CN116840601A - Method for acquiring power cable model parameters by using crocodile clip test line - Google Patents
Method for acquiring power cable model parameters by using crocodile clip test line Download PDFInfo
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Abstract
The invention relates to a method for acquiring power cable model parameters by using crocodile clip test wires, which comprises the following steps: acquiring scattering parameters of crocodile clamp test wires and a head-end reflection coefficient spectrum of a cable to be tested; and carrying out amplitude calibration on the scattering parameter, correcting amplitude phase distortion of the head-end reflection coefficient spectrum according to the scattering parameter after the amplitude calibration, obtaining a head-end impedance spectrum, and obtaining the power cable model parameter through the head-end impedance spectrum. The invention can obtain accurate model parameters of the cable and eliminate the influence of the electromagnetic reflection at the head end and the spectral amplitude and phase distortion of the reflection coefficient at the head end of the cable on the detection and positioning of the local defects of the cable.
Description
Technical Field
The invention relates to the technical field of power cable model parameters and local defect diagnosis acquisition, in particular to a method for acquiring power cable model parameters by using crocodile clamp test wires.
Background
The power cable is an important device for transmitting and distributing electric energy, is praised as a vessel and a nerve of national economy, and the importance of the cable will be more and more prominent with the further increase of the national economy. In the long-term operation process of the power cable, performance degradation is easy to cause under the comprehensive influence of external environmental factors and human factors, local defects such as water branches, thermal aging, mechanical aging and the like are formed, and the local defects gradually evolve into cable faults along with the increase of operation time, so that the safe and stable operation of the power system is seriously influenced. Therefore, research on detection technology of local defects of the cable has important significance in timely eliminating originating defects of the cable. In general, detection and positioning of a local defect of a cable require that model parameters thereof are obtained in advance, and accuracy of the model parameters directly determines sensitivity of detection and positioning accuracy of the local defect.
The acquisition of the power cable model parameters requires a series of scattering parameters of the cable to be measured in advance, and then the model parameters of the cable are extracted based on the measured data. In general, the scattering parameter of the device under test can be measured more accurately by connecting the device under test to a measuring instrument using a coaxial connector. However, the lateral dimensions of the power cable are large and there is currently no coaxial connector on the market that fits into it. Therefore, a power cable to be tested is typically connected to a measuring instrument using a coaxial connector-to-alligator clip test line (hereinafter referred to as alligator clip test line) that is poorly adapted, and then the scattering parameters of the cable are measured. However, there is a severe impedance mismatch at the alligator clip-to-cable junction, severely affecting the cable scattering parameter measurement accuracy and the acquired model parameter accuracy.
Disclosure of Invention
The invention aims to provide a method for acquiring power cable model parameters by using an alligator clip test line, which can acquire accurate model parameters of a cable, eliminate influence of head-end electromagnetic reflection, and spectral amplitude and phase distortion of a reflection coefficient of the head-end of the cable on detection and positioning of local defects of the cable, and solve difficulties faced by reflection of a signal of the head-end of the cable and phase and amplitude distortion of the reflection coefficient of the head-end of the cable caused by mismatching of impedance of a alligator clip test line and a cable connection point in application.
In order to achieve the above object, the present invention provides the following solutions:
a method of obtaining power cable model parameters using alligator clip test lines, comprising:
acquiring scattering parameters of crocodile clamp test wires and a head-end reflection coefficient spectrum of a cable to be tested;
and carrying out amplitude calibration on the scattering parameter, correcting amplitude phase distortion of the head-end reflection coefficient spectrum according to the scattering parameter after the amplitude calibration, obtaining a head-end impedance spectrum, and obtaining the power cable model parameter through the head-end impedance spectrum.
