CN107064761B - Method and system for detecting internal wave velocity characteristics of alternating current cable - Google Patents
Method and system for detecting internal wave velocity characteristics of alternating current cable Download PDFInfo
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- CN107064761B CN107064761B CN201710318944.7A CN201710318944A CN107064761B CN 107064761 B CN107064761 B CN 107064761B CN 201710318944 A CN201710318944 A CN 201710318944A CN 107064761 B CN107064761 B CN 107064761B
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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
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
Abstract
The invention provides a method and a system for detecting the internal wave velocity characteristics of an alternating current cable, wherein the method comprises the following steps: according to a frequency sweep method, sending a frequency sweep signal to a cable to be tested; respectively collecting detection signals and response signals at the head end and the tail end of a cable to be tested, and sequentially carrying out filtering and amplifying treatment to obtain two paths of pretreatment signals; and performing cross Fourier change processing on the two paths of pre-processed signals to obtain two paths of signal phase difference values, and further obtaining the internal wave speed characteristics of the cable to be tested. The invention can realize the characteristic research of the internal signal transmission speed of the high-voltage power cable with a certain length along with the frequency change, and has simple and feasible scheme, strong anti-interference performance and high sensitivity.
Description
Technical Field
The invention belongs to the technical field of electrical equipment, and particularly relates to a research method and a test system for the internal wave velocity characteristics of an alternating current cable based on a sweep frequency method.
Background
With the high-speed development of Chinese economy, the modern trend of towns is more obvious, and the power cable is extremely rapidly developed as an important component part of the urban power distribution network, and the annual average growth of the power cable reaches 35%. The crosslinked polyethylene insulated cable (XLPE cable for short) gradually replaces the oil-filled cable with excellent electrical property and mechanical and physical properties, becomes the cable type with the most wide application, and is widely used in the power grid with the voltage class of 10-220 kV at present.
Internal characteristic research on alternating-current high-voltage cables is also increasingly important, for example, for partial discharge detection and positioning of high-voltage power cables, for safe and stable operation of systems and for daily overhauling and maintenance requirements. With the continuous expansion of the power cable network, local faults of power cable equipment in the system occur, and the fault positioning is critical to the rapid and accurate implementation through the research of the wave velocity characteristics in the cable.
It is found that the propagation speed of the partial discharge signal in the cable is a function of frequency, and the propagation speed is faster (dispersion phenomenon) when the frequency is higher as the signal wave speeds of different frequency components are different. Since the partial discharge signal is a broadband signal from low frequency to high frequency, the positioning error caused by the conventional calculation by empirically fixing the wave speed is not negligible. Therefore, a set of wave velocity characteristic research system aiming at different frequency component signals inside a high-voltage power cable with a certain length is designed based on the frequency-dependent transmission characteristic of the cable, and accurate positioning of partial discharge and reliable fault detection of the cable are further completed based on a test conclusion, so that the system has important engineering significance.
Disclosure of Invention
The invention aims to solve the defects in the prior art and provides a method capable of effectively detecting the internal wave velocity characteristics of an alternating-current high-voltage cable.
In order to achieve the above object, the present invention provides a method for detecting the internal wave velocity characteristics of an ac cable, comprising the steps of:
(1) According to a frequency sweep method, sending a frequency sweep signal to a cable to be tested;
(2) Respectively collecting detection signals and response signals at the head end and the tail end of a cable to be tested, and sequentially carrying out filtering and amplifying treatment to obtain two paths of pretreatment signals;
(3) And performing cross Fourier change processing on the two paths of pre-processed signals to obtain two paths of signal phase difference values, and further obtaining the internal wave speed characteristics of the cable to be tested.
