Portable gas taking device and gas taking method for finished cable buffer layer

Abstract

The invention discloses a portable gas taking device and method for a finished cable buffer layer. The device comprises a gas taking valve, a gas pump, a drying pipe and a gas taking bag. Wherein an air taking opening of the air taking valve is used for being connected with an air taking hole of a cable, an air outlet of the air taking valve is connected with an air inlet of the air pump, an air outlet of the air pump is connected with an air inlet of the drying pipe, and an air outlet of the drying pipe is connected with the air taking bag. The detection device has the characteristic of plug and play, can be directly installed in a buffer layer of a finished cable for detection, and is simple and convenient to operate. By adopting the gas sampling device disclosed by the invention, various volatile byproducts, including methane, water, cumyl alcohol, acetophenone and the like, in the cable can be detected at the same time, and the residual condition of the byproducts after degassing treatment can be accurately reflected.

Description

Technical Field

[0001] The invention relates to a cable buffer layer gas collection and detection technology, and in particular to a portable gas collection device and a gas collection method for a completed cable buffer layer. Background Art

[0002] In the production process of high-voltage and ultra-high-voltage cross-linked polyethylene (XLPE) cables, the insulating material is transformed from a linear thermoplastic material to a three-dimensional network structure thermosetting material through a cross-linking reaction, which greatly improves the heat resistance and long-term stability of the cable. This cross-linking process is usually completed by a peroxide cross-linking agent (such as diisopropyl peroxide, DCP). Under high temperature conditions, DCP decomposes to produce free radicals, which react with polyethylene molecular chains to form a network structure, but also produce a variety of volatile by-products, such as methane, water, cumyl alcohol, acetophenone and α-methylstyrene. If these by-products cannot be completely removed, they will seriously affect the insulation performance of the cable, especially in high-voltage and ultra-high-voltage environments, which may lead to a decrease in dielectric properties and increase the risk of cable aging.

[0003] In order to ensure that the insulation performance of the cable meets the standards, after the cross-linking reaction is completed, the cable usually needs to be "degassed" to remove the volatile by-products generated during the cross-linking process. The common method of degassing is to place the cable insulation core in a degassing chamber at 65-75°C for several days or dozens of days to accelerate the escape of volatile by-products. Due to the different structures of cables with different voltage levels and conductor specifications, the required degassing time is also different. At present, most manufacturers rely on experience to set the degassing time. This empirical setting may cause insufficient degassing to affect the quality of the cable, and excessive degassing may cause unnecessary waste of resources. Therefore, it is necessary to test the degassing effect before the cable is put into use.

[0004] There is almost no method in current technology or patents that can simultaneously and quantitatively detect moisture and multiple volatile gases in cables. Most detection methods can only focus on certain components and cannot comprehensively analyze the content levels of by-products. The existing buffer layer gas extraction methods are mainly aimed at cables in operation, and the gas extraction device is fixed on the surface of the cable and cannot be reused. At the same time, the existing test method for the cross-linking by-product content of cable insulation solids is complicated in sample preparation, and it is easy to cause the loss of by-products during the sample preparation process, and the results are not accurate enough. Due to the wide variety of by-products of the cross-linking reaction, each has different effects on the performance of the cable, and there is a lack of a simple, fast, comprehensive and accurate method for the degassing effect of the finished cable. Therefore, it is necessary to propose a portable gas extraction device and gas extraction method for the finished cable buffer layer. Summary of the invention

[0005] In view of the shortcomings of the existing cable degassing effect detection methods, the present invention provides a portable air extraction device and air extraction method for a finished cable buffer layer. While being more convenient to use, it has higher accuracy and can effectively detect the moisture and other various by-product components and contents in the cable during the degassing process, thereby comprehensively evaluating the degassing effect of the cable and determining whether it meets the delivery standards to ensure the safe operation of the cable.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] In a first aspect, the present invention provides a portable gas extraction device for a completed cable buffer layer, comprising a gas extraction valve, an air pump, a drying tube and a gas extraction bag; wherein:

[0008] The air inlet of the air extraction valve is used to connect with the air extraction hole of the cable, the air outlet of the air extraction valve is connected with the air inlet of the air pump, the air outlet of the air pump is connected with the air inlet of the drying tube, and the air outlet of the drying tube is connected with the air extraction bag.