Optionally, obtaining the scattering parameter of the alligator clip test line and the head end reflection coefficient spectrum of the cable to be tested further includes: acquiring scattering parameters of the cable to be tested;
wherein, the scattering parameters of crocodile clip test line module include: first scattering parameter S 11_eyj Second scattering parameter S 21_eyj And a third scattering parameter S 12_eyj The method comprises the steps of carrying out a first treatment on the surface of the The scattering parameters of the cable to be tested comprise: first scattering parameter S 11_cable And a second scattering parameter S 21_cable 。
Optionally, the obtaining the head-end reflection coefficient spectrum is:
S 11_open ＝S 11_eyj +S 21_eyj ·S 11_cable_open ·S 12_eyj
S 11_short ＝S 11_eyj +S 21_eyj ·S 11_cable_short ·S 12_eyj
wherein S is 11_open The head end reflection coefficient spectrum measured when the cable to be tested is connected with an open circuit load is S 11_eyj 、S 12_eyj 、S 21_eyj Are all scattering parameters of crocodile clamp test line modules, S 11_short The head end reflection coefficient spectrum measured when the cable to be tested is connected with the short-circuit load is S 11_cable_open 、S 11_cable_short And the reflection coefficient spectrums of the head end of the cable terminal to be tested when the cable terminal is in an open-circuit load and a short-circuit load are respectively obtained.
Optionally, performing amplitude calibration on the scattering parameter includes:
obtaining a true first scattering parameter S 11_eyj By the true first scattering parameter S 11_eyj For the second scattering parameter S 21_eyj And the third scattering parameter S 12_eyj And performing amplitude calibration.
Optionally, the true first scattering parameter S is obtained 11_eyj The method of (1) is as follows:
wherein S is 11_eyj Is the true first scattering parameter, S 11_open The head end reflection coefficient spectrum measured when the cable to be tested is connected with an open circuit load is S 11_short And the head-end reflection coefficient spectrum measured when the cable to be tested is connected with the short-circuit load is measured.
Optionally by means of said true first scattering parameter S 11_eyj For the second scattering parameter S 21_eyj And the third scattering parameter S 12_eyj The method for carrying out amplitude calibration comprises the following steps:
for the second scattering parameter S 21_eyj The method for carrying out amplitude calibration comprises the following steps:
wherein, |S 21_eyj The I is the second scattering parameter S after calibration 21_eyj Amplitude of S 21_eyj_m 、S 11_eyj_m The scattering parameters of the crocodile clamp test line modules are actually measured, S 11_eyj Is a true first scattering parameter;
for the third scattering parameter S 12_eyj Performing amplitude correctionThe quasi-method comprises the following steps:
wherein, |S 12_eyj The I is the third scattering parameter S after calibration 12_eyj Amplitude of S 12_eyj_m 、S 22_eyj_m The scattering parameters of the crocodile clamp test line modules are actually measured, S 11_eyj Is the true first scattering parameter.
Optionally, correcting the amplitude phase distortion of the head-end reflection coefficient spectrum according to the scattering parameter after the amplitude calibration includes:
wherein S is 11_cable_open Head-end reflection coefficient spectrum S for amplitude phase distortion correction when cable to be tested is connected with open circuit load 11_open The head end reflection coefficient spectrum measured when the cable to be tested is connected with an open circuit load is S 11_eyj Is the true first scattering parameter, S 21_eyj S is the second scattering parameter after the amplitude calibration 12_eyj S is the third scattering parameter after the amplitude calibration 11_cable_short Head-end reflection coefficient spectrum S for amplitude phase distortion correction when cable to be tested is connected with short-circuit load 11_short And the head-end reflection coefficient spectrum measured when the cable to be tested is connected with the short-circuit load is measured.
Optionally, the method for obtaining the head-end impedance spectrum includes:
wherein Z is 11_cable_open The head end impedance spectrum measured when the cable to be tested is connected with the open circuit load S 11_cable_open Head-end reflection coefficient spectrum Z measured when cable to be tested for amplitude phase distortion correction is connected with open circuit load 11_cable_short The head end impedance spectrum measured when the cable to be tested is connected with the short-circuit load S 11_cable_short Head-end reflection coefficient spectrum Z measured when cable to be tested for amplitude phase distortion correction is connected with short-circuit load s For measuring the impedance in the instrument.
