Frequency domain dielectric spectrum unfolding method based on complex dielectric constant real and imaginary part conjoint analysis

Abstract

The invention discloses a frequency domain dielectric spectrum unfolding method based on complex dielectric constant real and imaginary part conjoint analysis, and the method comprises the steps: outputting a series of alternating voltages with different frequencies to a dielectric sample, so as to obtain the response current of the corresponding frequency; combining the waveform information of the response current and the output voltage to obtain a frequency domain dielectric response curve of each parameter; decomposing the frequency domain dielectric response curve into independent spectral lines of different dielectric relaxation processes; measuring the dielectric sample according to a thermal excitation depolarization current method, and determining the number of different relaxation processes in the dielectric sample and the type of generated charges; and based on the independent spectral lines and the types of the generated charges, combining two measurement methods of a frequency domain dielectric spectrum method and a thermal excitation depolarization current method to establish a frequency domain dielectric spectrum analysis model. According to the method, two measurement methods of FDS and TSDC are integrated, the FDS micromechanism of the PPLP film is effectively revealed, and an FDS analysis model with definite physical significance is established.

Description

Technical Field

[0001] The invention belongs to the field of insulation optimization of power equipment. Background Art

[0002] Frequency-Domain Spectroscopy (FDS) is an AC detection method. This method detects the insulation status of the cable by detecting the dielectric parameters of the cable at certain frequencies. It has the advantages of safety and easy extraction of characteristic quantities. The dielectric constant is a basic electrical parameter for measuring the capacitance of a dielectric. First of all, from the definition, an important difference between dielectrics and conductors is that their charges will be stored and accumulated under the action of the electric field force, thereby forming a "counteracting electric field" opposite to the external electric field inside the material. This phenomenon is called polarization. In theory, the charge inside an ideal dielectric material only accumulates. However, due to the inevitable structural defects of actual materials, such as lattice defects or impurity doping inside the crystal, the charge will also undergo directional transfer movement under the action of the electric field, that is, the conductivity process. The relevant theory in condensed matter physics believes that conduction and accumulation are the two main forms of movement of charge in dielectrics. If an alternating voltage U(t)=U is applied to the material m sinωt, the response current generated by the charge accumulation in the polarization process will lead the voltage phase by 90° and be capacitive. However, due to the energy loss of the medium, there will also be a resistive current IR in the same phase as the voltage.

[0003] Due to the polarization and conductivity movement of microscopic charges inside the material, the dielectric response current in the AC electric field will contain two components: capacitive and resistive current. The phase of the resistive response current is consistent with the excitation voltage, while the phase of the capacitive response current is 90° ahead of the excitation voltage. The combined effect of the two results in an acute phase difference φ between the actual response current and the excitation voltage. Therefore, dielectric physics derives the complex dielectric constant ε* based on the concept of dielectric constant in the complex plane, and uses the unit complex number i to characterize the relationship between the excitation voltage, response current and complex dielectric constant.

[0004] Complex dielectric constant ε*(ω) and dielectric loss tanδ(ω) are the most commonly used dielectric parameters by relevant experts and scholars when conducting FDS analysis. In addition, research on parameters such as dielectric modulus M*(ω), complex conductivity σ*(ω), and complex polarizability χ*(ω) has also been derived. However, due to the lack of a full understanding of the microscopic mechanism of dielectric response of insulating materials in a wide band on the one hand, and the lack of in-depth demonstration and analysis of the physical essence reflected by these macroscopic parameters on the other hand, there is often a certain controversy when using different parameters to analyze certain phenomena or curve characteristics in the measured FDS curve. Summary of the invention

[0005] In order to solve the above technical problems, the present invention, based on the analysis of the correlation between the complex dielectric constant and the dielectric relaxation process, firstly proposes a joint analysis method of the real and imaginary parts of the complex dielectric constant in the frequency domain, and decomposes the FDS curve of the PPLP film into independent spectral lines of different dielectric relaxation processes; then, by measuring the TSDC bias voltage method of the PPLP film, the number of different relaxation processes inside it and the type of charge generated are determined; then, with the potential barrier energy level as the key parameter, the two measurement methods of frequency domain dielectric spectroscopy (FDS) and thermally stimulated depolarization current method (TSDC) are linked, thereby effectively revealing the microscopic mechanism of FDS of the PPLP film, and thus establishing an FDS analysis model with clear physical significance.

