CN114414960A - Cable evaluation device and method based on pulse signal bidirectional propagation coefficient - Google Patents
Cable evaluation device and method based on pulse signal bidirectional propagation coefficient Download PDFInfo
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- CN114414960A CN114414960A CN202210041083.3A CN202210041083A CN114414960A CN 114414960 A CN114414960 A CN 114414960A CN 202210041083 A CN202210041083 A CN 202210041083A CN 114414960 A CN114414960 A CN 114414960A
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- 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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Abstract
The invention discloses a cable evaluation device and method based on pulse signal bidirectional propagation coefficient, comprising a signal generation system, a cable model and a measurement system; the pulse signal calibrator is connected with the middle of the cable and is used for generating a pulse signal with a certain charge amount; the two ends of the cable are respectively connected with the coaxial cable and connected with an oscilloscope in the measuring system, and pulse signals at the first end and the last end of the cable are collected; the oscilloscope in the measuring system is connected with the computer and the network analyzer, and the computer and the network analyzer are used for processing the pulse signals at the first end and the last end of the cable so as to obtain the actual propagation coefficient of the pulse signals in the cable. And comparing with a theoretical value to obtain the insulation uniform distribution coefficient of the cable, thereby carrying out state evaluation on the cable. The invention obtains the insulation uniform distribution coefficient of the cable based on the propagation coefficient of the pulse signal in the cable in two-way transmission, and can effectively evaluate the running state and the insulation aging degree of the cable.
Description
Technical Field
The invention relates to the technical field of power cable state monitoring, in particular to a cable evaluation device and method based on a pulse signal bidirectional propagation coefficient.
Background
The power cable is the main equipment for transmitting electric energy by a power grid, and the power cable has the advantages of safety, reliability, concealment, durability, small influence of weather, benefit for beautifying city layout and the like, and particularly, along with the use of a new cable technology, the cost of the cable is gradually reduced, and the power cable is more and more widely applied.
However, power cables are prone to defects during manufacture and transportation. And because the environment of the power cable is very complicated, the power cable is easily damaged by being in a dark and humid environment underground for a long time, and the stability and the safety of a power transmission network are affected. The semiconductor layer and the insulating layer of the power cable can enable the pulse signal to generate strong attenuation, so that the running state of the power cable can be evaluated by analyzing the transmission characteristic of the pulse signal in the cable, and the method has important significance for early warning of fault hidden danger of the power cable and improvement of stable running capability of a power system.
Disclosure of Invention
The invention provides a cable evaluation device and method based on a pulse signal bidirectional propagation coefficient, which can effectively measure the actual propagation coefficient of a pulse signal in a cable by a device with a simple structure, obtain the insulation distribution coefficient of the cable according to the ratio of the actual propagation coefficient to the theoretical propagation coefficient, reflect the insulation condition and the running state of the cable and are beneficial to predicting the service life of the cable.
In order to achieve the purpose, the cable evaluation device and method based on the pulse signal bidirectional propagation coefficient comprise a single-core cable model, a signal generation system and a measurement system;
the single-core cable model, the signal generating system and the measuring system are connected in sequence.
The single-core cable model sequentially comprises a cable sheath, a shielding layer, an outer semiconductor layer, an insulating layer, an inner semiconductor layer and a conductor layer from outside to inside.
Two ends of the single-core cable model are respectively connected with the coaxial cables, the middle part of the single-core cable model is connected with the pulse signal calibrator, and two ends of the single-core cable model are connected with the oscilloscope in the measurement system;
the signal generating system consists of a pulse signal calibrator capable of generating a pulse signal and is connected in the middle of the single-core cable model;
the measuring system consists of an oscilloscope, a computer and a network analyzer. The oscillograph is connected with two ends of the cable respectively, collects signals sent by the pulse signal calibrator and pulse signals at two ends of the cable, and is connected with a computer and a network analyzer which are both measurement systems.
Further, the pulse signal calibrator in the middle of the cable can generate pulse signals with different charge quantities, and the calculation formula is as follows:
wherein: u is the peak voltage of the pulse signal, r1Is the radius of the conductor layer (106), r2The radius of the insulating layer (104), ε is the dielectric constant of the insulating material, and k is the proportionality coefficient, which is 2.82.
A cable evaluation method based on pulse signal bidirectional propagation coefficients specifically comprises the following steps:
and starting a pulse signal calibrator of the system, giving pulse signal excitation with a certain electric charge quantity in the middle of the cable, and acquiring output signals of the head end and the tail end of the cable by using an oscilloscope respectively.
And when the output signal is acquired, analyzing and processing the output signal through a computer and a network analyzer which are connected with the oscilloscope.
