A Method for Simulating Partial Discharge in GIS under X-ray Excitation

Abstract

The present invention discloses a method for simulating partial discharge in GIS under X-ray excitation, which comprises the following steps: calculating the initial electric field distribution in GIS in a simulation software; importing the initial electric field distribution into a MATLAB model, defining each simulation parameter, and obtaining the initial effective electron generation rate in SF6 gas in GIS and the photoelectron rate generated under the action of X-ray photoionization; judging whether partial discharge occurs according to the internal electric field strength of GIS and the generated electron rate, simulating the conduction and attenuation of charges in SF6 gas, and describing the numerical change process of charged particles; after partial discharge occurs, outputting the charge quantity of partial discharge and the discharge repetition rate; the present invention quantitatively describes the change of electrons in the partial discharge process through a mathematical expression, judges the occurrence of partial discharge according to two characteristic quantities of electric field strength and electron number, and the obtained partial discharge quantity and discharge repetition rate are close to the actual discharge.

Description

Technical Field

[0001] The present invention relates to the technical field of GIS detection and maintenance, and specifically to a method for simulating partial discharge in GIS under X-ray excitation. Background Art

[0002] In the power system, the gas-insulated switchgear (GIS) is widely used. The inside of the GIS is filled with high-pressure SF 6 gas. It is difficult to avoid generating tiny defects such as bubbles, spikes, and metal dust during transportation, installation, and operation. Long-term development may lead to insulation breakdown. Partial discharge detection is an effective method for detecting defects, but the sensitivity of this method is generally average, and the detection effect for tiny defects is not good. Moreover, it is seriously affected by electromagnetic interference on site. Currently, there is a method of using X-ray to excite partial discharge of internal defects in GIS to improve the detection sensitivity, and it has a good effect.

[0003] The partial discharge in SF 6 gas excited by X-ray is a complex process, involving reactions between various particles and the action of X-ray. It is rather troublesome to analyze the influence mechanism of X-ray on partial discharge through experiments, and it is greatly affected by the environment. The simulation method can analyze more intuitively and conveniently, and can quantitatively analyze the change process of different particles and the photoionization of SF 6 gas molecules by X-ray. The simulation method of partial discharge in GIS excited by X-ray is a complex process. Some current methods do not consider the action process of various particles and the photoionization effect of X-ray. For example, the patent publication number CN113095019A discloses a method for simulating partial discharge of a plasma fluid model, but this method does not consider the photoionization effect of X-ray, and it simulates partial discharge in air, which is not applicable to simulating partial discharge in GIS excited by X-ray. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a method for simulating partial discharge in GIS under X-ray excitation, aiming to reveal the influence mechanism of X-ray 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, including the following steps:

[0006] Step S1: Calculate the initial electric field distribution inside the GIS in the simulation software;

[0007] Step S2: Import the initial electric field distribution into the MATLAB model, define each simulation parameter, and obtain SF inside the GIS 6The initial effective electron generation rate in the gas and the photoelectron rate generated under X-ray photoionization are summed to obtain the total electron rate generated in the GIS.

[0008] Step S3: Determine whether partial discharge occurs based on the internal electric field strength of the GIS and the total electron rate generated, and further simulate the conduction attenuation of charges in SF 6 gas to describe the numerical change process of charged particles.

[0009] Step S4: After partial discharge occurs, output the charge quantity and discharge repetition rate of the partial discharge.

[0010] Furthermore, the initial effective electron generation rate in SF 6 gas in the GIS is:

[0011] ;

[0012] ;

[0013] In the formula, represents the surface emission rate of free electrons generated by the previous discharge captured on the surface of SF 6 gas in the GIS; represents the number of free electrons generated per unit time in SF gas in the GIS under the initial field strength 6 ; represents the actual field strength in the GIS space during partial discharge; represents the actual field strength in the GIS space; represents the latest time; represents the time of partial discharge; represents the rate of surface-emitted electrons generated by the high-voltage guide rod and SF 6 gas; represents the effective charge decay time constant.

[0014] Furthermore, the initial electric field distribution in the GIS is expressed as:

[0015] ;

[0016] ;

[0017] In the formula, represents the electric field strength; represents the electric potential; represents the dielectric constant of air; represents the dielectric constant of the material; represents the total charge density; Indicates taking the derivative.

[0018] Furthermore, the rate of photoelectrons generated by X-ray photoionization of SF 6 gas is:

[0019] ;

[0020] In the formula, represents the rate of photoelectrons generated by X-ray photoionization of SF6 gas; represents the conversion coefficient; represents the X-ray dose; represents the air density; represents the effective ionization volume of air.

[0021] Furthermore, the rate of electrons generated by further ionization of SF 6 gas by photoelectrons is:

[0022] ;

[0023] ;

[0024] In the formula, represents the rate of electrons generated by further ionization of SF 6 gas by photoelectrons; represents the pressure of the mixed gas after mixing SF 6 gas and air; represents the pressure of SF 6 gas; represents the photon radiation probability; represents the migration velocity of electrons; represents the abscissa of the th simulation point; represents the photon absorption probability; represents the distance between the th simulation point and the th simulation point; is an infinitesimal finite element volume; d represents integration; represents the ordinate of the th simulation point; represents the ordinate of the th simulation point; represents the abscissa of the th simulation point; represents the number of partial discharges;

[0025] The sum of the rates of the photoelectrons generated by X-ray photoionization and the electrons generated by the further ionization of the photoelectrons is: .

