CN115410752A - Mixed gas insulating medium, gas insulating switch device and preparation method thereof - Google Patents
Mixed gas insulating medium, gas insulating switch device and preparation method thereof Download PDFInfo
- Publication number
- CN115410752A CN115410752A CN202211164392.6A CN202211164392A CN115410752A CN 115410752 A CN115410752 A CN 115410752A CN 202211164392 A CN202211164392 A CN 202211164392A CN 115410752 A CN115410752 A CN 115410752A
- Authority
- CN
- China
- Prior art keywords
- gas
- sealed container
- mixed gas
- percent
- insulated switchgear
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
- H01B3/16—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances gases
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02B—BOARDS, SUBSTATIONS OR SWITCHING ARRANGEMENTS FOR THE SUPPLY OR DISTRIBUTION OF ELECTRIC POWER
- H02B13/00—Arrangement of switchgear in which switches are enclosed in, or structurally associated with, a casing, e.g. cubicle
- H02B13/02—Arrangement of switchgear in which switches are enclosed in, or structurally associated with, a casing, e.g. cubicle with metal casing
- H02B13/035—Gas-insulated switchgear
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02B—BOARDS, SUBSTATIONS OR SWITCHING ARRANGEMENTS FOR THE SUPPLY OR DISTRIBUTION OF ELECTRIC POWER
- H02B13/00—Arrangement of switchgear in which switches are enclosed in, or structurally associated with, a casing, e.g. cubicle
- H02B13/02—Arrangement of switchgear in which switches are enclosed in, or structurally associated with, a casing, e.g. cubicle with metal casing
- H02B13/035—Gas-insulated switchgear
- H02B13/045—Details of casing, e.g. gas tightness
Abstract
The invention discloses a mixed gas insulating medium, a gas insulating switch device and a preparation method thereof, wherein the mixed gas insulating medium comprises the following gas components in percentage by volume: 20 to 25 percent of CF 3 SO 2 F. 3 to 5 percent of O 2 And 70 to 77% of N 2 . The mixed gas insulating medium can effectively reduce the greenhouse effect, has the insulating strength equivalent to SF6, and can ensure the safe operation of electric power equipment.
Description
Technical Field
The invention relates to the technical field of gas insulated switchgear, in particular to a mixed gas insulated medium, gas insulated switchgear and a preparation method thereof.
Background
In gas-insulated electrical apparatus, SF is generally used 6 As an insulating medium. But SF 6 Is a strong greenhouse gas, and the Global Warming Potential (GWP) of the gas is CO 2 23900 times of and due to SF 6 Has extremely stable chemical properties, can exist in the atmosphere for as long as 3200 years, basically does not naturally decompose once leaked into the atmosphere, and therefore has cumulative effect on the influence of global warming. According to the monitoring, SF in the global atmospheric environment 6 The content of the extract has been 3.67 × 10 from 1994 -7 % increase to 10.41X 10 of 2020 -7 % increase, 265%, SF only over the past five years 6 The content of the global atmospheric environment is increased by 16.3 percent by SF 6 The global temperature rise caused reaches 0.004 ℃, and shows an ascending trend. In the Kyoto protocol, signed in 1997, CO was well-defined 2 ，CH 4 ，N 2 O, PFC, HFC and SF 6 And the like belong to the range of greenhouse gases, and developed countries are required to freeze the emission of greenhouse gases at the level of 90 s in the 20 th century first. Therefore, it is highly desirable to find a suitable environment-friendly insulating medium to replace SF 6 Not only ensure with SF 6 Has similar insulating property, meets the industrial use requirements of no toxicity, no flammability and the like, and does not generate negative influence on the environment.
Disclosure of Invention
The invention aims to overcome the defect of using SF in the prior art 6 The greenhouse effect problem caused by gases, and provides a CF gas containing environment-friendly gases 3 SO 2 F, the gas-mixed insulating medium, the gas-insulated switchgear and the preparation method thereof can effectively reduce the greenhouse effect, and simultaneously, the insulating strength and the SF 6 Rather, safe operation of the power equipment can be ensured.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a mixed gas insulation medium comprising the following gas components in volume percent: 20 to 25 percent of CF 3 SO 2 F. 3 to 5 percent of O 2 And 70 to 77% of N 2 。
The invention also discloses gas insulated switchgear comprising a sealed container and the mixed gas insulating medium sealed in the sealed container.
