KR101570508B1 - Method for selecting optimal input signal of time-frequency domain reflectometry for examining cable - Google Patents

Abstract

The present invention relates to a method for selecting an optimal input signal of time-frequency domain reflectometry for diagnosing a cable. The method includes the following steps: (A) selecting minimum and maximum center frequencies as candidates of a center frequency band; (B) setting a time width; (C) calculating mutual correlation function value; (D) drawing a graph with the mutual correlation function values; (E) checking the whole length of the cable and selecting a band of the center frequencies; (F) selecting a certain frequency region; (G) selecting a bandwidth of the selected center frequencies; and (H) selecting a reference signal based on an input signal parameter.

Description

[0001] The present invention relates to a time-frequency domain reflectometry for examining cable,

The present invention relates to a method of designing an input signal having an optimum time-frequency domain characteristic according to the type of an insulator of a distance and a cable, and more particularly to a method of designing an input signal having a center frequency, a bandwidth, The present invention relates to a method for optimally designing three parameters for each application (propagation distance, distance resolution).

The power cable insulation diagnosis is to diagnose the deterioration that may lead to an accident. The whole cable system including the pavement layer is diagnosed, the deterioration state and deterioration location of the cable are evaluated, and ultimately the cable life is evaluated The purpose is to do.

In addition, for utilities and users, achieving this objective economically can be the primary goal of reducing line maintenance costs and ensuring reliability of power supply.

As climate change and energy crisis are becoming global problems, the spread of distributed power sources such as renewable energy is expanding and with the rapid increase of electric power demand due to economic development, the power industry is pushing to increase the pressure and capacity. Recently, due to the rapid spread of sensitive loads such as information devices such as computers, the necessity of uninterruptible power supply is gradually increasing, and accordingly, the efficient measurement, transmission and monitoring technology of a large amount of information in the world power system is established Research on the development of an intelligent automatic diagnosis system to prevent accidents is increasing day by day.

Most of the cable failures are due to electrical, mechanical, thermal, and chemical degradation during manufacture, assembly, or implementation, and the main deterioration factor is known to be caused by the water tree and manufacturing bond. Most of the power cable live-line diagnostics devices that are currently being commercialized or under development are very difficult to distinguish from noise due to a very small discharge amount of the partial discharge (PD), and the generation of the measurable partial discharge signal is likely to lead to an accident immediately, This is because the diagnostic meaning is discolored. In particular, it is known that there is no measurable partial discharge in the case of deterioration of the water tree.

Another way is to diagnose the cable through cable diagnostic echo processing.

This generates a diagnostic signal to the first side of the measuring cable and measures the diagnostic signal output from the end of the measurement cable or the diagnostic signal output to the second side of the measurement cable and output to the first side again, It is a method to diagnose a measurement cable using characteristics.

However, in this conventional cable diagnostic reflection processing method, the approximate limit value is selected as the attenuation characteristic of the cable in designing the reference signal, and the limit value is selected as the center frequency. However, since this method assumes that the cable length and the kind of insulator are known, it is difficult to actually apply the method. The bandwidth is set first considering only the resolution, and the reflected signal is obtained, There is a disadvantage that it can not be proved experimentally.

Therefore, the cable diagnosis method using the cable diagnostic reflection processing method is only studied, and the practical use thereof has not yet been achieved.

Patent Document 10-10-2010-0070813: Cable deterioration diagnosis system and method

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method for diagnosing cable defects through cable diagnostic reflection processing, In a time-frequency domain reflection processing method for measuring a distance from a point to an impedance discontinuity point, a method for designing an input signal having an optimum time-frequency domain characteristic according to a distance and an insulator type of a cable is provided .

Another object of the present invention is to provide a method for optimally designing three parameters, that is, a center frequency, a bandwidth, and a time width, which serve as a reference of a linear chip signal as an input signal, in accordance with each application (propagation distance and distance resolution).

