CN109408885B - Insulator space charge density model optimization method under high voltage direct current - Google Patents
Insulator space charge density model optimization method under high voltage direct current Download PDFInfo
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Abstract
The invention relates to an optimization method of an insulator space charge density model under high voltage direct current, which comprises the following steps: step S1: taking the temperature and the time-varying electric field as independent variables to obtain a conductivity mathematical model and a conductivity current density; step S2: establishing a dielectric relaxation function and obtaining relaxation polarization current density; step S3: summing the conductance current density, the relaxation polarization current density and the instantaneous polarization current density to obtain a volume current density; step S4: integrating the volume current density to obtain a space charge density data model. Compared with the prior art, the invention comprehensively considers the influence of temperature, electric field and dielectric relaxation on the space charge density, solves the problem of the existing model on the environmental factors, and simulates and analyzes the influence degree of each factor on the space charge density, thereby being used as the reference for the material selection and structural design of the high-voltage direct-current insulator.
Description
Technical Field
The invention relates to the field of electric power, in particular to an optimization method of an insulator space charge density model under high voltage direct current.
Background
Along with the increasing acceleration of the construction engineering of China high-voltage direct current transmission, the research on some key problems under high-voltage direct current is very important. The electric charge is easy to accumulate in the insulator under the action of direct current high voltage for a long time, so that the electric field distribution in the insulator is affected, the withstand voltage of the insulator is reduced, the insulation strength is possibly reduced when the withstand voltage is severe, and hidden danger is brought to an insulation system. Therefore, it is important to build a mathematical model for calculating the internal space charge density of the insulator.
Under the action of the direct current electric field, space charges accumulated in the insulator can obviously influence the electric field distribution and the insulation performance of the insulation system. Although there is a certain research on the space charge density of the insulator internationally at present, most of the theoretical models established in the prior literature are simplified through simulation and test, and the influence of a plurality of external environmental conditions is ignored, so that a plurality of unresolved problems still exist in theoretical research.
Currently, in research on insulators, a fixed conductivity is mostly used as a research basis. In fact, the running current in the direct current transmission system is large, and obvious heating phenomenon can occur in the transmission channel. The temperature change causes a change in the electrical properties of the insulator, which in turn causes a change in the electrical conductivity. The conductivity of solid media is also dependent on the change in field strength, in addition to being affected by temperature. The electric charge on the surface of the insulator accumulates to distort the electric field distribution of the insulator, thereby changing the conductivity. In the process of accumulating and dissipating charges on the surface of an insulator, a plurality of relaxation phenomena exist, and dielectric relaxation plays an important role on the time constant of the process, so that the influence of dielectric relaxation is also a critical research content.
The influence of temperature, time-varying electric field, dielectric relaxation and the like on the charge density is rarely considered in the existing experimental study, and the charge accumulation condition of the direct current insulator used in practical engineering is difficult to obtain. For this reason, a new mathematical model on insulator space charge density needs to be explored for the above problems.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an optimization method for the space charge density model of the insulator under high voltage direct current.
The aim of the invention can be achieved by the following technical scheme:
an optimization method of an insulator space charge density model under high voltage direct current comprises the following steps:
step S1: taking the temperature and the time-varying electric field as independent variables to obtain a conductivity mathematical model and a conductivity current density;
step S2: establishing a dielectric relaxation function and obtaining relaxation polarization current density;
step S3: summing the conductance current density, the relaxation polarization current density and the instantaneous polarization current density to obtain a volume current density;
step S4: integrating the volume current density to obtain a space charge density data model.
The step S1 specifically comprises the following steps:
step S11: taking the temperature and the time-varying electric field as independent variables to obtain a conductivity mathematical model:
σ＝σ 0 e αT+βE(t) (1)
wherein: sigma is the conductivity of the dielectric, sigma 0 For initial conductivity, T is temperature, E (T) is electric field strength, α is temperature coefficient, and β is field strength coefficient.