Further, the detection method of the invention comprises the following steps:
(1) According to a frequency sweep method, a sinusoidal frequency sweep signal is sent to a cable to be tested; the sinusoidal sweep frequency signal is a sinusoidal signal with preset frequency repeatedly scanned within a preset frequency range along with time; the preset frequency range is 100k-20Mhz;
(2) Synchronizing with the sine sweep signals sent in the step (1) at different times, respectively collecting detection signals and response signals at the head end and the tail end of the cable to be tested, and sequentially carrying out filtering and amplifying treatment to obtain two paths of preprocessing signals corresponding to the sine sweep signals with different preset frequencies;
(3) Acquiring wave speed transmission curves corresponding to a plurality of preset frequencies in a preset frequency range according to the sinusoidal sweep signals and the corresponding two paths of preprocessing signals in the step (2) under different frequencies; and performing cross Fourier transform processing on the two corresponding paths of preprocessing signals to obtain corresponding frequency domain phase difference values under different preset frequencies, thereby obtaining the internal frequency-varying transmission characteristics of the cable to be tested.
The frequency change mode of the sinusoidal sweep frequency signal in the step (1) is that the output is linearly increased in a preset frequency range; the output modes of the sweep frequency signals with different preset frequencies are continuous output or output in sequence at intervals of preset time length; the preset time period is longer than the sweep period of the sine sweep signal.
And (2) when filtering and amplifying the detection signals and the response signals acquired from the head end and the tail end of the cable to be tested, only extracting signals corresponding to the frequency of the sinusoidal sweep frequency signals in the detection signals and the response signals.
The specific process of the step (3) is as follows: according to two paths of preprocessing signals corresponding to sine sweep signals with different frequencies:
；
wherein, the liquid crystal display device comprises a liquid crystal display device,u 1 、u 2 two paths of preprocessing signals representing different frequencies, the initial phases are allThe initial phase difference value isThe two paths of preprocessing signals finally realize double-trace display on a digital oscilloscope in the time domain, and the two paths of preprocessing signals pass through a cross Fourier operation formula:
；
wherein:thereby realizing the digital conversion of the signal time domain and the signal frequency domain; calculating the difference delta of the propagation time of the signal in the cable channeltThereby according to-> L/∆tThe propagation velocity is derived and the propagation velocity,Lfor the total length of the cable to be tested; the acquired frequency-variable signals under all preset frequencies are subjected to mathematical analysis, so that different wave speed values corresponding to the signals with different frequencies one by one can be obtained; and drawing a characteristic diagram of the wave speed changing along with the frequency, and obtaining the internal frequency-dependent transmission characteristic of the cable to be tested.
The total length of the cable to be tested is 100m-500m.
The invention also provides a system for detecting the internal wave velocity characteristic of the alternating current cable, which comprises the following steps:
the sweep frequency signal generator outputs a sweep frequency signal to the cable to be tested;
the signal acquisition device is used for acquiring two paths of signals at the head end and the tail end of the cable to be tested through a double-shielding coaxial signal transmission line;
the signal adjusting device is used for filtering and amplifying after receiving two paths of signals of the signal acquisition device;
and the signal processing device performs cross Fourier transform on the signals processed by the signal adjusting device to obtain two paths of signal frequency domain phase difference values, and further obtains the internal wave speed characteristics of the cable to be tested.
The signal adjusting device comprises an RL filter and a signal amplifier; the signal acquisition device is connected with the signal processing device through the RL filter, the signal amplifier and the signal processing device in sequence; the signal acquisition device comprises an industrial personal computer and an acquisition card; the head end and the tail end of the cable to be tested are respectively connected with the acquisition card through double-shielding coaxial signal transmission lines; the acquisition card is respectively connected with the industrial personal computer and the sweep frequency signal generator; the industrial personal computer is connected with the RL filter.
The detection system also comprises two test signal matching impedances; the head end and the tail end of the cable to be tested are respectively connected with one end of the corresponding test signal matching impedance; the other end of the test signal matching impedance is grounded.
The signal processing device comprises a digital oscilloscope and a signal Fourier transform system; the signal amplifier is connected with the signal Fourier transform system through a digital oscilloscope.