[0006] The present invention provides the following technical solution: a frequency domain dielectric spectrum decomposition method based on joint analysis of real and imaginary parts of complex dielectric constants, comprising: Output a series of alternating voltages with different frequencies to the dielectric sample to obtain a response current with a corresponding frequency; Combining the waveform information of the response current and the output voltage to obtain a frequency domain dielectric response curve of each parameter; Decomposing the frequency domain dielectric response curve into independent spectral lines of different dielectric relaxation processes; Measuring the dielectric sample according to the thermally stimulated depolarization current method to determine the number of different relaxation processes inside the dielectric sample and the type of charge generated; Based on the independent spectral lines and the type of generated charges, two measurement methods, frequency domain dielectric spectroscopy and thermally stimulated depolarization current method, are combined to establish a frequency domain dielectric spectroscopy analysis model.

[0007] Preferably, the dielectric sample is polypropylene composite paper, which has high dielectric strength and good mechanical properties at low temperatures.

[0008] Preferably, the response current is obtained by a measuring device, and the measuring device includes: a broadband dielectric and impedance spectrometer, and a dielectric spectrum analyzer.

[0009] Preferably, the relevant parameters of the response current include: amplitude and phase of the response current.

[0010] Preferably, the method is implemented using a two-electrode system.

[0011] Preferably, the parameters include: at least one of a dielectric loss angle tanδ, a complex capacitance C*, and a complex dielectric constant ε*.

[0012] Preferably, the structure of the polypropylene composite paper is a "sandwich" geometric structure, which is composited by two layers of kraft paper and one layer of PP film.

[0013] Preferably, the amplitude range of the voltage applied by the dielectric spectrum analyzer is 0~200V.

[0014] Preferably, the frequency range of the dielectric spectrum analyzer is 0.1mHz~10kH.

[0015] Preferably, the frequency domain dielectric spectroscopy method includes: placing the material between the electrode plates of a capacitor, and then applying electrical signals of different frequencies. As the frequency changes, the electric field between the electrode plates will also change, thereby causing polarization of the material. By measuring the capacitance change between the electrode plates, the dielectric constant of the material can be calculated.

[0016] Preferably, the thermally stimulated depolarization current method includes: by measuring the thermally stimulated current of the material during a continuous heating process, the charge movement with different microscopic parameters such as relaxation time τ, polarization intensity p0 or potential barrier energy level H inside the material can be separated and solved separately.

[0017] For the FDS measurement results, the present invention comprehensively observes and analyzes the real and imaginary data characteristics, and on the basis of determining the number of relaxation processes and the corresponding frequency range, flexibly fits each independent dielectric process based on the classical equation, which can effectively reduce the error in the calculation of conductivity loss.

[0018] Considering that, in essence, the response current of the medium in the frequency domain and the depolarization current of the medium during the heating process are both derived from the relaxation motion of various charges inside the medium, they are the response forms of the same physical phenomenon under different condition variables. Therefore, it is proposed that the mature theory of TSDC in the analysis of the microscopic motion mechanism of the medium can provide a reliable criterion for the mechanism interpretation of FDS.

