents the location of the nth defect. if Let be the reflection coefficient of the i-th defect.

[0023] Optionally, the measurement results of the reflected pulse from the defect in the cable under test are obtained by modeling and calculating the cable under test, using the following formula:

[0024]

[0025] In the formula, V or The spectrum of the reflected pulse from the defect in the cable under test; Γ oD The inlet reflection coefficient at the cable inlet end.

[0026] Optionally, the inlet reflection coefficient Γ at the cable inlet end oD The inlet reflection coefficient Γ at the first defect location o1 The calculation is as follows:

[0027]

[0028] Γ o1 By recursively calculating, for a cable with m defects, Γ o1 The recursive calculation formula is as follows:

[0029]

[0030] In the formula, Γ on Z is the inlet reflection coefficient at the nth defect location; fn Let the inlet impedance at the nth defect location be given by the following formula:

[0031]

[0032] In the formula: γ c Let l be the propagation constant of the cable under test. f1 This indicates the location of the first defect.

[0033] Compared with the prior art, the cable multi-defect detection device and method based on pulse reconstruction provided by the application can effectively detect and locate multiple defects along the cable, eliminate the misjudgment problem of the traditional detection equipment and method, reduce the probability of false repair, and has important use value for the repair and operation of the cable line. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0035] Figure 1 is a device model diagram of the present application;

[0036] Figure 2 is a measurement result diagram of short circuit calibration in the specific embodiment;

[0037] Figure 3 is an equivalent model of two types of defects;

[0038] Figure 4 is a time-varying matched filter result of the measurement result in the specific embodiment;

[0039] Figure 5 is a reflection pulse reconstruction result diagram related to defect 1;

[0040] Figure 6 is a reflection pulse reconstruction result diagram related to defect 1 and defect 2. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0042] Embodiment 1

[0043] This embodiment discloses a cable multi-defect detection device based on pulse reconstruction, as shown in Figure 1As shown, the measurement device is composed of five parts, including: host computer, pulse source, T-type connector, acquisition device and connecting line. The host computer is connected with the acquisition device, used for receiving the result of data acquisition, and analyzing the measurement result; the pulse source is used for generating specific pulse signal and injecting into the cable; the T-type connector is used for connecting the pulse source, connecting line and acquisition device; the acquisition device is used for collecting the injected pulse and the reflected pulse from the cable, and delivering the collection result to the host computer; the connecting line is used for connecting the measurement device and the measured cable. The measurement includes two steps: step 1, short-circuit calibration of the measurement system, step 2, time-domain reflection detection of the measured cable;

[0044] The pulse source, T-type connector, acquisition device and connecting line, the input impedance of the pulse source and acquisition device, the characteristic impedance of the T-type connector and connecting line are equal. The length of the connecting line should ensure that the injected pulse and the reflected pulse of the cable entrance end D in the measurement result do not overlap.

[0045] The short-circuit calibration of the measurement system, before the formal time-domain reflection detection of the measured cable, the measurement system needs to be calibrated in short circuit, so as to obtain the reflected signal v os (t) of the short-circuit end of the connecting line, as Figure 2 v os (t) in the formula. During the short-circuit calibration, the measurement device is disconnected from the measured cable, and the end of the connecting line is short-circuited. Start the measurement device, measure the reflected pulse of the system, and obtain v os (t). After the short-circuit calibration of the system, the connecting line can be connected with the measured cable, and step 2, time-domain reflection detection of the measured cable, is carried out.

[0046] The embodiment also discloses a cable multi-defect detection method based on pulse reconstruction, which refers to any one of the cable multi-defect measurement devices based on pulse reconstruction, and includes the following steps:

[0047] Obtaining the measurement result of the measurement device, positioning the first defect on the cable, determining the type and equivalent resistance value of the first defect, establishing the equivalent model of the cable with the first defect, and reconstructing the first defect reflected pulse;

[0048] Removing the first defect reflected pulse from the measurement result to obtain the remaining measurement result;

[0049] The corresponding first reflected pulse in the remaining measurement result is caused by the next defect along the line of the cable, which is taken as the second defect, the position of the second defect is positioned, the type and equivalent resistance value of the second defect are determined, the equivalent model of the cable with all known defects including the second defect is established, and the reflected pulse of the current equivalent model is reconstructed.

