A method and device for measuring activation energy of cable insulation material based on dielectric spectrum

Abstract

The present invention specifically relates to a method for measuring activation energy of cable insulation materials based on dielectric spectrum, the method comprising the following steps: according to the dielectric spectrum curve of the cable insulation material at different test temperatures, obtaining the test frequency lnf and the test temperature 1 / T of the cable under a certain polarization state, fitting the linear function of the test frequency ln(f) and the test temperature 1 / T, calculating the activation energy of the cable insulation material under the polarization state through the slope of the linear function, taking the arithmetic mean of the activation energy of the cable insulation material under different polarization states, and obtaining the final activation energy value of the cable insulation material. The method of the present invention can quickly and non-destructively obtain the activation energy of the cable insulation material.

Description

Technical Field

[0001] The invention relates to the field of cable performance detection and life assessment, and in particular to a method and device for measuring activation energy of cable insulation materials based on dielectric spectrum. Background Art

[0002] In nuclear power plants and other civilian nuclear facilities, nuclear-grade cables are used for nuclear safety-related instrumentation and control signals and power transmission, which are crucial to the safe and reliable operation of nuclear reactors. Their insulating polymer materials have a greater risk of aging and degradation in high-temperature and high-irradiation service environments. Therefore, accurately detecting and evaluating the aging status of nuclear-grade cables has always been an important issue in the field of aging management in nuclear power plants.

[0003] The thermal aging process of cable insulation materials is a process in which heat acts on material molecules, causing chemical bonds to break, followed by changes in chemical composition, which deteriorates performance and even leads to failure. Therefore, the life of cable insulation materials is essentially a question of the speed of a certain chemical reaction. The slower the reaction speed, the longer the life, and vice versa. In the past decade, many experts and engineers have invested a lot of research efforts in cable aging status and life assessment.

[0004] The activation energy is an essential characteristic parameter that reflects the cable insulation material. The operating state characteristics of the cable insulation material can be obtained based on the activation energy parameter value, so as to achieve its subsequent aging state and life evaluation, and arrange corresponding maintenance measures. According to the activation energy of the cable insulation material, the expected cable identification life and the long-term operating temperature of the cable, the duration of accelerated thermal aging can be calculated by selecting the corresponding accelerated thermal aging test temperature, so as to evaluate the cable life. A slight deviation in the activation energy parameter will have a significant impact on the cable life evaluation results. Therefore, the activation energy value of the cable material must be accurately determined.

[0005] There are two main methods to obtain the activation energy of cable insulation materials: one is based on the kinetics of chemical thermal analysis, namely thermogravimetric method (or oxidation induction test method), which calculates the activation energy by using the relationship between the rate of change of physical quantities and temperature measured by thermal analysis method; the other is based on the Arrhenius equation, which uses the macroscopic performance indicators under the same aging state under different conditions to obtain the activation energy of the cable material, and the commonly used method is the elongation at break method.

[0006] The thermal analysis method is used to determine the activation energy of cables. The reaction temperature range involved is relatively large, and it often involves multiple elementary reactions of cable materials. Whether it can be consistent with the actual reaction mechanism of the cable is still lacking a reasonable explanation. The elongation at break method is used to determine the activation energy of cables. It involves fitting the test data of cables under different aging conditions. However, the activation energy of cables under different aging degrees is not fixed. Therefore, this method itself has errors. The elongation at break method is a destructive test method and is not suitable for cables in service. Summary of the invention

[0007] Based on this, it is necessary to provide a method and device for measuring the activation energy of cable insulation materials based on dielectric spectrum to address the problems of complex measurement process, large errors and great damage in the existing methods for measuring the activation energy of cable insulation materials. This method and device can quickly and non-destructively obtain the activation energy of cable insulation materials.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A method for measuring activation energy of cable insulation materials based on dielectric spectrum comprises the following steps:

[0010] According to the dielectric spectrum curve of the cable insulation material at different test temperatures, the test frequency lnf and the test temperature 1 / T of the cable under a certain polarization state are obtained, and the linear function of the test frequency ln(f) and the test temperature 1 / T is fitted. The activation energy of the cable insulation material under the polarization state is calculated by the slope of the linear function. The arithmetic average of the activation energy of the cable insulation material under different polarization states is taken to obtain the final activation energy value of the cable insulation material.