Calculating the actual propagation coefficient gamma of the pulse signal in the cable1、γ2The formula is as follows:
wherein: l is the cable length, UojFor outputting signals, UinIs the input signal.
Further, in step a, according to the formula
Determining the charge emitted by the pulse signal calibrator;
further, in step b, the time domain result obtained from the oscilloscope is converted into the frequency domain form by using Fourier transform
Further, solving the theoretical propagation coefficient gamma of the pulse signal in the cable0Determining R, L, C, G primary parameters of the single-core cable model:
the solving formula of the resistance R is
ω＝2πf
Wherein: mu.s0Is a vacuum permeability, mucoIs the permeability, σ, of the conductorcoIs the conductivity of the conductor and f is the signal frequency.
The solving formula of the inductance L is as follows:
when solving the capacitance C, the inner semiconductor layer (105), the insulating layer (104) and the outer semiconductor layer (103) need to be solved respectively, and the formula is as follows:
wherein: epsilonx(omega) is the dielectric constant, epsilon, of the respective layer medium0Is the dielectric constant in vacuum.
The capacitance value of the cable can be obtained according to the capacitance values of all layers, and the formula is as follows:
wherein: csc1Is an inner halfCapacitance of the conductor layer (105), Csc2Is the capacitance of the outer semiconductor layer (103), CinsIs the capacitance of the insulating layer (104).
The conductance is calculated as:
wherein: dsc1Is the thickness of the inner semiconductor layer (105), dinsIs the thickness of the insulating layer (104), dsc2Is the thickness of the outer semiconductor layer (103), sigmainsIs the insulation layer conductivity.
Theoretical propagation coefficient gamma of pulse signal in two-way propagation in cable0Comprises the following steps:
further, calculating the insulation uniform distribution coefficient P of the cablejThe calculation formula is as follows:
according to insulation uniform distribution coefficient PjThe insulation condition and the running state of the cable can be evaluated: when P is more than or equal to 0.9jWhen the insulation state is less than or equal to 1.2, the insulation condition of the cable is better, and the running state is stable; when P is presentj>1.2 or Pj<When 0.9, the insulation of the cable is seriously aged and the running state is unstable.
Compared with the prior art, the cable evaluation device based on the pulse signal bidirectional propagation coefficient is provided with a single-core cable model, a signal generation system and a measurement system, and a pulse signal calibrator is used for sending out a pulse signal to simulate the running condition of a power cable when a partial discharge phenomenon occurs. The system is simplified, the system is closer to the actual working condition, the measurement accuracy is guaranteed, signals at two ends of a single-core cable are measured through an oscilloscope, a PC (personal computer) end is used for carrying out frequency domain analysis on the measured signals, the propagation coefficient of the signals is determined, the propagation coefficient of the signals is compared with a theoretical calculated value, the insulation uniform distribution coefficient of the cable is obtained, reference is made for evaluating the insulation performance and the aging condition of the cable, and the method is favorable for predicting the service life of the cable
Drawings
FIG. 1 is a general profile of a measuring device according to the present invention;
FIG. 2 is a flow chart of a measurement method of the present invention;
in the figure:
1. power cable model, 2, signal generation system, 3, measurement system, 101, cable sheath, 102, shielding layer, 103, outer semiconductor layer, 104, insulating layer, 105, inner semiconductor layer, 106, conductor layer, 201, pulse signal calibrator, 301, oscilloscope, 302, network analyzer, 303, computer
Detailed Description
The invention will be further explained with reference to the drawings
As shown in fig. 1, a cable evaluation device and method based on pulse signal bidirectional propagation coefficient includes a single-core cable model 1, a signal generation system 2, and a measurement system 3;
the single-core cable model 1, the signal generating system 2 and the measuring system 3 are connected in sequence.
The single-core cable model sequentially comprises a cable sheath 101, a shielding layer 102, an outer semiconductor layer 103, an insulating layer 104, an inner semiconductor layer 105 and a conductor layer 106 from outside to inside.
Two ends of the single-core cable model 1 are respectively connected with a coaxial cable, the middle part of the single-core cable model is connected with a pulse signal calibrator 201, and two ends of the single-core cable model are connected with an oscilloscope 301 in the measurement system 3;
the signal generating system is composed of a pulse signal calibrator 201 which can generate pulse signals and is connected in the middle of the single-core cable model 1;
the measuring system 3 consists of an oscilloscope 301, a computer 302 and a network analyzer 303;
the oscilloscope 301 is connected to both ends of the cable, collects the signal from the pulse signal calibrator 201 and the pulse signal from both ends of the cable, and is connected to the computer 302 and the network analyzer 303, which are both the measurement system 3.
