High voltage cable overheating fault detection method and online monitoring device

Abstract

This invention discloses a method and online monitoring device for detecting overheating faults in high-voltage cables. The method includes: extracting characteristic decomposition products from the sealed cavity between the metal sheath and the buffer layer of the high-voltage cable. These characteristic decomposition products include styrene, benzaldehyde, toluene, and isobutylene; detecting the concentrations of these four characteristic decomposition products; and combining the concentration ratios of these four characteristic decomposition products to obtain the thermal fault temperature range and the corresponding fault location. This invention, by detecting the characteristic decomposition products in the sealed cavity between the buffer layer and the metal sheath of the high-voltage cable, can accurately characterize the temperature range and the location of overheating faults inside the high-voltage cable.

Description

Technical Field

[0001] The invention relates to a high-voltage cable fault diagnosis technology, and in particular to a high-voltage cable overheat fault detection method and an online monitoring device. Background Art

[0002] High-voltage cables are increasingly used in my country's power system. From the inside to the outside, their structure can be divided into: conductor, conductor shield, insulation layer, insulation shield, buffer layer, metal sheath, where there is a gap between the buffer layer and the metal sheath, forming a closed cavity. In recent years, high-voltage cable failures have occurred frequently, seriously affecting the safe and stable operation of my country's power grid system. When high-voltage cables are overloaded for a long time, due to the thermal effect of the current, the load current will cause the conductor to overheat, and the skin effect of the charge and the eddy current loss of the steel armor and the insulation medium loss will also generate additional heat, so that the temperature of the high-voltage cable continues to rise, resulting in the destruction of the insulation layer. In mild cases, it will cause a short circuit, and in severe cases, it will cause fire and explosion accidents. The existing traditional temperature measurement technology installs point temperature sensors on important parts of high-voltage cables for temperature measurement. The temperature measurement range is limited and it is easy to produce measurement blind spots; the application of distributed optical fiber temperature measurement systems in online monitoring of high-voltage cables is still in its early stages, and the technology is not yet mature. Summary of the invention

[0003] The present invention provides a high-voltage cable overheat fault detection method and an online monitoring device to solve the problem that the existing high-voltage cable temperature measurement effect is poor.

[0004] In order to achieve the above object, the present invention adopts the following technical solution.

[0005] In a first aspect, a method for detecting a high-voltage cable overheating fault is provided, comprising:

[0006] Extracting characteristic decomposition products in the closed cavity between the metal sheath and the buffer layer of the high-voltage cable, the characteristic decomposition products including styrene, benzaldehyde, toluene and isobutylene;

[0007] The concentrations of the four characteristic decomposition products are detected, and the thermal fault temperature range and the corresponding fault generating location are obtained by combining the concentration ratio relationship of the four characteristic decomposition products.

[0008] Furthermore, the isobutylene is a characteristic decomposition product produced by thermal decomposition of cross-linked polyethylene in the insulating layer and the insulating shielding layer; the styrene, benzaldehyde and toluene are characteristic decomposition products produced by thermal decomposition of organic polyethylene terephthalate in the buffer layer.

[0009] Further, the thermal fault temperature range is determined by the following method:

[0010] If there is no isobutylene and the concentration ratio of styrene: (benzaldehyde + toluene) is greater than 10:1, the thermal fault temperature range is 275℃-310℃, and the fault occurs in the buffer layer;

[0011] If there is no isobutylene and the concentration ratio of styrene to benzaldehyde is in the range of 6:1 to 4:1, the thermal fault temperature range is 310°C to 350°C, and the fault occurs in the buffer layer;

[0012] If there is no isobutylene and the concentration ratio of styrene to toluene is in the range of 7:1 to 5:1, the thermal fault temperature range is 350°C-400°C, and the fault occurs in the buffer layer;

[0013] If isobutylene is present, the thermal failure temperature range is above 400°C, and the failure occurs in the insulation layer and / or insulation shielding layer.