Compared with the prior art, the invention has the following advantages: the invention is based on a sweep frequency method, and reflects different responses of the cable to the sine scanning signals injected at intervals through signals collected from the head end and the tail end of the cable, so as to analyze and obtain the internal frequency-dependent transmission characteristics of the test cable. The invention can realize the characteristic research of the internal signal transmission speed of the high-voltage power cable with a certain length along with the frequency change, and has simple and feasible scheme, strong anti-interference performance and high sensitivity.
Drawings
FIG. 1 is a block diagram of a system for detecting the internal wave velocity characteristics of an AC cable based on a frequency sweep method (impulse response method);
FIG. 2 is a graph showing the observation results of a dual-trace sweep signal at a set of specific frequencies when the method for detecting the internal wave velocity characteristics of an AC cable according to the present invention is adopted;
fig. 3 is a graph showing a specific frequency-dependent transmission characteristic obtained by the method for detecting the internal wave velocity characteristic of the ac cable according to the present invention.
In the figure, a 1-sweep frequency signal generator, a 2-high voltage power cable, a 3-test signal matching impedance, a 4-signal transmission line, a 5-signal acquisition device, a 6-signal adjustment device, a 7-RL filter, an 8-signal amplifier and a 9-signal processing device are arranged.
In fig. 2, signal 1 is a first pre-processed signal and signal 2 is a second pre-processed signal.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
As shown in fig. 1, the system for testing the internal wave velocity characteristics of the alternating current cable based on the sweep frequency method comprises a sweep frequency signal generator 1, an experimental signal matching impedance 3, a signal transmission line 4, a signal acquisition device 5, a signal adjustment device 6 and a signal processing device 9. The signal transmission line 4 adopts a double-shielded coaxial signal transmission line. The signal conditioning means 6 comprise an RL filter 7 and a signal amplifier 8. The sweep frequency signal generator 1 injects sweep frequency signals with different voltage frequencies into the head end of the high-voltage power cable 2, and the signals are transmitted through the high-voltage power cable 2 with a certain length; the head end and the tail end of the high-voltage power cable 2 are respectively connected with two test signal matching impedances 3 in parallel; the double-shielding coaxial signal transmission line 4 collects two paths of sweep frequency signals simultaneously and stores the sweep frequency signals by the signal collection device 5; the two paths of sweep frequency signals are filtered and amplified through an RL filter 7 and a signal amplifier 8 to obtain two paths of preprocessing signals; the signal processing device 9 performs cross fourier transform on the two pre-processed signals passing through the signal adjustment device 6 to obtain a voltage phase difference Φ (ω) in the frequency domain, and further obtains the internal wave velocity characteristics of the power cable.
The preset frequency range of the sweep signal generator 1 can be specifically set according to practical situations, for example, in this embodiment, the preset frequency range is 100k-20 mhz. Sinusoidal swept frequency signals refer to signals that repeatedly sweep over time over a range of frequencies. In this embodiment, the sinusoidal sweep signal is a sinusoidal signal with a frequency that is repeatedly swept over time in the range of 100k-20 MHz. The sweep signal can be linearly increased in output by the sweep signal generator 1.
The high-voltage power cable 2 is a coaxial test cable, the length range of the test cable is 100-500m, the best effect is achieved based on the frequency band limitation of the sweep frequency signal, and the length of the corresponding test cable in the drawing is 450m.
Two ends of the high-voltage power cable 2 are connected with two test signal matching impedances 3 in parallel, and the other ends of the test signal matching impedances 3 keep equipotential with the ground.
The signal acquisition device consists of an industrial personal computer and an acquisition card, and two paths of sweep frequency signals are required to be acquired and stored simultaneously in the test process.
The signal adjusting device is used for filtering and amplifying the detection signal by the RL filter circuit and the preamplifier. The test requires that the preprocessed signals after filtering and amplifying meet higher resolution and sensitivity at the same time so as to ensure accurate and reliable test conclusion.
The signal processing device sequentially realizes waveform time domain display and cross Fourier transform of the dual-trace voltage sweep-frequency signal by a digital filter and a Fourier transform system. The internal frequency change speed characteristic of the cable is deduced according to the phase difference of the dual trace signals in the frequency domain.