Further, the pulse signal calibrator 201 in the middle of the cable can generate pulse signals with different charge amounts, and the calculation formula is as follows:
wherein: u is the peak voltage of the pulse signal, r1Is the radius of the conductor layer (106), r2The radius of the insulating layer (104), ε is the dielectric constant of the insulating material, and k is the proportionality coefficient, which is 2.82.
A cable evaluation method based on pulse signal bidirectional propagation coefficients specifically comprises the following steps:
the pulse signal calibrator 201 of the system is started, pulse signal excitation with a certain charge amount is given out in the middle of the cable, and output signals of the head end and the tail end of the cable are collected by an oscilloscope 301 respectively.
While the output signal is collected, the output signal is analyzed and processed by a computer 302 and a network analyzer 303 connected to the oscilloscope 301.
Calculating the actual propagation coefficient gamma of the pulse signal in the cable1、γ2The formula is as follows:
wherein: l is the cable length, UojFor outputting signals, UinIs the input signal.
Further, in step a, according to the formula
Determining the charge emitted by the pulse signal calibrator 201;
further, in step b, the time domain result obtained in the oscilloscope 301 is converted into a frequency domain form by fourier transform;
further, solving for the pulse signal at thisTheoretical propagation coefficient gamma in cable0Determining R, L, C, G primary parameters of the single-core cable model 1:
the solving formula of the resistance R is
ω＝2πf
Wherein: mu.s0Is a vacuum permeability, mucoIs the permeability, σ, of the conductorcoIs the conductivity of the conductor and f is the signal frequency.
The solving formula of the inductance L is as follows:
when solving the capacitance C, the inner semiconductor layer (105), the insulating layer (104) and the outer semiconductor layer (103) need to be solved respectively, and the formula is as follows:
wherein: epsilonx(omega) is the dielectric constant, epsilon, of the respective layer medium0Is the dielectric constant in vacuum.
The capacitance value of the cable can be obtained according to the capacitance values of all layers, and the formula is as follows:
wherein: csc1Is the capacitance of the inner semiconductor layer (105), Csc2Is the capacitance of the outer semiconductor layer (103), CinsIs the capacitance of the insulating layer (104).
The conductance is calculated as:
wherein: dsc1Is the thickness of the inner semiconductor layer (105), dinsIs the thickness of the insulating layer (104), dsc2Is the thickness of the outer semiconductor layer (103), sigmainsIs the insulation layer conductivity.
Theoretical propagation coefficient gamma of pulse signal in two-way propagation in cable0Comprises the following steps:
further, calculating the insulation uniform distribution coefficient P of the cablejThe calculation formula is as follows:
according to insulation uniform distribution coefficient PjThe insulation condition and the running state of the cable can be evaluated: when P is more than or equal to 0.9jWhen the insulation state is less than or equal to 1.2, the insulation condition of the cable is better, and the running state is stable; when P is presentj>1.2 or Pj<When 0.9, the insulation of the cable is seriously aged and the running state is unstable.
Example (b):
taking an AXCE-F14/24kV1X150/25LT cable as an example, the cable length is 10m, and the cable sheath thickness db2mm, outer semiconductor layer thickness dsc20.5mm, thickness d of insulating layerins3.5mm, inner semiconductor layer thickness dsc10.35mm and the radius r of the conductor layer1The experimental procedure, 6.4mm, comprises the following steps:
1) generating a partial discharge signal with a charge amount of 100pc by using a partial discharge calibrator, wherein the voltage amplitude of the partial discharge signal is 64 mv;
2) acquiring an output signal at the tail end of the cable by using an oscilloscope, and carrying out Fourier transform on the output signal by using a computer and a network analyzer;
3) determining the actual propagation coefficient gamma of the input signal in the cable by analyzing the ratio of the signal to the output signal1＝0.21+j7.1，γ2＝0.25+j7.2
4) The theoretical propagation coefficient gamma of the signal in the cable can be obtained by modeling the cable, obtaining the primary parameter R, L, C, G of the cable and obtaining the theoretical propagation coefficient gamma of the signal in the cable0＝0.24+j7.3；
5) The insulation uniform distribution coefficient P of the cable can be obtained according to a formula1＝0.9725，P2The insulation at both ends of the cable was good 0.986.
According to the technical scheme, the invention provides the cable evaluation device and method based on the pulse signal bidirectional propagation coefficient, and the insulation uniform distribution parameter of the cable is calculated by comparing the theoretical propagation coefficient and the actual propagation coefficient of the partial discharge signal in the cable, so that the insulation aging degree of the cable is evaluated, and the operation state of the cable is favorably predicted. In the above embodiments, the present invention is described only by way of example, but those skilled in the art, after reading the present patent application, may make various modifications to the present invention without departing from the spirit and scope of the present invention.