[0026] Furthermore, the sum of the rates of the photoelectrons generated by X-ray photoionization and the electrons generated by the further ionization of the initial effective electrons in the SF 6 gas is: For:

[0027] .

[0028] Furthermore, in step S3, the conditions for judging whether partial discharge occurs are:

[0029] ;

[0030] ;

[0031] ;

[0032] ;

[0033] In the formula, represents the actual field strength in the GIS; represents the inception field strength of partial discharge; represents the threshold electron generation rate at which partial discharge occurs; represents the extinction field strength of partial discharge; represents the sum of the initial effective electrons in the SF 6 gas.

[0034] Furthermore, the conduction attenuation of the simulated charges in the SF 6 gas, which describes the numerical change process of the charged particles, is expressed as:

[0035] ;

[0036] ;

[0037] ;

[0038] ;

[0039] ;

[0040] ;

[0041] In the formula, represents the field strength generated by the surface charge; is the field strength in the GIS without surface charge; Represents the surface free charge after partial discharge occurs; Represents the electric displacement field of the upper wall in GIS; Represents the electric displacement field of the GIS outer shell wall; Represents the field strength generated by the surface free charge after partial discharge occurs; Represents the total discharge charge from the start to after partial discharge occurs; Represents the true discharge amount of the th discharge; Represents the surface conductivity; Represents the initial surface conductivity; Represents the stress coefficient of surface conductivity; Represents the finite element area; Represents the total area of the solution domain; Represents the total electric field strength before partial discharge occurs; Represents the total electric field strength after partial discharge occurs.

[0042] Furthermore, in step S4, the charge quantity of partial discharge is output , expressed as:

[0043] ;

[0044] In the formula, represents the discharge current at time

[0045] Furthermore, the simulation parameters in step S2 include: SF 6 gas surface relative permittivity, SF 6 gas surface initial conductivity, SF 6 gas conductivity without discharge, SF 6 gas maximum conductivity during discharge, stress coefficient of surface conductivity, and effective charge decay time constant.

[0046] Furthermore, the specific process of step S1 is: establish a simulation model of GIS through simulation software; first, measure the partial discharge inception voltage in GIS through experiments, apply X-ray irradiation and gradually increase the voltage, and record it as the discharge inception voltage when partial discharge first appears; calculate the internal electric field distribution of GIS at different times by applying the discharge inception voltage on the high-voltage rod in GIS and adding grounding to the outer shell of GIS.

[0047] Compared with the existing technologies, the present invention has the following beneficial effects: By establishing a mathematical model of partial discharge, the present invention simulates the ionization effect of X-rays on gas molecules, quantitatively describes the change of electrons during the partial discharge process through a mathematical expression, and determines the occurrence of partial discharge based on two characteristic quantities, namely the electric field strength and the number of electrons. The obtained partial discharge quantity and discharge repetition rate are close to the actual discharge, accurately restoring the partial discharge in GIS under X-ray excitation and improving the accuracy of partial discharge simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flowchart of the method of the present invention.

[0049] Figure 2 It is a simulation model diagram of the GIS of the present invention.

[0050] Figure 3 It is a phase diagram of the partial discharge signal simulated by the present invention.

[0051] Figure 4 It is a phase diagram of the partial discharge signal measured experimentally. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] As Figure 1 shown, the present invention provides a technical solution: A method for simulating partial discharge in GIS under X-ray excitation, including the following steps:

[0053] Step S1: Calculate the initial electric field distribution in the GIS in the finite element simulation software (COMSOL Multiphysics 5.6).

[0054] In this embodiment, a simulation model of the GIS is established in the finite element simulation software. As Figure 2 shown in the figure, in the figure, 1 is the three-pillar insulator of the GIS, 2 is the high-voltage guide rod, and 3 is the outer shell; First, measure the initial voltage of partial discharge in the GIS through experiments, apply X-ray irradiation and gradually increase the voltage. When partial discharge first appears, record it as the discharge starting voltage; Apply the discharge starting voltage to the high-voltage guide rod 2 in the GIS and add grounding to the outer shell 3 of the GIS to calculate the electric field distribution inside the GIS at different times.

[0055] Among them, the initial electric field distribution in the GIS is expressed as:

[0056] (1);

[0057] (2);

[0058] In the formula, represents the electric field strength; represents the electric potential; represents the dielectric constant of air; represents the dielectric constant of the material; represents the total charge density; represents taking the derivative.

[0059] Step S2: Import the initial electric field distribution calculated in Step S1 into the MATLAB model (commercial mathematical software), define each simulation parameter, and obtain the initial effective electron generation rate in SF 6 gas in the GIS and the photoelectron rate generated under X-ray photoionization. Sum the initial effective electron generation rate and the photoelectron rate generated under photoionization to obtain the total electron rate generated in the GIS.