The invention also discloses a preparation method of the gas insulated switchgear, which comprises the following steps:
providing a sealed container, and vacuumizing the sealed container;
charging CF into the sealed container 3 SO 2 F、O 2 And N 2 Wherein, in the sealed container, the CF 3 SO 2 F accounts for 20 to 25 percent by volume, and O 2 Is 3 to 5 percent by volume, and N is 2 The volume percentage of (A) is 70% -77%;
and standing to obtain the gas insulated switchgear.
The embodiment of the invention has the following beneficial effects:
embodiments of the invention by selecting CF 3 SO 2 F as an insulating medium, first, CF 3 SO 2 F is an environment-friendly insulating gas which is colorless, tasteless, non-combustible and non-explosive, decomposition products under the current breaking condition belong to low-toxicity or non-toxic substances, the serious harm to human bodies is avoided, the influence on the greenhouse effect is extremely small, and meanwhile, common chlorine and bromine in refrigerants are not contained, and the ozone layer is not damaged; second, CF 3 SO 2 F has excellent electrical performance, and the insulation strength can reach SF under the same air pressure 6 More than 1.7 times of the total amount of the active sulfur and can completely replace SF 6 Simultaneous comparison of SF 6 The gas is more environment-friendly, and the global warming potential value is only SF 6 0.2 per mill of gas global warming potential value; n is a radical of hydrogen 2 The liquefied temperature of the mixed gas formed finally by the invention can be reduced to about minus 30 ℃, and the use requirements of most areas in China can be met; make itWith O 2 Is to suppress CF 3 SO 2 F discharge decomposition generates solid precipitates of carbon simple substances, generation of gas decomposition products is inhibited, and application reliability of the mixed gas is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Wherein:
FIG. 1 is CF 3 SO 2 And F is a molecular structure schematic diagram.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
The invention discloses a mixed gas insulating medium, which comprises the following gas components in percentage by volume: 20 to 25 percent of CF 3 SO 2 F. 3 to 5 percent of O 2 And 70 to 77% of N 2 。
In the present invention, CF 3 SO 2 The molecular structure diagram of F is shown in figure 1, and the F is influenced by halogen elements F and S in the molecule, has strong adsorption effect on free electrons, can adsorb the free electrons in the process of electron collapse generation in the initial stage of discharge, and inhibits the generation of impact ionization, thereby realizing insulation.
CF 3 SO 2 F is an environment-friendly insulating gas which is colorless, tasteless, non-combustible and non-explosive, and decomposition products under the condition of current cut-off are low-toxicity or non-toxicityThe material does not cause serious harm to human bodies, has little influence on greenhouse effect, does not contain common chlorine and bromine in the refrigerant, and does not cause damage to the ozone layer; furthermore, CF 3 SO 2 F is excellent in electrical performance, and the insulation strength can reach SF under the same air pressure 6 More than 1.7 times of the total amount of the active sulfur and can completely replace SF 6 Simultaneous comparison of SF 6 The gas is more environment-friendly, and the global warming potential value is only SF 6 0.2 per mill of gas global warming potential value.
For CF 3 SO 2 F, experimental study of discharge decomposition characteristics of mixed gas shows that: CF 3 SO 2 F can be decomposed under the conditions of partial discharge dominated by electron impact ionization, spark dominated by impact ionization and high-temperature thermal ionization and arc discharge dominated by electron impact ionization and generate a plurality of micromolecular decomposition products such as CO, perfluorocarbon and the like, simple substance carbon, O 2 The addition of (2) can inhibit the generation of solid educt and partial gas decomposition products to a certain extent, and improve the application reliability of the mixed gas. N is a radical of 2 The liquefied temperature of the mixed gas formed finally by the invention can be reduced to about minus 30 ℃, and the use requirements of most areas in China can be met.
In a preferred embodiment, the mixed gas insulating medium comprises the following components in percentage by volume: 25% CF 3 SO 2 F. 5% of O 2 And 70% of N 2 。
In some embodiments, CF 3 SO 2 Purity of F is more than 99.99%, O 2 Has a purity of more than 99.99%, N 2 The purity of (A) is more than 99.99%.
In some embodiments, the liquefaction temperature of the mixed gas insulating medium is-40 ℃ to-28 ℃, and the use requirements of most areas in China can be met.
The invention also discloses gas insulated switchgear comprising a sealed container and the mixed gas insulating medium sealed in the sealed container.
In some casesIn the embodiment, the upper part of the sealed container is provided with a first inflation interface which is used for filling CF into the sealed container 3 SO 2 F and O 2 The lower part of the sealed container is provided with a second inflation interface which is used for filling N into the sealed container 2 CF of high density 3 SO 2 F and O 2 N of small density charged from above 2 The gas is filled from the lower part, so that the standing time after mixing can be reduced, and the gas can be mixed more uniformly.