[0014] In a second aspect, a high-voltage cable overheat fault online monitoring device is provided, which is used to implement the high-voltage cable overheat fault detection method as described above, and comprises:

[0015] An air intake pipeline is used to communicate with the closed cavity between the metal sheath and the buffer layer of the high-voltage cable;

[0016] A vacuum pump, the input end of which is connected to the gas extraction pipeline, is used to extract characteristic decomposition products in the closed cavity between the metal sheath and the buffer layer of the high-voltage cable and transport them to the valve injection system; wherein the characteristic decomposition products include styrene, benzaldehyde, toluene and isobutylene;

[0017] A valve injection system is used to quantitatively sample characteristic decomposition products and deliver them to the chromatographic column;

[0018] A chromatographic column is used to separate the characteristic decomposition products according to their types and input them into the detector accordingly;

[0019] The detector is used to detect the input concentrations of the four characteristic decomposition products, and obtain the thermal fault temperature range and the corresponding fault generating location based on the ratio relationship of the four characteristic decomposition product concentrations.

[0020] Furthermore, the gas intake pipeline includes, from inside to outside, a conduit, a constant power electric heating belt, a thermal insulation layer and an outer sheath.

[0021] Furthermore, the head of the vacuum pump is equipped with an electronic heater; the valve injection system includes an electric six-way valve, a quantitative loop, and a carrier gas input unit, and the vacuum pump, the quantitative loop, the carrier gas input unit and the chromatographic column are all connected to the electric six-way valve.

[0022] Furthermore, the carrier gas delivered by the carrier gas input unit is 99.999% nitrogen.

[0023] Furthermore, the chromatographic column is a column filled with a 60-80 mesh or 80-100 mesh carbon molecular sieve as the stationary phase.

[0024] Furthermore, the detector is a catalytic combustion type detector.

[0025] Furthermore, it also includes a communication module connected to the detector, which is used for data exchange with the outside to realize remote data viewing and remote start and stop; when the detector detects isobutylene, it sends an alarm signal to the outside through the communication module.

[0026] The present invention proposes a high-voltage cable overheating fault detection method and an online monitoring device. By detecting the characteristic decomposition products in the closed cavity between the high-voltage cable buffer layer and the metal sheath, the temperature range of the overheating fault inside the high-voltage cable and the fault-involved parts can be accurately characterized. Compared with the traditional temperature measurement technology with a limited temperature measurement range, mostly targeting the cable joint position and prone to measurement blind spots, the present invention provides a new method for judging the latent overheating fault of the high-voltage cable body, the fault-involved parts and the overheating temperature development trend through characteristic decomposition products. By opening air holes in sections on the metal sheath of the high-voltage cable and connecting the air intake pipeline, the characteristic products are periodically detected using a high-voltage cable overheating fault online monitoring device. The detection sensitivity is high, and the overheating state of the high-voltage cable can be monitored and warned in real time to ensure the safe and stable operation of the power grid system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 It is a schematic structural diagram of a high-voltage cable overheat fault online monitoring device provided by an embodiment of the present invention.

[0029] In the figure: 1. high-voltage cable, 2. sampling solenoid valve, 3. gas extraction pipeline, 4. vacuum pump, 5. quantitative ring, 6. electric six-way valve, 7. carrier gas input unit, 8. injection port, 9. cleaning exhaust valve, 10. chromatographic column, 11. detector. DETAILED DESCRIPTION