[0060] The simulation parameters defined in this embodiment are shown in Table 1.

[0061] Table 1 Simulation Parameters

[0062]

[0063] Among them, the initial effective electron generation rate in SF 6 gas in the GIS is:

[0064] (3);

[0065] (4);

[0066] In the formula, represents the surface emission rate of free electrons generated by the previous discharge captured by the SF 6 gas surface in the GIS; represents the number of free electrons generated per unit time in the SF gas inside the GIS under the initial field strength 6 ; represents the actual field strength in the GIS space during partial discharge; represents the actual field strength in the GIS space; represents the latest time; represents the time of partial discharge; represents the rate of surface-emitted electrons generated by the high-voltage guide rod and the SF 6 gas; represents the effective charge decay time constant.

[0067] Among them, the photoelectron rate generated by X-ray photoionization of SF 6 gas is:

[0068] (5);

[0069] In the formula, Represents the rate of photoelectrons generated by X-ray photoionization of SF6 gas; Represents the conversion coefficient, taking 1.61×10 15 ; Represents the X-ray dose; Represents the air density, taking 1.226 ; Represents the effective ionization volume of air.

[0070] Among them, the rate of electrons generated by further ionization of SF 6 gas is:

[0071] (6);

[0072] (7);

[0073] In the formula, Represents the rate of electrons generated by further ionization of SF 6 gas; Represents the pressure of the mixed gas after mixing SF 6 gas and air; Represents the pressure of SF 6 gas; Represents the photon radiation probability; Represents the migration velocity of electrons; Represents the abscissa of the th simulation point; Represents the photon absorption probability; Represents the th simulation point and the th simulation point; Represents the probability density function; is an infinitesimal finite element volume; d represents integration; Represents the th simulation point; ordinate of the th simulation point; Represents the abscissa of the th simulation point; Represents the angle between two points; Represents the number of partial discharges.

[0074] The sum of the rates of photoelectrons generated by X-ray photoionization and electrons generated by further ionization of photoelectrons is: .

[0075] Photoelectrons generated by X-ray photoionization and SF6 The sum of the electron rates generated by the further ionization of the initial effective electrons in the gas is:

[0076] (8).

[0077] Step S3: Determine whether partial discharge occurs based on the internal electric field strength of the GIS and the total electron rate generated, and further simulate the conduction attenuation of charges in SF 6 gas to describe the numerical change process of charged particles.

[0078] In this embodiment, the conditions for partial discharge to occur are: the maximum field strength in the GIS is between the inception field strength and the extinction field strength, and the sum of the natural electron rate and the photoelectron rate generated by X-ray photoionization is greater than the set threshold.

[0079] Among them, the conditions for determining whether partial discharge occurs are:

[0080] (9);

[0081] (10);

[0082] (11);

[0083] (12);

[0084] In the formula, represents the actual field strength in the GIS; represents the inception field strength of partial discharge; represents the threshold electron generation rate for partial discharge to occur; represents the extinction field strength of partial discharge; represents SF 6 the sum of the initial effective electrons in the gas.

[0085] Among them, simulating the conduction attenuation of charges in SF 6 gas to describe the numerical change process of charged particles is expressed as:

[0086] (13);

[0087] (14);

[0088] (15);

[0089] (16);

[0090] (17);

[0091] (18);

[0092] Wherein, represents the field strength generated by surface charges; is the field strength in the GIS without surface charges; represents the surface free charges after partial discharge occurs; represents the electric displacement field of the upper wall in the GIS; represents the electric displacement field of the GIS outer shell wall; represents the field strength generated by the surface free charges after partial discharge occurs; represents the total discharge charge from the start to after partial discharge occurs; represents the true discharge amount of the th discharge; is the field strength generated by trapped charges after partial discharge occurs; represents the surface conductivity; represents the stress coefficient of surface conductivity; represents the finite element area; represents the total area of the solution domain; represents the total electric field strength before partial discharge occurs; represents the total electric field strength after partial discharge occurs.

[0093] Step S4: When partial discharge occurs, output the charge amount and discharge repetition rate of the partial discharge.

[0094] Among them, output the charge amount of the partial discharge , which is expressed as:

[0095] (19);

[0096] Wherein, represents the discharge current; represents the time.

[0097] As Figures 3 - 4 shown, the partial discharge signals simulated by the present invention and the partial discharge signals obtained by experimental measurement are compared under the same conditions. It can be seen from the figure that for the partial discharge signals simulated by the present invention and the partial discharge signals obtained by experimental measurement, the shapes of the discharge spectra and the overall discharge phases can correspond, and the deviation of the discharge amount is within 10%. In addition, the partial discharge signals simulated by the present invention and the partial discharge signals obtained by experimental measurement within more than 10,000 power frequency cycles are compared, and the deviation of the discharge amount is within 10% in both cases. Therefore, it can prove the effectiveness of the simulation method proposed by the present invention.

[0098] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and 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 the 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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