CN114414959A - A cable insulation detection device and method based on the bidirectional propagation coefficient of Gaussian pulse - Google Patents

Abstract

The invention discloses a cable evaluation device and method based on a Gaussian pulse two-way propagation coefficient, which comprises a signal generation system, a cable model and a measurement system, wherein the signal generation system comprises a signal generation module, a signal transmission module and a signal transmission module; the pulse signal calibrator is connected with the middle of the cable and is used for generating a Gaussian 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 Gaussian 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 Gaussian pulse signals at the first end and the last end of the cable so as to obtain the actual propagation coefficient of the Gaussian 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 Gaussian 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

A cable insulation detection device and method based on the bidirectional propagation coefficient of Gaussian pulse

technical field

The invention relates to the technical field of power cable state monitoring, in particular to a cable insulation detection device and method based on the bidirectional propagation coefficient of Gaussian pulses.

Background technique

Power cables are the main equipment for power transmission in the power grid. Cable power supply has the advantages of being safe, reliable, concealed and durable, less affected by climate, and conducive to beautifying urban layout. Especially with the use of new cable technologies, the cost of cables has gradually decreased. more and more widely used.

However, the impurities and air bubbles mixed in the insulation of the cable line during processing, and the bending of the line during the laying construction will cause damage to the insulation of the cable. And because the environment where the power cable is located is very complex, and it has been in a dark and humid underground environment for a long time, it is easy to cause damage to the cable insulation, which will affect the stability and security of the transmission network. Since the semiconductor layer and insulating layer of the power cable will cause strong attenuation of the high-frequency Gaussian pulse signal, the operation state of the power cable can be evaluated by analyzing the transmission characteristics of the high-frequency Gaussian pulse signal in the cable. It is of great significance to avoid hidden troubles and improve the stable operation ability of the power system.

SUMMARY OF THE INVENTION

The invention provides a cable insulation detection device and method based on the bidirectional propagation coefficient of Gaussian pulse. The device with a simple structure can effectively measure the actual propagation coefficient of the Gaussian pulse signal in the cable, and the ratio of the actual propagation coefficient to the theoretical propagation coefficient can be obtained. The insulation distribution coefficient reflects the insulation and operating status of the cable, which is helpful for predicting its service life.

In order to achieve the above purpose, a cable insulation detection device and method based on the bidirectional propagation coefficient of Gaussian pulses, including a single-core cable model, a signal generation system, and a measurement system;

In the single-core cable model, the signal generation system and the measurement system are connected in sequence;

The single-core cable model sequentially includes 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;

Both ends of the single-core cable model are connected to coaxial cables respectively, the pulse signal calibrator is connected to the middle, and the first and last ends are connected to the oscilloscope in the measurement system;

The signal generation system consists of a pulse signal calibrator capable of generating Gaussian pulse signals, which is connected to both ends of the single-core cable model;

The measurement system consists of an oscilloscope, a computer and a network analyzer;

The oscilloscope is connected to the two ends of the cable, respectively, to collect the signal sent by the pulse signal calibrator and the Gaussian pulse signal at both ends of the cable, and to be connected to the computer and network analyzer that are also measuring systems.

Further, the pulse signal calibrator in the middle of the cable can generate Gaussian pulse signals with different charge amounts, and its calculation formula is:

Where: U is the peak voltage of the Gaussian pulse signal, r ₁ is the radius of the conductor layer (106), r ₂ is the radius of the insulating layer (104), ε is the dielectric constant of the insulating material, and k is the proportionality coefficient, which is taken as 2.82.

A cable insulation detection method based on the bidirectional propagation coefficient of Gaussian pulse, which specifically includes the following steps:

Start the pulse signal calibrator of the system, give Gaussian pulse signal excitation with a certain amount of charge in the middle of the cable, and use the oscilloscope to collect the output signals of the head end and the tail end of the cable respectively.

When the output signal is collected, the output signal is analyzed and processed through the computer and network analyzer connected to the oscilloscope.

Calculate the actual propagation coefficients γ ₁ , γ ₂ of the Gaussian pulse signal in the cable, the formulas are:

Among them: L is the cable length, U _oj is the output signal, U _in is the input signal.

