Cable multi-defect measurement device and detection method based on pulse reconstruction

Abstract

The invention discloses a cable multi-defect measurement device and detection method based on pulse reconstruction, and relates to the field of power equipment state detection technology and application thereof. Comprising an upper computer, a pulse source, a T-shaped connector, acquisition equipment and a connecting line, the upper computer is connected with the acquisition equipment and is used for receiving a data acquisition result and analyzing a measurement result at the same time; the pulse source is used for generating a pulse signal and injecting the pulse signal into the cable; the T-shaped connector is used for connecting the pulse source, the connecting line and the acquisition equipment; and the acquisition equipment is used for acquiring injection pulses and reflected pulses from the interior of the cable, and transmitting an acquisition result to the upper computer. According to the method, the internal defects of the cable are measured by adopting a time domain reflection technology, equivalent parameters of the defects of the cable are estimated according to a reflection result, reflected pulses of the defects are reconstructed, interference pulses generated by secondary reflection are eliminated, and thus the multiple defects along the cable are identified and positioned.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment condition detection and its application field, and more specifically, to a cable multi-defect detection device and method based on pulse reconstruction. Background Art

[0002] When a cable line is in operation, it is affected by various factors and will inevitably have defects. Moreover, with the use of long-distance cable lines, the phenomenon of multiple defects existing simultaneously is becoming more and more significant.

[0003] Time-domain reflectometry is an effective cable defect detection and location technology. The existing time-domain reflectometry locates the position of a defect by calculating the arrival time difference of the defect reflection pulse. However, when there are multiple defects distributed along the cable, the pulse signal will be repeatedly reflected between multiple defects, resulting in numerous secondary or even multiple reflection signals in the measured results. If the measurement results are directly used to locate the defects along the cable, there will be a situation of misjudgment of the defects, resulting in the number of detected defects being more than the actual defect data, thus leading to incorrect maintenance. Summary of the Invention

[0004] In view of this, the present invention 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 reflection pulse of the defects, and eliminates the interference pulses generated by secondary reflections, so as to realize the identification and location of multiple defects along the cable.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A cable multi-defect measurement device based on pulse reconstruction, comprising: a host computer, a pulse source, a T-shaped connector, a collection device, and a connection line; the host computer is connected to the collection device for receiving the results of data collection and analyzing the measurement results at the same time; the pulse source is used to generate a pulse signal and inject it into the cable; the T-shaped connector is used to connect the pulse source, the connection line, and the collection device; the collection device is used to collect the injected pulse and the reflection pulse from inside the cable and send the collection results to the host computer.

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

[0008] A cable multi-defect detection method, referring to any one of the cable multi-defect measurement devices based on pulse reconstruction described above, comprising the following steps:

[0009] Obtain the measurement results of the measuring device, locate the first defect on the cable, determine the type and equivalent resistance value of the first defect, establish an equivalent model of the cable with the first defect, and reconstruct the reflection pulse of the first defect;

[0010] Remove the reflection pulse of the first defect from the measurement results to obtain the remaining measurement results;

[0011] The corresponding first reflection pulse in the remaining measurement results is caused by the next defect along 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 an equivalent model of the cable with all known defects including the second defect, and reconstruct the reflection pulse of the current equivalent model.

[0012] Repeat the above steps until the positioning result of the defect is the full length of the cable under test, and the reconstruction process of the reflection pulse ends.

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

[0014] Optionally, the first type of defect is an equivalent series resistance defect, and the equivalent resistance R of the defect s is calculated by the following formula:

[0015]

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

[0017] Optionally, the second type of defect is an equivalent parallel defect, and the equivalent resistance R of the defect p is calculated by the following formula:

[0018]

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

[0020] Optionally, for the reflection coefficient of the nth defect, it is obtained by using the measurement results and adopting a recursive calculation method. The recursive calculation formula for 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; Vofn is the spectrum of the nth defect reflection pulse in the measurement result; V oD is the spectrum of the reflection pulse at the cable inlet end D in the measurement result; V os is the spectrum of the reflection pulse at the short - circuited end of the connecting line in the calibration test; γ c is the propagation coefficient of the cable under test; l fn is the position of the nth defect; Γ if is the reflection coefficient of the ith defect.