[0011] Furthermore, the method for measuring activation energy of cable insulation materials based on dielectric spectrum specifically comprises the following steps:

[0012] S1: measuring the dielectric spectrum response of the cable insulation material at different test frequencies at different test temperatures, thereby obtaining the dielectric spectrum data of the cable insulation material at different test temperatures;

[0013] S2: Obtain dielectric spectrum curves of cable insulation materials at different test temperatures through dielectric spectrum data of cable insulation materials at different test temperatures;

[0014] S3: On the dielectric spectrum curve of the cable insulation material at different test temperatures, the test temperature T and the test frequency f of the cable insulation material in a certain polarization state are captured, and the linear function of the cable insulation material in the polarization state is obtained by linearly fitting the test frequency lnf and the test temperature 1 / T of the cable insulation material in the polarization state;

[0015] S4: The linear function of the cable insulation material under a certain polarization state, that is, the temperature compensation formula for the dielectric spectrum test of the cable insulation material. The activation energy of the cable insulation material can be obtained through its slope.

[0016] S5: Repeat S3 and S4 multiple times, take the arithmetic average of the activation energy of the cable insulation material under different polarization states, and obtain the final activation energy value of the cable insulation material.

[0017] Furthermore, in step S1, the dielectric spectrum response of the cable insulation material at different test frequencies is measured in a laboratory by using a frequency sweep method at different test temperatures.

[0018] Furthermore, in step S2, the dielectric spectrum curve adopts logarithmic coordinates, the abscissa is the test frequency, and the ordinate is the dielectric spectrum response of the cable insulation material at the test frequency.

[0019] Furthermore, in step S3, the linear fitting is a least squares linear fitting.

[0020] Furthermore, in step S3, the linear function of the cable insulation material in a certain polarization state is: lnf=a·(1 / T)+b, where a is a constant and b is an intercept.

[0021] Furthermore, in step S4, the temperature compensation formula for the dielectric spectrum test of the cable insulation material in a certain polarization state is: lnf=(-Ea / R)·(1 / T)+b, where R is Avogadro's constant.

[0022] Furthermore, in step S4, the activation energy of the cable insulation material in a certain polarization state is Ea=-a·R.

[0023] A device for measuring activation energy of cable insulation materials based on dielectric spectrum, comprising:

[0024] A signal generating module, used for outputting a power frequency voltage signal and sending it to a frequency conversion module;

[0025] The frequency conversion module is used to receive the power frequency voltage signal sent by the signal generation module and convert it into a broadband voltage signal and then send it to the data acquisition module;

[0026] A signal amplification module, used to amplify the current signal of the test loop and send it to the data acquisition module;

[0027] Temperature control module, used to control and adjust the cable test temperature, and send the temperature data to the data acquisition module;

[0028] A data acquisition module is used to receive the broadband voltage signal sent by the frequency conversion module, the current signal sent by the signal amplification module and the temperature data sent by the temperature control module, and send them to the data processing module;

[0029] A data processing module is used to receive and analyze the data sent by the data acquisition module to obtain dielectric spectrum curves of the cable insulation material at different test temperatures;

[0030] The temperature correction module, by calling the data processing module, captures the test temperature T and test frequency f of the cable insulation material in a certain polarization state on the dielectric spectrum curve of the cable insulation material at different test temperatures, and obtains the linear function of the cable insulation material in the polarization state by linearly fitting the test frequency lnf and the test temperature 1 / T of the cable insulation material in the polarization state, which is the dielectric spectrum test temperature compensation formula of the cable insulation material in the polarization state, and obtains the activation energy of the cable insulation material in the polarization state by slope calculation;

[0031] The human-computer interaction module is used to input cable sample parameters, set test parameters and display all test results.