The sine sweep frequency signal is injected into the head end of the high-voltage power cable 2, the same sine sweep frequency signal can be continuously injected, or the sine sweep frequency signal can be sequentially injected at intervals of preset duration, for example, after the sine sweep frequency signal is injected for a period of time for the first time, the same sine sweep frequency signal is injected again. The preset time length is required to be longer than the sweep period of the sine sweep signal.
The first detection signal and the second detection signal are acquired from the head end and the tail end of the high-voltage power cable 2 respectively, and the first detection signal and the second detection signal are filtered and amplified respectively to obtain a first preprocessing signal and a second preprocessing signal.
The acquisition of the first detection signal and the second detection signal is synchronous with sine sweep signals injected at different times. Specifically, a detection signal corresponding to a first sinusoidal sweep frequency signal is synchronously collected from the head end of the high-voltage power cable 2 to obtain a first detection signal, and then a response signal of the tail end of the high-voltage power cable 2 is synchronously collected to obtain a second detection signal.
The time for which the swept sine signal is injected from the head end of the high-voltage power cable 2 and transmitted through a cable body of a certain length is different, and the response signal acquired from the tail end of the cable may be different. Thus, the acquired first and second detection signals may reflect different responses of the high voltage cable to the intermittently injected sinusoidal sweep signal.
By filtering and amplifying the first detection signal and the second detection signal, only the signal corresponding to the frequency of the sinusoidal sweep signal in the first detection signal and the second detection signal can be extracted, and the signal-to-noise ratio and the anti-interference performance of the signal can be improved.
And acquiring a plurality of preset frequencies in a preset frequency range respectively corresponding to the wave speed transmission curves according to the sinusoidal sweep frequency signal and the first preprocessing signal. The sine wave signal transmission curves with different amplitudes and phases can be obtained by displaying the digital oscilloscope dual trace channels (shown in figure 2). And performing cross Fourier transform on the signals with a certain phase difference value in the time domain to obtain frequency domain phase difference values in different frequencies, and finally obtaining the frequency-varying transmission characteristics of the signals in the test cable through mathematical calculation.
The invention relates to a method for detecting the internal wave velocity characteristic of an alternating current cable, which comprises the following specific steps:
step 1: signal generation: according to the requirement of the sweep frequency method, the frequency range of the sweep frequency signal is controlled to be 100k-20Mhz, and the output sweep frequency signal in the preset frequency band range is linearly increased in the test process.
The preset frequencies generated by the sweep frequency signal generator 1 can form a preset frequency sequence, and the values and the number of the preset frequencies can be specifically set according to actual conditions. For example, in this embodiment, the preset frequencies are equal difference sequences between 100k-20Mhz, the first preset frequency is 100 khz, the last preset frequency is 20Mhz, the difference between adjacent preset frequencies is 100k, i.e., f=100k, 200k,300k … M, and the total number of preset frequencies is 200.
Step 2: and (3) signal acquisition: the testers reliably connect the head end and the tail end of the high-voltage power cable 2 by adopting the coaxial double-shielding signal transmission line 4, and the process needs to pay attention to reliable connection among joints so as to prevent attenuation loss of signals. The two ends of the high-voltage power cable 2 are connected with two test signal matching impedances 3 in parallel, and the other ends of the test signal matching impedances 3 are effectively grounded. Because the cable is a lossy transmission line, the transmission signal can be attenuated in the cable propagation process, and waveform signal distortion is caused, so that the matching impedance can reduce waveform distortion and protect a test system. Through the internal transmission of the cable, the detection signals collected and stored by the industrial personal computer and the acquisition card have different amplitudes and phases. The present test method is particularly focused on the phase difference parameter.
Step 3: and (3) signal adjustment: and the two paths of detection signals are effectively filtered through an RL filter circuit according to the optimal resolution and sensitivity requirements of the system, and are further effectively amplified by a preamplifier to obtain two paths of preprocessing signals, and the two paths of preprocessing signals are transmitted to a subsequent signal processing device. This procedure aims at correcting the two detection signals in order to better enable subsequent mathematical processing and computation.