Step S12: obtaining a conductivity current density based on the obtained conductivity mathematical model:
j 1 (t)＝σ 0 e βE(t)+αT E(t)
wherein: j (j) 1 And (t) is the conductance current density.
The field intensity coefficient and the temperature coefficient are obtained through fitting experimental data.
The step S2 specifically includes:
step S21: measuring the relaxation values of the insulator material with time at different temperatures and the conductivities of the insulator volumes;
step S22: from the measured relaxation coefficients, a dielectric relaxation function f (t) is established:
f(t)＝At -n
wherein: a and n are relaxation coefficients obtained by fitting, and t is time;
step S23: obtaining relaxation polarization current density according to the convolution of the established dielectric relaxation function and the electric field intensity:
wherein: j (j) 3 (t) is ChiRelaxation polarization current density, ε 0 For the vacuum dielectric constant, τ is the time before t.
The instantaneous polarization current density is specifically:
wherein: j (j) 2 (t) is instantaneous polarized current density, ε ∞ Is the optical frequency dielectric constant.
The method further comprises the steps of:
step S5: and simulating and verifying the obtained space charge density data model.
Compared with the prior art, the invention has the following beneficial effects:
1) The influence of temperature, electric field and dielectric relaxation on space charge density is comprehensively considered, the problem that the existing model is poor in consideration of environmental factors is solved, the influence degree of various factors on the space charge density is simulated and analyzed, and the method can be used as a reference for the material selection and structural design of the high-voltage direct-current insulator.
2) By establishing special mathematical models of three current densities, the accuracy can be improved while ensuring that the computational load is not excessive.
3) Simulation verification is carried out after renting, so that guidance can be provided for subsequent improvement, and the optimization effect is further improved.
Drawings
FIG. 1 is a schematic flow chart of the main steps of the method of the present invention.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical scheme of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following examples.
An optimization method for an insulator space charge density model under High Voltage Direct Current (HVDC), as shown in figure 1, comprises the following steps:
step S1: taking the temperature and the time-varying electric field as independent variables to obtain a conductivity mathematical model and a conductivity current density, wherein the conductivity increases exponentially along with the increase of the temperature and the electric field, and the method specifically comprises the following steps:
step S11: taking the temperature and the time-varying electric field as independent variables to obtain a conductivity mathematical model:
σ＝σ 0 e αT+βE(t) (1)
wherein: sigma is the conductivity of the dielectric, sigma 0 For initial conductivity, T is temperature, E (T) is electric field strength, α is temperature coefficient, and β is field strength coefficient.
Step S12: obtaining a conductivity current density based on the obtained conductivity mathematical model:
j 1 (t)＝σ 0 e βE(t)+αT E(t)
wherein: j (j) 1 And (t) is the conductance current density.
The field intensity coefficient and the temperature coefficient are obtained through fitting experimental data.
Step S2: establishing a dielectric relaxation function and obtaining a relaxation polarization current density, which specifically comprises the following steps:
step S21: measuring the relaxation values of the insulator material with time at different temperatures and the conductivities of the insulator volumes;
step S22: from the measured relaxation coefficients, a dielectric relaxation function f (t) is established:
f(t)＝At -n
wherein: a and n are relaxation coefficients obtained by fitting, and t is time;
step S23: obtaining relaxation polarization current density according to the convolution of the established dielectric relaxation function and the electric field intensity:
wherein: j (j) 3 (t) is the relaxation polarization current density, τ is the time before t.
Step S3: summing the conductance current density, the relaxation polarization current density and the instantaneous polarization current density to obtain a volume current density;
wherein, instantaneous polarization current density specifically is:
wherein: j (j) 2 (t) is instantaneous polarized current density, ε ∞ Is the optical frequency dielectric constant.
The volume current density is therefore.
Wherein j is 1 (t) is the conductivity current density, j 2 (t) is instantaneous polarized current density, j 3 (t) is the relaxation polarization current density, j (t) is the volume current density, ε 0 Is vacuum dielectric constant.