[0050] In the embodiment, the multi-defect locating method comprises four parts: first defect locating, defect equivalent parameter estimation, defect cable modeling and reflected pulse reconstruction.

[0051] The first defect locating is to locate the first defect in the measurement result of the time domain reflection device, which is caused by the first defect and is not affected by the second or multiple pulses between defects. Therefore, the location of the first reflected pulse can obtain the location of the first defect. The location of the reflected pulse can use the conventional energy method, phase method and other existing methods.

[0052] The defect equivalent parameter estimation is to divide the defects in the cable into two categories according to the characteristics of the reflected signals of the defects, as shown in the following table. Figure 3 The first category of defects is equivalent series resistance defects, and the reflected pulse of the defects is of the same polarity as the injected pulse, that is, if the injected pulse is a positive polarity pulse, the reflected pulse of the defects is also a positive polarity pulse. The second category of defects is equivalent parallel resistance defects, and the reflected pulse of the defects is of opposite polarity to the injected pulse, that is, if the injected pulse is a positive polarity pulse, the reflected pulse of the defects is a negative polarity pulse. For the first category of equivalent series resistance defects, the calculation formula of the equivalent resistance R s of the defects is as follows:

[0053]

[0054] In the formula, Γ f is the reflection coefficient of the defects; and Z c is the characteristic impedance of the measured cable.

[0055] For the second category of equivalent parallel defects, the calculation formula of the equivalent resistance R p of the defects is as follows:

[0056]

[0057] The reflection coefficient of the defects is defined as the reflection coefficient of the defect port position when the cable is infinitely long and only has the defect. For the reflection coefficient of the nth defect, the reflection coefficient of the nth defect can be obtained by using the measurement result and recursive calculation, and the recursive calculation formula of the reflection coefficient of the nth defect is as follows:

[0058]

[0059] In the formula, Γ nf is the reflection coefficient of the nth defect; V ofn is the frequency spectrum of the nth defect reflected pulse in the measurement result; V oD is the frequency spectrum of the cable entrance end D reflected pulse in the measurement result; and V osThe frequency spectrum of the end reflection pulse of the connecting line short circuit in the calibration test; γ c The propagation coefficient of the cable to be measured, which can be found in the cable manual or measured in advance by a vector network analyzer instrument; l fn The position of the nth defect, which can be calculated by the arrival time of the defect reflection pulse; Γ if The reflection coefficient of the ith defect.

[0060] The measured results of the defect reflection pulse of the cable to be measured can be calculated by modeling the cable to be measured, and the calculation formula is as follows:

[0061]

[0062] In the formula, V or The frequency spectrum of the defect reflection pulse of the cable to be measured; Γ oD The entrance reflection coefficient of the cable entrance D when the pulse is transmitted from the connecting line to the cable to be measured.

[0063] The entrance reflection coefficient of the cable entrance D is Γ oD , Γ oD The entrance reflection coefficient of the first defect position Γ o1 can be calculated, and the calculation formula is as follows:

[0064]

[0065] Γ o1 can be calculated recursively. For a cable with m defects, Γ o1 The recursive calculation formula of Γ

[0066]

[0067] In the formula, Γ on The entrance reflection coefficient of the nth defect position; Z fn The entrance impedance of the nth defect position, and the calculation formula is as follows:

[0068]

[0069] Example 2

[0070] The difference between this embodiment and example 1 is only as follows:

[0071] The reflection pulse reconstruction of this embodiment determines the defects on the cable one by one in an iterative manner. The specific operation process is as follows:

[0072] Step S1: For the measurement result of the cable reflection pulse, the first defect on the cable is located by using the first defect locating method. After locating, the type of the defect and the equivalent resistance value of the defect are estimated. Then the equivalent model of the cable with the defect is established, and the reflection pulse of the defect is reconstructed;

[0073] Step S2: The reflection pulse of the cable reconstructed in the last step is subtracted from the measurement result of the cable reflection pulse, and the remaining measurement result is obtained;

[0074] Step S3: The first reflection pulse in the remaining measurement result is caused by the next defect along the cable, and the location of the defect is located by using the first defect locating method. After locating, the type of the defect and the equivalent resistance value of the defect are estimated. Then the model of the cable with all known defects is established, and the reflection pulse with all known defects is reconstructed;

[0075] Step S4: Repeat steps S2 and S3 until the location of the defect is the full length of the measured cable, and the reflection pulse reconstruction process is completed.