Step 4: and (3) signal processing: displaying the two paths of pre-processed signals subjected to effective filtering and amplifying treatment through a digital filter dual-trace channel, wherein the phase delay of the dual-trace voltage signal in a time domain is set as phi (omega), and the expression is as follows:
；
wherein, the liquid crystal display device comprises a liquid crystal display device,u 1 、u 2 two paths of preprocessing signals representing different frequencies, the initial phases are allThe initial phase difference value isThe two paths of preprocessing signals finally realize double-trace display on a digital oscilloscope in the time domain, and the two paths of preprocessing signals pass through a cross Fourier operation formula:
；
wherein:thereby realizing the digital conversion of the signal time domain and the signal frequency domain; calculating the difference delta of the propagation time of the signal in the cable channeltThereby according to-> L/∆tThe propagation velocity is derived and the propagation velocity,Lfor the total length of the cable to be tested;
through mathematical analysis of all collected frequency-varying signals, wave velocity values of 200 different frequencies corresponding to different frequency signals one by one can be obtained. By drawing a sampling discrete point diagram (shown in fig. 3) of speed versus frequency change in the same plane through drawing software, and fitting each sampling point, an accurate wave speed characteristic conclusion can be obtained.
In the description of the present invention, it should be understood that the terms "head" and "tail" and "one way" and "two way" and the like indicate relative positioning of various major devices based on the drawings, and are merely for convenience in describing the present invention, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present invention.
The foregoing examples merely illustrate certain embodiments of the invention, which are described in greater detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that variations and modifications can be made based on circuit topology or test means without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (9)
1. A detection method for the internal wave velocity characteristic of an alternating current cable is characterized by comprising the following steps: the detection method comprises the following steps:
(1) According to a frequency sweep method, sending a frequency sweep signal to a cable to be tested;
(2) Respectively collecting detection signals and response signals at the head end and the tail end of a cable to be tested, and sequentially carrying out filtering and amplifying treatment to obtain two paths of pretreatment signals;
(3) Performing cross Fourier change processing on the two paths of pre-processed signals to obtain two paths of signal phase difference values, and further obtaining the internal wave speed characteristics of the cable to be tested;
the specific process of the step (3) is as follows: according to two paths of preprocessing signals corresponding to sine sweep signals with different frequencies:
wherein u is 1 、u 2 Two paths of preprocessing signals representing different frequencies, the initial phase is theta 0 The initial phase difference value isThe two paths of preprocessing signals finally realize double-trace display on a digital oscilloscope in the time domain, and the two paths of preprocessing signals pass through a cross Fourier operation formula:
wherein: ΔΦ (ω) =ω·Δt, thereby realizing digital conversion of the signal time domain and the frequency domain; calculating a propagation time difference delta t of the signal in the cable channel, so as to obtain a propagation speed according to v=L/delta t, wherein L is the total length of the cable to be tested; the acquired frequency-variable signals under all preset frequencies are subjected to mathematical analysis, so that different wave speed values corresponding to the signals with different frequencies one by one can be obtained; and drawing a characteristic diagram of the wave speed changing along with the frequency, and obtaining the internal frequency-dependent transmission characteristic of the cable to be tested.
2. The method of claim 1, wherein: the detection method comprises the following steps:
(1) According to a frequency sweep method, a sinusoidal frequency sweep signal is sent to a cable to be tested; the sinusoidal sweep frequency signal is a sinusoidal signal with preset frequency repeatedly scanned within a preset frequency range along with time; the preset frequency range is 100k-20Mhz;
(2) Synchronizing with the sine sweep signals sent in the step (1) at different times, respectively collecting detection signals and response signals at the head end and the tail end of the cable to be tested, and sequentially carrying out filtering and amplifying treatment to obtain two paths of preprocessing signals corresponding to the sine sweep signals with different preset frequencies;
(3) Acquiring wave speed transmission curves corresponding to a plurality of preset frequencies in a preset frequency range according to the sinusoidal sweep signals and the corresponding two paths of preprocessing signals in the step (2) under different frequencies; and performing cross Fourier transform processing on the two corresponding paths of preprocessing signals to obtain corresponding frequency domain phase difference values under different preset frequencies, thereby obtaining the internal frequency-varying transmission characteristics of the cable to be tested.