[0030] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0031] The traditional temperature measurement technology installs point temperature sensors at important parts of the cable for temperature measurement, which has a limited temperature measurement range and is prone to measurement blind spots. In view of the shortcomings of the prior art, the present invention triggers from the structure and material of the high-voltage cable and proposes a new high-voltage cable overheating fault detection technology. The structure of the high-voltage cable from the inside to the outside can be divided into: conductor, conductor shielding layer, insulation layer, insulation shielding layer, buffer layer, metal sheath, wherein there is a gap between the buffer layer and the metal sheath, forming a closed cavity. At present, most buffer layers use polyester fiber non-woven fabrics, the main component of which is organic polyethylene terephthalate, and the main components of the insulation layer and the insulation shielding layer are cross-linked polyethylene. Due to the heat generated by the current, the cross-linked polyethylene will produce decomposition gas at high temperature. At the same time, the inventor's previous research found that the buffer layer (polyethylene terephthalate) will decompose under the action of thermal oxygen to produce aromatic organic characteristic decomposition products. Therefore, the present invention is based on the characteristic decomposition products in the closed cavity between the buffer layer and the metal sheath to characterize the temperature range of the internal overheating fault of the high-voltage cable and the corresponding fault generating location. The technical scheme of the present invention is described in detail below in conjunction with specific embodiments.

[0032] An embodiment of the present invention provides a method for detecting a high-voltage cable overheating fault, comprising:

[0033] S1: Extract characteristic decomposition products in the closed cavity between the metal sheath and the buffer layer of the high-voltage cable. The characteristic decomposition products include styrene, benzaldehyde, toluene and isobutylene.

[0034] It should be noted that isobutylene is a characteristic decomposition product produced by thermal decomposition of cross-linked polyethylene in the insulating layer and the insulating shielding layer; and the styrene, benzaldehyde and toluene are characteristic decomposition products produced by thermal decomposition of the organic substance polyethylene terephthalate in the buffer layer.

[0035] S2: Detect the concentrations of the four characteristic decomposition products, and obtain the thermal fault temperature range and the corresponding fault location by combining the concentration ratio of the four characteristic decomposition products.

[0036] More specifically, the thermal fault temperature range and the corresponding fault generating location are determined by the following method:

[0037] (1) When the temperature is between 275°C and 310°C, the characteristic decomposition product is mainly styrene. Therefore, if isobutylene is not detected and the concentration ratio of styrene: (benzaldehyde + toluene) is greater than 10:1, the thermal fault temperature range is judged to be 275°C-310°C;

[0038] (2) When the temperature is between 310℃ and 350℃, the concentration of benzaldehyde in the characteristic decomposition products increases significantly, while the concentration of toluene is still low. Therefore, if no isobutylene is detected and the concentration ratio of styrene to benzaldehyde is between 6:1 and 4:1, the thermal fault temperature range is 310℃ to 350℃.

[0039] (3) When the temperature is between 350°C and 400°C, the concentration of benzaldehyde in the characteristic decomposition products decreases significantly and the concentration of toluene increases. Therefore, if isobutylene is not detected and the concentration ratio of styrene to toluene is in the range of 7:1 to 5:1, the thermal failure temperature range is 350°C to 400°C;

[0040] (4) When the temperature reaches above 400°C, the insulation layer and the insulation shielding layer will be damaged to produce the pyrolysis product isobutylene. Therefore, if isobutylene is detected, the thermal failure temperature range is above 400°C.

[0041] Because the temperature of a high-voltage cable may generally reach more than 200 degrees Celsius during normal operation, the detection of overheating faults in this embodiment mainly focuses on the situation above 275°C to determine the thermal fault temperature range. The corresponding fault location in the above three cases (1), (2) and (3) is the buffer layer, and the corresponding fault location in the fourth case is the insulation layer and / or insulation shielding layer.

[0042] In order to implement the high-voltage cable overheat fault detection method provided in the above embodiment, another embodiment of the present invention provides a high-voltage cable overheat fault online monitoring device, such as Figure 1 As shown, it includes a gas extraction pipeline 3, a vacuum pump 4, a valve injection system, a chromatographic column 10, and a detector 11 which are connected in sequence.

