CN113884814A - Four-term three-order Lutaler window function cable body damp defect positioning algorithm - Google Patents
Four-term three-order Lutaler window function cable body damp defect positioning algorithm Download PDFInfo
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- 230000007547 defect Effects 0.000 title claims abstract description 85
- 230000002950 deficient Effects 0.000 claims abstract description 15
- 238000000034 method Methods 0.000 claims description 9
- 238000009736 wetting Methods 0.000 claims description 7
- 238000001453 impedance spectrum Methods 0.000 claims description 6
- 238000005096 rolling process Methods 0.000 claims description 6
- 230000035945 sensitivity Effects 0.000 abstract description 8
- 210000001503 joint Anatomy 0.000 description 7
- 230000008859 change Effects 0.000 description 6
- 230000008054 signal transmission Effects 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
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- 239000004703 cross-linked polyethylene Substances 0.000 description 2
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- 239000000463 material Substances 0.000 description 2
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- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000013016 damping Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
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- 238000006731 degradation reaction Methods 0.000 description 1
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- 238000009413 insulation Methods 0.000 description 1
- 238000013178 mathematical model Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
Abstract
The invention discloses a four-item three-order Lutaler window function cable body moisture defect positioning algorithm, which is used for testing cable data; respectively modeling and positioning analyzing the intact cable and the defective cable by using a mathematical formula model of the input impedance of the head end of the intact cable and the input impedance of the head end of the defective cable obtained by calculation by using discrete Fourier transform, and obtaining a positioning spectrogram of the local defect/intermediate joint of the cable; selecting four third-order Lutaler window functions to carry out windowing treatment on the body defect cable positioning spectrogram to obtain a body defect position; and aiming at the positioning spectrogram of the cable with the damp defect of the intermediate joint, selecting a second-order Nuttall self-convolution window to perform windowing treatment on the positioning spectrogram, and obtaining the damp defect position of the intermediate joint. The invention can greatly improve the positioning and identifying sensitivity of the cable body to the moisture defect, so that the positioning result is more intuitive, and the position and the moisture area of the local moisture defect of the body can be more conveniently judged.
Description
Technical Field
The invention relates to the technical field of cable defect positioning, in particular to a four-term three-order Lutaler window function cable body damp defect positioning algorithm.
Background
If there is a defect (such as damage, insulation degradation, moisture, etc.) at the local position of the cable or an intermediate joint is made, the distribution parameters at the local position of the cable are changed, and an impedance discontinuity is formed, so that the transmission characteristics of signals in the cable are changed. In order to compare the signal transmission difference between the intact cable and the defective cable, the influence of the existence of the local defect on the cable signal transmission characteristic needs to be analyzed for the defective cable according to a defective cable model containing the local defect, and the local defect is positioned according to the difference between the signal transmission characteristic and the intact cable signal transmission characteristic. However, when the input impedance spectrum at the head end of the cable is analyzed and processed by using inverse fourier transform at present, spectrum leakage and a fence effect are brought, so that the sensitivity of identifying the local damp defect of the cable body is reduced, if the damp degree of the local damp defect of the cable body is in a slight damp state and the cable is a long cable, the position of the local damp defect and the range of a damp area are difficult to judge through the weak reflection intensity of the local damp defect of the cable body.
Disclosure of Invention
The invention aims to provide a four-item three-order Lutall window function cable body moisture defect positioning algorithm, after an original positioning result is processed by a four-item three-order Nuttall window with good use performance, the position of a moisture defect can be obviously seen by comparing the positioning results before and after windowing, the positioning and identifying sensitivity of the moisture defect of a cable body can be greatly improved, the positioning result is more intuitive, and the position and the moisture area of the local moisture defect of the body can be more conveniently judged. And the positioning reflection characteristics of the body moisture defects under different severity degrees (positions, moisture severity degrees and moisture area ranges) can be obtained.
