CN-121978480-A - Calculation method of high-voltage direct-current insulator surface breakdown field intensity

CN121978480ACN 121978480 ACN121978480 ACN 121978480ACN-121978480-A

Abstract

The invention provides a method for calculating the surface breakdown field intensity of a high-voltage direct-current insulator, which comprises the following steps of 1) calculating a direct-current air gap discharge field intensity expected value E d , 2) designing the specification of a tested insulating sample according to E d obtained in the step 1), 3) loading the tested insulating sample into a testing device for breakdown testing to obtain a lightning impulse voltage and direct-current voltage superposition breakdown voltage U 0 , and 4) calculating the lightning impulse voltage and direct-current voltage superposition breakdown field intensity E of the insulating sample according to U 0 . The invention provides a complete method for calculating the superposition breakdown field intensity of lightning impulse voltage and direct-current voltage, which reasonably determines the specification of an insulating sample to be tested based on the expected value of the negative polarity direct-current air gap discharge field intensity, further calculates the field intensity and provides a field intensity design reference of a direct-current insulator for the design of a high-voltage direct-current insulator.

Inventors

ZHANG CHANGHONG
Tang Xuanwei
HUANG JIAJIE
LV JINZHUANG
LI MINGYANG
YANG SIMIN
LI WEIGUO
LI XINGKANG
HOU MINGCHUN
TANG LINGLING
YANG XU
LIU RUONAN

Assignees

中国南方电网有限责任公司超高压输电公司电力科研院
江苏金鑫电器有限公司

Dates

Publication Date: 20260505
Application Date: 20260203

Claims (8)

1. The method for calculating the surface breakdown field intensity of the high-voltage direct-current insulator is characterized by comprising the following steps of: 1) Calculating an expected value E d of the direct current air gap discharge field intensity; 2) Designing the specification of the tested insulating sample according to E d obtained in the step 1); 3) The tested insulation sample is put into a testing device for breakdown testing, and the lightning impulse voltage and direct current voltage superposition breakdown voltage U 0 is obtained; 4) And calculating the superposition breakdown field strength E of the lightning impulse voltage and the direct-current voltage of the insulating sample according to the U 0 .
2. The method for calculating the surface breakdown field strength of the high-voltage direct-current insulator according to claim 1, wherein the step 1) specifically comprises the following steps: 1.1 Calculating the 50% breakdown field strength E 50% of the air gap under the negative polarity lightning impulse voltage, wherein the unit kV/mm is as follows: E 50% =63p+2.4; wherein p is absolute air pressure, and is unit MPa; 1.2 Calculating the air gap alternating current breakdown field strength E a according to E 50% , wherein the unit kV/mm is the unit; E a =E 50% /1.3; 1.3 Calculating an expected value E d of the negative DC air gap discharge field intensity in kV/mm based on E a ; E d =E a /M; Wherein M is in the range of 1.2-1.4.
3. The method for calculating the surface breakdown field strength of the high-voltage direct-current insulator according to claim 2, wherein the insulating sample to be measured in the step 2) is cylindrical, and the diameter L and the height H of the insulating sample are determined; The diameter L is smaller than the distance from the side surface of the tested insulating sample to the inner wall of the testing device; The height H is determined according to the expected experimental voltage U d and the expected insulator surface flashover field intensity E τ , specifically, the expected insulator surface flashover field intensity E τ =E d /2 is calculated; The height H is required to be satisfied, wherein H is more than or equal to U d /E τ ; Wherein U d is the expected breakdown experimental voltage of the insulating part, and U d =E τ ×h is the height of the insulating table.
4. The method for calculating the surface breakdown field strength of the high-voltage direct-current insulator according to claim 3, wherein the specific steps of step 3) are as follows: 3.1 Loading the insulating sample into a testing device, heating the upper part of the insulating table to a target temperature, and keeping the lower part of the insulating table at room temperature; 3.2 A negative polarity dc voltage is applied first, After the negative polarity direct current voltage with the initial voltage value of U d reaches the preset time, applying positive polarity voltage with the value of 2.39U d , then gradually boosting according to the preset voltage value, applying positive polarity voltage until breakdown, recording the breakdown voltage, replacing an insulating sample, repeating the test for not less than 5 times, taking arithmetic average of all obtained values, and obtaining the lightning impulse voltage and direct current voltage superposition breakdown voltage U 0 .
5. A method for calculating the breakdown field strength of a high-voltage direct-current insulator surface according to claim 3, wherein, In the step 4), the surface breakdown field strength E of the insulating sample is calculated in the following steps: 4.1 First calculate Calculation of insulation withstand voltage by 50% flashover voltage measured at superposition test U tds = U 0 X (1-3 sigma) X N, wherein sigma=0.05 is a standard deviation value of lightning impulse voltage, N is a design margin, and the value range is 0.7 to 1; 4.2 Calculating the electric field of the row under the voltage of U tds to obtain the allowable value E of the tangential field strength of the surface design of the insulating part under the superimposed voltage.
6. The method for calculating the surface breakdown field strength of the high-voltage direct-current insulator according to claim 4, wherein the target temperature in the step 3.1) is 100-120 ℃.
7. The method for calculating the surface breakdown field strength of the high-voltage direct-current insulator according to claim 4, wherein the preset time in the step 3.2) is not less than 40000 seconds, and the preset voltage value ranges from 5 to 15 KV.
8. The method for calculating the breakdown field strength of the surface of the high-voltage direct-current insulator according to claim 4, wherein the step 4.2) is a method for calculating the allowable tangential field strength value E of the surface design of the insulator under the superimposed voltage: Taking the relative dielectric constant epsilon I =4.95 of the insulator, The relative dielectric constant epsilon 0 =1.002 of the insulating gas; Based on boundary conditions: ; Solving a domain control equation for the whole electrostatic field of formula (1): ; relationship between charge density and current density of insulating sample of formula (2): ; In the formula (2), t is time, K VI is the conductivity of the insulating sample, Insulating sample charge density; The gaussian theorem in electrostatic field of formula (3): ; ρ + in the formula (3) is positive and negative charge density, ρ - is positive and negative charge density, ρ V is insulating sample charge density; engagement conditions at the dielectric interface of formula (4): ; In the formula (4), D 1 is a gas side electric displacement vector, D 2 is an insulating table side electric displacement vector, n is a unit normal vector of the boundary, and ρ s is the free charge density at the interface; formula (5) formula for calculating electric displacement vector: ; And (3) solving the formula (1), the formula (2), the formula (3), the formula (4) and the formula (5) simultaneously to obtain the lightning impulse voltage and the direct current voltage superposition breakdown field intensity E.

