CN111913046A - Principle for measuring steady-state relaxation polarizability of insulating dielectric medium based on polarization current time domain spectrum - Google Patents

Abstract

The invention discloses a principle for measuring the steady-state relaxation polarizability of an insulating dielectric medium based on a polarization current time domain spectrum, belongs to the field of dielectric parameter measurement of the insulating dielectric medium, and mainly solves the technical problems of low efficiency and large error of the existing method for measuring the steady-state relaxation polarizability of the insulating dielectric medium. The basic principle of the invention is as follows: testing and recording the polarization current time domain spectrum of the insulating dielectric medium under the action of direct current voltage based on the pervasive relaxation polarization law (I)_p(t)＝At^‑n) Or relaxed polarization debye expansion model

Polarization absorption current I reflecting relaxation polarization behavior is obtained through least square fitting of polarization current time domain spectrum_p(t); absorbing current I to polarization in time domain space_p(t) integration to obtain relaxed polarization P for a finite period of time_r(t) then applying a saturation function of the sum of the three exponential and constant terms to the relaxed polarization P_r(t) least squares fitting, and inferring the relaxation polarization intensity steady state value P by the fitting theory_rmax。

Description

Principle for measuring steady-state relaxation polarizability of insulating dielectric medium based on polarization current time domain spectrum

Technical Field

The invention relates to the field of dielectric parameters of insulating dielectrics, in particular to a principle for measuring the steady-state relaxation polarizability of the insulating dielectrics based on a polarized current time domain spectrum.

Background

The polarizability (χ) of an insulating dielectric is one of the basic parameters characterizing the properties of the insulating dielectric. Dielectric physics establishes the dielectric polarizability (χ) and static polarizability (χ) for a given frequency for a particular dielectric (which satisfies the single Debye relaxation polarization mechanism)_s) Infinite high frequency polarizability (χ)_∞) And frequency (f). Static polarizability (χ)_s) The external manifestation after polarization is fully established under the action of a direct current electric field is the sum of instantaneous displacement polarization and all relaxation polarization. Theoretically for a particular insulating dielectric, the polarization ratio (χ) at infinity is known_∞) And static polarizability (χ)_s) The polarizability (χ) at any given frequency can be calculated under the conditions.

Steady state relaxed polarizability (χ)_rs) Can be defined as the static polarizability (χ)_s) And high frequency polarizability (χ)_∞) The difference between the two requirements for stable relaxation polarizability is different in different applications. When dielectrics are used in energy storage elements such as capacitors, a large steady state relaxation polarizability is required so that more energy is stored per unit volume. When a dielectric is used for the insulator, the steady state relaxation polarizability is required to be small to reduce the capacitance current flowing. In order to examine and evaluate the performance of electrical equipment and elements, proper materials are selected, and the steady state relaxation polarizability of the dielectric must be measured. Thus achieving a steady state relaxed polarizability (χ)_rs) The measurement and the conjecture of the method have important theoretical significance and engineering significance.

Generally steady state relaxed polarizability (χ)_rs) Can be obtained by a broadband dielectric spectrometer and the like. Such as by usingDielectric spectrum testing of a wide-frequency dielectric spectrometer, such as Novocontrol Concept80, can be performed at a frequency of 10^-3Hz-10⁷Polarizability in the Hz range, will be at a frequency of 10^-3Polarizability in Hz and 10⁷The difference in polarizability in Hz was taken as the steady state relaxed polarizability (χ)_rs). But at a frequency of 10^-3Polarizability in Hz and static polarizability (χ)_s) There is a certain deviation, resulting in inaccurate steady-state relaxation polarizability obtained. Theoretically speaking, the polarizability under lower frequency can be obtained by prolonging the test time, and the obtained result is closer to the static polarizability (x)_s). But simply extending the test time does not solve the problem fundamentally because true steady state is never achieved. In addition, the efficiency is low due to the fact that the testing time is simply prolonged. Therefore, an effective test method for achieving the stable relaxation polarizability (χ) of the dielectric material in a short time is urgently needed_rs) High precision estimation and measurement.