[0019] The technical advantages of the present invention are as follows: Based on the analysis of the correlation between the complex dielectric constant and the dielectric relaxation process, the present invention first proposes a joint analysis method for the real and imaginary parts of the complex dielectric constant in the frequency domain, takes the barrier energy level as the key parameter, and links the two measurement methods of FDS and TSDC, thereby effectively revealing the microscopic mechanism of FDS of PPLP films, thereby establishing an FDS analysis model with clear physical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure of a broadband dielectric and impedance spectrometer; Figure 2 It is a structural schematic diagram of a dielectric spectrum analyzer; Figure 3 It is a schematic diagram of the structure of polypropylene laminated paper; Figures 4(a) to 4(c) show the dielectric spectrum test results of polypropylene laminated paper at different temperatures, where: Figure 4 (a) is a schematic diagram of the spectrum of the real part of the dielectric constant, where the x-axis is the frequency and the y-axis is the real part of the dielectric constant; Figure 4 (b) is a schematic diagram of the imaginary part spectrum of the dielectric constant, where the x-axis is the frequency and the y-axis is the imaginary part of the dielectric constant; Figure 4 (c) is a schematic diagram of the dielectric loss factor spectrum, where the x-axis is the frequency and the y-axis is the dielectric loss factor; Figure 5 The low frequency relaxation FDS fitting diagram of polypropylene laminated paper insulation material; Figure 6 It is a schematic diagram of the conductivity spectrum fitting of polypropylene laminated paper insulation material; Figure 7 The present invention is a flow chart of a method for frequency domain dielectric spectrum decomposition based on joint analysis of real and imaginary parts of complex dielectric constant. DETAILED DESCRIPTION

[0021] The following will refer to the attached Figure 1 to Figure 7 Specific embodiments of the present invention are described in detail. Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0022] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0023] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0024] The present invention provides a frequency domain dielectric spectroscopy (FDS) spectrum analysis method based on the joint analysis of the real and imaginary parts of the complex dielectric constant, comprising: using a broadband dielectric and impedance spectrometer ( Figure 1 ) and dielectric spectrum analyzer ( Figure 2 ) Two devices were used to perform dielectric spectrum testing and analysis on polypropylene laminated paper (PPLP).

[0025] As a preferred scheme of the spectrum decomposition method described in the present invention, a series of alternating voltages with different frequencies are continuously output to the dielectric sample Cx between the high and low voltage electrodes through a variable frequency voltage source, and the internal charges of the dielectric move under the influence of the alternating electric field, generating a response current of the corresponding frequency (usually at the pA level). After the measuring device obtains the amplitude and phase of the response current through its internal microcurrent measurement module, it calculates the corresponding dielectric loss angle tanδ, complex capacitance C* and complex dielectric constant ε* at each frequency point in the wide band in combination with the waveform information of the output voltage, thereby obtaining the frequency domain dielectric response curves of each parameter.

[0026] As a preferred solution of the spectrum interpretation method of the present invention, the present invention adopts a two-electrode system, the diameter of the upper electrode plate is 50 mm, and the diameter of the lower electrode plate is 100 mm.

[0027] As a preferred embodiment of the spectrum analysis method of the present invention, PPLP (also known as polypropylene composite paper) is formed by pressing a porous pulp material with a polypropylene film and has good impregnation properties. Figure 3 As shown, the PPLP structure is a "sandwich" geometric structure, which is composed of two layers of kraft paper and a layer of PP film. Its dielectric strength and dielectric loss are smaller than those of ordinary kraft paper. In addition, under this structure, PPLP has higher dielectric strength and good mechanical properties at low temperatures.

[0028] As a preferred solution of the spectrum analysis method described in the present invention, the electrical signal measurement part in the system (i.e., outputting a series of alternating voltages with different frequencies to the dielectric sample through a variable frequency voltage source to obtain the response current of the corresponding frequency) is realized by a dielectric spectrum analyzer, the amplitude range of the applied voltage is 0~200V, the frequency range is 0.1mHz~10kHz, and the number and position of frequency points can be freely set. The main technical parameters of the dielectric spectrum analyzer are as follows: the measurement range of the frequency domain spectrum is 0.1mHz~10kHz, the measurement accuracy is 1%±3×10-4; the effective value of the output voltage is 140V. The tester can control the software inside the dielectric spectrum analyzer by operating the upper computer to perform FDS test on the sample.