Optionally, the method for obtaining the power cable model parameters includes:
wherein l is the length of the cable to be tested, gamma is the propagation coefficient of the cable, atanh is the inverse hyperbolic tangent function, Z 11_cable_short Head-end impedance spectrum Z measured when short-circuit load is connected to cable to be tested 11_cable_open And (3) measuring the head-end impedance spectrum when the cable to be measured is connected with an open-circuit load.
Optionally, the method further comprises: and positioning the cable terminal by combining the power cable model parameters with a positioning algorithm.
The beneficial effects of the invention are as follows:
the method fully considers the structural size of the power cable, realizes the acquisition of the power cable model parameters by using the common crocodile clip test wire, fully discusses the problems existing when the crocodile clip test wire is used for measuring the power cable scattering parameters, and provides an effective solution, and the method for acquiring the power cable model parameters is simple and has higher accuracy;
according to the invention, the crocodile clamp test line is used for connecting the measuring instrument and the cable to be measured, the scattering parameter of the power cable is measured, the model parameter of the cable is extracted from the measured data, data support can be provided for the detection and positioning of the local defect of the cable, and the influences such as head electromagnetic reflection, defect peak value reduction and positioning position deviation when the detection and positioning of the local defect of the power cable are performed based on the crocodile clamp test line are eliminated.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a power cable model parameter acquisition system according to an embodiment of the present invention;
FIG. 2 is a schematic view of the scattering of signals transmitted to the crocodile clip test line according to an embodiment of the present invention;
FIG. 3 is a flow chart of a method for obtaining power cable model parameters using alligator clip test lines according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a test line for a coaxial connector to crocodile clip according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of the phase coefficient test results according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of the attenuation coefficient test results of an embodiment of the present invention;
fig. 7 is a schematic diagram of a positioning result of a 110kV high-voltage power cable terminal according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
At present, when the crocodile clamp test wire is used for acquiring power cable model parameters and carrying out local defect detection and positioning of a power cable, the crocodile clamp test wire and a connection point of the crocodile clamp test wire and the power cable have serious impedance mismatch, so that cable scattering parameter measurement, model parameter acquisition and local defect positioning are seriously affected. The invention mainly solves the difficulties faced by the signal reflection at the head end of the cable caused by the mismatching of the impedance of the alligator clip test wire and the cable connection point and the distortion of the spectral phase and amplitude of the reflection coefficient of the head end of the cable caused by the alligator clip test wire.
As shown in fig. 1, the power cable model parameter acquisition system consists of an upper computer, a measuring instrument, an alligator clip test line, a cable to be tested and a cable terminal load. The upper computer establishes a communication channel with the measuring instrument through the communication bus, can control the measuring instrument to measure data and upload the data to the upper computer, integrates a processing program of the measuring data in the upper computer, and can extract model parameters of the cable from the measuring data. One end of the crocodile clip test wire is a radio frequency coaxial connector, and the other end is a positive crocodile clip outgoing wire and a negative crocodile clip outgoing wire of the connector. The standard cable is a port outgoing line provided for the measuring instrument, and the influence of the standard cable in the whole measuring process can be ignored after the instrument is calibrated. When the scattering parameters are measured, one end of the standard cable is connected with a Port1 Port of the measuring instrument, the other end of the standard cable is connected with a coaxial connector end of the crocodile clamp test line, positive and negative crocodile clamp terminals of the latter are respectively connected with a core wire and an outer conductor of the power cable to be measured, the cable terminal to be measured is connected with an open-circuit load and a short-circuit load, the scattering parameters of the cable to be measured under the two loads are measured, and then the model parameters of the cable are obtained through an upper computer processing program.