[0009] Optionally, the portable air extraction device for the finished cable buffer layer further comprises an air extraction drill bit, and the air extraction drill bit is used to punch holes in the aluminum sheath of the cable to form air extraction holes in the cable.

[0010] Optionally, the air extraction drill bit is provided with an air extraction drill bit stopper, and the reserved length of the air extraction drill bit stopper is slightly larger than the thickness of the aluminum sheath and smaller than the corrugation depth of the aluminum sheath.

[0011] Optionally, the air extraction valve includes a copper tube, a ball valve and a pagoda interface; one end of the ball valve is connected to the copper tube as an air intake port, and the other end is connected to the pagoda interface as an air outlet; a copper tube limiter is arranged in the copper tube, and the reserved length of the copper tube limiter is greater than the thickness of the cable aluminum sheath and less than the corrugation depth of the aluminum sheath.

[0012] Optionally, the diameter of the copper tube is larger than the diameter of the air intake hole, so that the copper tube and the air intake hole are connected by interference fit.

[0013] In a second aspect, the present invention provides a method for extracting gas from a completed cable buffer layer, the method comprising:

[0014] The outer sheath of the cable is stripped to expose the aluminum sheath, and a hole is drilled in the aluminum sheath to form an air intake hole, and then an air intake valve is sealed and connected to be installed in the air intake hole;

[0015] Use sealing tubes to seal both ends of the cable, and then connect a barometer to the air outlet of the air extraction valve to detect the air tightness of the cable; if the air tightness test is passed, proceed to the next step;

[0016] Close the air extraction valve, seal the air outlet of the air extraction valve with the air inlet of the air pump, start the air pump, and exhaust the air in the pipeline between the air extraction valve and the air pump; after the exhaust is completed, close the air pump, seal the air outlet of the air pump with the air inlet of the drying pipe, and seal the air outlet of the drying pipe with the air extraction bag to complete the connection and installation of the air extraction device;

[0017] After the connection and installation of the gas extraction device is completed, open the gas extraction valve, start the air pump, and the gas in the cable enters the drying tube and the sampling bag in turn to complete the gas sampling;

[0018] After the gas sampling is completed, the gas sampling device is disassembled, and then the gas sampling hole is sealed by the lead sealing process;

[0019] The moisture content in the gas is calculated by the mass difference of the desiccant in the drying tube before and after water absorption; the gas in the air bag is subjected to gas chromatography analysis to check the gas components and their concentrations in the gas;

[0020] Verify the degassing effect based on the moisture content and gas components and their concentrations.

[0021] Optionally, the step of calculating the moisture content in the gas by the mass difference of the desiccant in the drying tube before and after absorbing water includes:

[0022] Use the ideal gas state equation to calculate the total amount of gas:

[0023] pV=nRT

[0024] Where p is the gas pressure inside the buffer layer, V is the volume of gas extracted from the buffer layer, n is the amount of gas, R is the molar gas constant of air, and T is the temperature of the gas inside the buffer layer;

[0025] The amount of water n water Calculated by the mass difference of the desiccant, using the formula:

[0026]

[0027] Where m is the mass difference of the drying tube before and after the gas is taken out, and M is the molar mass of water;

[0028] The calculation process of moisture content is:

[0029]

[0030] Optionally, during the gas chromatography analysis of the gas in the air bag, the type of each component gas is determined by the peak time in the chromatogram, and a normalization method is used for quantitative analysis. The detection needs to be repeated at least three times during the detection process.

[0031] Optionally, after the gas sampling is completed, the gas sampling device is disassembled and the gas sampling hole is sealed.

[0032] Optionally, during the punching process of the aluminum sheath, a wave crest position is selected for punching.

[0033] Optionally, a copper tube is connected to the air intake port of the air intake valve, and a copper tube limiter is provided in the copper tube; the diameter of the copper tube is larger than the diameter of the air intake hole, so that the copper tube and the air intake hole are connected by interference fit.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] Plug-and-play convenience: The detection device of the present invention has the characteristics of plug-and-play, can be directly installed in the buffer layer of the completed cable for detection, and is easy to operate.

[0036] Synchronous detection of multiple gases and moisture: By adopting the gas extraction device of the present invention, multiple volatile by-products in the cable can be detected simultaneously, including methane, water, cumyl alcohol, acetophenone and other components, and can accurately reflect the residual situation of by-products after degassing treatment.