[0029] As a preferred scheme of the spectrum decomposition method described in the present invention, firstly, a joint analysis method of the real and imaginary parts of the complex dielectric constant in the frequency domain is proposed to decompose the FDS curve of the PPLP film into independent spectral lines of different dielectric relaxation processes; then, by measuring the TSDC bias voltage method of the PPLP film, the number of different relaxation processes inside it and the type of charge generated are determined.

[0030] As a preferred embodiment of the spectrum decomposition method of the present invention, the dielectric relaxation process refers to the process in which the dielectric reaches a new polarization equilibrium state from the instantaneously established polarization state after the external electric field acts (or is removed).

[0031] As a preferred solution of the spectrum decomposition method described in the present invention, the potential barrier energy level is used as the key parameter, and the two measurement methods of frequency domain dielectric spectroscopy (FDS) and thermally stimulated depolarization current (TSDC) are linked, thereby effectively revealing the microscopic mechanism of PPLP film FDS, thereby establishing an FDS analysis model with clear physical significance.

[0032] Specifically, no matter whether the dominant charge in the relaxation process is a dipole, an ion, or a space charge, when subjected to an electric field force in a certain direction, the charges inside the dielectric material that originally tend to be distributed at the position with the lowest potential energy will jump over the energy barrier and move in a directional manner.

[0033] The barrier energy level H is an intrinsic parameter of the dielectric process that is independent of temperature. Its physical meaning is the energy level that needs to be overcome for charge detrapping. This parameter can be calculated by two independent dielectric analysis methods, TSDC and FDS. For a material with multiple relaxation processes, if the barrier energy level H obtained by two different measurement methods is consistent in value, the barrier energy level H is used as a "bridge" to establish the correlation between FDS and TSDC.

[0034] As a preferred embodiment of the spectrum analysis method of the present invention, the frequency domain dielectric spectroscopy (FDS) includes placing the material between the electrode plates of a capacitor and then applying electrical signals of different frequencies. As the frequency changes, the electric field between the electrode plates will also change, thereby causing the polarization of the material. By measuring the change in capacitance between the electrode plates, the dielectric constant of the material can be calculated.

[0035] As a preferred solution of the spectrum analysis method described in the present invention, the thermally stimulated depolarization current method (TSDC) includes: by measuring the thermally stimulated current of the material during a continuous heating process, the charge movement of microscopic parameters such as different relaxation times τ, polarization intensity p0 or barrier energy level H inside the material can be separated and solved separately. It should be noted that the mechanism explanation of the dielectric spectrum test results is still imperfect, but the microscopic mechanism explanation of the thermally stimulated depolarization current test results is relatively complete, and in essence, the response current of the medium in the frequency domain and the depolarization current of the medium during the heating process are both derived from the relaxation movement of various charges inside the medium, which are the response forms of the same physical phenomenon under different condition variables. Therefore, with the help of the mature theory of TSDC in the analysis of the microscopic motion mechanism of the medium, a reliable criterion can be provided for the mechanism explanation of FDS.

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification. Example

[0037] The present invention provides a frequency domain dielectric spectrum decomposition method based on the joint analysis of the real and imaginary parts of the complex dielectric constant, such as Figure 7 As shown, the steps include: Output a series of alternating voltages with different frequencies to the dielectric sample to obtain a response current with a corresponding frequency; Combining the waveform information of the response current and the output voltage to obtain a frequency domain dielectric response curve of each parameter; Decomposing the frequency domain dielectric response curve into independent spectral lines of different dielectric relaxation processes; Measuring the dielectric sample according to the thermally stimulated depolarization current method to determine the number of different relaxation processes inside the dielectric sample and the type of charge generated; Based on the independent spectral lines and the type of generated charges, two measurement methods, frequency domain dielectric spectroscopy and thermally stimulated depolarization current method, are combined to establish a frequency domain dielectric spectroscopy analysis model.

