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

Abstract

The application discloses a kind of cable evaluation device and method based on Gaussian pulse bidirectional propagation coefficient, including signal generating system, cable model and measuring system;Impulse signal calibrator is connected with cable intermediate, for generating certain charge amount Gaussian pulse signal;Coaxial cable is respectively connected at the two ends of cable, and is connected with oscilloscope in measuring system, and the Gaussian pulse signal of cable first, last two ends is collected;Oscilloscope in measuring system is connected with computer, network analyzer, and computer and network analyzer are used to process the Gaussian pulse signal of cable first, last two ends, so that the actual propagation coefficient of Gaussian pulse signal in the cable is obtained.Compared with theoretical value, the uniform distribution coefficient of cable insulation is obtained, so as to evaluate the state of cable.The application obtains the uniform distribution coefficient of the insulation of the cable based on the propagation coefficient of the Gaussian pulse signal in the bidirectional propagation of the cable, which can effectively evaluate the running state and insulation aging degree of the cable.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of power cable state monitoring, and particularly relates to a cable insulation detection device and method based on a Gaussian pulse bidirectional propagation coefficient. BACKGROUND

[0002] Power cables are main equipment for power transmission of power grids, and power supply by cables has the advantages of safety and reliability, concealment and durability, small influence by climate, and benefit to beautification of city layout, etc. Especially, with the use of new cable technologies, the cost of cables gradually decreases, and the cables are more and more widely applied.

[0003] However, impurities and bubbles mixed in the insulation during processing of the cable line and bending of the line during laying construction can damage the insulation of the cable. Moreover, the environment where the power cable is located is very complex, and the cable is long-term placed in a dark and humid underground environment, which can easily cause damage to the cable insulation and affect the stability and safety of the power transmission network. Since the semiconductor layer and the insulation layer of the power cable can cause strong attenuation of the high-frequency Gaussian pulse signal, the transmission characteristics of the high-frequency Gaussian pulse signal in the cable can be analyzed to evaluate the operation state of the power cable, which is of great significance for early warning of the fault hidden danger of the power cable and improvement of the stable operation ability of the power system. SUMMARY

[0004] The application provides a cable insulation detection device and method based on a Gaussian pulse bidirectional propagation coefficient, which has a simple structure and can effectively measure the actual propagation coefficient of the Gaussian pulse signal in the cable, and the insulation distribution coefficient of the cable can be obtained from the ratio of the actual propagation coefficient and the theoretical propagation coefficient, so that the insulation condition and the operation state of the cable are reflected, and the service life of the cable is predicted.

[0005] To achieve the above object, a cable insulation detection device and method based on a Gaussian pulse bidirectional propagation coefficient comprises a single-core cable model, a signal generation system, and a measurement system.

[0006] The single-core cable model, the signal generation system and the measurement system are sequentially connected.

[0007] The single-core cable model sequentially comprises, from outside to inside, a cable sheath, a shielding layer, an outer semiconductor layer, an insulation layer, an inner semiconductor layer and a conductor layer.

[0008] The two ends of the single-core cable model are respectively connected with coaxial cables, and a pulse signal calibrator is connected in the middle, and the first end and the last end are connected with an oscilloscope in the measurement system.

[0009] The signal generation system is composed of a pulse signal calibrator capable of generating a Gaussian pulse signal and is connected at the two ends of the single-core cable model.

[0010] The measurement system consists of an oscilloscope, a computer, and a network analyzer;

[0011] The oscilloscope is connected to both ends of the cable to acquire the signal emitted by the pulse signal calibrator and the Gaussian pulse signal from both ends of the cable, and is also connected to the computer and network analyzer, which are also part of the measurement system.

[0012] Furthermore, the pulse signal calibrator in the middle of the cable can generate Gaussian pulse signals with different charge amounts, and its calculation formula is as follows:

[0013]

[0014] Where: U is the peak voltage of the Gaussian pulse signal, r1 is the radius of the conductor layer (106), r2 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.

[0015] A cable insulation testing method based on the bidirectional propagation coefficient of Gaussian pulses specifically includes the following steps:

[0016] The system's pulse signal calibrator is activated, and a Gaussian pulse signal with a certain charge is applied to the middle of the cable for excitation. The output signals at the beginning and end of the cable are then acquired using an oscilloscope.

[0017] While acquiring the output signal, the output signal is analyzed and processed by a computer and network analyzer connected to the oscilloscope.