确定脉冲信号校准器发出的电荷；Further, in step a, according to the formula

Determine the charge emitted by the pulse signal calibrator;

Further, in step b, the time domain result obtained in the oscilloscope is transformed into the form of the frequency domain by Fourier transform;

Further, solve the theoretical propagation coefficient γ ₀ of the Gaussian pulse signal in the cable, and determine the primary parameters R, L, C, G of the single-core cable model:

The formula for solving the bending resistance R is:

ω=2πf

Among them: μ ₀ vacuum permeability μ _co is the magnetic permeability of the conductor, σ _co is the electrical conductivity of the conductor, and f is the signal frequency.

The calculation method of bending cable inductance L, the formula is:

D=0.916sinθ

Among them: R _l is the radius of arc bending, θ is the central angle corresponding to the length of the wire.

When solving the bending cable capacitance C, it is necessary to solve the inner semiconductor layer (105), the insulating layer (104), and the outer semiconductor layer (103) respectively, and the formula is:

Among them: ε _x (ω) is the dielectric constant of each layer of medium, and ε ₀ is the vacuum dielectric constant.

From the capacitance value of each layer, the capacitance value of the cable can be obtained, and the formula is:

Wherein: C _sc1 is the capacitance of the inner semiconductor layer (105), C _sc2 is the capacitance of the outer semiconductor layer (103), and C _ins is the capacitance of the insulating layer (104).

The formula for calculating the conductance G of the curved cable is:

Wherein: d _sc1 is the thickness of the inner semiconductor layer (105), d _ins is the thickness of the insulating layer (104), d _sc2 is the thickness of the outer semiconductor layer (103), and σ _ins is the conductivity of the insulating layer.

The theoretical propagation coefficient γ ₀ of the Gaussian pulse signal propagating in both directions in a curved cable is:

Further, calculate the insulation uniform distribution coefficient P _j of the cable, and its calculation formula is:

The insulation condition and operating state of the cable can be evaluated according to the uniform distribution coefficient of insulation P _j : when 0.9≤P _j ≤1.2, the insulation condition of the cable is good and the operating state is stable; when P _j >1.2 or P _j <0.9, the cable The insulation aging is serious and the running state is unstable.

Compared with the prior art, a cable insulation detection device and method based on the bidirectional propagation coefficient of Gaussian pulse proposed in this paper is set up with a single-core cable model, a signal generation system and a measurement system, and a Gaussian pulse signal is sent out through a pulse signal calibrator. Simulate the operation of the power cable when partial discharge occurs; while simplifying the system, make it closer to the actual working condition to ensure the accuracy of the measurement. The signal is analyzed in the frequency domain to determine its propagation coefficient, and compared with the theoretical calculation value, the uniform distribution coefficient of the cable's insulation is obtained.

Description of drawings

Fig. 1 is the overall distribution diagram of the measuring device of the present invention;

Fig. 2 is the flow chart of the measuring method of the present invention;

In the picture:

1. Power cable model, 2. Signal generation system, 3. Measurement system, 101, Cable sheath, 102, Shielding layer, 103, Outer semiconductor layer, 104, Insulation layer, 105, Inner semiconductor layer, 106, Conductor layer, 201, pulse signal calibrator, 301, oscilloscope, 302, network analyzer, 303, computer

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings

As shown in FIG. 1 , a cable insulation detection device and method based on the bidirectional propagation coefficient of Gaussian pulses 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 generation system 2 and the measurement system 3 are connected in sequence.

The single-core cable model sequentially includes 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 the outside to the inside.

Both ends of the single-core cable model 1 are respectively connected to coaxial cables, the middle is connected to the pulse signal calibrator 201, and the first and last ends are respectively connected to the oscilloscope 301 in the measurement system 3;

The signal generation system is composed of a pulse signal calibrator 201 capable of generating Gaussian pulse signals, which is connected in the middle of the single-core cable model 1;

The measurement system 3 consists of an oscilloscope 301, a computer 302 and a network analyzer 303;

The oscilloscope 301 is respectively connected to both ends of the cable, collects the signal sent by the pulse signal calibrator 201 and the Gaussian pulse signal at both ends of the cable, and is connected to the computer 302 and the network analyzer 303 which are also the measurement system 3 .

Further, the pulse signal calibrator 201 at the head end of the cable can generate Gaussian pulse signals with different charge amounts, and the calculation formula is:

Where: U is the peak voltage of the Gaussian pulse signal, r ₁ is the radius of the conductor layer (106), r ₂ is the radius of the insulating layer (104), ε is the dielectric constant of the insulating material, and k is the proportionality coefficient, which is taken as 2.82.

A cable insulation detection method based on the bidirectional propagation coefficient of Gaussian pulse, which specifically includes the following steps:

Start the pulse signal calibrator 201 of the system, give a Gaussian pulse signal excitation with a certain amount of charge in the middle of the cable, and use the oscilloscope 301 to collect the output signals of the head end and the tail end of the cable respectively.