Other objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, an optimum input signal selecting method of a time-frequency domain reflection measuring method for cable diagnosis according to the present invention is characterized by (A) determining a frequency attenuation characteristic and a phase using a network analyzer, (b) selecting the candidate center frequency to be three times the bandwidth based on the theoretical background; and (c) selecting the minimum and maximum center frequencies as candidates for the center frequency band in the linearly varying section based on the phase change. Setting a time width such that a product of a bandwidth and a time width is a minimum value of 0.5 based on an uncertainty principl; (C) setting a time width of a reference signal having a minimum value among the set candidate center frequency bandwidths, And calculating a cross-correlation function value at a cable end; and (D) Repeating the steps (B) and (C) until a section assuming that the frequency has a linear characteristic by sweeping the wave number, and deriving a cross-correlation function value at the end of each center frequency as a graph; E) Based on the peak value of the cross-correlation function graph at the end according to the derived frequency, the value at 0m, which is the reference signal, is 1, the interval corresponding to the reflected wave is 0.3 or more, Selecting a band of the center frequency; (F) determining a center frequency at which the time-frequency cross-correlation function value is less than 0.2 based on the selected center frequency band and a resolution of the cross-correlation function that does not satisfy the blind spot Selecting a specific frequency domain by controlling the frequency domain; (G) if the predetermined center frequency is selected, Selecting a bandwidth of the selected center frequency by changing the bandwidth within a theoretical preference interval; and (H) selecting a bandwidth of the selected center frequency based on the center frequency characteristic and the input signal parameter including the center frequency, And selecting a signal.

Preferably, in the step (A), 50 to 140 MHz, which is linear in frequency attenuation characteristic and phase, is selected as a center frequency candidate.

Preferably, the step (C) is characterized by increasing the center frequency by 10 MHz.

Preferably, in the step (F), the specific center frequency region is 60 to 90 MHz considering the magnitude of the peak value of the cross-correlation function according to the reference signal and the blind spot.

Preferably, the step (G) includes the steps of: selecting a resolution (unit m) of a diagnosis to be required; selecting a minimum value of the bandwidth using the resolution of the selected diagnosis; A step of sweeping a bandwidth of a predetermined interval and selecting a bandwidth interval considering a resolution and a damping characteristic of the cable on a cross correlation function and setting a time width suitable for the bandwidth.

Preferably, the time width is selected so that the product of the time width and the bandwidth is at least 0.5 in consideration of the resolution in the time axis, while satisfying the minimum value of 0.5 or more based on the uncertainty principle.

Preferably, the step (H) comprises the steps of (A) through (G) applied to at least two or more manufacturer cables to generate an input signal including a center frequency, a bandwidth, And selecting common reference signals that are all applicable by setting intersection parameters of the respective cables according to the selected input signal parameters.

According to another aspect of the present invention, there is provided a method of selecting an optimal input signal of a time-frequency domain reflection measurement method for cable diagnosis according to the present invention, comprising: determining a frequency attenuation characteristic and a phase using a network analyzer; The center frequency band is linearly changed based on the change, the frequency is swept over the interval, and the value at 0m, which is the reference signal, is 1 using a normalized cross-correlation function. A step of determining the total length of the cable and the center frequency band by searching the interval of 0.3 or more and selecting the resolution of the diagnosis to be required and then selecting the minimum value of the bandwidth by using this to determine the bandwidth of the predetermined interval from the minimum value , The interval of the bandwidth considering the resolution on the cross-correlation function and the attenuation characteristic of the cable is selected It may makin comprises the steps of selecting a reference signal with the center frequency characteristic and a center frequency, bandwidth, based on the input signal parameters including the time width according to the degree of change for selecting the pulse width matched to this.

As described above, the optimum input signal selecting method of the time-frequency domain reflection measuring method for cable diagnosis according to the present invention has the following effects.

First, by designing a method having an optimal signal, it is possible to diagnose a cable by obtaining an optimum signal experimentally and theoretically, thereby greatly reducing the time required for selecting an input signal necessary for diagnosis.

Secondly, it is possible to increase the reliability of the bad line determination and to provide convenience in analyzing the work performance in the field during the insulation condition evaluation in selecting and managing the lines with high possibility of accidents. Therefore, There is an effect that tests can be performed and evaluated without training and training.

Third, since it is possible to monitor the target line at all times in the live condition, it has an excellent effect in the field.

Fourth, it is possible to efficiently achieve the objective of insulation condition evaluation in terms of economical efficiency such as test method, device, test process, and price of unit price. And it can be used for monitoring deterioration of all types of coaxial transmission lines including low voltage signal lines, distribution cables, It is applicable to diagnosis.

1 is a flowchart illustrating a method for selecting an optimum input signal in a time-frequency domain reflection measurement method for cable diagnosis according to an embodiment of the present invention.
2 is a diagram showing frequency characteristics of a cable to be designed for an optimum signal of the present invention
FIG. 3 is a graph showing a cross-correlation function graph modification according to each frequency in the present invention
FIG. 4 is a graph showing a peak value of a cross-correlation function graph at an end according to each frequency derived in the present invention
FIG. 5 is a diagram for explaining a process of selecting an optimum center frequency bandwidth in FIG.
6 is a Wigner time-frequency distribution diagram for an optimized common input signal of the present invention

Other objects, features and advantages of the present invention will become apparent from the detailed description of the embodiments with reference to the accompanying drawings.