[0032] Furthermore, the signal generating module is communicatively connected to the frequency conversion module, the frequency conversion module, signal amplifying module and temperature control module are respectively communicatively connected to the data acquisition module, the frequency conversion module and signal amplifying module are respectively connected to the test loop circuit, the data processing module is respectively communicatively connected to the data acquisition module and the temperature correction module, and the human-computer interaction module is respectively communicatively connected to the frequency conversion signal and the temperature control module.

[0033] Furthermore, the shell of the temperature control module is a box-type structure, a heating and cooling device, a multi-point infrared temperature measuring device and a temperature regulating device are arranged inside the temperature control module, and a cable sample bracket is welded on the shell of the temperature control module.

[0034] Furthermore, the cable sample holder is a stainless steel cylindrical structure.

[0035] Furthermore, the surface of the cable sample holder is covered with a silicone pad.

[0036] Furthermore, the silicone pad and the stainless steel cylinder are both hollow structures.

[0037] Furthermore, the cable sample parameters include cable model, cable material and manufacturer.

[0038] Furthermore, the test parameters include test voltage, test frequency and test temperature.

[0039] Furthermore, the test result includes a dielectric spectrum curve.

[0040] Beneficial technical effects of the present invention:

[0041] The method and device for measuring activation energy of cable insulation materials based on dielectric spectrum provided by the present invention can be used for determining activation energy of active or inactive nuclear-grade cables. This activation energy determination method is fast, non-destructive, and has good repeatability, and can provide more accurate activation energy for condition monitoring and life assessment of cable insulation materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of a device for measuring activation energy of a cable insulation material according to the present invention;

[0043] Figure 2 The dielectric spectrum curve diagram of the cable insulation material at different test temperatures in Example 1;

[0044] Figure 3 It is a fitted linear graph of the test frequency lnf and the test temperature 1 / T of the cable insulation material of Example 1 under different polarization states;

[0045] Figure 4 It is a schematic diagram of the cable sample bracket structure in the temperature control module of the present invention. DETAILED DESCRIPTION

[0046] A method for measuring activation energy of cable insulation materials based on dielectric spectrum comprises the following steps:

[0047] S1: Under different test temperatures, the dielectric spectrum response of the cable insulation material at different test frequencies is measured in the laboratory by using a frequency sweep method, so as to obtain the dielectric spectrum data of the cable insulation material at different test temperatures.

[0048] S2: Obtain dielectric spectrum curves of the cable insulation material at different test temperatures through the dielectric spectrum data of the cable insulation material at different test temperatures, wherein the dielectric spectrum curve uses a logarithmic coordinate, wherein the horizontal coordinate is the test frequency, and the vertical coordinate is the dielectric spectrum response of the cable insulation material at the test frequency.

[0049] S3: On the dielectric spectrum curve of the cable insulation material at different test temperatures, the test temperature T and test frequency f of the cable insulation material under the same polarization state are captured, and the test frequency lnf and test temperature 1 / T of the cable insulation material under the same polarization state are linearly fitted by the least squares method to obtain the following linear function: lnf = a·(1 / T)+b, where a is a constant and b is the intercept.

[0050] S4: The activation energy Ea=-a·R of the cable insulation material under the same polarization state is calculated based on the temperature compensation formula of the dielectric spectrum test of the cable insulation material (the dielectric loss temperature compensation factor formula).

[0051] Through step S3 and step S4, the activation energy Ea of the cable insulation material in a certain polarization state can be obtained; by selecting multiple polarization states, and repeating steps S3 and S4 in each polarization state, the activation energy Ea of the cable insulation material in each polarization state can be obtained, and the arithmetic average thereof is taken as the final activation energy measurement result.

[0052] Definition of the temperature compensation formula for dielectric spectrum test: Under a certain polarization state, the test frequency lnf of the dielectric spectrum test of the cable insulation material is linearly related to the test temperature 1 / T as follows: lnf = (-Ea / R)·(1 / T)+b. The linear relationship is the temperature compensation formula for the dielectric spectrum test of the cable insulation material under a certain polarization state.