Step S4: integrating the volume current density to obtain a space charge density data model.
Wherein, the model of charge density when there is initial accumulated charge without an applied electric field can be rewritten as:
where ε is the dielectric constant of the material.
Step S5: the obtained space charge density data model is simulated and verified, specifically, the influence of various factors such as temperature, electric field, polarization and initial conductivity on the change trend of the space charge density is simulated and analyzed, specifically, the change trend of the charge density under various influence factors, especially the influence on the charge accumulation or dissipation speed, is simulated, and the influence of a single variable on the instantaneous polarization current density, the conductance current density, the relaxation polarization current density and the total current density is respectively analyzed, and the specific gravity of various current density components in the total current density under the condition is analyzed.
Claims (3)
1. The optimization method of the insulator space charge density model under high voltage direct current is characterized by comprising the following steps of:
step S1: taking the temperature and the time-varying electric field as independent variables to obtain a conductivity mathematical model and a conductivity current density;
step S2: establishing a dielectric relaxation function and obtaining relaxation polarization current density;
step S3: summing the conductance current density, the relaxation polarization current density and the instantaneous polarization current density to obtain a volume current density;
step S4: integrating the volume current density to obtain a space charge density data model;
the step S1 specifically comprises the following steps:
step S11: taking the temperature and the time-varying electric field as independent variables to obtain a conductivity mathematical model:
σ＝σ 0 e αT+βE(t) (1)
wherein: sigma is the conductivity of the dielectric, sigma 0 For initial conductivity, T is temperature, E (T) is electric field strength, alpha is temperature coefficient, and beta is field strength coefficient;
step S12: obtaining a conductivity current density based on the obtained conductivity mathematical model:
j 1 (t)＝σ 0 e βE(t)+αT E(t)
wherein: j (j) 1 (t) is the conductivity current density;
the field intensity coefficient and the temperature coefficient are obtained through fitting experimental data;
the step S2 specifically includes:
step S21: measuring the relaxation values of the insulator material with time at different temperatures and the conductivities of the insulator volumes;
step S22: from the measured relaxation coefficients, a dielectric relaxation function f (t) is established:
f(t)＝At -n
wherein: a and n are relaxation coefficients obtained by fitting, and t is time;
step S23: obtaining relaxation polarization current density according to the convolution of the established dielectric relaxation function and the electric field intensity:
wherein: j (j) 3 (t) is the relaxation polarization current density, ε 0 For the vacuum dielectric constant, τ is the time before t.
2. The optimization method of the space charge density model of the insulator under high voltage direct current according to claim 1, wherein the instantaneous polarization current density is specifically:
wherein: j (j) 2 (t) is instantaneous polarized current density, ε ∞ Is the optical frequency dielectric constant.
3. The method for optimizing a space charge density model of an insulator under high voltage direct current according to claim 1, wherein the method further comprises:
step S5: and simulating and verifying the obtained space charge density data model.
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| CN111562440B (en) * | 2020-05-27 | 2022-11-15 | 哈尔滨理工大学 | Method for measuring resistivity of insulating dielectric medium based on time domain least square fitting |
| CN112380672B (en) * | 2020-10-21 | 2022-06-03 | 天津大学 | Simulation method for determining density distribution of post insulator and disc insulator |
| CN112698115B (en) * | 2020-12-03 | 2021-11-23 | 华北电力大学 | Electric field distribution determination method and system in multilayer composite medium transient process |
| CN112711823A (en) * | 2020-12-09 | 2021-04-27 | 国网宁夏电力有限公司检修公司 | Method for calculating surface charge of extra-high voltage sleeve supporting insulator and optimization method |
| CN113533870B (en) * | 2021-06-23 | 2024-03-22 | 国网山东省电力公司青岛供电公司 | Prediction method and system for correcting space charge density in corona cage by considering environmental factors |
| CN114137281B (en) * | 2021-11-25 | 2023-04-07 | 北京交通大学 | Space charge evaluation method based on conductive current |
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