A preferred embodiment of a method for selecting an optimal input signal of the time-frequency domain reflection measurement method for cable diagnosis according to the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It is provided to let you know. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents It should be understood that water and variations may be present.

1 is a flowchart illustrating a method for selecting an optimal input signal in a time-frequency domain reflection measurement method for cable diagnosis according to an embodiment of the present invention.

Referring to FIG. 1, first, a network analyzer is used to linearly change a frequency based on attenuation characteristics and phase changes as shown in FIGS. 2 (a) and 2 (b) The minimum and maximum center frequencies are selected as candidates for the center frequency band in step S10. FIG. 2 is a diagram showing a frequency characteristic of a cable to be subjected to the optimum signal design. In the selected center frequency candidate, 50 to 140 MHz, which is linear in frequency attenuation characteristic and phase, is selected as a candidate for the center frequency band.

Then, the bandwidth is set for the candidate center frequency based on the theoretical background (S20). At this time, the center frequency is set to be three times the bandwidth, and the time width is set so that the product of the bandwidth and the time width becomes the minimum value 0.5 based on the uncertainty principle (uncertainty principl).

In step S30, a cross-correlation function value at a reference signal and a cable end is calculated for a reference signal having a minimum value among the set candidate center frequency bandwidths.

3, the center frequency is increased by an interval of 10 MHz, and the above procedure is repeated until it is assumed that the frequency has a linear characteristic, (Step S40).

4 is a graph showing a peak value of a cross-correlation function graph at an end according to the derived angular frequency. The graph shown in FIG. 4 is a result graph obtained by repeating the above process by increasing the center frequency by 10 MHz from the minimum center frequency, the maximum center frequency, and the bandwidth / center frequency as the input values.

As shown in FIG. 4, it can be seen that the T-F correlation value of the reflected wave is 0.3 as the maximum frequency that can allow round-trip in the TFDR.

Accordingly, the entire length of the cable is checked and the center frequency band is selected (S50) by searching for a section having a value of 0 at the reference signal of 1m and a value corresponding to the reflected wave of 0.3 or more.

Next, the center frequency where the time-frequency cross-correlation function value is less than 0.2 and the frequency domain where the resolution of the cross-correlation function does not satisfy the blind spot is controlled based on the selected center frequency band, (S60). The results shown in FIG. 3 can be expressed as shown in Table 1 below. The optimal center frequency range is determined to be 60 to 90 MHz considering the magnitude of the peak value of the cross-correlation function according to the reference signal and the blind spot.

Center frequency
[MHz] Time width
[ns] Cross-correlation function peak
[0 ~ 1] Blind spot
[m] 50 69 0.72 1.92 60 58 0.73 1.83 70 50 0.82 1.63 80 43 0.68 1.55 90 39 0.72 1.32 100 35 0.66 1.11 110 32 0.52 0.95 120 29 0.42 0.83 130 27 0.33 0.70

If the optimal center frequency is selected, the selected center frequency band is fixed, and then the bandwidth is changed within the theoretical preferred interval, and the optimum center frequency bandwidth is selected (S70).

To do this, as shown in FIG. 5, the resolution (unit m) of the diagnosis to be required is selected, and the minimum value of the bandwidth is selected using the resolution. Then, a bandwidth of a certain interval is swept from a minimum value of the selected bandwidth, a bandwidth interval considering a resolution and a damping characteristic of the cable on the cross-correlation function is selected, and a time width corresponding thereto is set. At this time, the time width satisfies the minimum value of 0.5 or more based on the uncertainty principle, and the product of the time width and the bandwidth is at least 0.5 in consideration of the resolution in the time axis.

Table 2 shows the results of applying these methods for A, B, C and D manufacturer cables.

Center frequency
[MHz] Bandwidth
[MHz] Time width
[ns] A for manufacturer cable
Optimal input signal parameter 50 to 90 50-100 70 B for manufacturer cable
Optimal input signal parameter 50 to 110 50-100 60 C for manufacturer cable
Optimal input signal parameter 60 to 90 70-100 50 D for manufacturer cable
Optimal input signal parameter 50 to 60 50 to 65 50 For 4 cables
Optimized Common Input Signal 60 65 60

As shown in Table 2, it can be seen that the optimum input signal parameters (center frequency, bandwidth, and time width) are different depending on the frequency characteristics and the degree of change of the cable. Therefore, the common reference signal according to each cable manufacturer sets the intersection parameter that satisfies the optimum condition of each cable, and selects the applicable signal for all four cables.