[0037] High detection accuracy and reliability: The present invention uses the precise analysis technology of gas chromatography to quantitatively detect the content of different gas components in the degassing process with high accuracy. This high-precision detection method can help construction personnel determine whether the degassing process is thorough, thereby ensuring the quality stability of the cable during the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of the air extraction drill bit;

[0039] Figure 2 It is the overall structural schematic diagram of the air extraction valve;

[0040] Figure 3 It is a schematic diagram of the internal structure of the air extraction valve;

[0041] Figure 4 This is a schematic diagram of air tightness testing;

[0042] Figure 5 A schematic diagram of the connection of a portable air extraction device for a completed cable buffer layer provided in an embodiment of the present application;

[0043] Figure 6 A flow chart of a method for extracting air from a completed cable buffer layer provided in an embodiment of the present application;

[0044] In the figure: 1. air extraction drill bit; 2. air extraction drill bit limiter; 3. valve stem; 4. ball valve; 5. valve body; 6. copper tube limiter; 7. copper tube; 8. ball valve; 9. barometer; 10. air extraction pipe; 11. air extraction valve; 12 outer sheath; 13. aluminum sheath; 14. air pump; 15. drying tube; 16. air extraction bag; 17. pagoda joint. DETAILED DESCRIPTION

[0045] Example:

[0046] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0047] See also Figure 1 As shown, the portable air extraction device for the finished cable buffer layer provided in this embodiment mainly includes an air extraction valve 11, an air pump 14, a drying tube 15 and an air extraction bag 16; wherein,

[0048] The air intake port of the air intake valve 11 is used to be sealed and connected with the air intake hole of the cable, the air outlet of the air intake valve 11 is sealed and connected with the air inlet of the air pump 14, the air outlet of the air pump 14 is sealed and connected with the air inlet of the drying pipe 15, and the air outlet of the drying pipe 15 is sealed and connected with the air intake bag 16.

[0049] Specifically, the air extraction hole of the cable is formed by drilling a hole with an air extraction drill bit 1, and the air extraction drill bit 1 is provided with an air extraction drill bit stopper 2, and the reserved length of the air extraction drill bit stopper 2 is slightly larger than the thickness of the aluminum sheath and smaller than the corrugation depth of the aluminum sheath to ensure the depth of the drilling hole without damaging the cable buffer zone structure; the air extraction valve 11 mainly includes a valve stem 3, a ball valve 4, a copper tube 7, a pagoda interface 17 and a valve body 5, one end of the ball valve 7 is connected to the copper tube 7 as a gas extraction port, and the other end is connected to the pagoda interface 17 is connected to serve as an air outlet; a copper tube stopper is arranged in the copper tube, and the reserved length of the copper tube stopper is greater than the thickness of the cable aluminum sheath and less than the corrugation depth of the aluminum sheath, so as to ensure that the copper tube 7 is smoothly inserted into the air intake hole without damaging the cable buffer belt structure. In addition, the diameter of the copper tube is greater than the diameter of the air intake hole, so that the copper tube and the air intake hole are connected by interference fit to ensure sealing, so that it can be directly installed in the buffer layer of the completed cable for detection, which is easy to operate and has the characteristics of plug-and-play.

[0050] It can be seen that the portable air extraction device for the buffer layer of the finished cable provided by the present invention has the characteristics of plug-and-play, can be directly installed in the buffer layer of the finished cable for detection, and is easy to operate.

[0051] Accordingly, this embodiment also provides a portable gas extraction method for a completed cable buffer layer, which performs a gas extraction test on a completed 110kV XLPE insulated cable, and mainly includes the following steps:

[0052] S1, peel off the outer sheath 12 of the cable to expose the aluminum sheath 13, drill a hole in the aluminum sheath 13 to form an air intake hole, and then seal and connect the air intake valve 11 in the air intake hole;

[0053] Specifically, during the process of stripping the outer sheath 12, the peak position of the outer sheath 12 of the high-voltage cable is selected, and a circumferential stripping operation of more than 10 cm is performed, and then a non-woven cloth is dipped in diesel to wipe the asphalt on the surface of the aluminum sheath 13; during the drilling process, a 2.8mm diameter air drill bit with a limiter of 5mm depth is used for drilling; when installing the air valve 11, the copper tube 7 with an outer diameter of 3mm of the stainless steel tube is interference-fitted with the air hole to ensure that the air valve is in a closed state. Then a round aluminum cover is used to seal it by argon arc welding.