In order to achieve the purpose, the invention provides the following technical scheme: a four-item three-order Lutaler window function cable body damp defect positioning algorithm comprises the following steps:
step S1, testing cable data;
step S2, processing the input impedance spectrum of the head end of the cable by using discrete Fourier transform, respectively modeling and positioning and analyzing the intact cable and the defective cable by using the mathematical formula models of the input impedance of the head end of the intact cable and the input impedance of the head end of the defective cable, and obtaining a positioning spectrogram of the local defect/intermediate joint of the cable;
s3, selecting four three-order Lutaler window functions to carry out windowing treatment on the body defect cable positioning spectrogram, and then comparing positioning results before and after the four three-order Lutaler window functions are subjected to windowing treatment to obtain a body defect position;
and step S4, aiming at the positioning spectrogram of the cable with the damp defect of the intermediate joint, selecting a second-order Nuttall self-rolling window to carry out windowing processing on the positioning spectrogram, and then comparing positioning results before and after the windowing processing of the second-order Nuttall self-rolling window to obtain the damp defect position of the intermediate joint.
Preferably, in step S2, the head end (x ═ 0) of the intact cable inputs the impedance Zh(f) Comprises the following steps:
wherein Z is0hγ h is the propagation constant, Γ Lh is the reflection coefficient at the end of the intact cable (x ═ l), and l is the cable length, which is the characteristic impedance of the intact cable.
Preferably, in step S2, the leading end (x ═ 0) of the defective cable having the local defect has an input impedance Zd(f) Comprises the following steps:
where la denotes the distance of the head end of the local defect from the head end of the cable, lb denotes the distance of the tail end of the local defect from the head end of the cable, where la < lb.
Preferably, in step S3, the time domain w is windowed by the four-term third-order Lutaler window functionNUTTALLThe expression of (n) is:
in the formula: m, N are the number of terms of the window function and the window length, respectively; bm is a cosine combination term coefficient; n is 0, 1, …, N-1.
Preferably, the p-order nuttally self-convolution window is formed by performing convolution operation on p identical nuttally window functions, that is, the second-order nuttally self-convolution window is formed by performing convolution operation on 2 identical nuttally window functions.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, after the original positioning result is processed by using the four-item three-order Nuttall window with good use performance, the positioning result before and after windowing processing is compared, the position of the affected defect can be seen obviously, the positioning and identifying sensitivity of the cable body affected with damp defects can be greatly improved, the positioning result is more intuitive, and the local affected defect position and the affected area of the body can be judged more conveniently.
2. The invention can also obtain the positioning reflection characteristics of the body moisture defects under different severity degrees (position, moisture severity degree and moisture area range).
3. In the positioning spectrogram processed by windowing, compared with an intact body cable, the positions corresponding to the two distortion point peak values are positions where the damp defects are located, the distance between the two distortion point peak values is a damp area range, and the positioning reflection intensity of the damp defects is in a positive correlation with the damp severity. It should be noted that the method of the present invention is also suitable for the localized diagnosis of the body moisture defect in different moisture-affected area ranges and different moisture-affected severity degrees, and is not affected by the change of the cable length.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2(a) is a chart illustrating the location of a moisture defect in an un-windowed cable body according to the present invention;
FIG. 2(b) is a chart of the location of a cable body moisture defect after the windowing treatment in accordance with the present invention;
FIG. 3(a) is a graph of a moisture-localized position of an un-windowed cable intermediate joint in accordance with the present invention;
fig. 3(b) is a moisture-bearing location spectrum of the cable intermediate joint after the windowing treatment.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
The invention provides a technical scheme that: a four-term three-order Lutaler window function cable body damp defect positioning algorithm is shown in figure 1 and comprises the following steps:
step S1, the cable data is tested.
And step S2, processing the input impedance spectrum of the head end of the cable by using discrete Fourier transform, respectively modeling and positioning and analyzing the intact cable and the defective cable by using the mathematical formula models of the input impedance of the head end of the intact cable and the input impedance of the head end of the defective cable, and obtaining a positioning spectrogram of the local defect/intermediate joint of the cable.
Input impedance Z of intact cable head end (x ═ 0)h(f) Comprises the following steps:
wherein Z is0hγ h is the propagation constant, Γ Lh is the reflection coefficient at the end of the intact cable (x ═ l), and l is the cable length, which is the characteristic impedance of the intact cable.
Defective cable with local defect and its head end (x ═ 0) input impedance Zd(f) Comprises the following steps:
where la denotes the distance of the head end of the local defect from the head end of the cable, lb denotes the distance of the tail end of the local defect from the head end of the cable, where la < lb.