As shown in fig. 3, the invention discloses a method for acquiring parameters of a power cable model by using crocodile clip test wires:
after the high-frequency sweep signal output by the measuring instrument is transmitted to the crocodile clamp test line by a standard cable, the transmission and reflection conditions are shown as figure 2, a 1 、b 1 An incident signal and a reflected signal of the crocodile clip test line module respectively, a 2 、b 2 Respectively represent the electric power to be measuredIncident and reflected signals of the cable module S 11_eyj 、S 21_eyj 、S 12_eyj For crocodile clip test line module scattering parameter S 11_cable 、S 21_cable And the scattering parameter of the power cable module to be tested. According to the transmission line theory and the definition of the scattering parameters, the following can be obtained:
a 2 ＝a 1 ·S 21_eyj (1)
b 2 ＝a 2 ·S 11_cable ＝a 1 ·S 21_eyj ·S 11_cable (2)
b 1 ＝a 1 ·S 11_eyj +b 2 ·S 12_eyj ＝a 1 ·S 11_eyj +a 1 ·S 21_eyj ·S 11_cable ·S 12_eyj (3)
the measured head-end reflectance spectrum is:
the cable terminal load only affects the scattering parameter of the power cable module, and when the cable terminal to be tested is respectively connected with an open circuit load and a short circuit load, the reflection coefficient spectrum of the head end of the power cable module to be tested is respectively recorded as S 11_cable_open 、S 11_cable_short The measured head-end reflectance spectra are respectively:
S 11_open ＝S 11_eyj +S 21_eyj ·S 11_cable_open ·S 12_eyj (5)
S 11_short ＝S 11_eyj +S 21_eyj ·S 11_cable_short ·S 12_eyj (6)
wherein S is 11_open The head end reflection coefficient spectrum measured when the cable to be tested is connected with an open circuit load is S 11_eyj 、S 12_eyj 、S 21_eyj Are all scattering parameters of crocodile clamp test line modules, S 11_short The head end reflection coefficient spectrum measured when the cable to be tested is connected with the short-circuit load is S 11_cable_open 、S 11_cable_short And the reflection coefficient spectrums of the head end of the cable terminal to be tested when the cable terminal is in an open-circuit load and a short-circuit load are respectively obtained.
S of crocodile clip test line module measured by using measuring instrument 11_eyj Is usually inaccurate, resulting in measured S 12_eyj And S is 21_eyj Is inaccurate in magnitude, so that an accurate S needs to be obtained 11_eyj And to S 12_eyj And S is 21_eyj The amplitude is calibrated. For the same section of cable to be tested, there is S 11_cable_open ＝-S 11_cable_short Thus, S of the crocodile clip test line module can be obtained by the formula (7) 11_eyj S is then calibrated according to equation (8) and equation (9) 12_eyj And S is 21_eyj Amplitude values.
Wherein S is 11_eyj Is the true first scattering parameter, S 11_open The head end reflection coefficient spectrum measured when the cable to be tested is connected with an open circuit load is S 11_short And the head-end reflection coefficient spectrum measured when the cable to be tested is connected with the short-circuit load is measured.
Wherein, |S 21_ e yj The I is the second scattering parameter S after calibration 21_eyj Amplitude of S 21_eyj_m 、S 11_eyj_m The scattering parameters of the crocodile clamp test line modules are actually measured, S 11_eyj Is a true first scattering parameter; s 12_eyj The I is the third scattering parameter S after calibration 12_eyj Amplitude of S 12_eyj_m 、S 22_eyj_m The scattering parameters of the crocodile clamp test line modules are actually measured, S 11_eyj Is the true first scattering parameter.
In the above, S 11_eyj_m 、S 21_eyj_m 、S 12_eyj_m 、S 22_eyj_m The scattering parameters of the wire modules were tested for the measured crocodile clips.
The power cable module head-end reflection coefficient spectra shown in the formulas (10) and (11) can be further obtained by deducting the formulas (5), (6), (7), (8) and (9). Equation right numerator minus S 11_eyj Indicating elimination of electromagnetic reflection due to alligator clip test line to cable junction impedance mismatch divided by (S 21_eyj ·S 12_eyj ) The method is used for correcting amplitude phase distortion of the reflectance spectrum of the cable to be measured, which is caused by crocodile clamp test lines in measured data.
