Partial discharge simulation method in GIS (Gas Insulated Switchgear) under X-ray excitation

Abstract

The invention discloses a method for simulating partial discharge in a GIS (Gas Insulated Switchgear) under X-ray excitation. The method comprises the following steps: calculating initial electric field distribution in the GIS in simulation software; importing the initial electric field distribution into an MATLAB model, defining each simulation parameter, and obtaining an initial effective electron generation rate in the SF6 gas in the GIS and a photoelectron rate generated under the action of X-ray photoionization; whether partial discharge is generated or not is judged according to the internal electric field intensity of the GIS and the generated electron rate, conduction attenuation of charges in SF6 gas is simulated, and the numerical value change process of charged particles is described; after partial discharge is generated, the charge quantity of partial discharge and the discharge repetition rate are output; according to the method, the change of electrons in the partial discharge process is quantitatively described through a mathematical expression, the generation of partial discharge is judged according to two characteristic quantities, namely the electric field intensity and the number of electrons, and the obtained partial discharge quantity and the discharge repetition rate are close to those of actual discharge.

Description

Technical Field

[0001] The invention relates to the technical field of GIS detection and maintenance, and in particular to a local discharge simulation method in GIS under X-ray excitation. Background Art

[0002] Gas Insulated Switchgear (GIS) is widely used in power systems. GIS is filled with high-pressure SF6 gas. It is difficult to avoid tiny defects during transportation, installation, and operation, such as bubbles, spikes, metal dust, etc. Long-term development may cause insulation breakdown. Partial discharge detection is an effective method for detecting defects, but the sensitivity of this method is average, the effect of detecting tiny defects is not good, and it is seriously affected by electromagnetic interference on site. At present, there is a method of using X-rays to stimulate partial discharge of internal defects in GIS to improve the sensitivity of detection, which has a good effect.

[0003] X-ray excitation of local discharge in SF6 gas is a complex process, involving reactions between multiple particles and the effects of X-rays. Experimental analysis of the mechanism of the influence of X-rays on local discharge is rather cumbersome and greatly affected by the environment. The simulation method can be more intuitive and convenient for analysis, and can quantitatively analyze the change process of different particles and the X-ray photoionization of SF6 gas molecules. The simulation method of X-ray excitation of local discharge in GIS is a complex process. Some current methods do not take into account the action process of multiple particles and the photoionization of X-rays. For example, patent publication number CN113095019A discloses a local discharge simulation method for a plasma fluid model, but this method does not take into account the photoionization of X-rays, and simulates local discharge in the air, which is not suitable for X-ray excitation of local discharge simulation in GIS. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for simulating partial discharge in GIS under X-ray excitation, which aims to reveal the influence mechanism of X-rays on partial discharge in GIS and obtain partial discharge signals more accurately.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for simulating partial discharge in GIS under X-ray excitation, comprising the following steps: Step S1: Calculate the initial electric field distribution in the GIS in the simulation software; Step S2: Import the initial electric field distribution into the MATLAB model, define various simulation parameters, obtain the initial effective electron generation rate in the SF6 gas in the GIS and the photoelectron rate generated by the X-ray photoionization, sum the initial effective electron generation rate and the photoelectron rate generated by the photoionization, and obtain the total electron rate generated in the GIS; Step S3: judging whether partial discharge occurs by the electric field strength inside the GIS and the total electron velocity generated, and further simulating the conduction attenuation of the charge in the SF6 gas to describe the numerical change process of the charged particles; Step S4: After the partial discharge is generated, the charge amount of the partial discharge and the discharge repetition rate are output.

[0006] Furthermore, the initial effective electron generation rate in the SF6 gas in the GIS is: ; ; In the formula, It represents the surface emission rate of free electrons generated by the previous discharge captured by the SF6 gas surface in the GIS; Indicates the starting field strength The number of free electrons generated inside the SF6 gas in the GIS per unit time is as follows; It indicates the actual field strength in the GIS space when partial discharge occurs; Represents the actual field strength in GIS space; Indicates the latest time; Indicates the time when partial discharge occurs; Indicates the rate at which electrons are emitted from the surface of the high-voltage guide rod and SF6 gas; Represents the effective charge decay time constant.