When the output signal is collected, the output signal is analyzed and processed through the computer 302 and the network analyzer 303 connected to the oscilloscope 301 .

Calculate the actual propagation coefficients γ ₁ , γ ₂ of the Gaussian pulse signal in the cable, the formulas are:

Among them: L is the cable length, U _oj is the output signal, U _in is the input signal.

确定高斯脉冲信号校验器201发出的电荷Further, in step a, according to the formula

Determine the charge from the Gaussian pulse signal checker 201

Further, in step b, we convert the time domain result obtained in the oscilloscope 301 into the form of the frequency domain by Fourier transform

Further, solve the theoretical propagation coefficient γ ₀ of the Gaussian pulse signal in the cable, and determine the primary parameters R, L, C, G of the single-core cable model 1:

The formula for solving the bending resistance R is:

ω=2πf

Among them: μ ₀ vacuum permeability μ _co is the magnetic permeability of the conductor, σ _co is the electrical conductivity of the conductor, and f is the signal frequency.

The calculation method of bending cable inductance L, the formula is:

D=0.916sinθ

Among them: R _l is the radius of arc bending, θ is the central angle corresponding to the length of the wire.

When solving the bending cable capacitance C, it is necessary to solve the inner semiconductor layer (105), the insulating layer (104), and the outer semiconductor layer (103) respectively, and the formula is:

Among them: ε _x (ω) is the dielectric constant of each layer of medium, and ε ₀ is the vacuum dielectric constant.

From the capacitance value of each layer, the capacitance value of the cable can be obtained, and the formula is:

Wherein: C _sc1 is the capacitance of the inner semiconductor layer (105), C _sc2 is the capacitance of the outer semiconductor layer (103), and C _ins is the capacitance of the insulating layer (104).

The formula for calculating the conductance G of the curved cable is:

Wherein: d _sc1 is the thickness of the inner semiconductor layer (105), d _ins is the thickness of the insulating layer (104), d _sc2 is the thickness of the outer semiconductor layer (103), and σ _ins is the conductivity of the insulating layer.

The theoretical propagation coefficient γ ₀ of the Gaussian pulse signal propagating in both directions in a curved cable is:

Further, calculate the insulation uniform distribution coefficient P _j of the cable, and its calculation formula is:

The insulation condition and operating state of the cable can be evaluated according to the uniform distribution coefficient of insulation P _j : when 0.9≤P _j ≤1.2, the insulation condition of the cable is good and the operating state is stable; when P _j >1.2 or P _j <0.9, the cable The insulation aging is serious and the running state is unstable.

Take the cable model AXCE-F14/24kV1X150/25LT as an example, the cable length is 10m, the cable sheath thickness db = 2mm, the outer semiconductor layer thickness _{d sc2} = 0.45mm, the insulation layer thickness d _ins = 4.1mm, the inner semiconductor layer thickness d sc2 = 0.45mm The layer thickness d _sc1 =0.44mm and the conductor layer radius r ₁ =6.7mm, the experimental operation method includes the following steps:

1) Use the pulse signal calibrator to generate a Gaussian pulse signal with a charge of 100pc, and its voltage amplitude is 64mv;

2) Use the oscilloscope to collect the output signal at the end of the cable, and the computer and the network analyzer will Fourier transform the output signal;

3) By analyzing the ratio of the input signal to the output signal, determine the actual propagation coefficient of the signal in the cable γ ₁ =0.23+j7.3. γ ₂ =0.36+j11.3

4) Model the cable and obtain the primary parameters R, L, C, and G of the cable, and obtain the theoretical propagation coefficient of the signal in the cable γ ₀ =0.19+j6.5;

5) According to the formula, the uniform distribution coefficient of insulation of the cable can be obtained: P ₁ =1.123, P ₂ =1.738. The insulation of one end of the cable is good, and the insulation of the other end is poor, which needs to be repaired and maintained.

It can be seen from the above technical solutions that the present invention provides a cable insulation detection device and method based on the bidirectional propagation coefficient of Gaussian pulses. Distributed parameters to evaluate the insulation aging degree of the cable, which is beneficial to predict the operation status of the cable. In the above-described embodiments, the present invention is only exemplarily described, but those skilled in the art can make various modifications to the present invention without departing from the spirit and scope of the present invention after reading this patent application.