Wherein S is 11_cable_open Head-end reflection coefficient spectrum S for amplitude phase distortion correction when cable to be tested is connected with open circuit load 11_open The head end reflection coefficient spectrum measured when the cable to be tested is connected with an open circuit load is S 11_eyj Is the true first scattering parameter, S 21_eyj S is the second scattering parameter after the amplitude calibration 12_eyj S is the third scattering parameter after the amplitude calibration 11_cable_short Head-end reflection coefficient spectrum S for amplitude phase distortion correction when cable to be tested is connected with short-circuit load 11_short And the head-end reflection coefficient spectrum measured when the cable to be tested is connected with the short-circuit load is measured.
The head-end impedance spectrum is further calculated as:
wherein Z is 11_cable_open The head end impedance spectrum measured when the cable to be tested is connected with the open circuit load S 11_cable_open Head-end reflection coefficient spectrum Z measured when cable to be tested for amplitude phase distortion correction is connected with open circuit load 11_cable_short The head end impedance spectrum measured when the cable to be tested is connected with the short-circuit load S 11_cable_short Head-end reflection coefficient spectrum Z measured when cable to be tested for amplitude phase distortion correction is connected with short-circuit load s For measuring the impedance in the instrument.
In the formula (12) and the formula (13), Z s The internal impedance of the measuring instrument is generally 50 omega, and the model parameters of the power cable can be further calculated as follows:
wherein l is the length of the cable to be tested, gamma is the propagation coefficient of the cable, atanh is the inverse hyperbolic tangent function, Z 11_cable_short Head-end impedance spectrum Z measured when short-circuit load is connected to cable to be tested 11_cable_open And (3) measuring the head-end impedance spectrum when the cable to be measured is connected with an open-circuit load.
In the formula (14), l is the length of the cable to be tested, gamma is the propagation coefficient of the cable, the real part is called an attenuation coefficient, the imaginary part is called a phase coefficient and the phase coefficient is used for calculating the wave velocity of the cable, and each model of cable has specific model parameters.
The effect of the invention is verified through experiments, the invention adopts the experimental arrangement shown in figure 1, the upper computer is a PC, the communication bus is a segment of miniUSB data line, the measuring instrument adopts a vector network analyzer, the standard cable is a self-matching cable of the analyzer, the crocodile clip test line adopts a 1-meter long radio frequency N male connector to be converted into a crocodile clip test line, the cable to be tested is a coaxial cable with the length of 29.88 meters, one end of the cable to be tested is provided with a core wire and an outgoing line of a shielding layer, the crocodile clip is convenient to clamp, and the other end of the cable to be tested is provided with a coaxial connector joint for connecting open-circuit and short-circuit loads.
The vector network analyzer is controlled by the upper computer to measure the required scattering parameters, and the measured data are processed by adopting the method provided by the invention, so that the test results are shown in fig. 5 and 6. Fig. 5 shows calculated phase coefficients, which are seen to be substantially identical to the theoretical values. Fig. 6 shows the calculated attenuation coefficient of the cable to be tested, and it can be observed that the calculated value has ripple, and the fitting value obtained by fitting the calculated value is basically consistent with the theoretical value. The test results verify the effectiveness of the present invention.
Through test verification, the method can eliminate the influence of electromagnetic reflection caused by impedance mismatch between the crocodile clip test wire and the power cable on the detection and positioning of the local defects of the cable. The test configuration is shown in fig. 1, and the specific implementation method is similar to that of the calculation example 1, except that the cable to be tested in the calculation example is a 110kV high-voltage power cable with the length of 117 meters. Firstly, the propagation coefficient of the cable, namely the model parameter of the cable, is obtained according to the method provided by the invention, and then the terminal position of the cable is positioned, and the positioning result is shown in figure 7. The ordinate in the figure represents the cable local defect diagnosis function, and since the processed data is the data measured when the cable terminal is open, the theoretical value of the reflection coefficient is 1. The Normal group curve represents a positioning result obtained by directly processing data measured by the vector network analyzer, because impedance mismatch exists between the crocodile clamp test line and the power cable, signal reflection occurs at the impedance mismatch point, and as can be seen from the positioning curve, a reflection peak exists at the head end of the cable, and the terminal reflection peak is smaller than 1, and the peak position is 117.39 meters and is larger than the actual cable length. The PM group curve represents a positioning result obtained by eliminating impedance mismatch between the crocodile clamp test line and the cable by using the method provided by the invention, and the figure shows that the positioning curve has no head end reflection, the peak value of the terminal reflection is 0.999963, the position is 117.06 meters close to the theoretical value of 1, and the relative error between the positioning curve and the actual cable length is 0.05%.