[0038] Example 2 The present invention designs an FDS measurement test chamber with a two-electrode structure, wherein the test tank body is a cylindrical fully sealed organic glass tank body, the main body is made of organic glass material, and the interior is designed with a two-electrode structure. When calculating the capacitance of the medium, the effective diameter of the sample is 20 cm. It is worth mentioning that, considering that temperature has a significant effect on the microscopic dielectric relaxation process of the dielectric and the FDS spectrum, this paper adds a temperature sensor in the test chamber and makes it directly contact the sample surface to accurately obtain the sample temperature information during the FDS measurement process.

[0039] During the test, the PPLP film sample is placed between the high voltage electrode and the measuring electrode. The test tank is equipped with a temperature sensor to monitor and adjust the temperature inside the device. The temperature sensor has a resolution of 0.1°C and is attached to the surface of the PPLP film sample to accurately measure the sample temperature. Figures 4 (a) to 4 (c) show the dielectric spectrum test results of PPLP at different temperatures.

[0040] The real and imaginary parts of the dielectric constant are used to measure the capacitive and resistive components of the response current, respectively, and have clear physical meanings. At the same time, the theoretical model with the complex dielectric constant as a variable can quantitatively describe the typical spectra of various single dielectric relaxation processes. Relatively speaking, among the derived dielectric parameters related to FDS analysis, although the correlation between the dielectric loss factor tanδ and the oil-paper insulation state has been widely proven, tanδ(ω) is numerically determined by the ratio of ε”(ω) and ε'(ω). Therefore, when reflecting the microscopic dielectric relaxation process, ε*(ω) is more direct than tanδ(ω), where ε*(ω) is the complex dielectric constant, ε'(ω) is the real part of the complex dielectric constant, and ε”(ω) is the imaginary part of the complex dielectric constant. The dielectric modulus M*(ω), which is calculated by the complex dielectric constant through relevant derivation, is a FDS derived analysis parameter that has been frequently used in recent years. The characteristics shown in its spectrum and the corresponding mechanism are still controversial in interpretation. Therefore, the complex dielectric constant has the advantage of being directly related to microscopic dielectric motion and having a clear meaning.

[0041] Note r ” (ω) is the relaxation loss component of ε” (ω), ε σ ” (ω) is the conductivity loss component of ε” (ω). Usually, ε” (ω) and ε are calculated first. r ” (ω), and then according to the formula ε” (ω) = ε r ”(ω)+ε σ ” (ω) to obtain the relaxation loss component. However, due to the r "(ω) calculation requires an approximate solution and multiple steps of calculation, so ε r The derivation of low-frequency relaxation loss based on ε" (ω) will cause certain errors. For the high-frequency band of the complex dielectric constant, the measured data of ε" (ω) can intuitively show a relaxation process response curve with a small amplitude but not affected by other processes. Therefore, the process can be directly fitted by the data. Taking the spectrum curve measured at -20℃ as an example, the low-frequency relaxation process is recorded as r1 , then the fitting e r1 ’ ( oh ) and based on e r1 ’ ( oh ) derived from e r2 ” ( oh ) Curve such as Figure 5 shown.

[0042] e r1 ’ ( oh )and e r2 ” ( oh ) all show good fitting results. e r1 ” ( oh ) can be directly obtained through the measured data "eh" ( oh )and e r1 ” ( oh ) is subtracted to obtain the conductivity loss component measured at discrete frequencies e σ ” ( oh ), and then fit the data to obtain e σ ” ( oh ), the result is as follows Figure 6 As shown in the figure, the deviation between the conductivity loss and the theoretical value is significantly reduced. The FDS analysis strategy proposed in this paper, through comprehensive observation and analysis of the real and imaginary data characteristics, determines the number of relaxation processes and the corresponding frequency range, and flexibly fits each independent dielectric process based on the classical equation. It has a clear physical meaning, which is an important difference from traditional fitting methods.