[0023] Optionally, the measurement result of the defect reflection pulse of the cable under test is obtained by modeling and calculating the cable under test, and the calculation formula is as follows:

[0024]

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

[0026] Optionally, the inlet reflection coefficient Γ of the cable inlet end oD is calculated through the inlet reflection coefficient Γ at the position of the first defect o1 and the calculation formula is as follows:

[0027]

[0028] Γ o1 is calculated recursively. For a cable with m defects, the recursive calculation formula of Γ o1 is as follows:

[0029]

[0030] In the formula, Γ on is the inlet reflection coefficient at the position of the nth defect; Z fn is the inlet impedance at the position of the nth defect, and its calculation formula is as follows:

[0031]

[0032] In the formula: γ c is the propagation constant of the cable under test, l f1 is the position of the first defect.

[0033] As can be seen from the above technical solutions, compared with the prior art, the present invention provides a cable multi-defect detection device and method based on pulse reconstruction. Based on the time-domain reflectometry detection technology, a detection method for detecting and locating multiple defects along the cable is designed. At the same time, based on this method, the existing detection device is improved to obtain a device for detecting and locating multiple cable defects. This method and device can effectively detect and locate multiple defects along the cable, eliminate the misjudgment problem of traditional detection equipment and methods, reduce the probability of incorrect maintenance, and have important application value for the maintenance and operation of cable lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

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

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

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

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

[0039] Figure 5 is the schematic diagram of the reconstructed reflection pulse related to Defect 1;

[0040] Figure 6 is the schematic diagram of the reconstructed reflection pulses related to Defect 1 and Defect 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the 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 of 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 shall fall within the protection scope of the present invention.

[0042] Embodiment 1

[0043] This embodiment discloses a cable multi-defect detection device based on pulse reconstruction, as Figure 1As shown in the figure, it includes: The measuring device consists of five parts, including: a host computer, a pulse source, a T-shaped connector, a data acquisition device, and a connecting wire. The host computer is connected to the data acquisition device, used to receive the results of data acquisition and analyze the measurement results at the same time; the pulse source is used to generate specific pulse signals and inject them into the cable; the T-shaped connector is used to connect the pulse source, the connecting wire, and the data acquisition device; the data acquisition device is used to acquire the injected pulses and the reflected pulses from inside the cable and send the acquisition results to the host computer; the connecting wire is used to connect the measuring device and the cable under test. The measurement includes two steps: Step 1, short-circuit calibration of the measurement system; Step 2, time-domain reflectometry detection of the cable under test;

[0044] For the pulse source, T-shaped connector, data acquisition device, and connecting wire mentioned above, the input impedance of the pulse source and the data acquisition device, and the characteristic impedance of the T-shaped connector and the connecting wire are equal. The length of the connecting wire should ensure that the injected pulse and the reflected pulse at the cable inlet end D in the measurement results do not overlap.

[0045] For the short-circuit calibration of the measurement system, before formally performing time-domain reflectometry detection on the cable under test, it is necessary to perform short-circuit calibration on the measurement system to obtain the reflected signal v os (t) as shown in Figure 2 v os (t). During short-circuit calibration, disconnect the measuring device from the cable under test and short-circuit the end of the connecting wire. Start the measuring device, measure the reflected pulse of the measurement system, and obtain v os (t). After performing short-circuit calibration on the system, the connecting wire can be connected to the cable under test to perform Step 2, time-domain reflectometry detection of the cable under test.

[0046] This embodiment also discloses a method for detecting multiple cable defects based on pulse reconstruction. Referring to any one of the described cable multi-defect measuring devices based on pulse reconstruction, it includes the following steps:

[0047] Obtain the measurement results of the measuring device, locate the first defect on the cable, determine the type and equivalent resistance value of the first defect, establish an equivalent model of the cable with the first defect, and reconstruct the reflected pulse of the first defect;

[0048] Remove the reflected pulse of the first defect from the measurement results to obtain the remaining measurement results;

[0049] The corresponding first reflected pulse in the remaining measurement results is caused by the next defect along the cable, which is used as the second defect. Locate the position of the second defect, determine the type and equivalent resistance value of the second defect, establish an equivalent model of the cable with all known defects including the second defect, and reconstruct the reflected pulse of the current equivalent model.