[0053] Specifically, based on the Arrhenius equation and the dielectric polarization principle, the relationship between the test frequency and the test temperature of the dielectric spectrum test of the cable insulation material is studied. When using the dielectric spectrum test to evaluate the aging state of the cable insulation material, the influence of the ambient temperature on the dielectric spectrum test results must be considered. The reference temperature of the dielectric spectrum test is set as T 2 , the test temperature is T 1 According to the dielectric polarization principle, the polarization characteristic offset relationship of cable insulation materials in the time domain and frequency domain is generally expressed by functions f and χ:

[0054]

[0055]

[0056] Among them, α T1,T2 and τ T1,T2 are the amplitude offset and time offset of dielectric loss in the time domain, β T1,T2 and Ω T1,T2 They are the amplitude offset and frequency offset of dielectric loss in the frequency domain, respectively.

[0057] According to formula 1, formula 2 and inverse Fourier transform, we can get:

[0058]

[0059] For the polarization characteristics of cable insulation materials in the time domain, the time required for the cable insulation material to reach a certain polarization state can be calculated based on the classic Arrhenius equation:

[0060] τ=A exp(Ea / RT) Formula 4

[0061] Where A is the pre-exponential factor, also known as the Arrhenius constant; Ea is the activation energy value of the cable insulation material (in J / mol); R is the molar gas constant (8.31 J / (mol*K)); and T is the absolute temperature (in K).

[0062] According to Formula 3 and Formula 4, the frequency required for the cable insulation material to reach a certain polarization state is:

[0063] ω=A'exp(-Ea / RT) Formula 5

[0064]

[0065] Taking the natural logarithm of both sides of formula 5, we have

[0066]

[0067]

[0068] When the cable insulation material reaches a certain polarization state, ln(f) and 1 / T are linearly related in the rectangular coordinate system. In the logarithmic coordinate system, according to Formula 8, the cable insulation material at a certain test temperature T 1 By translating the dielectric spectrum response curve along the frequency axis, the cable insulation material at the reference temperature T 2 The dielectric spectrum response curve under , Formula 8 is the formula for the dielectric loss temperature compensation factor of the cable insulation material, and its slope is -Ea / R, which is directly related to the activation energy value Ea of the cable insulation material.

[0069] Dielectric spectrum test: Output voltage signals of different frequencies to the test cable sample, and calculate the dielectric spectrum response by testing the loop voltage and current signals.

[0070] A device for measuring activation energy of cable insulation materials based on dielectric spectrum comprises a signal generation module, a frequency conversion module, a signal amplification module, a temperature control module, a data acquisition module, a data processing module and a temperature correction module.

[0071] The signal generating module is connected to the frequency conversion module for outputting a 50 Hz power frequency voltage signal and sending it to the frequency conversion module;

[0072] The frequency conversion module is connected to the test loop circuit and is in communication connection with the data acquisition module, and is used to receive the power frequency voltage signal sent by the signal generation module and convert it into a broadband voltage signal with a frequency range from 0.01 Hz to 10 kHz and then send it to the data acquisition module;

[0073] A signal amplification module is connected to the test loop circuit and is in communication connection with the data acquisition module, and is used to amplify the current signal of the test loop and send it to the data acquisition module;

[0074] The temperature control module is connected to the data acquisition module for controlling and adjusting the cable test temperature and sending the temperature data to the data acquisition module;

[0075] The data acquisition module is used to receive the broadband voltage signal sent by the frequency conversion module, the current signal sent by the signal amplification module and the temperature data sent by the temperature control module, so as to obtain the dielectric spectrum data of the cable insulation material at different test temperatures and send it to the data processing module.

[0076] The data processing module is connected to the data acquisition module for receiving and analyzing the dielectric spectrum data sent by the data acquisition module to obtain the dielectric spectrum curves of the cable insulation material at different test temperatures;

[0077] The temperature correction module is connected to the data processing module for communication. By calling the data processing module, the test temperature T and the test frequency f of the cable insulation material under a certain polarization state are captured on the dielectric spectrum curve of the cable insulation material under different test temperatures. The linear function of the cable insulation material under the polarization state is obtained by linearly fitting the test frequency lnf and the test temperature 1 / T of the cable insulation material under the polarization state, which is the dielectric spectrum test temperature compensation formula of the cable insulation material under the polarization state. The activation energy of the cable insulation material under the polarization state is obtained by slope calculation.