[0018] The formulas for calculating the actual propagation coefficients γ1 and γ2 of the Gaussian pulse signal in the cable are as follows:

[0019]

[0020] Where: L is the cable length, U oj For the output signal, U in This is the input signal.

[0021] Furthermore, in step a, according to the formula Determine the charge emitted by the pulse signal calibrator;

[0022] Furthermore, in step b, the time-domain results obtained from the oscilloscope are transformed into frequency-domain form using Fourier transform.

[0023] Furthermore, the theoretical propagation coefficient γ0 of the Gaussian pulse signal in the cable is solved to determine the primary parameters R, L, C, and G of the single-core cable model:

[0024] The formula for calculating the bending resistance R is as follows:

[0025]

[0026] ω=2πf

[0027] Where: μ0 is the vacuum permeability μ co Let σ be the permeability of the conductor. co Let f be the conductivity of the conductor, and f be the signal frequency.

[0028] The formula for calculating the inductance L of a bent cable is as follows:

[0029]

[0030] D = 0.916sinθ

[0031] Where: R l Let θ be the radius of the arc bend, and θ be the central angle corresponding to the length of the conductor.

[0032] When calculating the capacitance C of a bent cable, it is necessary to solve for the inner semiconductor layer (105), the insulating layer (104), and the outer semiconductor layer (103) separately. The formula is as follows:

[0033]

[0034] Where: ε x (ω) represents the dielectric constant of each layer of the medium, and ε0 represents the vacuum dielectric constant.

[0035] The capacitance of the cable can be calculated from the capacitance values ​​of each layer using the following formula:

[0036]

[0037] Where: C sc1 For the capacitance of the inner semiconductor layer (105), C sc2 For the capacitance of the outer semiconductor layer (103), C ins The capacitor is an insulating layer (104).

[0038] The formula for calculating the conductivity G of a bent cable is:

[0039]

[0040] Where: d sc1 d is the thickness of the inner semiconductor layer (105). ins d is the thickness of the insulating layer (104). sc2 The thickness of the outer semiconductor layer (103) is σ. ins The conductivity of the insulating layer.

[0041] The theoretical propagation coefficient γ0 of a Gaussian pulse signal propagating bidirectionally in a curved cable is:

[0042]

[0043] Furthermore, the insulation uniformity distribution coefficient P of the cable was calculated. j The calculation formula is as follows:

[0044]

[0045] Based on the insulation uniformity distribution coefficient P j It can assess the insulation condition and operating status of cables: when 0.9 ≤ P j When P ≤ 1.2, the cable insulation is good and the operating condition is stable; when P j >1.2 or P j When the value is less than 0.9, the cable insulation is severely aged and its operating condition is unstable.

[0046] Compared with existing technologies, this paper proposes a cable insulation testing device and method based on the bidirectional propagation coefficient of Gaussian pulses. It sets up a single-core cable model, a signal generation system, and a measurement system. A Gaussian pulse signal is emitted through a pulse signal calibrator to simulate the operation of a power cable under partial discharge. This simplifies the system while making it closer to actual operating conditions, ensuring measurement accuracy. The signals at both ends of the single-core cable are measured using an oscilloscope, and the measured signals are analyzed in the frequency domain using a PC to determine the propagation coefficient. This value is then compared with theoretical calculations to obtain the cable insulation uniformity distribution coefficient. This provides a reference for evaluating cable insulation performance and aging conditions, and is beneficial for predicting cable service life. Attached Figure Description

[0047] Figure 1 This is an overall distribution diagram of the measuring device of the present invention;

[0048] Figure 2 This is a flowchart of the measurement method of the present invention;

[0049] In the picture:

[0050] 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 Implementation

[0051] The invention will be further described below with reference to the accompanying drawings.

[0052] like Figure 1 As shown, a cable insulation testing device and method based on Gaussian pulse bidirectional propagation coefficient includes a single-core cable model 1, a signal generation system 2, and a measurement system 3.

[0053] The single-core cable model 1, signal generation system 2, and measurement system 3 are connected in sequence.

[0054] The single-core cable model includes, from the outside to the inside, a cable sheath 101, a shielding layer 102, an outer semiconductor layer 103, an insulation layer 104, an inner semiconductor layer 105, and a conductor layer 106.

[0055] The two ends of the single-core cable model 1 are connected to coaxial cables, the middle is connected to the pulse signal calibrator 201, and the beginning and end are connected to the oscilloscope 301 in the measurement system 3.