[0050] In this embodiment, the multi-defect identification and location method includes four parts: first defect location, defect equivalent parameter estimation, defective cable modeling, and reflected pulse reconstruction.

[0051] For the first defect location, for a cable with multiple defects, when measuring with a time-domain reflection device, the first defect reflection pulse in the measurement result must be caused by the first defect and will not be affected by secondary or multiple pulses between defects. Therefore, the location of the first reflection pulse can obtain the location of the first defect. The location of the reflection pulse can adopt existing methods such as the conventional energy method and phase method.

[0052] For the defect equivalent parameter estimation, the defects inside the cable can be divided into two categories according to the characteristics of their reflection signals as Figure 3 shown. The first type of defect is an equivalent series resistance defect. The reflection pulse of this type of defect has the same polarity as the injection pulse. That is, if the injection pulse is a positive-polarity pulse, the reflection pulse of the defect is also a positive-polarity pulse. The second type of defect is an equivalent parallel resistance defect. The reflection pulse of this type of defect has the opposite polarity to the injection pulse. That is, if the injection pulse is a positive-polarity pulse, the reflection pulse of the defect is a negative-polarity pulse. For the first type of equivalent series resistance defect, the equivalent resistance R s of the defect is calculated by the following formula:

[0053]

[0054] In the formula, Γ f is the reflection coefficient of the defect; Z c is the characteristic impedance of the cable under test.

[0055] For the second type of equivalent parallel defect, the equivalent resistance R p of the defect is calculated by the following formula:

[0056]

[0057] The reflection coefficient of the defect is defined as the reflection coefficient at the defect port position when the cable is infinitely long and there is only this defect. For the reflection coefficient of the nth defect, it can be obtained by using the measurement results and adopting a recursive calculation method. The recursive calculation formula for 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 spectrum of the nth defect reflection pulse in the measurement result; V oD is the spectrum of the reflection pulse at the cable inlet end D in the measurement result; V osFor calibrating the spectrum of the reflected pulse at the short - circuited end of the connecting line in the calibration test; γ c is the propagation coefficient of the cable under test, which can be found in the cable manual or pre - measured by a vector network analyzer; l fn is the position of the nth defect, which can be calculated from the arrival time of the defect - reflected pulse; Γ if is the reflection coefficient of the ith defect.

[0060] For the defect cable modeling mentioned above, the measurement results of the defect - reflected pulses of the cable under test can be obtained by modeling and calculating the cable under test. The calculation formula is as follows:

[0061]

[0062] In the formula, V or is the spectrum of the defect - reflected pulse of the cable under test; Γ oD is the input reflection coefficient at the cable inlet D when the pulse is transmitted from the connecting line to the cable under test.

[0063] The input reflection coefficient Γ of the cable inlet D mentioned above oD , Γ oD can be calculated from the input reflection coefficient Γ at the position of the first defect o1 The calculation formula is as follows:

[0064]

[0065] Γ o1 can be calculated recursively. For a cable with m defects, the recursive calculation formula of Γ o1 is as follows:

[0066]

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

[0068]

[0069] Example 2

[0070] The difference between this example and Example 1 is only the following content:

[0071] In this example, the reflected pulse reconstruction adopts an iterative method to determine the defects on the cable one by one. The specific operation process is as follows:

[0072] Step S1: For the measurement results of the cable reflection pulses, use the first defect location method to locate the first defect on the cable. After location, estimate the type of the defect and the equivalent resistance value of the defect. Then establish an equivalent model of the cable with the defect and reconstruct the reflection pulse of the defect;

[0073] Step S2: Subtract the reconstructed cable reflection pulse from the previous step from the measurement results of the cable reflection pulses to obtain the remaining measurement results;

[0074] Step S3: The first reflection pulse in the remaining measurement results is caused by the next defect along the cable. Use the first defect location method to locate the position of the defect. After location, estimate the type of the defect and the equivalent resistance value of the defect. Then establish a model of the cable with all known defects and reconstruct the reflection pulse with all known defects;

[0075] Step S4: Repeat Step S2 and Step S3 until the location result of the defect is the full length of the cable under test, and the reconstruction process of the reflection pulse ends.