FIG. 6 shows a Wigner's time-frequency distribution diagram for an optimized common input signal, which shows an optimum signal showing a center frequency of 60 MHz, a bandwidth of 65 MHz, and a time width of 60 ns.

Accordingly, the present invention can be applied regardless of the type of cable.

In actual situations, most cables are diagnosed without knowing the type and length of the cable insulation insulator. Therefore, when designing the input signal with this information, it is the best signal to diagnose the cable. It is unreasonable to assure you of finding potential defects. Therefore, by providing a method with an optimal signal, it is possible to diagnose a cable by obtaining an optimum signal experimentally and theoretically.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the present invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (8)

(A) selecting a minimum and a maximum center frequency as candidates of a center frequency band in a linearly varying section based on attenuation characteristics and phase changes of a frequency using a network analyzer;
(B) setting the selected candidate center frequency to be three times the bandwidth, setting a time width such that the product of the bandwidth and the time width is 0.5, which is the minimum value, based on the uncertainty principle,
(C) calculating a cross-correlation function value at a reference signal and a cable end for a reference signal having a minimum value among the set candidate center frequency bandwidths,
(D) sweeping the center frequency using the calculated cross-correlation function value, and repeating the steps (B) and (C) until the frequency is assumed to have a linear characteristic, Deriving a cross-correlation function value of the cross-
(E) Based on the peak value of the cross-correlation function graph at the end according to the derived frequency, the value at 0m, which is the reference signal, is 1, and the interval corresponding to the reflected wave is 0.3 or more. And selecting a band of the center frequency,
(F) a center frequency in which the time-frequency cross-correlation function value is less than 0.2 and a frequency range in which the resolution of the cross-correlation function does not satisfy the blind spot is controlled based on the selected center frequency band, Selecting,
(G) fixing the selected center frequency band when the specific center frequency is selected, changing the bandwidth within the theoretical preference period and selecting the selected center frequency bandwidth,
(H) selecting a reference signal based on an input signal parameter including a center frequency, a bandwidth, and a time width according to the center frequency characteristic and the degree of change. Method of selecting input signal of reflected wave measurement method. The method according to claim 1,
Wherein the step (A) selects a center frequency candidate of 50 ~ 140 MHz, which is linear in frequency attenuation characteristic and phase, as a candidate for a center frequency. The method according to claim 1,
Wherein the step (C) increases the center frequency by an interval of 10 MHz. The method according to claim 1,
Wherein the specific center frequency region is 60 to 90 MHz in consideration of the magnitude of the peak value of the cross-correlation function according to the reference signal and the blind spot in the step (F). Input signal selection method. 2. The method of claim 1, wherein step (G)
Selecting a resolution (unit m) of the diagnosis to be required,
Selecting a minimum value of the bandwidth using the resolution of the selected diagnosis;
A step of sweeping a bandwidth of a predetermined interval from a minimum value of the selected bandwidth and selecting a bandwidth interval considering a resolution and a damping characteristic of a cable on a cross correlation function and setting a time width corresponding thereto; A Method for Selecting Input Signal in Time - Frequency Domain Reflectometry for Cable Diagnosis. 6. The method of claim 5,
Wherein the time width is selected so that the product of the time width and the bandwidth is at least 0.5 in consideration of the resolution in the time axis while satisfying the minimum value of 0.5 or more based on the uncertainty principle. Of the input signal. 2. The method of claim 1, wherein step (H)
Selecting input signal parameters including a center frequency, a bandwidth, and a time width according to a frequency characteristic and a variation degree of each cable by applying the steps (A) to (G) to at least two manufacturer cables,
And selecting common reference signals that are all applicable by setting intersection parameters of the respective cables according to the selected input signal parameters. ≪ Desc / Clms Page number 19 > Using a network analyzer, the center frequency band is selected as a linearly varying section based on attenuation characteristics and phase changes of the frequency, the frequency is swept over the section, and a normalized cross-correlation function is used Determining a total length of a cable and a center frequency band by searching for a section having a reference signal of 0 at a value of 1 and a value corresponding to a reflected wave of at least 0.3;
The bandwidth of a certain interval is swept from the minimum value by selecting the minimum value of the bandwidth by using the resolution of the diagnosis to be required and the interval of the bandwidth considering the resolution and the attenuation characteristics of the cross correlation function is selected, Selecting a matching time width,
And selecting a reference signal based on an input signal parameter including a center frequency, a bandwidth, and a time width according to the center frequency characteristic and the degree of change. Input signal selection method.

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