[0007] Furthermore, the initial electric field distribution in GIS is expressed as: ; ; In the formula, Indicates the electric field strength; represents electric potential; represents the dielectric constant of air; Represents the dielectric constant of the material; represents the total charge density; It means to find the derivative.

[0008] Furthermore, the photoelectron rate generated by X-ray photoionization of SF6 gas is: ; In the formula, It indicates the photoelectron rate produced by X-ray photoionization of SF6 gas; represents the conversion coefficient; Indicates the X-ray dose; Indicates the air density; Represents the effective ionized volume of air.

[0009] Furthermore, the electron rate generated by the photoelectrons further ionizing the SF6 gas is: ; ; In the formula, It indicates the electron rate produced by the further ionization of SF6 gas by photoelectrons; It indicates the pressure of the mixed gas after SF6 gas and air are mixed; Indicates the pressure of SF6 gas; represents the probability of photon radiation; It indicates the migration speed of electrons; Indicates The horizontal coordinate of each simulation point; represents the probability of photon absorption; Indicates The simulation point and The distance between simulation points; represents the probability density function; is an infinitely small finite element volume; d represents the integral; Indicates The vertical coordinate of each simulation point; Indicates The vertical coordinate of each simulation point; Indicates The horizontal coordinate of each simulation point; express The horizontal coordinate of each simulation point; It represents the angle between two points; Indicates the number of partial discharges; The sum of the photoelectrons generated by X-ray photoionization and the electron rates generated by further ionization of photoelectrons is: .

[0010] Furthermore, the sum of the photoelectrons generated by the X-ray photoionization and the electron rates generated by the further ionization of the initial effective electrons in the SF6 gas is for: .

[0011] Furthermore, in step S3, the condition for determining whether partial discharge occurs is: ; ; ; ; In the formula, Indicates the actual field strength within the GIS; Indicates the starting field strength of partial discharge; Indicates the threshold electron generation rate for the occurrence of partial discharge; Indicates the extinction field strength of partial discharge; Represents the total number of initial effective electrons in SF6 gas.

[0012] Furthermore, the conduction attenuation of the charge in SF6 gas is simulated to describe the numerical change process of the charged particles, which is expressed as: ; ; ; ; ; ; In the formula, It represents the field strength generated by the surface charge; is the field strength in GIS when there is no surface charge; It indicates the free charge on the surface after partial discharge occurs; represents the electric displacement field of the upper wall in GIS; represents the electric displacement field of the GIS housing wall; It indicates the field strength generated by free charges on the surface after partial discharge occurs; Indicates the total discharge charge from 0 to the occurrence of partial discharge; Indicates The actual discharge amount of each discharge; It is the field strength generated by trapped charges after a partial discharge occurs; represents the surface conductivity; represents the initial surface conductivity; Stress coefficient representing surface conductivity; represents the finite element area; Represents the total area of ​​the solution domain; Indicates the total electric field strength before partial discharge occurs; Indicates the total electric field strength after partial discharge occurs.

[0013] Furthermore, in step S4, the charge amount of the partial discharge is outputted , expressed as: ; In the formula, express Discharge current at all times.

[0014] Furthermore, the simulation parameters in step S2 include: relative dielectric constant of SF6 gas surface, initial conductivity of SF6 gas surface, conductivity of SF6 gas without discharge, maximum conductivity of SF6 gas during discharge, stress coefficient of surface conductivity and effective charge decay time constant.

[0015] Furthermore, the specific process of step S1 is as follows: a simulation model of GIS is established through simulation software; first, the starting voltage of local discharge in GIS is measured through experiments, and X-ray irradiation is applied to gradually increase the voltage. When local discharge occurs for the first time, it is recorded as the discharge starting voltage; by applying the discharge starting voltage on the high-voltage conductor in GIS, grounding is added to the outer shell of GIS, and the electric field distribution inside GIS at different times is calculated.

[0016] Compared with the existing technology, the present invention has the following beneficial effects: the present invention simulates the ionization effect of X-rays on gas molecules by establishing a mathematical model of local discharge, quantitatively describes the changes of electrons in the local discharge process by mathematical expressions, and judges the generation of local discharge based on two characteristic quantities: electric field intensity and the number of electrons. The obtained local discharge amount and discharge repetition rate are close to the actual discharge, accurately restores the local discharge in GIS under X-ray excitation, and improves the accuracy of local discharge simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a flow chart of the method.