[0078] The human-computer interaction module is respectively connected to the frequency conversion signal and temperature control modules for communication, and is used to input cable sample parameters such as cable sample model, cable sample material and cable sample manufacturer, set test parameters such as test voltage, test frequency and test temperature, and display test results such as dielectric spectrum curves. The human-computer interaction module remotely controls the frequency conversion signal and temperature control module to reach the set test voltage, test frequency and test temperature.

[0079] The shell of the temperature control module is a box-type structure. A heating and cooling device, a multi-point infrared temperature measuring device and a temperature regulating device are arranged inside the temperature control module. A cable sample holder with a stainless steel cylinder structure is welded on the shell of the temperature control module. The surface of the cable sample holder is covered with a silicone pad. During the test, the cable sample is wound around the sample holder. To ensure the temperature uniformity inside the temperature control box, the silicone pad and the stainless steel cylinder are both hollow structures. The temperature control module can accurately adjust and control the test temperature of the cable sample as needed.

[0080] The present invention is further described in detail below in conjunction with embodiments and drawings.

[0081] Example 1

[0082] A method for measuring activation energy of cable insulation material based on dielectric spectrum, wherein the cable is a nuclear-grade K1 cable used in a nuclear power plant, and the insulation material thereof is a halogen-free flame-retardant cross-linked polyolefin material, comprising the following steps:

[0083] S1: With a temperature interval of 10°C, at different test temperatures (30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C), the dielectric spectrum response of the cable insulation material at different test frequencies is measured in the laboratory using a frequency sweep method, thereby obtaining the dielectric spectrum data of the cable insulation material at different test temperatures (30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C).

[0084] S2: Through the dielectric spectrum data of the cable insulation material at different test temperatures (30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃), the dielectric spectrum curves of the cable insulation material at different test temperatures (30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃) are obtained (see Figure 2 ), the dielectric spectrum curve adopts logarithmic coordinates, the horizontal axis is the test frequency, and the vertical axis is the dielectric spectrum response of the cable insulation material under the test frequency.

[0085] S3: Take 6 different dielectric loss values ​​on the dielectric spectrum curve of the cable insulation material at different test temperatures, such as Figure 2 As shown by the horizontal dotted line in the figure, the test temperature T and test frequency f of the cable insulation material in each polarization state are obtained, and the test frequency lnf and test temperature 1 / T of the cable insulation material in each polarization state are linearly fitted by the least squares method to obtain the following linear function in each polarization state:

[0086] lnf=a 1 (1 / T), lnf = a 2 (1 / T), lnf = a 3 (1 / T), lnf = a 4 (1 / T), lnf = a 5 ·(1 / T), a 5 is a constant; lnf = a 6 ·(1 / T), a 1 、a 2 、a 3 、a 4 、a 5 and a 6 are all constants.

[0087] S4: The activation energy Ea of the cable insulation material under different polarization states is calculated based on the temperature compensation formula of the dielectric spectrum test of the cable insulation material. 1 =-a 1 ·R, Ea 2 =-a 2 ·R;Ea 3 =-a 3 ·R;Ea4 =-a 4 ·R;Ea 5 =-a 5 ·R;Ea 6 =-a 6 ·R, see Figure 3 The activation energy values ​​under different polarization states are not much different, indicating that the activation energy results obtained by this method are highly reliable; the arithmetic mean of the activation energy of the cable insulation material under each polarization state is taken, and the final activation energy result of the cable insulation material is 81.35 kJ / mol.

[0088] The above-mentioned method for measuring activation energy of cable insulation materials based on dielectric spectrum adopts a device for measuring activation energy of cable insulation materials based on dielectric spectrum.