3. The detection method according to claim 2, wherein: the frequency change mode of the sinusoidal sweep frequency signal in the step (1) is that the output is linearly increased in a preset frequency range; the output modes of the sweep frequency signals with different preset frequencies are continuous output or output in sequence at intervals of preset time length; the preset time period is longer than the sweep period of the sinusoidal sweep signal.
4. A detection method according to claim 3, wherein: and (2) only extracting signals corresponding to the frequency of the sine sweep frequency signal in the detection signals and the response signals when filtering and amplifying the detection signals and the response signals acquired from the head end and the tail end of the cable to be tested in the step (2).
5. The method of claim 4, wherein: the total length of the cable to be tested is 100m-500m.
6. A system for detecting characteristics of wave velocity inside an ac cable, comprising:
the sweep frequency signal generator outputs a sweep frequency signal to the cable to be tested;
the signal acquisition device is used for acquiring two paths of signals at the head end and the tail end of the cable to be tested through a double-shielding coaxial signal transmission line;
the signal adjusting device is used for filtering and amplifying after receiving two paths of signals of the signal acquisition device;
the signal processing device performs cross Fourier transform on the signals processed by the signal adjusting device to obtain two paths of signal frequency domain phase difference values, and further obtains the internal wave speed characteristics of the cable to be tested;
the internal wave velocity characteristic of the cable to be tested is obtained by the following method:
according to two paths of preprocessing signals corresponding to sine sweep signals with different frequencies:
wherein u is 1 、u 2 Two paths of preprocessing signals representing different frequencies, the initial phase is theta 0 The initial phase difference value isThe two paths of preprocessing signals finally realize double-trace display on a digital oscilloscope in the time domain, and the two paths of preprocessing signals pass through a cross Fourier operation formula:
wherein: ΔΦ (ω) =ω·Δt, thereby realizing digital conversion of the signal time domain and the frequency domain; calculating a propagation time difference delta t of the signal in the cable channel, so as to obtain a propagation speed according to v=L/delta t, wherein L is the total length of the cable to be tested; the acquired frequency-variable signals under all preset frequencies are subjected to mathematical analysis, so that different wave speed values corresponding to the signals with different frequencies one by one can be obtained; and drawing a characteristic diagram of the wave speed changing along with the frequency, and obtaining the internal frequency-dependent transmission characteristic of the cable to be tested.
7. The detection system of claim 6, wherein: the signal adjusting device comprises an RL filter and a signal amplifier; the signal acquisition device is connected with the signal processing device through the RL filter, the signal amplifier and the signal processing device in sequence; the signal acquisition device comprises an industrial personal computer and an acquisition card; the head end and the tail end of the cable to be tested are respectively connected with the acquisition card through double-shielding coaxial signal transmission lines; the acquisition card is respectively connected with the industrial personal computer and the sweep frequency signal generator; the industrial personal computer is connected with the RL filter.
8. The detection system of claim 7, wherein: the detection system also comprises two test signal matching impedances; the head end and the tail end of the cable to be tested are respectively connected with one end of the corresponding test signal matching impedance; the other end of the test signal matching impedance is grounded.
9. The detection system of claim 8, wherein: the signal processing device comprises a digital oscilloscope and a signal Fourier transform system; the signal amplifier is connected with the signal Fourier transform system through a digital oscilloscope.
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| 高树国 ; 刘贺晨 ; 范辉 ; 裴少通 ; 刘云鹏 ; 潘瑾 ; 王芷路 ; .考虑波速特性的小波变换模极大值法的电力电缆局部放电定位研究.电网技术.2016,40(07),第2244-2250页. * |
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| CN107064761A (en) | 2017-08-18 |
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