[0018] Figure 2 This is a simulation model diagram of the GIS of the present invention.

[0019] Figure 3 This is a phase diagram of the local discharge signal simulated by the present invention.

[0020] Figure 4 This is the phase diagram of the partial discharge signal measured experimentally. DETAILED DESCRIPTION

[0021] like Figure 1 As shown, the present invention provides a technical solution: a method for simulating partial discharge in GIS under X-ray excitation, comprising the following steps:

[0022] Step S1: Calculate the initial electric field distribution within the GIS in the finite element simulation software (COMSOL Multiphysics 5.6).

[0023] In this embodiment, a simulation model of GIS is established in the finite element simulation software, such as Figure 2 As shown in the figure, 1 is the three-pillar insulator of GIS, 2 is the high-voltage conductor, and 3 is the shell; first, the starting voltage of local discharge in GIS is measured experimentally, and X-ray irradiation is applied to gradually increase the voltage. When local discharge occurs for the first time, it is recorded as the discharge starting voltage; by applying the discharge starting voltage on the high-voltage conductor 2 in the GIS, adding grounding on the shell 3 of the GIS, the electric field distribution inside the GIS at different times is calculated.

[0024] Among them, the initial electric field distribution in GIS is expressed as: (1); (2); In the formula, Indicates the electric field strength; represents electric potential; represents the dielectric constant of air; Represents the dielectric constant of the material; represents the total charge density; It means to find the derivative.

[0025] Step S2: Import the initial electric field distribution calculated in step S1 into the MATLAB model (commercial mathematical software), define various simulation parameters, obtain the initial effective electron generation rate in the SF6 gas in the GIS and the photoelectron rate generated by the X-ray photoionization, sum the initial effective electron generation rate and the photoelectron rate generated by the photoionization, and obtain the total electron rate generated in the GIS.

[0026] The simulation parameters defined in this embodiment are shown in Table 1.

[0027] Table 1 Simulation parameters

[0028] Among them, the initial effective electron generation rate in SF6 gas in GIS is: (3); (4); In the formula, It represents the surface emission rate of free electrons generated by the previous discharge captured by the SF6 gas surface in the GIS; Indicates the starting field strength The number of free electrons generated inside the SF6 gas in the GIS per unit time is as follows; It indicates the actual field strength in the GIS space when partial discharge occurs; Represents the actual field strength in GIS space; Indicates the latest time; Indicates the time when partial discharge occurs; Indicates the rate at which electrons are emitted from the surface of the high-voltage guide rod and SF6 gas; Represents the effective charge decay time constant.

[0029] Among them, the photoelectron rate generated by X-ray photoionization of SF6 gas is: (5); In the formula, It indicates the photoelectron rate produced by X-ray photoionization of SF6 gas; represents the conversion coefficient, which is 1.61×10 15 ; Indicates the X-ray dose; Indicates the air density, take 1.226 ; Represents the effective ionized volume of air.

[0030] Among them, the electron rate generated by the further ionization of SF6 gas by photoelectrons is: (6); (7); In the formula, It indicates the electron rate produced by the further ionization of SF6 gas by photoelectrons; It indicates the pressure of the mixed gas after SF6 gas and air are mixed; Indicates the pressure of SF6 gas; represents the probability of photon radiation; It indicates the migration speed of electrons; Indicates The horizontal coordinate of each simulation point; represents the probability of photon absorption; Indicates The simulation point and The distance between simulation points; represents the probability density function; is an infinitely small finite element volume; d represents the integral; Indicates The vertical coordinate of each simulation point; Indicates The vertical coordinate of each simulation point; Indicates The horizontal coordinate of each simulation point; express The horizontal coordinate of each simulation point; It represents the angle between two points; Indicates the number of partial discharges.

[0031] The sum of the photoelectrons generated by X-ray photoionization and the electron rates generated by further ionization of photoelectrons is: .

[0032] The sum of the photoelectrons generated by X-ray photoionization and the electron rates generated by the further ionization of the initial effective electrons in the SF6 gas for: (8). Step S3: Determine whether partial discharge occurs by the electric field strength inside the GIS and the total electron velocity generated, and further simulate the conduction attenuation of the charge in the SF6 gas to describe the numerical change process of the charged particles.