The positioning algorithm comprises the following steps:
carrying out matched filtering on the acquired reflection coefficient spectrum, and firstly constructing a matched filter set:
wherein H is a matched filter, x j Is the j-th space distance point, f i For the ith frequency point, e is a natural constant, N is the total number of frequency points, M is the total number of spatial distance points, and gamma is the acquired cable propagation coefficient.
After the reflection coefficient spectrum is matched and filtered, the reflection coefficient spectrum is accumulated along the frequency dimension and divided by the total number of frequency points to obtain a diagnosis function of the cable local defect:
wherein RC (x j ) Is a cable fault diagnosis function.
The cable fault diagnosis function is obtained through the processing, the peak value in the function curve represents the local defect of the cable, the peak value position is the position of the local defect, and the peak value size is the reflection coefficient of the local defect. The extent of the cable local defect can be assessed on the basis of the reflection coefficient.
As shown in fig. 4, the coaxial connector turns the alligator clip test line; vector network analyzer: the vector network analyzer is mainly used for measuring scattering parameters of a cable system to be measured, a Part1 port of the vector network analyzer is connected with a standard cable, the vector network analyzer is connected with an upper computer through a miniUSB data line, and then data are measured.
The upper computer: the upper computer is connected with the vector network analyzer through a miniUSB data line, and has two main functions, namely, the upper computer sends an instruction to the vector network analyzer to control the vector network analyzer to measure the S parameter of the cable system to be tested and read the data into the upper computer for storage; and secondly, processing the measurement data to obtain model parameters of the cable.
The above embodiments are merely illustrative of the preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but various modifications and improvements made by those skilled in the art to which the present invention pertains are made without departing from the spirit of the present invention, and all modifications and improvements fall within the scope of the present invention as defined in the appended claims.
Claims (10)
1. A method for obtaining power cable model parameters using alligator clip test lines, comprising:
acquiring scattering parameters of crocodile clamp test wires and a head-end reflection coefficient spectrum of a cable to be tested;
and carrying out amplitude calibration on the scattering parameter, correcting amplitude phase distortion of the head-end reflection coefficient spectrum according to the scattering parameter after the amplitude calibration, obtaining a head-end impedance spectrum, and obtaining the power cable model parameter through the head-end impedance spectrum.
2. The method of obtaining parameters of a power cable model using alligator clip test lines according to claim 1, wherein obtaining scattering parameters of alligator clip test lines and a head-end reflectance spectrum of a cable under test further comprises: acquiring scattering parameters of the cable to be tested;
wherein, the scattering parameters of crocodile clip test line module include: first scattering parameter S 11_eyj Second scattering parameter S 21_eyj And a third scattering parameter S 12_eyj The method comprises the steps of carrying out a first treatment on the surface of the The scattering parameters of the cable to be tested comprise: first scattering parameter S 11_cable And a second scattering parameter S 21_cable 。
3. The method of obtaining parameters of a power cable model using alligator clip test lines of claim 1, wherein obtaining the head-end reflectance spectrum is:
S 11_open ＝S 11_eyj +S 21_eyj ·S 11_cable_open ·S 12_eyj
S 11_short ＝S 11_eyj +S 21_eyj ·S 11_cable_short ·S 12_eyj
wherein S is 11_open The head end reflection coefficient spectrum measured when the cable to be tested is connected with an open circuit load is S 11_eyj 、S 12_eyj 、S 21_eyj Are all scattering parameters of crocodile clamp test line modules, S 11_short The head end reflection coefficient spectrum measured when the cable to be tested is connected with the short-circuit load is S 11_cable_open 、S 11_cable_short And the reflection coefficient spectrums of the head end of the cable terminal to be tested when the cable terminal is in an open-circuit load and a short-circuit load are respectively obtained.