[0043] In addition, as a measurement method at constant temperature, FDS can only display independent spectral lines of dielectric processes with different characteristic frequencies in the frequency domain in sequence, and cannot directly realize reliable judgment of the microscopic mechanism of each dielectric process. The thermally stimulated current method measures the charge depolarization current of the medium at variable temperature, and uses the motion characteristics of different charges to distinguish them one by one. At present, a relatively complete theory has been formed. In essence, the response current of the medium in the frequency domain and the depolarization current of the medium during the heating process are both derived from the relaxation motion of various charges inside the medium, and are the response forms of the same physical phenomenon under different conditional variables. Therefore, with the help of TSDC's mature theory in the analysis of the microscopic motion mechanism of the medium, a reliable criterion can be provided for the mechanism interpretation of FDS.

[0044] The following should be noted during the measurement process: The electrical signal measurement part of the system is realized by the dielectric spectrum analyzer, which can provide an excitation voltage with an amplitude of up to 200V. The amplitude range of the applied voltage is 0~200V, the frequency range is 0.1mHz~10kHz, and the number and position of frequency points can be freely set. The main technical parameters of the dielectric spectrum analyzer are as follows: the measurement range of the frequency domain spectrum is 0.1mHz~10kHz, the measurement accuracy is 1%±3×10-4; the effective value of the output voltage is 140V.

[0045] The measurement range selected in this study is 0.01Hz~10Hz, the measurement voltage is 200V (peak value), and the frequency points to be measured are selected using the principle of equal spacing of logarithmic coordinates, with 20 frequency points selected for every 10 times frequency interval.

[0046] The above general description of the invention involved in this application and the description of its specific implementation methods should not be understood as limiting the technical solutions of the invention. Based on the disclosure of this application, those skilled in the art can, without violating the constituent elements of the invention involved, add, reduce or combine the disclosed technical features in the above general description or / and specific implementation methods (including examples) to form other technical solutions within the scope of protection of this application.

Claims

1. A frequency domain dielectric spectrum decomposition method based on joint analysis of real and imaginary parts of complex dielectric constant, characterized in that: The method comprises: Output a series of alternating voltages with different frequencies to the dielectric sample to obtain a response current with a corresponding frequency; Combining the waveform information of the response current and the output voltage to obtain a frequency domain dielectric response curve of each parameter; Decomposing the frequency domain dielectric response curve into independent spectral lines of different dielectric relaxation processes; Measuring the dielectric sample according to the thermally stimulated depolarization current method to determine the number of different relaxation processes inside the dielectric sample and the type of charge generated; Based on the independent spectral lines and the type of generated charges, two measurement methods, frequency domain dielectric spectroscopy and thermally stimulated depolarization current method, are combined to establish a frequency domain dielectric spectroscopy analysis model.

2. The method according to claim 1, characterized in that Preferably, the dielectric sample is polypropylene composite paper.

3. The method according to claim 1, characterized in that: The response current is obtained by measuring equipment, and the measuring equipment includes: a broadband dielectric and impedance spectrometer and a dielectric spectrum analyzer.

4. The method according to claim 1, characterized in that: The method is implemented using a two-electrode system.

5. The method according to claim 1, characterized in that The parameters include: at least one of dielectric loss angle tanδ, complex capacitance C*, and complex dielectric constant ε*.

6. The method according to claim 2, characterized in that The structure of the polypropylene composite paper is a "sandwich" geometric structure.

7. The method according to claim 3, characterized in that The dielectric spectrum analyzer applies a voltage whose amplitude ranges from 0 to 200V.

8. The method according to claim 3, characterized in that The frequency range of the dielectric spectrum analyzer is 0.1mHz~10kH.

9. The method according to claim 1, characterized in that: Frequency domain dielectric spectroscopy involves placing the material between the electrode plates of a capacitor and applying electrical signals of different frequencies. As the frequency changes, the electric field between the electrode plates will also change, causing polarization of the material. By measuring the change in capacitance between the electrode plates, the dielectric constant of the material can be calculated.

10. The method according to claim 1, characterized in that The thermally stimulated depolarization current method includes: by measuring the thermally stimulated current of the material during a continuous heating process, the charge movement with different microscopic parameters such as relaxation time τ, polarization intensity p0 or potential barrier energy level H inside the material can be separated and solved separately.

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