[0089] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for measuring activation energy of cable insulation materials based on dielectric spectrum, characterized in that: The steps include: S1: measuring the dielectric spectrum response of the cable insulation material at different test frequencies at different test temperatures, thereby obtaining the dielectric spectrum data of the cable insulation material at different test temperatures; S2: Obtain dielectric spectrum curves of cable insulation materials at different test temperatures through dielectric spectrum data of cable insulation materials at different test temperatures; S3: On the dielectric spectrum curve of the cable insulation material at different test temperatures, the test temperature T and the test frequency f of the cable insulation material in a certain polarization state are captured, and the linear function of the cable insulation material in the polarization state is obtained by linearly fitting the test frequency lnf and the test temperature 1 / T of the cable insulation material in the polarization state; S4: The linear function of the cable insulation material under a certain polarization state is the temperature compensation formula for the dielectric spectrum test of the cable insulation material. The activation energy of the cable insulation material can be obtained through its slope. S5: Repeat S3 and S4 multiple times, take the arithmetic average of the activation energy of the cable insulation material under different polarization states, and obtain the final activation energy value of the cable insulation material; In step S1, the dielectric spectrum response of the cable insulation material at different test frequencies is measured in a laboratory by using a frequency sweep method at different test temperatures; In step S2, the dielectric spectrum curve adopts logarithmic coordinates, the abscissa is the test frequency, and the ordinate is the dielectric spectrum response of the cable insulation material at the test frequency; In step S3, the linear function of the cable insulation material in a certain polarization state is: lnf=a·(1 / T)+b, a is a constant, and b is an intercept; the dielectric spectrum test temperature compensation formula of the cable insulation material in a certain polarization state is: lnf=(-Ea / R)·(1 / T)+b, and R is Avogadro's constant; In step S4, the activation energy of the cable insulation material in a certain polarization state is Ea=-a·R.

2. A device for measuring activation energy of cable insulation materials based on dielectric spectrum, applied to the method for measuring activation energy of cable insulation materials based on dielectric spectrum as claimed in claim 1, characterized in that: include: A signal generating module, used for outputting a power frequency voltage signal and sending it to a frequency conversion module; The frequency conversion module is used to receive the power frequency voltage signal sent by the signal generation module and convert it into a broadband voltage signal and then send it to the data acquisition module; A signal amplification module, used to amplify the current signal of the test loop and send it to the data acquisition module; Temperature control module, used to control and adjust the cable test temperature, and send the temperature data to the data acquisition module; A data acquisition module is used to receive the broadband voltage signal sent by the frequency conversion module, the current signal sent by the signal amplification module and the temperature data sent by the temperature control module, and send them to the data processing module; A data processing module is used to receive and analyze the data sent by the data acquisition module to obtain dielectric spectrum curves of the cable insulation material at different test temperatures; The temperature correction module, by calling the data processing module, captures the test temperature T and test frequency f of the cable insulation material in a certain polarization state on the dielectric spectrum curve of the cable insulation material at different test temperatures, and obtains the linear function of the cable insulation material in the polarization state by linearly fitting the test frequency lnf and the test temperature 1 / T of the cable insulation material in the polarization state, which is the dielectric spectrum test temperature compensation formula of the cable insulation material in the polarization state, and obtains the activation energy of the cable insulation material in the polarization state by slope calculation; The human-computer interaction module is used to input cable sample parameters, set test parameters and display all test results.

3. The device for measuring activation energy of cable insulation materials based on dielectric spectrum according to claim 2, characterized in that: The signal generating module is communicatively connected with the frequency conversion module, the frequency conversion module, the signal amplifying module and the temperature control module are respectively communicatively connected with the data acquisition module, the frequency conversion module and the signal amplifying module are respectively connected with the test loop circuit, the data processing module is respectively communicatively connected with the data acquisition module and the temperature correction module, and the human-computer interaction module is respectively communicatively connected with the frequency conversion signal and the temperature control module.

4. The device for measuring activation energy of cable insulation materials based on dielectric spectrum according to claim 2, characterized in that: The shell of the temperature control module is a box-type structure, a heating and cooling device, a multi-point infrared temperature measuring device and a temperature regulating device are arranged inside the temperature control module, and a cable sample bracket is welded on the shell of the temperature control module.

5. The device for measuring activation energy of cable insulation materials based on dielectric spectrum according to any one of claims 2 to 4, characterized in that: The cable sample holder is a stainless steel cylinder structure, and the surface of the cable sample holder is covered with a silicone pad.

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