[0076] Through the above steps, the location of the defect, the type of the defect and the equivalent resistance value of the defect are calculated one by one.

[0077] More specifically, the embodiment discloses a specific wiring model of a measuring device as shown in Figure 1 , which comprises a measuring device and a measured cable. The measuring device is composed of a pulse source, an acquisition device, an upper computer, a T-shaped connector and a connecting cable. The pulse source generates a pulse signal with a rising edge and a falling edge of 20 ns and a pulse width of 100 ns, and the amplitude of the signal is 5 V. The connecting cable is a coaxial cable with a length of 50 m and a model of SYV50. The measured cable is a single-core power cable with a length of 600 meters and a model of 8.7 / 15 kV YJV 35 mm2. Two defects are set on the line, the first defect is set at a position of 100 m, the type of the defect is the second type of defect, and the equivalent resistance of the defect is 50 Ω; the second defect is set at a position of 400 m, the type of the defect is the first type of defect, and the equivalent resistance of the defect is 80 Ω.

[0078] The cable is measured: the first step is to calibrate the measurement system, disconnect the connecting cable from the measured cable, short-circuit the end of the connecting cable, and measure the reflection pulse of the short-circuit end of the connecting cable as shown in Figure 2 , wherein v os (t) is the reflection signal of the short-circuit end. The second step is to measure the reflection signal of the measured cable, connect the connecting cable to the measured cable, and measure the reflection signal of the measured cable as shown in Figure 4 . Figure 4The image shows the reflected signals from defects and cable ends. It also shows that the measurement results include many other reflected signals caused by secondary or multiple reflections between defects and between defects and connectors. Figure 4 In the measurement results, defect 1 is the reflected signal of the first defect inside the cable. This signal is not affected by multiple reflections and can be directly located. The calculated arrival time difference between the reflected pulse from this defect and the reflected pulse from the cable inlet D is 1.176 μs. Therefore, the defect location result is 99.96 m, with a relative error of -0.04% compared to the actual location. Figure 4 The measurement results show that the injected pulse is a positive polarity pulse, while the reflected pulse from the defect is a negative polarity pulse. Therefore, defect 1 is a type II defect. Further estimation of the equivalent resistance of defect 1 yields a result of 49.95 Ω, with a relative error of -0.1% compared to the actual value. A cable model with only defect 1 is established, and the reflected pulse from defect 1 is reconstructed. The reconstructed pulse results are as follows: Figure 5 As shown. From Figure 5 As can be seen, the reflected pulses related to defect 1 are reconstructed. This includes not only the first reflected pulse of the defect but also the pulses from multiple reflections between defect 1 and cable entry end D. Based on the reconstruction results, we can determine that the first reflected pulse of the next defect is around 5.1 μs. Using the localization method, the arrival time difference between the next defect's reflected pulse and the reflected pulse at cable entry end D is 4.699 μs, resulting in a defect location of 399.415 m, with a relative error of -0.15% compared to the actual location. The second defect's reflected pulse is positive, indicating it is a type I defect. Further estimation of the defect's equivalent resistance is 78.09 Ω, with a relative error of -2.39% compared to the actual value. A cable model with defects 1 and 2 is established, and the reflected pulses of defects 1 and 2 are reconstructed. The pulse reconstruction results are shown below. Figure 6 As shown. (Through) Figure 6The first reflection pulse of the next defect can be determined to be around 7.658 μs. The reflection pulse of the defect is located, and the time difference between the pulse and the cable entrance end D reflection pulse is calculated to be 7.064 μs, the location of the defect is calculated to be 600.44 m, and the full length of the cable is considered to be 600 m, so the reflection pulse is generated by the open end of the cable, and the reflection pulse reconstruction is ended. In summary, it is calculated that the cable has two defects, which are located at 99.96 m and 399.415 m, respectively; the relative errors of the location results of the two defects are-0.04% and-0.15%, respectively; the defect types of the two defects are the second type of defect and the first type of defect, respectively; the equivalent resistance calculation results of the two defects are 49.95 Ω and 78.09 Ω, respectively; and the relative errors of the calculation results of the equivalent resistance and the actual values are-0.1% and-2.39%, respectively. The above calculation results show that the present application can effectively detect and locate multiple defects along the cable, and has high positioning accuracy.