[0054] S2. Use sealing tubes to seal both ends of the cable, such as Figure 4 As shown, a barometer is then connected to the air outlet of the air extraction valve to detect air tightness; after the air tightness test is passed, the next step is entered;

[0055] Specifically, during the air tightness check, open the air valve and record the air pressure value p. If the air pressure remains stable over a period of time, it means that the air tightness is good; if the air pressure is unstable, additional sealing measures must be taken.

[0056] S3. Seal and connect the air outlet of the air extraction valve with the air inlet of the air pump, then close the air extraction valve, start the air pump, and evacuate the air in the pipeline between the air extraction valve and the air pump. During the process of evacuating the air in the pipeline, when the pipeline pressure is lower than -50KPa, it means that the evacuation is completed. After the air is evacuated, turn off the air pump, seal and connect the air outlet of the air pump with the air inlet of the drying pipe, and seal and connect the air outlet of the drying pipe with the air extraction bag. The connection and installation of the entire air extraction device are completed as follows. Figure 5 shown.

[0057] Specifically, after completing the connection and installation of the gas extraction device, it is necessary to inspect each device, fill the drying tube with a sufficient amount of anhydrous calcium chloride and measure the quality of the drying tube to ensure that everything is normal during the inspection process. During the connection of the equipment, the air pump should be equipped with a flow meter.

[0058] S4. After the connection and installation of the gas extraction device is completed, the gas extraction valve is opened, the air pump is started, and the gas in the cable enters the drying tube and the sampling bag in turn to complete the gas sampling;

[0059] Specifically, during the vacuum process, the vacuum volume is set to 2L. When the vacuum volume reaches 2L, the stopcock side valve, air pump and air extraction valve of the air extraction bag are closed in sequence, and the silicone tubes at both ends of the drying tube are clamped to seal the drying tube.

[0060] S5. After the gas sampling is completed, the gas sampling device is disassembled, and then the gas sampling hole is sealed by the lead sealing process.

[0061] Specifically, in the process of sealing the air intake hole, after lead sealing, waterproof tape and PVC self-adhesive tape are used to wrap and prevent moisture from entering the cable.

[0062] S6. Calculate the moisture content in the gas by the mass difference of the desiccant before and after water absorption, including:

[0063] Use the ideal gas state equation to calculate the total amount of gas:

[0064] pV=nRT

[0065] Where p is the gas pressure inside the buffer layer, V is the volume of gas extracted from the buffer layer, n is the amount of gas, R is the molar gas constant of air, and T is the temperature of the gas inside the buffer layer;

[0066] The amount of water n water Calculated by the mass difference of the desiccant, using the formula:

[0067]

[0068] Where m is the mass difference of the drying tube before and after the gas is taken out, and M is the molar mass of water;

[0069] The calculation process of moisture content is:

[0070]

[0071] In this way, the moisture content can be accurately calculated by the above-mentioned calculation method.

[0072] The collected gas samples were tested by gas chromatography:

[0073] Specifically, during the gas chromatography analysis of the gas in the air bag, the type of each component gas (including methane, cumyl alcohol, acetophenone and other components) is determined by the peak time in the chromatogram, and the normalization method is used for quantitative analysis. The test needs to be repeated at least three times during the test process to ensure the accuracy of the results.

[0074] S7, that is, the degassing effect can be verified according to the moisture content, gas components and their concentrations.

[0075] It can be seen that the device of the present invention can simultaneously detect a variety of volatile by-products in the cable, including methane, water, cumyl alcohol, acetophenone and other components, and can accurately reflect the residual situation of the by-products after degassing treatment.

[0076] At the same time, the present invention can quantitatively detect the content of different gas components in the degassing process with high precision through the precise analysis technology of gas chromatography. This high-precision detection method can help construction personnel determine whether the degassing process is thorough, thereby ensuring the quality stability of the cable during the production process.