[0056] The signal generation system consists of a pulse signal calibrator 201 that can generate Gaussian pulse signals, connected in the middle of the single-core cable model 1.

[0057] The measurement system 3 consists of an oscilloscope 301, a computer 302, and a network analyzer 303;

[0058] The oscilloscope 301 is connected to both ends of the cable to acquire the signal emitted 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 part of the measurement system 3.

[0059] Furthermore, the pulse signal calibrator 201 at the cable end can generate Gaussian pulse signals with different charge amounts, calculated using the following formula:

[0060]

[0061] Where: U is the peak voltage of the Gaussian pulse signal, r1 is the radius of the conductor layer (106), r2 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.

[0062] A cable insulation testing method based on the bidirectional propagation coefficient of Gaussian pulses specifically includes the following steps:

[0063] The pulse signal calibrator 201 of the system is activated, and a Gaussian pulse signal with a certain charge is given to the middle of the cable for excitation. The output signals at the beginning and end of the cable are collected by the oscilloscope 301.

[0064] While acquiring the output signal, the computer 302 and network analyzer 303 connected to the oscilloscope 301 analyze and process the output signal.

[0065] The formulas for calculating the actual propagation coefficients γ1 and γ2 of the Gaussian pulse signal in the cable are as follows:

[0066]

[0067] Where: L is the cable length, Uoj For the output signal, U in This is the input signal.

[0068] Furthermore, in step a, according to the formula Determine the charge emitted by the Gaussian pulse signal verifier 201

[0069] Furthermore, in step b, we transform the time-domain results obtained from the oscilloscope 301 into the frequency-domain form using Fourier transform.

[0070] Furthermore, the theoretical propagation coefficient γ0 of the Gaussian pulse signal in the cable is solved to determine the primary parameters R, L, C, and G of the single-core cable model 1:

[0071] The formula for calculating the bending resistance R is as follows:

[0072]

[0073] ω=2πf

[0074] Where: μ0 is the vacuum permeability μ co Let σ be the permeability of the conductor. co Let f be the conductivity of the conductor, and f be the signal frequency.

[0075] The formula for calculating the inductance L of a bent cable is as follows:

[0076]

[0077] D = 0.916sinθ

[0078] Where: R l Let θ be the radius of the arc bend, and θ be the central angle corresponding to the length of the conductor.

[0079] When calculating the capacitance C of a bent cable, it is necessary to solve for the inner semiconductor layer (105), the insulating layer (104), and the outer semiconductor layer (103) separately. The formula is as follows:

[0080]

[0081] Where: ε x (ω) represents the dielectric constant of each layer of the medium, and ε0 represents the vacuum dielectric constant.

[0082] The capacitance of the cable can be calculated from the capacitance values ​​of each layer using the following formula:

[0083]

[0084] Where: C sc1 For the capacitance of the inner semiconductor layer (105), C sc2 For the capacitance of the outer semiconductor layer (103), Cins The capacitor is an insulating layer (104).

[0085] The formula for calculating the conductivity G of a bent cable is:

[0086]

[0087] Where: d sc1 d is the thickness of the inner semiconductor layer (105). ins d is the thickness of the insulating layer (104). sc2 The thickness of the outer semiconductor layer (103) is σ. ins The conductivity of the insulating layer.

[0088] The theoretical propagation coefficient γ0 of a Gaussian pulse signal propagating bidirectionally in a curved cable is:

[0089]

[0090] Furthermore, the insulation uniformity distribution coefficient P of the cable was calculated. j The calculation formula is as follows:

[0091]

[0092] Based on the insulation uniformity distribution coefficient P j It can assess the insulation condition and operating status of cables: when 0.9 ≤ P j When P ≤ 1.2, the cable insulation is good and the operating condition is stable; when P j >1.2 or P j When the value is less than 0.9, the cable insulation is severely aged and its operating condition is unstable.