In some embodiments, the lower part of the sealed container is also provided with an air suction interface which is used for vacuumizing the sealed container.
It is noted that the "upper portion" refers to the upper portion of the sealed container, including the top portion of the sealed container and the upper portion of the sidewall, and the "lower portion" refers to the lower portion of the sealed container, including the bottom portion of the sealed container and the lower portion of the sidewall.
In a specific embodiment, a first inflation valve is arranged at the first inflation interface, a second inflation valve is arranged at the second inflation interface, and a vacuum pumping valve is arranged at the air suction interface.
The invention also discloses a preparation method of the gas insulated switchgear, which comprises the following steps:
s1: providing a sealed container, and vacuumizing the sealed container.
Specifically, the evacuation valve is connected to a vacuum generator, and the sealed container is evacuated to a degree of vacuum of less than 10Pa. The arrangement position and connection relation of the vacuum valve are referred to the previous description.
S2: charging CF into the sealed container 3 SO 2 F、O 2 And N 2 Wherein, in a sealed container, CF 3 SO 2 F is 20-25% by volume, and O 2 Is 3 to 5 percent by volume, N 2 The volume percentage of (A) is 70-77%.
Preferably, in this step, the sealed container is filled with CF 3 SO 2 F、O 2 And N 2 The method comprises the following steps:
s21: CF is prepared by 3 SO 2 F、O 2 The sealed container is filled from the upper part of the sealed container.
Specifically, CF is charged through the first charging valve 3 SO 2 F、O 2 Respectively filling into sealed containers.
S22: will N 2 The sealed container is filled from the lower part of the sealed container.
Specifically, N is pumped through a second inflation valve 2 Filling into a sealed container.
S3: and standing to ensure that the mixed gas in the sealed container is fully and uniformly mixed to obtain the gas insulated switchgear.
In some embodiments, the time of standing is 12 hours to 16 hours.
Referring to table 1, which is a formulation of a mixed gas insulation medium of specific examples, wherein,% means volume percentage.
Table 1: formulation of the Mixed gas insulating Medium of the examples
| CF 3 SO 2 F(％) | O 2 (％) | N 2 (％) | |
| 1 | 25 | 5 | 70 |
| 2 | 20 | 3 | 77 |
| 3 | 22.5 | 4 | 73.5 |
| 4 | 15 | 5 | 80 |
| 5 | 25 | 0 | 75 |
The mixed-gas insulation media of the examples of table 1 were subjected to performance tests.
The insulation test is carried out in the same experimental device (metal sealed container with height less than 5 m), the sealed container is pumped to a vacuum state below 10Pa, and then CF is sequentially filled in 3 SO 2 F、O 2 And N 2 And (4) standing the gas and the mixed gas for 24 hours and uniformly mixing. Performing insulation test on mixed gas insulating medium by using SF 6 The gas is a comparative example, the test voltage is a power frequency voltage and a lightning impulse voltage respectively, the electrodes are spherical plate electrodes, the electrode gap distance is 5mm, and the test air pressure is 0.1MPa-0.7MPa. The results of the experiment are shown in table 2.
Table 2: insulation test results of the mixed gas insulation media of the respective examples
From table 2 it can be seen that: gas mixtures of examples 1 to 3Breakdown voltage of the bulk is compared with SF under the same condition 6 Preferably at least 1.06 times, and has good insulating properties. CF in Mixed gas of example 4 3 SO 2 Since the content of F was less than those in examples 1 to 3 and 5, the breakdown voltage values at each atmospheric pressure were lower than those in examples 1 to 3 and 5. Therefore, 20% to 25% CF 3 SO 2 F can provide a better breakdown voltage value.
The Global Warming Potential (GWP) of the mixed gas insulation medium was calculated from the GWP of each gas component, and the results are shown in table 3. Known as CF 3 SO 2 GWP of F CF3SO2F Is 3687,N 2 GWP of N2 Is 0,O 2 GWP of O2 The global warming potential value GWP of the mixed gas insulation medium is 0, and the calculation formula is as follows:
GWP＝V CF3SO2F *GWP CF3SO2F +V N2 *GWP N2 +V O2 *GWP O2
in the formula, V CF3SO2F Denotes CF 3 SO 2 Volume percent of F, V N2 Represents N 2 Volume percent of (1), V O2 Represents O 2 Volume percent of (c).
The liquefaction temperature of the mixed gas was measured by a vapor pressure tester, and the results are shown in Table 3.