[0076] Through the above steps, the position 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 specific wiring model of the measuring device disclosed in this embodiment is as Figure 1 shown, which includes: a measuring device and a cable under test. The measuring device is composed of a pulse source, a collection device, a host computer, a T-type connector, and a connecting cable. The pulse source generates a pulse signal with a rising edge and a falling edge both 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 cable under test is a single-core power cable with a length of 600 m and a model of 8.7 / 15 kV YJV35mm2. Two defects are set on the line. The first defect is set at the 100 m position, 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 the 400 m position, the type of the defect is the first type of defect, and the equivalent resistance of the defect is 80 Ω.

[0078] Measure the cable: In the first step, calibrate and measure the measurement system. Disconnect the connecting cable from the cable under test and short-circuit the end of the connecting cable. Measure the reflection pulse at the short-circuited end of the connecting cable as Figure 2 shown, where v os (t) is the reflection signal at the short-circuited end. In the second step, measure the reflection signal of the cable under test. Connect the connecting cable to the cable under test and measure the reflection signal of the cable under test as Figure 4 shown. Figure 4The defects and the reflection signals at the cable ends are marked. At the same time, it can also be seen that in the measurement results, there are many other reflection signals, which are caused by secondary or multiple reflections between the defects and between the defects and the connectors. Figure 4 In the measurement results in Figure 4 , the reflection signal of defect 1 is the reflection signal of the first defect inside the cable. This signal is not affected by multiple reflections of the signal and the defect can be directly located. After calculation, the time difference between the arrival time of the reflection pulse of this defect and the arrival time of the reflection pulse at the cable inlet end D is 1.176 μs. Then the location result of the defect is 99.96 m, and the relative error from the actual position is -0.04%. From Figure 4 the measurement results in Figure 4 , it can be seen that the injection pulse is a positive pulse, while the reflection pulse of the defect is a negative pulse. Therefore, defect 1 is a type-II defect. Further estimating the equivalent resistance of defect 1, the calculation result is 49.95 Ω, and the relative error from the actual value is -0.1%. Establish a cable model with only defect 1 and reconstruct the reflection pulse of defect 1. The reconstructed pulse result is as Figure 5 shown. From Figure 5 it can be seen that the reflection pulse related to defect 1 is reconstructed. This includes not only the first reflection pulse of the defect but also the pulses of multiple reflections between defect 1 and the cable inlet end D. Through the reconstruction result, we can determine that the first reflection pulse of the next defect is around 5.1 μs. By the location method, the time difference between the arrival time of the reflection pulse of the next defect and the arrival time of the reflection pulse at the cable inlet end D is 4.699 μs. The location result of the defect is 399.415 m, and the relative error from the actual position is -0.15%. The second defect reflection pulse is positive, and it can be judged that this defect is a type-I defect. Further estimating the equivalent resistance of the defect is 78.09 Ω, and the relative error from the actual value is -2.39%. Establish a cable model with defect 1 and defect 2 and reconstruct the reflection pulses of defect 1 and defect 2. The pulse reconstruction result is as Figure 6 shown. Through Figure 6It can be determined that the first reflection pulse of the next defect is near 7.658 μs. Locate the reflection pulse of this defect. After calculation, the arrival time difference between this pulse and the reflection pulse at the cable inlet end D is 7.064 μs, and the location result of the defect position is 600.44 m. Considering that the total length of the cable is 600 m, this reflection pulse is generated by the open end of the cable. Therefore, the reconstruction of the reflection pulse ends. In summary, after calculation, there are 2 defects in this cable, 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 calculated results of the equivalent resistances of the two defects are 49.95 Ω and 78.09 Ω respectively; the relative errors of the calculated results of the equivalent resistances and the actual values are -0.1% and -2.39% respectively. The above calculation results show that the present invention can effectively detect and locate multiple defects along the cable and has high location accuracy.