[0093] Taking the cable with model number AXCE-F14 / 24kV1X150 / 25LT as an example, the cable length is 10m, and the cable sheath thickness is d. b =2mm, outer semiconductor layer thickness d sc2 =0.45mm, insulation layer thickness d ins = 4.1mm, inner semiconductor layer thickness d sc1 =0.44mm and conductor layer radius r1=6.7mm, the experimental procedure includes the following steps:

[0094] 1) Use a pulse signal calibrator to generate a Gaussian pulse signal with a charge of 100pc and a voltage amplitude of 64mV;

[0095] 2) Use an oscilloscope to acquire the output signal at the end of the cable, and use a computer and network analyzer to perform Fourier transform on the output signal;

[0096] 3) By analyzing the ratio of the input signal to the output signal, the actual propagation coefficient of the signal in the cable is determined as γ1 = 0.23 + j7.3. γ2 = 0.36 + j11.3

[0097] 4) Model the cable and calculate its primary parameters R, L, C, and G. Then, the theoretical propagation coefficient γ0 of the signal in the cable can be obtained as 0.19 + j6.5.

[0098] 5) According to the formula, the insulation uniformity distribution coefficient of the cable can be calculated as P1 = 1.123 and P2 = 1.738. The insulation of one end of the cable is good, while the insulation of the other end is poor, requiring inspection and maintenance.

[0099] As can be seen from the above technical solutions, the present invention provides a cable insulation detection device and method based on the bidirectional propagation coefficient of a Gaussian pulse. By comparing the theoretical propagation coefficient of the Gaussian pulse signal in the cable with the actual propagation coefficient, the insulation uniformity distribution parameters of the cable are calculated, thereby assessing the insulation aging degree of the cable and helping to predict the operating condition of the cable. In the above embodiments, the present invention is only described illustratively; however, those skilled in the art can make various modifications to the present invention without departing from the spirit and scope of the invention after reading this patent application.

Claims

1. A cable insulation detection method based on 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 generation system (2), and the measurement system (3) are connected in sequence; The single-core cable model includes, from the outside to the inside, a cable sheath (101), a shielding layer (102), an outer semiconductor layer (103), an insulation layer (104), an inner semiconductor layer (105), and a conductor layer (106). The two ends of the single-core cable model (1) are connected to coaxial cables, and both ends are connected to the oscilloscope (301) in the measurement system (3); The signal generation system consists of a pulse signal calibrator (201) that can generate Gaussian pulse signals, 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 connected to both ends of the cable to collect the signal emitted 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 network analyzer (303), which are also part of the measurement system (3); The method specifically includes the following steps: a. Start the pulse signal calibrator (201) of the system, give a Gaussian pulse signal with a certain amount of charge in the middle of the cable, and use an oscilloscope (301) to collect the output signals at the beginning and end of the cable respectively; b. While the output signal is acquired, the output signal is analyzed and processed by the computer (302) and network analyzer (303) connected to the oscilloscope (301); c. Calculate the actual propagation coefficient of the Gaussian pulse signal in the cable. , The formula is: ； Where: L is the cable length For output signal, For input signals; Solve for the theoretical propagation coefficient of the Gaussian pulse signal in the cable. Determine the primary parameters R, L, C, and G of the single-core cable model (1): The formula for calculating the bending resistance R is: ； ； in: Vacuum permeability, Let be the magnetic permeability of the conductor. Let r be the electrical conductivity of the conductor, r1 be the radius of the conductor layer (106), and r2 be the radius of the insulating layer (104). The signal frequency; The formula for calculating the inductance L of a bent cable is as follows: ； ； in: Let be the radius of the arc. The central angle corresponding to the length of the conductor; When calculating the capacitance C of a bent cable, it is necessary to solve for the inner semiconductor layer (105), the insulating layer (104), and the outer semiconductor layer (103) separately. The formula is as follows: ； in: Here are the dielectric constants of each dielectric layer. It is the vacuum permittivity; The capacitance of the cable can be calculated from the capacitance values ​​of each layer using the following formula: ； in: For the capacitance of the inner semiconductor layer (105), The capacitance of the outer semiconductor layer (103) The capacitor is an insulating layer (104); The formula for calculating the conductivity G of a bent cable is: ； in: The thickness of the inner semiconductor layer (105) is... The thickness of the insulating layer (104) is... The thickness of the outer semiconductor layer (103) is... The conductivity of the insulating layer; Theoretical propagation coefficient of a Gaussian pulse signal propagating bidirectionally in a curved cable for: ； Calculate the insulation uniformity distribution coefficient of the cable. The calculation formula is as follows: ； Based on the insulation uniformity distribution coefficient It can assess the insulation condition and operating status of cables: when 0.9 ≤ When the value is ≤1.2, the cable insulation is good and the operating condition is stable; when >1.2 or When the value is less than 0.9, the cable insulation is severely aged and its operating condition is unstable.

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