[0079] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. For the device disclosed by the embodiments, since it corresponds to the method disclosed by the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0080] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for cable multi-defect detection based on pulse reconstruction, characterized in that, The utility model relates to a kind of cable defect locating system, including: Host computer, pulse source, T-shaped connector, acquisition device and connecting line; The host computer is connected with the acquisition device, for receiving the result of data acquisition, while analyzing the measurement result;The pulse source is used to generate pulse signal and inject into the cable interior; The T-shaped connector is used to connect the pulse source, the connecting line and the acquisition device; The acquisition device is used to collect injected pulse and reflected pulse from the cable interior, and deliver the acquisition result to the host computer; The output impedance of the pulse source, the input impedance of the acquisition device, the characteristic impedance of the T-shaped connector and the connecting line are equal;The length of the connecting line ensures that the injected pulse and the reflected pulse at the entrance end of the cable in the measurement result do not overlap; The method comprises the following steps: Obtain the measurement result of the measuring device, locate the first defect on the cable, determine the type and equivalent resistance value of the first defect, establish the equivalent model of the cable with the first defect, and reconstruct the first defect reflected pulse; Remove the first defect reflected pulse from the measurement result to obtain the remaining measurement result; The corresponding first reflected pulse in the remaining measurement result is caused by the next defect along the line of the cable, as the second defect, locate the position of the second defect, determine the type and equivalent resistance value of the second defect, establish the equivalent model of the cable with all known defects including the second defect, and reconstruct the reflected pulse of the current equivalent model; Repeat the above steps until the location result of the defect is the full length of the measured cable, and the reconstruction process of the reflected pulse ends.

2. The method of claim 1, wherein, The defects in the cable are divided into the first type of defects and the second type of defects according to the characteristics of their reflected signals, the first type of defects is equivalent series resistance defects, and the polarity of the reflected pulse is the same as that of the injected pulse;The second type of defects is equivalent parallel resistance defects, and the polarity of the reflected pulse is opposite to that of the injected pulse.

3. The method of claim 2, wherein, The first type of defect is an equivalent series resistance defect, and the defect equivalent resistance The calculation formula is as follows: ； wherein is the reflection coefficient of the defect; is the characteristic impedance of the cable under test.

4. The method of claim 2, wherein, The second type of defect is an equivalent parallel defect, and the calculation formula of the equivalent resistance of the defect is as follows: The calculation formula is as follows: ； wherein is the reflection coefficient of the defect; is the characteristic impedance of the cable under test.

5. The method of claim 1, wherein, For the reflection coefficient of the nth defect, the measurement result is used to obtain the reflection coefficient of the nth defect by using recursive calculation, and the recursive calculation formula of the reflection coefficient of the nth defect is as follows: wherein is the reflection coefficient of the n-th defect; is the spectrum of the n-th defect reflection pulse in the measurement result; is the spectrum of the cable entry end D reflection pulse in the measurement result; is the spectrum of the connection line short end reflection pulse in the calibration test; is the propagation coefficient of the cable under test; is the position of the n-th defect; is the reflection coefficient of the i-th defect.

6. The method of claim 1, wherein, The measurement result of the defect reflected pulse of the measured cable is obtained by modeling and calculating the measured cable, and the calculation formula is as follows: ； wherein is the frequency spectrum of the measured cable defect reflection pulse; the entrance reflection coefficient of the cable entrance end.

7. The method of claim 1, wherein, Entrance reflection coefficient of cable entry Entrance reflection coefficient through first defect location The calculation is as follows: ； By recursive calculation, for a cable with m defects, The recursive calculation formula is as follows: ； wherein is the entrance reflection coefficient for the n-th defect position; is the entrance impedance for the n-th defect position, which is calculated as follows: wherein: is the propagation constant of the cable under test, is the position of the first defect.

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