[0043] Among them, one end of the gas extraction pipeline 1 is connected to the closed cavity between the metal sheath and the buffer layer of the high-voltage cable 1, and the other end thereof is connected to the input end of the vacuum pump 4, and the output end of the vacuum pump 4 is connected to the valve sampling system. When the vacuum pump 4 is working, the characteristic decomposition products are extracted from the closed cavity between the metal sheath and the buffer layer of the high-voltage cable 4 through the gas extraction pipeline 3 and transported to the valve sampling system, and then the characteristic decomposition products are quantitatively sampled through the valve sampling system, and then transported to the chromatographic column 10, the characteristic decomposition products are separated in the chromatographic column 10, and then sequentially input into the detector 11, the detector 11 detects the concentrations of the four characteristic decomposition products input, and obtains the thermal fault temperature range and the corresponding fault occurrence location in combination with the concentration ratio relationship of the four characteristic decomposition products.

[0044] Specifically, the gas extraction pipeline 3 is an integrated insulation pipeline, which includes a conduit, a constant power electric heating belt, an insulation layer and an outer sheath from the inside to the outside. The conduit is made of PFA, FEP, PVDF, copper or stainless steel, the outer sheath material is reinforced flame-retardant PVC, and the insulation material is glass fiber wool; the constant power electric heating belt uses a platinum resistor or a thermocouple temperature probe to control the temperature, meeting the requirements of precise temperature control of 40-250°C; in this embodiment, a sampling solenoid valve 2 is provided on the gas extraction pipeline 3, and the gas extraction pipeline is 1m long. Of course, it can also be 1.5m, 2m or other lengths as needed.

[0045] The vacuum pump 4 is a micro vacuum pump, the maximum vacuum degree of the vacuum pump 4 is -85kPa, the material is high temperature resistant, and the head of the vacuum pump 4 is equipped with an electronic heater, which can be heated to 250°C. The valve injection system includes an electric six-way valve 6, a quantitative ring 5, and a carrier gas input unit 7. The vacuum pump 4, the quantitative ring 5, the carrier gas input unit 7 and the chromatographic column 10 are all connected to the electric six-way valve 6. Figure 1 As shown, the six ports of the electric six-way valve 6 are named a, b, c, d, e, and f in clockwise order, the output end of the vacuum pump 4 is connected to port a, the two ends of the quantitative ring 5 are connected to port b and port e, the carrier gas input unit 7 is connected to port c, the chromatographic column 10 is connected to port d through the injection port, and port f is connected to the cleaning exhaust valve. During sampling, port a and port b of the electric six-way valve 6 are connected, port c and port d are connected, and port e and f are connected. The sampling solenoid valve 2 is opened, and the vacuum pump 4 works to extract the characteristic decomposition and transport it to the quantitative ring 5. After the sampling is completed, the electric six-way valve 6 is switched. At this time, port b and port c are connected, port d and port e are connected, and port f is connected to port a. Then the carrier gas input unit 7 inputs the carrier gas, and the characteristic decomposition product to be measured is substituted into the chromatographic column 10 through the flow of the carrier gas. In this embodiment, the carrier gas is 99.999% nitrogen.

[0046] In this embodiment, the chromatographic column 10 is a column filled with a 60-80 mesh or 80-100 mesh carbon molecular sieve as a stationary phase (such as Carbopack B, chromsorb-G, TDX-01, etc.) The detector 11 is a catalytic combustion detector.

[0047] Preferably, it also includes a communication module (not shown) connected to the detector 11, which interacts with the outside world through a 4G / 5G private network or wireless remote transmission to achieve remote data viewing and remote start and stop; when the detector detects isobutylene, it sends an alarm signal to the outside through the communication module.

[0048] The effect of the technical solution of the present invention is further illustrated below in conjunction with a simulation experiment.

[0049] A high-voltage cable overheating fault simulation test platform was built. A 3-meter-long high-voltage cable was selected, and air holes were opened at both ends. At the same time, point temperature sensors were arranged on the buffer layer and surface of the cable body. In the simulation experiment, the online monitoring device was controlled to sample once every 2 hours. The test results are shown in the following table.