[0033] The conditions for the occurrence of partial discharge in this embodiment are: the maximum field strength in the GIS is between the starting field strength and the extinction field strength, and the sum of the naturally generated electron rate and the photoelectron rate generated by X-ray photoionization is greater than a set threshold.

[0034] The conditions for determining whether partial discharge occurs are: (9); (10); (11); (12); In the formula, Indicates the actual field strength within the GIS; Indicates the starting field strength of partial discharge; Indicates the threshold electron generation rate for the occurrence of partial discharge; Indicates the extinction field strength of partial discharge; Represents the total number of initial effective electrons in SF6 gas.

[0035] Among them, the conduction attenuation of charge in SF6 gas is simulated to describe the numerical change process of charged particles, which is expressed as: (13); (14); (15); (16); (17); (18); In the formula, It represents the field strength generated by the surface charge; is the field strength in GIS when there is no surface charge; It indicates the free charge on the surface after partial discharge occurs; represents the electric displacement field of the upper wall in GIS; represents the electric displacement field of the GIS housing wall; It indicates the field strength generated by free charges on the surface after partial discharge occurs; Indicates the total discharge charge from 0 to the occurrence of partial discharge; Indicates The actual discharge amount of each discharge; It is the field strength generated by trapped charges after a partial discharge occurs; represents the surface conductivity; represents the initial surface conductivity; Stress coefficient representing surface conductivity; represents the finite element area; Represents the total area of ​​the solution domain; Indicates the total electric field strength before partial discharge occurs; Indicates the total electric field strength after partial discharge occurs.

[0036] Step S4: when partial discharge occurs, the charge amount and discharge repetition rate of the partial discharge are output.

[0037] Among them, the output partial discharge charge , expressed as: (19); In the formula, Indicates the discharge current; Indicates time.

[0038] like Figure 3-Figure 4 As shown, the simulated partial discharge signal of the present invention and the partial discharge signal obtained by experimental measurement under the same conditions are compared. It can be seen from the figure that the shapes of the discharge spectra and the discharge phases of the simulated partial discharge signal of the present invention and the partial discharge signal obtained by experimental measurement correspond to each other as a whole, and the deviation of the discharge amount is within 10%. In addition, the simulated partial discharge signal of the present invention and the partial discharge signal obtained by experimental measurement over more than 10,000 power frequency cycles are compared, and the deviation of the discharge amount is within 10%, thereby proving the effectiveness of the simulation method proposed in the present invention.

[0039] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for simulating partial discharge in GIS under X-ray excitation, characterized in that: The steps include: Step S1: Calculate the initial electric field distribution in the GIS in the simulation software; Step S2: Import the initial electric field distribution into the MATLAB model, define various simulation parameters, obtain the initial effective electron generation rate in the SF6 gas in the GIS and the photoelectron rate generated by the X-ray photoionization, sum the initial effective electron generation rate and the photoelectron rate generated by the photoionization, and obtain the total electron rate generated in the GIS; Step S3: judging whether partial discharge occurs by the electric field strength inside the GIS and the total electron velocity generated, and further simulating the conduction attenuation of the charge in the SF6 gas to describe the numerical change process of the charged particles; Step S4: after the partial discharge is generated, the charge amount of the partial discharge and the discharge repetition rate are output; Simulate the conduction attenuation of charge in SF6 gas and describe the numerical change process of charged particles, which can be expressed as: ； ； ； ； ； ； In the formula, It represents the field strength generated by the surface charge; Represents the actual field strength in GIS space; is the field strength in GIS when there is no surface charge; Indicates the latest time; It indicates the free charge on the surface after partial discharge occurs; Indicates the time when partial discharge occurs; Represents the total area of ​​the solution domain; represents the electric displacement field of the upper wall in GIS; represents the electric displacement field of the GIS shell wall; d represents the integral; represents the finite element area; It indicates the field strength generated by free charges on the surface after partial discharge occurs; Indicates the total discharge charge from 0 to the occurrence of partial discharge; Indicates the total electric field strength before partial discharge occurs; Indicates The actual discharge amount of each discharge; Indicates the number of partial discharges; It is the field strength generated by trapped charges after a partial discharge occurs; Indicates the total electric field strength after partial discharge occurs; represents the surface conductivity; represents the initial surface conductivity; Stress coefficient that represents the conductivity of the surface.