Claims (6)

1. A cable insulation detection device and method based on a Gaussian pulse bidirectional propagation coefficient, comprising 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 includes 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 the outside to the inside ; Both ends of the single-core cable model (1) are respectively connected to coaxial cables, and both the first and last ends are connected to the oscilloscope (301) in the measurement system (3); The signal generating system consists of a pulse signal calibrator (201) capable of generating Gaussian pulse signals, which is connected in the middle of the single-core cable model (1); The measurement system (3) consists of an oscilloscope (301), a computer (302) and a network analyzer (303); The oscilloscope (301) is respectively connected to both ends of the cable, collects the signal sent by the pulse signal calibrator (201) and the Gaussian pulse signal at both ends of the cable, and communicates with the computer (302) and the network analyzer (303) which are also the measurement system (3). )connect. 2. a kind of cable insulation detection device and method based on Gaussian pulse bidirectional propagation coefficient according to claim 1, is characterized in that, the pulse signal calibrator (201) of cable head end can produce the Gaussian pulse signal of different charge amounts, its The calculation formula is:

Where: U is the peak voltage of the Gaussian pulse, r ₁ is the radius of the conductor layer (106), r ₂ is the radius of the insulating layer (104), ε is the dielectric constant of the insulating material, and k is the proportionality coefficient, which is taken as 2.82. 3. A cable insulation detection method based on the bidirectional propagation coefficient of Gaussian pulse, which specifically comprises the following steps: a. Start the pulse signal calibrator (201) of the system, give a Gaussian pulse signal excitation with a certain amount of charge in the middle of the cable, and use the oscilloscope (301) to collect the output signals of the head end and the tail end of the cable respectively; b. While collecting the output signal, analyze and process the output signal through the computer (302) and the network analyzer (303) connected to the oscilloscope (301); c. Calculate the actual propagation coefficients γ ₁ , γ ₂ of the Gaussian pulse signal in the cable, the formulas are:

Among them: L is the cable length, U _oj is the output signal, U _in is the input signal. 4. a kind of cable insulation detection device and method based on Gaussian pulse bidirectional propagation coefficient according to claim 3, is characterized in that, in step a, according to formula

Determine the charge sent by the Gaussian pulse signal checker (201); in step b, convert the time domain result obtained in the oscilloscope (301) into the form of the frequency domain by Fourier transform. 5 . The cable insulation detection device and method based on the bidirectional propagation coefficient of Gaussian pulse according to claim 1 , wherein the theoretical propagation coefficient γ ₀ of the Gaussian pulse signal in the cable is calculated to determine the single-core cable. 6 . The primary parameters R, L, C, G of model (1): The formula for solving the bending resistance R is:

ω=2πf Among them: μ ₀ vacuum permeability μ _co is the magnetic permeability of the conductor, σ _co is the electrical conductivity of the conductor, and f is the signal frequency. The calculation method of bending cable inductance L, the formula is:

D=0.916sinθ Among them: R _l is the radius of arc bending; θ is the central angle corresponding to the length of the wire. When solving the bending cable capacitance C, it is necessary to solve the inner semiconductor layer (105), the insulating layer (104), and the outer semiconductor layer (103) respectively, and the formula is:

Among them: ε _x (ω) is the dielectric constant of each layer of medium, and ε ₀ is the vacuum dielectric constant. From the capacitance value of each layer, the capacitance value of the cable can be obtained, and the formula is:

Wherein: C _sc1 is the capacitance of the inner semiconductor layer (105), C _sc2 is the capacitance of the outer semiconductor layer (103), and C _ins is the capacitance of the insulating layer (104). The formula for calculating the conductance G of the curved cable is:

Wherein: d _sc1 is the thickness of the inner semiconductor layer (105), d _ins is the thickness of the insulating layer (104), d _sc2 is the thickness of the outer semiconductor layer (103), and σ _ins is the conductivity of the insulating layer. The theoretical propagation coefficient γ ₀ of the Gaussian pulse signal propagating in both directions in a curved cable is:

6. a kind of cable evaluation device and method based on Gaussian pulse signal bidirectional propagation coefficient according to claim 3 to 5, is characterized in that, calculates the insulation uniform distribution coefficient P _j of cable, its calculation formula is:

The insulation condition and operating state of the cable can be evaluated according to the uniform distribution coefficient of insulation P _j : when 0.9≤P _j ≤1.2, the insulation condition of the cable is good and the operating state is stable; when P _j >1.2 or P _j <0.9, the cable The insulation aging is serious and the running state is unstable.

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