Before and after the discharge test, the gas is taken by using the sampling bag to carry out gas chromatography mass spectrometry detection, so that the change of gas components before and after the test can be obtained, the gas decomposition rate can be obtained, and the result is shown in table 3.
The plate-shaped electrodes used in each discharge test were the same in size, and the weight of the solid precipitates was measured by scraping the solid particles and dust adhering to the surface of the plate-shaped electrode with a brush after each discharge test, and the results are shown in table 3.
Table 3: performance index of the Mixed gas insulating Medium of each example
| GWP | Liquefaction temperature (. Degree. C.) | Decomposition rate | Amount of solid precipitated | |
| 1 | 921.75 | -28 | 5％ | 32mg |
| 2 | 737.4 | -40 | 9％ | 39mg |
| 3 | 829.575 | -34 | 7％ | 33mg |
| 4 | 553.05 | -49 | 5％ | 20mg |
| 5 | 921.75 | -28 | 11％ | 43mg |
| SF 6 | 23900 | -62 | Does not decompose | No precipitate is generated |
From table 3 it can be seen that: 1) The GWP values of the mixed gas insulating mediums of examples 1 to 5 were only SF 6 About 3.85% of gas, it can be seen that the invention uses CF 3 SO 2 F instead of SF 6 The GWP can be obviously reduced; 2) The mixed gas insulating medium of example 5 contains no O 2 The decomposition rate was 11%, the amount of precipitated solid was 43mg, and O was added in the ratio of the decomposition rate to the amount of precipitated solid 2 Examples 1 to 4 are high; 3) Comparing examples 1-3 with example 4, CF of examples 1-3 3 SO 2 F content by volume 20% to 25%, whereas example 4 CF 3 SO 2 The F content was 15% by volume, as can be seen from Table 3, example 4 is due to CF 3 SO 2 F is small in volume content, so that the decomposition rate and the amount of precipitated solids are low, and thus, CF is observed 3 SO 2 Too high F content can result in too high decomposition rate and solid precipitation, and influence the use stability of the insulating gas; 4) CF of example 1 and example 5 compared to example 1 and example 5 3 SO 2 The volume content of F is the same, however, example 5 is due to the lack of O 2 The composition, decomposition rate and solid precipitation amount were significantly higher than those of example 1, and it can be seen that, in the present invention, O is present 2 The increase of the component can inhibit CF 3 SO 2 F, decomposition and solid precipitation inhibition; 5) Reference is made to examples 1 to 5, wherein N in example 4 2 Highest content of component, which has the lowest liquefaction temperature, with N 2 The reduction of the content of the components increases the liquefaction temperature.
To sum up, the breakdown voltage is high, the liquefaction temperature meets the use requirements of most areas in China, the decomposition rate is low, solid precipitates are few, and preferably, CF 3 SO 2 F is 20-25% by volume, O 2 The volume content is 3-5% and N 2 The volume content is 70-77%.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the claims. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A mixed gas insulating medium, characterized by comprising the following gas components in volume percent: 20 to 25 percent of CF 3 SO 2 F. 3 to 5 percent of O 2 And 70 to 77% of N 2 。
2. The mixed gas insulation medium according to claim 1, comprising the following components in volume percent: 25% CF 3 SO 2 F. 5% of O 2 And 70% of N 2 。
3. The mixed gas insulation medium according to claim 1, characterized in that the liquefaction temperature of the mixed gas insulation medium is-40 ℃ to-28 ℃.
4. The mixed gas insulation medium of claim 1, wherein the CF is 3 SO 2 The purity of F is more than 99.99%;
said O is 2 The purity of (2) is more than 99.99%;
said N is 2 The purity of (A) is more than 99.99%.
5. A gas-insulated switchgear apparatus, comprising a sealed vessel and the mixed-gas insulating medium according to any one of claims 1 to 4 sealed in the sealed vessel.
6. The gas insulated switchgear as claimed in claim 5, wherein the upper part of the said sealed container is provided with a first gas filling port for filling the said CF into the said sealed container 3 SO 2 F and said O 2 The lower part of the sealed container is provided with a second inflation port, and the second inflation port is used for filling the N gas into the sealed container 2 。
7. The gas insulated switchgear as claimed in claim 6, wherein the lower part of the sealed container is further provided with a suction port for evacuating the sealed container.