Description

Calculation method of high-voltage direct-current insulator surface breakdown field intensity Technical Field The invention belongs to the technical field of high-voltage direct-current insulators, and particularly relates to a method for calculating the surface breakdown field intensity of a high-voltage direct-current insulator. Background GIL (gas insulated power transmission line) is a high voltage, high current power transmission device ‌ employing gas insulation, a housing coaxially arranged with a conductor. The conductor adopts an aluminum alloy pipe, the shell adopts an aluminum alloy coiled plate for sealing, and the coaxial pipeline bus ‌ is similar to that in SF6 gas insulated metal sealing switch equipment (GIS). The main advantages of GIL include no influence from severe weather and special terrain, effective utilization of space resources, reduced electromagnetic influence, increased current capacity, low failure rate, convenient maintenance, etc. ‌ A The insulator is an important component in ‌ GIL and is used for fixing a conductor in a shell, the structural shape of the insulator can influence the surface charge distribution and further influence the insulation performance of the conductor, the lightning impulse voltage and the direct current voltage superposition breakdown field strength are an important parameter for designing the shape of the insulator for the high-voltage direct current ‌ GIL, however, in the prior art, only the reference of the surface breakdown field strength of the insulator for the high-voltage alternating current GIL is provided, the reference of the surface breakdown field strength of the high-voltage direct current insulator with a mature specification is not provided, the design often depends on an empirical value, and a unified and standard design standard cannot be formed. Therefore, it is needed to design a method for calculating the breakdown field strength of the surface of the high-voltage direct-current insulator, and provide a field strength design reference of the direct-current insulator for the design of the high-voltage direct-current insulator. Disclosure of Invention Aiming at the technical problems, the invention provides a method for calculating the surface breakdown field intensity of a high-voltage direct-current insulator, which provides a powerful support for the shape design of the high-voltage direct-current ‌ GIL insulator. The technical scheme of the invention is that the method for calculating the breakdown field intensity of the surface of the high-voltage direct-current insulator comprises the following steps: 1) Calculating an expected value E d of the direct current air gap discharge field intensity; 2) Designing the specification of the tested insulating sample according to E d obtained in the step 1); 3) The tested insulation sample is put into a testing device for breakdown testing, and the lightning impulse voltage and direct current voltage superposition breakdown voltage U 0 is obtained; 4) And calculating the superposition breakdown field strength E of the lightning impulse voltage and the direct-current voltage of the insulating sample according to the U 0. Preferably, step 1) specifically includes: 1.1 Calculating the 50% breakdown field strength E 50% of the air gap under the negative polarity lightning impulse voltage, wherein the unit kV/mm is as follows: E50%=63p+2.4 ; wherein p is absolute air pressure, and is unit MPa; 1.2 Calculating the air gap alternating current breakdown field strength E a according to E 50%, wherein the unit kV/mm is the unit; Ea= E50%/1.3; 1.3 Calculating an expected value E d of the negative DC air gap discharge field intensity in kV/mm based on E a; Ed=Ea/M; Wherein M is in the range of 1.2-1.4. Preferably, the insulating sample to be measured in the step 2) is cylindrical, and the diameter L and the height H of the insulating sample are determined; The diameter L is smaller than the distance from the side surface of the tested insulating sample to the inner wall of the testing device; The height H is determined according to the expected experimental voltage U d and the expected insulator surface flashover field intensity E τ, specifically, the expected insulator surface flashover field intensity E τ=Ed/2 is calculated; The height H is required to be satisfied, wherein H is more than or equal to U d/Eτ; Where Ud is the expected breakdown experimental voltage of the insulation, ud=eτ×h, and h is the insulation stand height. Preferably, step 3) comprises the specific steps of: 3.1 Loading the insulating sample into a testing device, heating the upper part of the insulating table to a target temperature, and keeping the lower part of the insulating table at room temperature; 3.2 Applying negative polarity direct current voltage, applying positive polarity voltage with the value of 2.39Ud after the negative polarity direct current voltage with the initial voltage value of Ud reaches the preset ti