And step S3, selecting four third-order Lutaler window functions to carry out windowing treatment on the body defect cable positioning spectrogram, and then comparing positioning results before and after the four third-order Lutaler window functions are subjected to windowing treatment to obtain a body defect position.
Time domain w subjected to windowing by four-term third-order Lutaler window functionNUTTALLThe expression of (n) is:
in the formula: m, N are the number of terms of the window function and the window length, respectively; bm is a cosine combination term coefficient; n is 0, 1, …, N-1.
And step S4, aiming at the positioning spectrogram of the cable with the damp defect of the intermediate joint, selecting a second-order Nuttall self-rolling window to carry out windowing processing on the positioning spectrogram, and then comparing positioning results before and after the windowing processing of the second-order Nuttall self-rolling window to obtain the damp defect position of the intermediate joint.
The p-order Nuttall self-convolution window is formed by carrying out convolution operation on p identical Nuttall window functions, namely the second-order Nuttall self-convolution window is formed by carrying out convolution operation on 2 identical Nuttall window functions.
In order to verify the feasibility of the method, the method aims at the analysis result of capacitance change before and after the cable body is affected with damp, and models the cable with the local damp defect through a cable distribution parameter equivalent model and a mathematical model of cable head end input impedance Zd (f) with the local defect. The input impedance spectrum of the head end of the defective cable is obtained through simulation, and the positioning method of the cable defect provided by the invention is used for positioning the moisture defect of the body, so that the positioning reflection characteristics of the moisture defect of the body under different severity degrees (position, moisture severity degree and moisture area range) are obtained.
FIG. 2(a-b) is a positioning result of local moisture defects of a simulated 20m long 10kV XLPE cable at 9 m-11 m positions of the cable. From the simulation results shown in fig. 2(a-b), it can be found that the method for positioning the cable body moisture defect of the present invention can not only determine the positions of the first end and the last end of the cable, but also position the local moisture defect of the cable body. When the input impedance spectrum of the head end of the cable is analyzed and processed by using Fourier transform, spectrum leakage and a fence effect can be brought, so that the identification sensitivity of the local damp defect of the cable body is reduced, if the damp degree of the local damp defect of the cable body is in a slight damp state and the cable is a long cable, the position of the local damp defect and the range of a damp area are difficult to judge through the weak reflection intensity of the local damp defect of the body. And after the original positioning result is processed by the four-item three-order Nuttall window with good use performance, the positioning results before and after windowing processing are compared, so that the positioning and identifying sensitivity of the cable body to the damp defect can be greatly improved, the positioning result is more intuitive, and the local damp defect position and the damp area of the body can be more conveniently judged. In addition, in the positioning spectrogram processed by windowing, compared with a perfect body cable, the positions corresponding to the two distortion point peak values are positions where the damp defects are located, the distance between the two distortion point peak values is a damp area range, and the positioning reflection intensity of the damp defects is in a positive correlation with the damp severity. It should be noted that the method provided by the invention is also suitable for positioning and diagnosing the body moisture defects in different moisture-affected area ranges and different moisture-affected severity degrees, and is not affected by the change of the length of the cable.
TABLE 1 positioning results of different severity cable body wetting defects
Table.3-9 Location results of damp defects with different damp degrees for cable body
Fig. 3(a-b) shows the positioning results of a simulated 500m long 10kV XLPE cable with a normal splice (Cj0 ═ 0.844Cb0), a lightly-damped splice (Cj1 ═ 0.912Cb0), and a heavily-damped splice (Cj2 ═ 0.976Cb0) at 250 m. From the simulation results of fig. 3(a-b), it can be found that the cable positioning method provided by the invention not only can determine the positions of the first end and the last end of the cable, but also can accurately position the middle joint.