4. The method of obtaining power cable model parameters using alligator clip test lines of claim 2, wherein amplitude calibrating the scattering parameters comprises:
obtaining a true first scattering parameter S 11_eyj By the true first scattering parameter S 11_eyj For the second scattering parameter S 21_eyj And the third scattering parameter S 12_eyj And performing amplitude calibration.
5. The method for obtaining parameters of a power cable model using alligator clip test lines as claimed in claim 4, wherein the actual first scattering parameter S is obtained 11_eyj The method of (1) is as follows:
wherein S is 11_eyj Is the true first scattering parameter, S 11_open The head end reflection coefficient spectrum measured when the cable to be tested is connected with an open circuit load is S 11_short And the head-end reflection coefficient spectrum measured when the cable to be tested is connected with the short-circuit load is measured.
6. The method for obtaining parameters of a power cable model using alligator clip test lines according to claim 4, wherein the real first scattering parameters S 11_eyj For the second scattering parameter S 21_eyj And the third scattering parameter S 12_eyj The method for carrying out amplitude calibration comprises the following steps:
for the second scattering parameter S 21_eyj The method for carrying out amplitude calibration comprises the following steps:
wherein, |S 21_eyj The I is the second scattering parameter S after calibration 21_eyj Amplitude of S 21_eyj_m 、S 11_eyj_m The scattering parameters of the crocodile clamp test line modules are actually measured, S 11_eyj Is a true first scattering parameter;
for the third scattering parameter S 12_eyj The method for carrying out amplitude calibration comprises the following steps:
wherein, |S 12_eyj The I is the third scattering parameter S after calibration 12_eyj Amplitude of S 12_eyj_m 、S 22_eyj_m The scattering parameters of the crocodile clamp test line modules are actually measured, S 11_eyj Is the true first scattering parameter.
7. The method of claim 1, wherein correcting the amplitude phase distortion of the head-end reflectance spectrum based on the amplitude calibrated scattering parameter comprises:
wherein S is 11_cable_open Head-end reflection coefficient spectrum S for amplitude phase distortion correction when cable to be tested is connected with open circuit load 11_open The head end reflection coefficient spectrum measured when the cable to be tested is connected with an open circuit load is S 11_eyj Is the true first scattering parameter, S 21_eyj S is the second scattering parameter after the amplitude calibration 12_eyj S is the third scattering parameter after the amplitude calibration 11_cable_short Head-end reflection coefficient spectrum S for amplitude phase distortion correction when cable to be tested is connected with short-circuit load 11_short And the head-end reflection coefficient spectrum measured when the cable to be tested is connected with the short-circuit load is measured.
8. The method for obtaining parameters of a power cable model using alligator clip test lines according to claim 1, wherein the method for obtaining the head-end impedance spectrum is:
wherein Z is 11_cable_open The head end impedance spectrum measured when the cable to be tested is connected with the open circuit load S 11_cable_open Head-end reflection coefficient spectrum Z measured when cable to be tested for amplitude phase distortion correction is connected with open circuit load 11_cable_short The head end impedance spectrum measured when the cable to be tested is connected with the short-circuit load S 11_cable_short Head-end reflection coefficient spectrum Z measured when cable to be tested for amplitude phase distortion correction is connected with short-circuit load s For measuring the impedance in the instrument.
9. The method of obtaining power cable model parameters using alligator clip test lines of claim 1, wherein the method of obtaining the power cable model parameters is:
wherein l is the length of the cable to be tested,gamma is the propagation coefficient of the cable, atanh is the inverse hyperbolic tangent function, Z 11_cable_short Head-end impedance spectrum Z measured when short-circuit load is connected to cable to be tested 11_cable_open And (3) measuring the head-end impedance spectrum when the cable to be measured is connected with an open-circuit load.
10. The method of obtaining power cable model parameters using alligator clip test lines of claim 1, further comprising: and positioning the cable terminal by combining the power cable model parameters with a positioning algorithm.
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