Claims (6)
1. A cable assessment device and method based on pulse signal two-way propagation coefficient comprises a single-core cable model (1), a signal generation system (2) and a measurement system (3);
the single-core cable model (1), the signal generating system (2) and the measuring system (3) are sequentially connected;
the single-core cable model sequentially comprises a cable sheath (101), a shielding layer (102), an outer semiconductor layer (103), an insulating layer (104), an inner semiconductor layer (105) and a conductor layer (106) from outside to inside;
two ends of the single-core cable model (1) are respectively connected with a coaxial cable, and the first end and the last end of the single-core cable model are both connected with an oscilloscope (301) in the measuring system (3);
the signal generating system is composed of a pulse signal calibrator (201) capable of generating a pulse signal and is connected to the middle of the single-core cable model (1);
the measuring system (3) consists of an oscilloscope (301), a computer (302) and a network analyzer (303);
the wave filter (301) is respectively connected with two ends of the cable, collects signals sent by the pulse signal calibrator (201) and pulse signals at two ends of the cable, and is connected with a computer (302) and a network analyzer (303) which are both used as a measuring system (3).
2. The cable assessment device and method based on the bidirectional propagation coefficient of the pulse signal as claimed in claim 1, wherein the pulse signal calibrator (201) at the head end of the cable can generate pulse signals with different charge amounts, and the calculation formula is:
wherein: u is the peak voltage of the pulse signal, r1Is the radius of the conductor layer (106), r2The radius of the insulating layer (104), ε is the dielectric constant of the insulating material, and k is the proportionality coefficient, which is 2.82.
3. A cable evaluation method based on pulse signal bidirectional propagation coefficients specifically comprises the following steps:
a. a pulse signal calibrator (201) of the system is started, pulse signal excitation with a certain charge quantity is given out in the middle of the cable, and output signals of the head end and the tail end of the cable are collected by an oscilloscope (301) respectively.
b. And analyzing and processing the output signal through a computer (302) and a network analyzer (303) connected with the oscilloscope (301) while acquiring the output signal.
c. Calculating the actual propagation coefficient gamma of the pulse signal in the cable1、γ2The formula is as follows:
wherein: l is the cable length, UojFor outputting signals, UinIs the input signal.
4. According to the rightThe method for cable assessment based on the bidirectional propagation coefficient of the pulse signal as claimed in claim 3, wherein in the step a, the formula is based on
Determining the charge emitted by the pulse signal calibrator (201); in the step b, the time domain signal acquired in the oscilloscope (301) is converted into a frequency domain form by Fourier transform.
5. The cable assessment device and method according to claim 1, wherein the theoretical propagation coefficient γ of the pulse signal in the cable is obtained0Determining R, L, C, G primary parameters of the single-core cable model (1): the solving formula of the resistance R is as follows:
ω＝2πf
wherein: mu.s0Is a vacuum permeability, mucoIs the permeability, σ, of the conductorcoIs the conductivity of the conductor and f is the signal frequency.
The solving formula of the inductance L is as follows:
when solving the capacitance C, the inner semiconductor layer (105), the insulating layer (104) and the outer semiconductor layer (103) need to be solved respectively, and the formula is as follows:
wherein: epsilonx(omega) is the dielectric constant, epsilon, of the respective layer medium0Is the dielectric constant in vacuum.
The capacitance value of the cable can be obtained according to the capacitance values of all layers, and the formula is as follows:
wherein: csc1Is the capacitance of the inner semiconductor layer (105), Csc2Is the capacitance of the outer semiconductor layer (103), CinsIs the capacitance of the insulating layer (104).
The conductance is calculated as:
wherein: dsc1Is the thickness of the inner semiconductor layer (105), dinsIs the thickness of the insulating layer (104), dsc2Is the thickness of the outer semiconductor layer (103), sigmainsIs the insulation layer conductivity.
Theoretical propagation coefficient gamma of pulse signal in two-way propagation in cable0Comprises the following steps:
6. the method as claimed in claims 3 to 5, wherein the insulation uniformity distribution coefficient P of the cable is calculatedjThe calculation formula is as follows:
according to insulation uniform distribution coefficient PjThe insulation condition and the running state of the cable can be evaluated: when P is more than or equal to 0.9jWhen the insulation state is less than or equal to 1.2, the insulation condition of the cable is better, and the running state is stable; when P is presentj>1.2 or Pj<When 0.9, the insulation of the cable is seriously aged and the running state is unstable.
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