SUMMARY OF THE PATENT FOR INVENTION

Aiming at the defects of the existing dielectric medium steady state relaxation polarizability measuring method, the invention provides a steady state relaxation polarizability (x) based on a polarization current time domain spectrum_rs) The measurement principle of the method can simply, conveniently and accurately obtain the stable relaxation polarizability of the dielectric medium, solves the technical problem of low efficiency of obtaining the stable relaxation polarizability of the insulating dielectric medium, and is easy to realize the measurement of the stable relaxation polarizability under a high electric field.

The above purpose is realized by the following technical scheme:

the principle for measuring the steady-state relaxation polarizability of the insulating dielectric medium based on the time-domain spectrum of the polarized current is characterized in that the polarized absorption current I is measured in the time-domain space_p(t) integration to obtain relaxed polarization P for a finite period of time_r(t) then applying a saturation function of the sum of the three exponential and constant terms to the relaxed polarization P_r(t) least squares fitting, and inferring the relaxation polarization intensity steady state value P by the fitting theory_rmaxThereby accurately obtaining the steady-state relaxation polarizability x_rs。

Further, employing universal relaxation polarizationLaw (I)_p(t)＝At^-n) And extended Debye model

Respectively carrying out least square fitting to determine a fitting function form I of relaxation polarization absorption current by fitting effect_p(t)。

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a measurement principle of steady-state relaxation polarizability of an insulating dielectric medium, which is used for obtaining a polarization absorption current by performing least square fitting on a polarized current time domain spectrum based on a universal relaxation polarization law so as to obtain relaxation polarization strength. And obtaining a stable relaxation polarization intensity value through least square fitting of the relaxation polarization intensity, and realizing the stable relaxation polarization rate chi of the insulating dielectric medium under the corresponding excitation electric field by utilizing the stable relaxation polarization intensity value and the direct current electric field result_rsThe measurement of (2). The method can simply, conveniently and accurately obtain the stable relaxation polarizability of the dielectric medium, and solves the technical problem of low efficiency of obtaining the stable relaxation polarizability of the insulating dielectric medium.

Drawings

FIG. 1 is a schematic diagram of a linear dielectric polarization current test system;

FIG. 2 is a response current density measurement and a generalized relaxation polarization model fitting result for a linear insulating dielectric in an example;

FIG. 3 is a response current density measurement and extended Debye model fitting results for a linear insulating dielectric in an example;

FIG. 4 is a measured and fitted result of the relaxed polarization of the linear insulating dielectric in an example;

reference numerals: 1-a direct current high voltage power supply; 2-a switch; 3-a high voltage electrode; 4-measured insulating dielectric; 5-a measuring electrode; 6-a guard electrode; 7-an electrometer; 8-computer communication line.

Detailed Description

The present invention will be described in detail with reference to the following embodiments and examples. It should be emphasized that this summary is intended to be illustrative, and not limiting, of the invention.

Detailed description of the invention

A principle for measuring the steady-state relaxation polarizability of insulating dielectric based on the time-domain spectrum of polarized current is disclosed, which is characterized by that the polarized absorbed current I is measured in time-domain space_p(t) integrating to obtain the relaxation polarization strength Pr (t) of the limited time period, and then adopting a saturation function of the sum of three exponential terms and constant terms to perform the relaxation polarization strength P_r(t) least squares fitting, and inferring the relaxation polarization intensity steady state value P by the fitting theory_rmaxThereby accurately obtaining the steady-state relaxation polarizability x_rs。

Detailed description of the invention

On the basis of the first embodiment, specifically, a universal relaxation polarization model (I) is adopted_p(t)＝At-ⁿ) And extended Debye model

Respectively carrying out least square fitting to determine a fitting function form I of relaxation polarization absorption current by fitting effect_p(t)。

Detailed description of the invention

On the basis of the first embodiment, specifically, the relaxed polarization P_r(t) is calculated by the formula

In particular, said P_r(t) formula for calculating t₁For the polarized current test time, S is the electrode area, P_rd0The initial relaxed polarization.