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

[0080] 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, and 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 will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cable multi-defect measurement device based on pulse reconstruction, characterized in that: include: Host computer, pulse source, T-connector, acquisition equipment and connecting wires; The host 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 a pulse signal and inject it into the cable; The T-type connector is used to connect the pulse source, the connecting line and the acquisition device; The acquisition device is used to acquire the injected pulse and the reflected pulse from the inside of the cable, and transmit the acquisition result to the host computer.

2. A cable multi-defect measurement device based on pulse reconstruction according to claim 1, characterized in that: The output impedance of the pulse source, the input impedance of the acquisition device, the characteristic impedance of the T-connector and the connecting line are equal; the length of the connecting line ensures that the injected pulse in the measurement result and the reflected pulse at the cable entrance end do not overlap.

3. A cable multiple defect detection method based on pulse reconstruction, referring to a cable multiple defect measurement device based on pulse reconstruction as described in any one of claims 1-2, characterized in that: The following steps are involved: Obtaining measurement results of the measuring device, locating the first defect on the cable, determining the type of the first defect and the equivalent resistance value, establishing an equivalent model of the cable with the first defect, and reconstructing the reflection pulse of the first defect; removing the first defect reflection pulse from the measurement result to obtain a remaining measurement result; The corresponding first reflected pulse in the remaining measurement results is caused by the next defect along the cable. As the second defect, the position of the second defect is located, the type of the second defect and the equivalent resistance value are determined, an 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. Repeat the above steps until the defect location result is the entire length of the measured cable and the reconstruction process of the reflected pulse is completed.

4. A cable multiple defect detection method based on pulse reconstruction according to claim 3, characterized in that: The defects inside 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 are equivalent series resistance defects, and the polarity of the reflected pulse is the same as that of the injected pulse. The second type of defect is an equivalent parallel resistance defect, where the polarity of the reflected pulse is opposite to that of the injected pulse.

5. A cable multiple defect detection method based on pulse reconstruction according to claim 4, characterized in that: The first type of defect is the equivalent series resistance defect. The defect equivalent resistance R s The calculation formula is as follows: In the formula, Γ f is the reflection coefficient of the defect; Z c is the characteristic impedance of the cable under test.

6. A cable multiple defect detection method based on pulse reconstruction according to claim 4, characterized in that: The second type of defect is an equivalent parallel defect, and the defect equivalent resistance R p The calculation formula is as follows: In the formula, Γ f is the reflection coefficient of the defect; Z c is the characteristic impedance of the cable under test.

7. A cable multiple defect detection method based on pulse reconstruction according to claim 3, characterized in that: The reflection coefficient of the nth defect is obtained by recursive calculation using the measurement results. The recursive calculation formula of the reflection coefficient of the nth defect is as follows: In the formula, Γ nf is the reflection coefficient of the nth defect; V ofn is the spectrum of the nth defect reflection pulse in the measurement result; V oD is the spectrum of the reflected pulse at the cable entrance D in the measurement result; V os is the spectrum of the reflected pulse at the short-circuited end of the connecting line in the calibration test; c is the propagation coefficient of the cable to be tested; l fn is the position of the nth defect; Γ if is the reflection coefficient of the i-th defect.

8. The method for detecting multiple defects of a cable based on pulse reconstruction according to claim 3 is characterized in that: The measurement result of the reflected pulse of the defect in the tested cable is obtained by modeling the tested cable. The calculation formula is as follows: Where V or is the spectrum of the reflected pulse of the defect in the tested cable; Γ oD Entrance reflection coefficient at the cable entry port.

9. A cable multiple defect detection method based on pulse reconstruction according to claim 8, characterized in that: The entrance reflection coefficient Γ at the cable entrance oD The entrance reflection coefficient Γ through the first defect location o1 The calculation formula is as follows: Γ o1 By recursive calculation, for a cable with m defects, Γ o1 The recursive calculation formula is as follows: In the formula, Γ on is the entrance reflection coefficient of the nth defect position; Z fn is the entrance impedance of the nth defect position, and its calculation formula is as follows: Where: γ c is the propagation constant of the cable under test, l f1 is the location of the first defect.

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