2. The method for simulating partial discharge in GIS under X-ray excitation according to claim 1, characterized in that: The initial effective electron generation rate in SF6 gas in GIS is: ； ； In the formula, It represents the surface emission rate of free electrons generated by the previous discharge captured by the SF6 gas surface in the GIS; Indicates the electric field strength; Indicates the starting field strength The number of free electrons generated inside the SF6 gas in the GIS per unit time is as follows; It indicates the actual field strength in the GIS space when partial discharge occurs; Indicates the rate at which electrons are emitted from the surface of the high-voltage guide rod and SF6 gas; Represents the effective charge decay time constant.

3. The method for simulating partial discharge in GIS under X-ray excitation according to claim 2, characterized in that: The initial electric field distribution in GIS is expressed as: ； ； In the formula, represents electric potential; represents the dielectric constant of air; Represents the dielectric constant of the material; represents the total charge density; It means to find the derivative.

4. The method for simulating partial discharge in GIS under X-ray excitation according to claim 3, characterized in that: The photoelectron rate generated by X-ray photoionization of SF6 gas is: ； In the formula, It indicates the photoelectron rate produced by X-ray photoionization of SF6 gas; represents the conversion coefficient; Indicates the X-ray dose; Indicates the air density; Represents the effective ionized volume of air.

5. The method for simulating partial discharge in GIS under X-ray excitation according to claim 4, characterized in that: The electron rate produced by the further ionization of SF6 gas by photoelectrons is: ； ； In the formula, It indicates the electron rate produced by the further ionization of SF6 gas by photoelectrons; It indicates the pressure of the mixed gas after SF6 gas and air are mixed; Indicates the pressure of SF6 gas; represents the probability of photon radiation; Indicates the migration speed of electrons; Indicates The horizontal coordinate of each simulation point; represents the probability of photon absorption; Indicates The simulation point and The distance between simulation points; represents the probability density function; is an infinitely small finite element volume; Indicates The vertical coordinate of each simulation point; Indicates The vertical coordinate of each simulation point; Indicates The horizontal coordinate of each simulation point; express The horizontal coordinate of each simulation point; It represents the angle between two points; The sum of the photoelectrons generated by X-ray photoionization and the electron rates generated by further ionization of photoelectrons is: .

6. The method for simulating partial discharge in GIS under X-ray excitation according to claim 5, characterized in that: The sum of the photoelectrons generated by X-ray photoionization and the electron rates generated by the further ionization of the initial effective electrons in the SF6 gas for: 。 7. The method for simulating partial discharge in GIS under X-ray excitation according to claim 6, characterized in that: In step S3, the conditions for determining whether partial discharge occurs are: ； ； ； ； In the formula, Indicates the actual field strength within the GIS; Indicates the starting field strength of partial discharge; Indicates the threshold electron generation rate for the occurrence of partial discharge; Indicates the extinction field strength of partial discharge; Represents the total number of initial effective electrons in SF6 gas.

8. The method for simulating partial discharge in GIS under X-ray excitation according to claim 7, characterized in that: In step S4, the amount of charge of partial discharge is output , expressed as: ； In the formula, express Discharge current at all times.

9. The method for simulating partial discharge in GIS under X-ray excitation according to claim 2, characterized in that: The simulation parameters in step S2 include: relative dielectric constant of SF6 gas surface, initial conductivity of SF6 gas surface, conductivity of SF6 gas without discharge, maximum conductivity of SF6 gas during discharge, stress coefficient of surface conductivity and effective charge decay time constant.

10. The method for simulating partial discharge in GIS under X-ray excitation according to claim 1, characterized in that: The specific process of step S1 is as follows: a simulation model of GIS is established through simulation software; first, the starting voltage of local discharge in GIS is measured experimentally, and X-ray irradiation is applied to gradually increase the voltage. When local discharge occurs for the first time, it is recorded as the discharge starting voltage; by applying the discharge starting voltage on the high-voltage conductor in GIS, grounding is added to the outer shell of GIS, and the electric field distribution inside GIS at different times is calculated.

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