[0050]

[0051] It can be understood that the same or similar parts of the above embodiments can be referenced to each other, and the contents not described in detail in some embodiments can refer to the same or similar contents in other embodiments.

[0052] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for detecting overheating faults of high-voltage cables, characterized in that: include: Extracting characteristic decomposition products in the closed cavity between the metal sheath and the buffer layer of the high-voltage cable, the characteristic decomposition products including styrene, benzaldehyde, toluene and isobutylene; Detect the concentrations of the four characteristic decomposition products, and obtain the thermal fault temperature range and the corresponding fault location by combining the concentration ratio of the four characteristic decomposition products; The isobutylene is a characteristic decomposition product produced by thermal decomposition of cross-linked polyethylene in the insulating layer and the insulating shielding layer; the styrene, benzaldehyde and toluene are characteristic decomposition products produced by thermal decomposition of the organic substance polyethylene terephthalate in the buffer layer; The thermal fault temperature range and the corresponding fault location are determined by the following method: If there is no isobutylene and the concentration ratio of styrene: (benzaldehyde + toluene) is greater than 10:1, the thermal fault temperature range is 275 o C-310 o C, the fault occurs at the buffer layer; If there is no isobutylene and the concentration ratio of styrene to benzaldehyde is between 6:1 and 4:1, the thermal failure temperature range is 310 o C~350 o C, the fault occurs at the buffer layer; If there is no isobutylene and the concentration ratio of styrene to toluene is in the range of 7:1 to 5:1, the thermal failure temperature range is 350 o C-400 o C, the fault occurs at the buffer layer; If isobutylene is present, the thermal fault temperature range is 400 o C or above, the fault occurs in the insulation layer and / or insulation shielding layer.

2. A high-voltage cable overheat fault online monitoring device, characterized in that: The method for detecting overheating fault of a high-voltage cable according to claim 1 comprises: An air intake pipeline is used to communicate with the closed cavity between the metal sheath and the buffer layer of the high-voltage cable; A vacuum pump, the input end of which is connected to the gas extraction pipeline, is used to extract characteristic decomposition products in the closed cavity between the metal sheath and the buffer layer of the high-voltage cable and transport them to the valve injection system; wherein the characteristic decomposition products include styrene, benzaldehyde, toluene and isobutylene; A valve injection system is used to quantitatively sample characteristic decomposition products and deliver them to the chromatographic column; A chromatographic column is used to separate characteristic decomposition products according to their types and input them into the detector in sequence; the chromatographic column is a column filled with a 60-80 mesh or 80-100 mesh carbon molecular sieve as a stationary phase; The detector is used to detect the input concentrations of the four characteristic decomposition products, and obtain the thermal fault temperature range and the corresponding fault generating location based on the ratio relationship of the four characteristic decomposition product concentrations.

3. The high-voltage cable overheat fault online monitoring device according to claim 2 is characterized in that: The air intake pipeline includes a conduit, a constant power electric heating belt, a thermal insulation layer and an outer sheath from the inside to the outside.

4. The high-voltage cable overheat fault online monitoring device according to claim 2 is characterized in that: The head of the vacuum pump is equipped with an electronic heater; the valve injection system includes an electric six-way valve, a quantitative loop, and a carrier gas input unit, and the vacuum pump, the quantitative loop, the carrier gas input unit and the chromatographic column are all connected to the electric six-way valve.

5. The high-voltage cable overheat fault online monitoring device according to claim 4 is characterized in that: The carrier gas delivered by the carrier gas input unit is 99.999% nitrogen.

6. The high-voltage cable overheat fault online monitoring device according to claim 2 is characterized in that: The detector is a catalytic combustion type detector.

7. The high-voltage cable overheat fault online monitoring device according to claim 2 is characterized in that: It also includes a communication module connected to the detector, which is used for data exchange with the outside to realize remote data viewing and remote start and stop; when the detector detects isobutylene, it sends an alarm signal to the outside through the communication module.

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