[0077] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A portable air extraction device for a completed cable buffer layer, characterized in that: It includes an air extraction valve, an air pump, a drying tube and an air extraction bag; wherein, The air inlet of the air extraction valve is used to connect with the air extraction hole of the cable, the air outlet of the air extraction valve is connected with the air inlet of the air pump, the air outlet of the air pump is connected with the air inlet of the drying tube, and the air outlet of the drying tube is connected with the air extraction bag.

2. The portable air extraction device for the finished cable buffer layer as claimed in claim 1, characterized in that: The utility model also comprises an air extraction drill bit, which is used for punching holes in the aluminum sheath of the cable to form air extraction holes in the cable.

3. The portable air extraction device for the finished cable buffer layer as claimed in claim 2, characterized in that: The air extraction drill bit is provided with an air extraction drill bit stopper, and the reserved length of the air extraction drill bit stopper is slightly larger than the thickness of the aluminum sheath and smaller than the corrugation depth of the aluminum sheath.

4. The portable air extraction device for the finished cable buffer layer as claimed in claim 1, characterized in that: The air intake valve includes a copper tube, a ball valve and a pagoda interface; one end of the ball valve is connected to the copper tube as an air intake port, and the other end is connected to the pagoda interface as an air outlet; a copper tube stopper is arranged in the copper tube, and the reserved length of the copper tube stopper is greater than the thickness of the cable aluminum sheath and less than the corrugation depth of the aluminum sheath.

5. The portable air extraction device for the finished cable buffer layer as claimed in claim 4, characterized in that: The diameter of the copper tube is larger than the diameter of the air intake hole, so that the copper tube and the air intake hole are connected by interference fit.

6. A method for extracting air from a completed cable buffer layer, characterized in that: The method comprises: The outer sheath of the cable is stripped to expose the aluminum sheath, and a hole is drilled in the aluminum sheath to form an air intake hole, and then an air intake valve is sealed and connected to be installed in the air intake hole; Use sealing tubes to seal both ends of the cable, and then connect a barometer to the air outlet of the air extraction valve to detect the air tightness of the cable; if the air tightness test is passed, proceed to the next step; Close the air extraction valve, seal the air outlet of the air extraction valve with the air inlet of the air pump, start the air pump, and exhaust the air in the pipeline between the air extraction valve and the air pump; after the exhaust is completed, close the air pump, seal the air outlet of the air pump with the air inlet of the drying pipe, and seal the air outlet of the drying pipe with the air extraction bag to complete the connection and installation of the air extraction device; After the connection and installation of the gas extraction device is completed, open the gas extraction valve, start the air pump, and the gas in the cable enters the drying tube and the sampling bag in turn to complete the gas sampling; After the gas sampling is completed, the gas sampling device is disassembled, and then the gas sampling hole is sealed by the lead sealing process; The moisture content in the gas is calculated by the mass difference of the desiccant in the drying tube before and after water absorption; the gas in the air bag is subjected to gas chromatography analysis to check the gas components and their concentrations in the gas; Verify the degassing effect based on the moisture content and gas components and their concentrations.

7. The method for extracting air from a finished cable buffer layer as claimed in claim 6, characterized in that: The method of calculating the moisture content in the gas by the mass difference before and after the desiccant in the drying tube absorbs water comprises: Use the ideal gas state equation to calculate the total amount of gas: pV=nRT Where p is the gas pressure inside the buffer layer, V is the volume of gas extracted from the buffer layer, n is the amount of gas, R is the molar gas constant of air, and T is the temperature of the gas inside the buffer layer; The amount of water n water Calculated by the mass difference of the desiccant, using the formula: Where m is the mass difference of the drying tube before and after the gas is taken out, and M is the molar mass of water; The calculation process of moisture content is:

8. The method for extracting air from a finished cable buffer layer as claimed in claim 6, characterized in that: During the gas chromatography analysis of the gas in the air bag, the type of each component gas is determined by the peak time in the chromatogram, and the normalization method is used for quantitative analysis. The detection process needs to be repeated at least three times.

9. The method for extracting air from a finished cable buffer layer as claimed in claim 6, characterized in that: When the gas sampling is completed, the gas sampling device is disassembled and the gas sampling hole is sealed.

10. The method for extracting gas from a finished cable buffer layer as claimed in claim 6, characterized in that: During the drilling process of the aluminum sheath, the wave crest position is selected for drilling.

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