As shown in fig. 3(a), in the original positioning spectrogram without windowing, the amplitudes of the distortion peak points of the intermediate joints under different degrees of moisture in the positioning spectrogram are different, and the amplitudes of the distortion peak points are reduced with the increase of the degree of moisture. Due to spectrum leakage and barrier effect caused by Fourier transform analysis, the identification sensitivity of the positioning algorithm provided by the invention on the intermediate joint is greatly reduced, and if the intermediate joint is seriously affected by damp or a cable line is a multi-joint line, the position of the intermediate joint is difficult to be determined directly through an original positioning spectrogram. After the original positioning result is windowed by using the second-order Nuttall self-convolution window, it can be seen from fig. 3(b) that after the windowing, the recognition sensitivity of the middle joint is improved, so that the positioning spectrogram has more intuitiveness, and the position of the middle joint is more easily judged from the distortion peak point in the positioning spectrogram. In addition, compared with the positioning reflection characteristic of a normal intermediate joint, the amplitude corresponding to the distortion peak point of the damped intermediate joint in the positioning spectrogram is in a decreasing trend, and along with the increase of the damping severity degree of the intermediate joint, the amplitude of the damped intermediate joint in the positioning spectrogram decreases faster, because the intermediate joint serving as an impedance discontinuous point can increase the capacitance of the intermediate joint after being damped, so that the input impedance of the intermediate joint at the corresponding local position is reduced, and the amplitude corresponding to the distortion peak point of the intermediate joint in the positioning spectrogram is represented by reduction. This is in contrast to the localized reflection signature of the localized wetting defect of the cable body of fig. 2(a-b), and therefore this signature can be used as a criterion for diagnosing wetting of the intermediate joint. It should be noted that the method of the present invention is also applicable to positioning and diagnosing the intermediate joints under different moisture severity levels, and is not affected by the change of the cable length, the change of the number of the intermediate joints, and the change of the positions of the intermediate joints.
In the description of the present invention, it is to be understood that the indicated orientations or positional relationships are based on the orientations or positional relationships shown in the drawings and are only for convenience in describing the present invention and simplifying the description, but are not intended to indicate or imply that the indicated devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are not to be construed as limiting the present invention.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (5)
1. The utility model provides a four third order lutaler window function cable body defect location algorithm that wets which characterized in that: the method comprises the following steps:
step S1, testing cable data;
step S2, processing the input impedance spectrum of the head end of the cable by using discrete Fourier transform, respectively modeling and positioning and analyzing the intact cable and the defective cable by using the mathematical formula models of the input impedance of the head end of the intact cable and the input impedance of the head end of the defective cable, and obtaining a positioning spectrogram of the local defect/intermediate joint of the cable;
s3, selecting four three-order Lutaler window functions to carry out windowing treatment on the body defect cable positioning spectrogram, and then comparing positioning results before and after the four three-order Lutaler window functions are subjected to windowing treatment to obtain a body defect position;
and step S4, aiming at the positioning spectrogram of the cable with the damp defect of the intermediate joint, selecting a second-order Nuttall self-rolling window to carry out windowing processing on the positioning spectrogram, and then comparing positioning results before and after the windowing processing of the second-order Nuttall self-rolling window to obtain the damp defect position of the intermediate joint.
2. The four-term third-order Lutaler window function cable body wetting defect positioning algorithm of claim 1, characterized in that: in step S2, the leading end (x ═ 0) of the intact cable inputs the impedance Zh(f) Comprises the following steps:
wherein Z is0hγ h is the propagation constant, Γ Lh is the reflection coefficient at the end of the intact cable (x ═ l), and l is the cable length, which is the characteristic impedance of the intact cable.
3. The four-term third-order Lutaler window function cable body wetting defect positioning algorithm of claim 1, characterized in that: in step S2, the leading end (x ═ 0) of the defective cable having the local defect has an input impedance Zd(f) Comprises the following steps:
where la denotes the distance of the head end of the local defect from the head end of the cable, lb denotes the distance of the tail end of the local defect from the head end of the cable, where la < lb.
4. The four-term third-order Lutaler window function cable body wetting defect positioning algorithm of claim 1, characterized in that: step S3, time domain w of windowing by four-term third-order Lutaler window functionNUTTALLThe expression of (n) is:
in the formula: m, N are the number of terms of the window function and the window length, respectively; bm is a cosine combination term coefficient; n is 0, 1, …, N-1.
5. The four-term third-order Lutaler window function cable body wetting defect positioning algorithm of claim 1, characterized in that: the p-order Nuttall self-convolution window is formed by carrying out convolution operation on p identical Nuttall window functions, namely the second-order Nuttall self-convolution window is formed by carrying out convolution operation on 2 identical Nuttall window functions.
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