8. A method of manufacturing a gas-insulated switchgear, characterized by comprising the following processes:
providing a sealed container, and vacuumizing the sealed container;
charging CF into the sealed container 3 SO 2 F、O 2 And N 2 Wherein, in the sealed container, the CF 3 SO 2 The volume percentage of F is 20 to 25 percent, and the percentage of O 2 Is 3 to 5 percent by volume, and N is 2 The volume percentage of (A) is 70-77%;
and standing to obtain the gas insulated switchgear.
9. The method for manufacturing a gas insulated switchgear according to claim 8, wherein said charging of CF into said sealed container 3 SO 2 F、O 2 And N 2 The method comprises the following steps:
subjecting the CF to 3 SO 2 F and the O 2 Filling the container from the upper part of the sealed containerThe sealed container;
the N is 2 The sealed container is filled from the lower portion thereof.
10. The method for producing a gas insulated switchgear according to claim 8, wherein the degree of vacuum for evacuating the hermetic container is less than 10Pa;
the standing time is 12-16 hours.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211164392.6A CN115410752A (en) | 2022-09-23 | 2022-09-23 | Mixed gas insulating medium, gas insulating switch device and preparation method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211164392.6A CN115410752A (en) | 2022-09-23 | 2022-09-23 | Mixed gas insulating medium, gas insulating switch device and preparation method thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN115410752A true CN115410752A (en) | 2022-11-29 |
Family
ID=84166395
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202211164392.6A Pending CN115410752A (en) | 2022-09-23 | 2022-09-23 | Mixed gas insulating medium, gas insulating switch device and preparation method thereof |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN115410752A (en) |
-
2022
- 2022-09-23 CN CN202211164392.6A patent/CN115410752A/en active Pending
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP6042344B2 (en) | Dielectric insulation medium | |
| WO2021139070A1 (en) | Arc extinguishing and/or insulated electrical device | |
| Taki et al. | Interruption capability of CF/sub 3/I Gas as a substitution candidate for SF/sub 6/gas | |
| CN112510565A (en) | Mixed gas insulating medium containing environment-friendly gas heptafluoroisobutyronitrile and preparation method thereof | |
| CN105761857A (en) | Method for fluorinating insulator through use of CF4 plasma | |
| Dervos et al. | Thermal stability of SF6 associated with metallic conductors incorporated in gas insulated switchgear power substations | |
| CN109557257A (en) | A kind of sulfur hexafluoride substitution gas selection method | |
| Xiao et al. | Insulation performance and electrical field sensitivity properties of HFO-1336mzz (E)/CO 2: A new eco-friendly gas insulating medium | |
| CN109173319A (en) | A kind of environment-friendly type insulated gas screening technique and the method for improving direct current transportation pipe-line wrapping | |
| CN109300575A (en) | The mixed gas insulating medium and preparation method thereof of the trifluoroiodomethane of gas containing environment-friendly type | |
| CN115410752A (en) | Mixed gas insulating medium, gas insulating switch device and preparation method thereof | |
| CN113284723A (en) | Containing C5F10Formula gas of O gas transformer insulating medium | |
| Zhang et al. | Insulation Characteristics of HFO-1336mzz (E) and its mixtures as eco-friendly alternatives to SF 6 for medium-voltage switchgears | |
| Zhang et al. | Insulation properties of C 4 F 7 N/CO 2 mixtures under lightning impulse | |
| CN115083661A (en) | Mixed gas insulation medium, gas insulation switch device and preparation method thereof | |
| CN114113952A (en) | Experimental device and method for researching arc characteristics of high-voltage switch equipment | |
| CN113257459A (en) | Perfluoropentanone mixed gas type electrical equipment insulating medium, preparation method and application | |
| CN208314118U (en) | The flashover voltage of the insulator detection device in mixed gas under cryogenic conditions | |
| CN107968350A (en) | A kind of mixed gas arc-extinguishing medium of the trifluoroiodomethane of gas containing environment-friendly type and preparation method thereof | |
| CN109887644B (en) | Mixed dielectric and medium-voltage or high-voltage electrical equipment | |
| CN112467599A (en) | Medium-high pressure equipment shell filled with mixed gas of heptafluoroisobutyronitrile and difluoromethane | |
| CN112489852A (en) | Mixed gas arc-extinguishing medium containing environment-friendly gas heptafluoroisobutyronitrile and preparation method thereof | |
| CN102327727A (en) | Method for recovering sulfur hexafluoride in gas mixture by using membrane separation method | |
| CN113325104A (en) | C suitable for gas-insulated electrical equipment4F7N/CO2/O2Mixed gas optimal ratio selection method and platform | |
| CN111081435A (en) | Fluorinated 110kV basin-type insulator |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |