A cable insulation aging evaluation device and method based on high-frequency signal characteristic impedance

Abstract

The application discloses a kind of cable insulation ageing evaluation device and method based on high frequency signal characteristic impedance, including signal generation system, cable model and measurement system;High frequency signal calibrator is connected with cable head, for generating certain charge amount of high frequency signal;Coaxial cable is respectively connected at the two ends of cable, and is connected with oscilloscope in measurement system, respectively signal emitted by high frequency signal calibrator and high frequency signal at the end of cable are collected;Oscilloscope in measurement system is connected with computer, network analyzer, computer and network analyzer are used to process high frequency signal at the end of cable, obtain the frequency of signal, so as to obtain the characteristic impedance of high frequency signal in the cable.And compared with theoretical value, obtain the uniform distribution coefficient of cable insulation, so as to carry out state evaluation to cable.The application obtains the uniform distribution coefficient of cable insulation based on the characteristic impedance of high frequency signal when unidirectional propagation in curved cable, and the running state of cable can be effectively evaluated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power cable state monitoring, in particular to a cable insulation aging evaluation device and method based on high-frequency signal characteristic impedance. BACKGROUND

[0002] Power cable is the main equipment for power transmission in power grid. Compared with the traditional overhead line, power cable has the characteristics of hidden installation position and space saving. With the development of smart grid, power cable is applied more and more widely.

[0003] However, the impurities and bubbles mixed in the insulation during the processing of the cable line and the mechanical damage caused by the bending of the line during the laying construction can cause damage to the cable insulation, thereby affecting the stability and safety of the power transmission network. Since the high-frequency signal phenomenon can reflect the degradation degree of the power cable insulation to a certain extent, many power supply bureaus regularly detect the high-frequency signal condition of the power cable to judge the running state of the power cable. When the cable line is in normal operation, only the power frequency 50Hz signal exists on the line. When the power cable has a partial discharge phenomenon, abundant high-frequency signals will be generated on the line. If the high-frequency signals can be analyzed and the characteristics of the high-frequency signals in the power cable are studied, the running state of the power cable can be evaluated based on this, which is of great significance for early warning of the fault hidden danger of the power cable and improving the stable operation ability of the power system. SUMMARY

[0004] The present application provides a cable insulation aging evaluation device and method based on high-frequency signal characteristic impedance, which has a simple structure. The device can effectively measure the actual characteristic impedance of the high-frequency signal in the one-way propagation of the curved cable, and the insulation distribution coefficient of the cable can be obtained from the ratio of the actual characteristic impedance and the theoretical characteristic impedance, reflecting the insulation condition and running state of the cable, which is beneficial to predict the service life.

[0005] To achieve the above purpose, a cable insulation aging evaluation device and method based on high-frequency signal characteristic impedance, comprising a single-core cable model, a signal generating system, and a measuring system.

[0006] The single-core cable model, the signal generating system and the measuring system are connected in sequence.

[0007] The single-core cable model comprises, in sequence 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. The two ends of the single-core cable model are respectively connected to coaxial cables, the first end is connected to a high-frequency signal calibrator, and the last end is connected to an oscilloscope in the measuring system.

[0008] The signal generating system is composed of a calibrator capable of generating high-frequency signals and is connected to the first end of the single-core cable model.

[0009] The measuring system is composed of an oscilloscope, a computer and a network analyzer. The oscilloscope is connected with the cable at both ends, collects the signal from the high-frequency signal calibrator and the high-frequency signal at the tail end of the cable, and is connected with the computer and the network analyzer which are also part of the measuring system.

[0010] Further, the high-frequency signal calibrator at the head end of the cable can generate high-frequency signals with different charge amounts, and the calculation formula is:

[0011]

[0012] Wherein: U is the peak voltage of the high-frequency signal, r1 is the radius of the conductor layer (106), r2 is the radius of the insulation layer (104), ε is the dielectric constant of the insulation material, k is the proportional coefficient, and the value is 2.82.

[0013] A cable insulation aging evaluation method based on high-frequency signal characteristic impedance, specifically comprising the following steps:

[0014] Start the high-frequency signal calibrator of the system, give a certain charge amount of high-frequency signal excitation at the head end of the cable, and collect the output signal at the tail end of the cable with the oscilloscope respectively.

[0015] At the same time of collecting the output signal, the output signal is analyzed and processed through the computer and the network analyzer connected with the oscilloscope.

[0016] The actual characteristic impedance Z1 of the high-frequency signal in the cable is obtained;

[0017] Further, in step a, the charge amount of the high-frequency signal calibrator is determined according to the formula

[0018] Further, the theoretical characteristic impedance Z0 of the high-frequency signal in the cable is solved, and the first order parameters R, L, C and G of the single-core cable model are determined:

[0019] The solving formula of the inductance L of the curved cable is:

[0020]

[0021] D=0.916sinθ

[0022] Wherein: μ0 is the magnetic permeability of vacuum, R l is the radius of the circular arc bending; θ is the central angle corresponding to the length of the wire.

[0023] The solving formula of the resistance R of the curved cable is:

[0024]

[0025] ω=2πf​

[0026] wherein: μ co is the magnetic permeability of the conductor, σ co is the electrical conductivity of the conductor, and f is the signal frequency.

[0027] To solve the capacitance C of the curved cable, the inner semiconductor layer (105), the insulating layer (104), and the outer semiconductor layer (103) are solved respectively, and the formula is:

[0028]

[0029] wherein: ε x (ω) is the dielectric constant of each layer of medium, and ε0 is the dielectric constant of vacuum.

[0030] The capacitance value of the cable can be obtained from the capacitance value of each layer, and the formula is:

[0031]

[0032] 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).

[0033] The calculation formula of the conductance G of the curved cable is:

[0034]

[0035] wherein: d sc1 is the thickness of the inner semiconductor layer (105), d ins is the thickness of the insulating layer (104), and d sc2 is the thickness of the outer semiconductor layer (103), and σ ins is the electrical conductivity of the insulating layer.

[0036] The theoretical characteristic impedance Z0 of the high-frequency signal when propagating unidirectionally in the curved cable is:

[0037]

[0038] Further, the insulation uniform distribution coefficient P of the cable is calculated, and the calculation formula is:

[0039]

[0040] According to the insulation uniform distribution coefficient P, the insulation condition and running state of the cable can be evaluated: when 0.9≤P≤1.2, the insulation condition of the cable is good, and the running state is stable; when P>1.2 or P<0.9, the insulation of the cable is seriously aged, and the running state is unstable.

[0041] Compared with the prior art, the cable insulation aging evaluation device based on high-frequency signal characteristic impedance provided in the present application sets a single-core cable model, a signal generation system and a measurement system, high-frequency signals are sent out through a high-frequency signal calibrator, the operation condition when high-frequency signals occur in power cables is simulated, the system is simplified, the influence of cable bending on its own parameters is considered, the actual working condition is approached more, the measurement accuracy is ensured, the signals at the two ends of the single-core cable are measured through an oscilloscope, the signals measured are analyzed in the frequency domain through a PC end, the characteristic impedance is determined, and compared with the theoretical calculation value, the uniform distribution coefficient of the cable insulation is obtained, which is used as a reference for evaluating the cable insulation performance and aging condition, and is beneficial to predicting the service life of the cable. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is the overall distribution diagram of the measuring device of the present application;

[0043] Figure 2 is the flow chart of the measuring method of the present application;

[0044] In the drawings:

[0045] 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, high-frequency signal calibrator, 301, oscilloscope, 302, network analyzer, 303, computer DETAILED DESCRIPTION

[0046] The present application will be further described below in combination with the drawings:

[0047] As Figure 1 shown, a cable insulation aging evaluation device and method based on high-frequency signal characteristic impedance, comprising a single-core cable model 1, a signal generation system 2, and further comprising a measurement system 3.

[0048] The single-core cable model 1, the signal generation system 2 and the measurement system 3 are connected in sequence.

[0049] The single-core cable model comprises, in sequence from outside to 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 respectively connected with coaxial cables, the first end is connected with a high-frequency signal calibrator 201, and the tail end is connected with an oscilloscope 301 in the measurement system 3.

[0050] The signal generation system is composed of a high-frequency signal calibrator 201 capable of generating high-frequency signals, which is connected to the first end of the single-core cable model 1.

[0051] The measuring system 3 is composed of an oscilloscope 301, a computer 302 and a network analyzer 303.

[0052] The oscilloscope 301 is connected with the cable at both ends, collects the signal from the high-frequency signal calibrator 201 and the high-frequency signal at the tail end of the cable, and is connected with the computer 302 and the network analyzer 303 which are also the measuring system 3.

[0053] Further, the high-frequency signal calibrator 201 at the head end of the cable can generate high-frequency signals with different charge amounts according to the cable properties and rated voltage strength, and the calculation formula is:

[0054]

[0055] Wherein, U is the peak voltage of the high-frequency signal, r1 is the radius of the conductor layer (106), r2 is the radius of the insulation layer (104), ε is the dielectric constant of the insulation material, k is the proportional coefficient, and the value is 2.82.

[0056] A cable insulation aging evaluation method based on high-frequency signal characteristic impedance, specifically comprising the following steps:

[0057] Start the high-frequency signal calibrator 201 of the system, give a certain charge amount of high-frequency signal excitation at the head end of the cable, and collect the output signal at the tail end of the cable with the oscilloscope 301 respectively.

[0058] At the same time of collecting the output signal, the output signal is analyzed and processed through the computer 302 and the network analyzer 303 connected with the oscilloscope 301.

[0059] The actual characteristic impedance Z1 of the high-frequency signal in the cable is obtained

[0060] Further, in step a, according to the formula Determine the charge of the high-frequency signal calibrator 201

[0061] Further, solve the theoretical characteristic impedance Z0 of the high-frequency signal in the cable, and determine the first-order parameters R, L, C and G of the single-core cable model 1:

[0062] The solving formula of the inductance L of the curved cable is:

[0063]

[0064] D=0.916sinθ

[0065] Wherein, μ0 is the magnetic permeability of vacuum, R l is the radius of the circular arc bending; θ is the central angle corresponding to the length of the wire.

[0066] The solving formula of the resistance R of the curved cable is:

[0067]

[0068] ω = 2πf

[0069] Where: μ co is the permeability of the conductor, σ co is the conductivity of the conductor, and f is the signal frequency.

[0070] To solve the capacitance C of the curved cable, the inner semiconductor layer (105), the insulating layer (104), and the outer semiconductor layer (103) are solved respectively, and the formula is:

[0071]

[0072] Where: ε x (ω) is the dielectric constant of each layer, and ε0 is the vacuum dielectric constant.

[0073] From the capacitance value of each layer, the capacitance value of the cable can be obtained, and the formula is:

[0074]

[0075] Where: 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).

[0076] The calculation formula of the conductance G of the curved cable is:

[0077]

[0078] Where: d sc1 is the thickness of the inner semiconductor layer (105), d ins is the thickness of the insulating layer (104), and d sc2 is the thickness of the outer semiconductor layer (103), and σ ins is the conductivity of the insulating layer.

[0079] The theoretical characteristic impedance Z0 of the high-frequency signal in the curved cable when propagating in one direction is:

[0080]

[0081] Further, the uniform distribution coefficient P of the cable is calculated, and the formula is:

[0082]

[0083] The insulation condition and operation state of the cable can be evaluated according to the insulation uniform distribution coefficient P: when 0.9≤P≤1.2, the insulation condition of the cable is good, and the operation state is stable; when P>1.2 or P<0.9, the insulation of the cable is seriously aged, and the operation state is unstable.

[0084] Taking a cable with a model of AXCE7 / 12kV1X95 / 25LT as an example, the cable length is 10 m, the cable sheath thickness d b =2mm, the outer semiconductor layer thickness d sc2 =0.7mm, the insulation layer thickness d ins =3.5mm, the inner semiconductor layer thickness d sc1 =0.9mm and the conductor layer radius r1=5.5mm, the experimental operation method comprises the following steps:

[0085] 1) a high-frequency signal with a charge amount of 100pc is generated by using a high-frequency signal calibrator, and the voltage amplitude is 64mv;

[0086] 2) the output signal of the cable end is collected by using an oscilloscope, and the output signal is subjected to Fourier transform by a computer and a network analyzer;

[0087] 3) by analyzing the ratio of the input signal and the output signal, the actual characteristic impedance |Z1| of the signal in the cable is determined =47Ω;

[0088] 4) the cable is modeled, and the first parameters R, L, C and G of the cable are calculated, so that the theoretical characteristic impedance |Z0| of the signal in the cable can be calculated =50Ω;

[0089] 5) according to the formula, the insulation uniform distribution coefficient P of the cable can be calculated =0.96, and it can be known that the insulation condition of the cable is good.

[0090] It can be known from the above technical scheme that the application provides a cable insulation aging evaluation device and method based on high-frequency signal characteristic impedance, by comparing the theoretical characteristic impedance and the actual characteristic impedance of the high-frequency signal in the cable, the insulation uniform distribution parameter of the cable is calculated, so that the insulation aging degree of the cable is evaluated, which is beneficial to predicting the operation state of the cable. In the above embodiment, only the application is described demonstratively, but those skilled in the art can make various modifications to the application without departing from the spirit and scope of the application after reading the patent application.

Claims

1. A method for evaluating cable insulation aging based on the characteristic impedance of high-frequency signals, 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 respectively. The first end is connected to the high-frequency signal calibrator (201), and the last end is connected to the oscilloscope (301) in the measurement system (3). The signal generation system consists of a high-frequency signal calibrator (201) that can generate high-frequency signals, connected to the head end 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 high-frequency signal calibrator (201) and the high-frequency signal at the end 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 high-frequency signal calibrator (201) of the system, give a high-frequency signal excitation of a certain amount of charge at the beginning of the cable, and use an oscilloscope (301) to collect the output signal at the end of the cable. b. While acquiring the output signal, the output signal is analyzed and processed by a computer (302) and a network analyzer (303) connected to the oscilloscope (301); c. Determine the actual characteristic impedance of the high-frequency signal in the cable. ; Solve for the theoretical characteristic impedance of high-frequency signals in this cable. At that time, a method for calculating the inductance L of a bent cable was proposed, and the formula is as follows: ； ； in: The permeability of free space, Let r be the radius of the arc bend, and r1 be the radius of the conductor layer (106). The central angle corresponding to the length of the conductor; The formula for calculating the resistance R of a bent cable is: ； ； in: Let be the magnetic permeability of the conductor. r is the conductivity of the conductor, and r2 is the radius of the insulating layer (104). The signal frequency; 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 characteristic impedance of high-frequency signals propagating unidirectionally in a bent cable for: ； The insulation uniformity distribution coefficient P of the cable is calculated using the following formula: ； The insulation condition and operating status of a cable can be assessed based on the insulation uniformity distribution coefficient P: when 0.9≤P≤1.2, the cable insulation condition is good and the operating status is stable; when P>1.2 or P<0.9, the cable insulation is severely aged and the operating status is unstable.

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