Detailed description of the invention

On the basis of the second embodiment, specifically, the current fitting formulas are respectively

I(t)＝At^-n+I_dc

In particular, the current fitting equation includes a relaxed polarization component I_p(t) and a direct current component I_dcRelaxation polarization component I in the Universal relaxation polarization model_p(t) is closely related to constant A, n and time t, and the extended Debye model is related to coefficient A_iAnd relaxation time constant τ_iClosely related, direct current component I_dcIndependent of the time t.

Detailed description of the invention

Based on the second and fourth embodiments, specifically, to obtain the relaxation polarization steady-state value P_rmaxThe selected fitting function is

P_r(t)＝P_rmax-P_rmax1exp(-t/τ₁)-P_rmax2exp(-t/τ₂)-P_rmax3exp(-t/τ₃)

Parameter P in the fitting formula_rmax、P_rmax1、P_rmax2And P_rmax3Are respectively constant, parameter tau₁、τ₂And τ₃Respectively, relaxation time constants. From the formula, P_rmax＝P_rmax1+P_rmax2+P_rmax3When t is 0, the polarization P is relaxed_r(0) 0; when t → ∞ is reached, the polarization P is relaxed_r(∞)＝P_rmax。

Detailed description of the invention

On the basis of the first and fifth embodiments, specifically, the calculation of the insulation dielectric steady-state relaxation polarizability χ_rsIs calculated by the formula

Examples

The insulating dielectric of this example is a 10 wt% silicon carbide/polyethylene composite insulating dielectric, and the electrode area S is 2122.64mm²The thickness d is 0.2mm, a 1kV direct-current high voltage is applied to the tested insulating dielectric by adopting the testing system shown in figure 1, and the model of the electrometer is Gittiley 6517B, the test time t is 0-7200 s, and the change curve of the test current I (t) along with the time t is shown in figure 2.

The fitting current results obtained by fitting the response current by using the universal relaxation polarization model are shown in fig. 2, the fitting parameters obtained in this embodiment are respectively a-1001.53 pA, n-0.99, and the correlation coefficient R-square is 0.35966; the fitting currents obtained by fitting the currents using the extended debye model are shown in fig. 3, where the fitting parameters obtained in this example are a₁＝76.94pA，A₂＝288.70pA，A₃＝11.52pA，τ₁＝26.08s，τ₂＝4.64s，τ₃The correlation coefficient R-square is 0.35955 s 231.92 s. By contrast, the fitting effect of the universal relaxation polarization model is better, so that the universal relaxation polarization model is adopted to fit the polarization current, and the polarization absorption current I is obtained_p(t)＝At^–n. The polarized absorption current density J can be obtained according to the effective area S of the electrode_p(t) of (d). Absorbed current density J for polarization_p(t) integration over time and relaxation of the initial value of polarization P_rd0Obtaining relaxed polarization P at 0_r(t) as shown in FIG. 4. Using fitting formula to relaxation polarization P_r(t) performing time domain least square fitting to obtain a relaxation polarization intensity steady state value P_rmax＝4.56×10^-6C/m². This example gives the steady-state relaxed polarizability χ of the dielectric_rs＝0.103。

Claims (2)

1. The principle for measuring the steady-state relaxation polarizability of the insulating dielectric medium based on the time-domain spectrum of the polarized current is characterized in that the polarized absorption current I is measured in the time-domain space_p(t) integrating to obtain the relaxation polarization strength Pr (t) of the limited time period, and then adopting a saturation function of the sum of three exponential terms and constant terms to perform the relaxation polarization strength P_r(t) least squares fitting, and inferring the relaxation polarization intensity steady state value P by the fitting theory_rmax。

2. In claim 1, the pervasive relaxation of polarization law (I) is used_p(t)＝At^-n) And extended Debye model

Respectively carrying out least square fitting to determine a fitting function form I of relaxation polarization absorption current by fitting effect_p(t)。

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