Device and method for detecting gas escaped from high-voltage cable joint

Abstract

The invention discloses a device and a method for detecting gas escaping from a high-voltage cable joint. Comprising a photoacoustic cell, a detection module, a light source, an FPGA core control and demodulation system and a display analysis module, the photoacoustic cell is used for storing gas escaping from the high-voltage cable connector, and the light source is used for emitting light beams with characteristic wavelengths and irradiating the gas escaping from the high-voltage cable connector stored in the photoacoustic cell; the detection module is used for receiving and exciting escaped gas to generate a photoacoustic signal and determining the type and concentration information of the escaped gas according to the photoacoustic signal, and the FPGA core control and demodulation system is used for processing the type and concentration information of the escaped gas to obtain a demodulated digital signal; and the display analysis module is used for analyzing the demodulated digital signal to judge whether the high-voltage cable joint has defects or not and judge the defect type. The method has the characteristics of high sensitivity, high reliability, high defect detection rate and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of optical detection of high-voltage cable joints, and in particular relates to a device and method for detecting gas escaping from a high-voltage cable joint. Background Art

[0002] As the in-and-out lines of major substations in urban areas and important power supply connection lines between important users and substations, the safe operation of 110kV and above high-voltage transmission cables is an important guarantee for the reliable power supply of the power grid. In recent years, the number and scope of cables used in new construction projects have expanded rapidly. However, the design, operation and maintenance, and management personnel still lack understanding of the application of high-voltage cables. It is common to lay cables ahead of schedule and install cable intermediate joints without a license, resulting in frequent cable failures. In particular, high-voltage cable joints have become a high-incidence point of failure, which has seriously affected the safe and reliable operation of the power grid, causing huge economic losses and serious social impacts. Therefore, the state of high-voltage cable joints directly determines whether the high-voltage cable system can operate safely and stably.

[0003] At present, the intermediate joints of high-voltage cables are installed by construction personnel or manufacturers at the project site. The insulation prefabricated parts of cable joints have high requirements for environmental cleanliness, complex internal structures of joints, and difficult key process control. As a result, the cable joints often have potential insulation defects such as impurities mixed in, installation dimensions offset, and unqualified insulation shielding fracture treatment during installation. Such defects are difficult to detect and highly concealed. It usually takes 1 to 5 years of gradual development in the insulation prefabricated parts before detectable partial discharge or abnormal heating will gradually appear. In addition, during operation, since most joints are laid in underground passages such as tunnels, drainage pipes, and cable trenches, problems such as moisture and water ingress frequently occur. Since the insulation design margin of cable joints is large and there are few effective detection methods, the potential defects generated during the installation process are usually difficult to detect through power outage tests such as insulation resistance and AC withstand voltage. Existing high-voltage cable joint live detection technologies, such as partial discharge detection, sheath circulation monitoring, and infrared temperature measurement, are not sensitive to common problems such as joint water ingress and early insulation defects, and have limitations such as low defect detection rate and high interference from the electromagnetic environment. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies of the above-mentioned background technology and to provide a device and method for detecting gas escaping from a high-voltage cable joint.

[0005] The technical solution adopted by the present invention is: a gas detection device for escaping from a high-voltage cable joint, comprising a photoacoustic cell, a detection module, a light source, an FPGA core control and demodulation system and a display analysis module.

[0006] The photoacoustic cell is used to store gas escaping from a high-voltage cable joint, the light source is used to emit a light beam with a characteristic wavelength and irradiate the gas escaping from the high-voltage cable joint stored in the photoacoustic cell, the detection module is used to receive the excited escaping gas to generate a photoacoustic signal, and determine the type and concentration information of the escaping gas based on the photoacoustic signal, the FPGA core control and demodulation system is used to process the type and concentration information of the escaping gas to obtain a demodulated digital signal, and the display analysis module is used to analyze the demodulated digital signal to determine whether the high-voltage cable joint has defects and the type of defects.

[0007] It also includes a detection interface, a solenoid valve and an air pump. The detection interface is used to connect to the detection hole of the protective copper shell of the high-voltage cable connector. The air pump is connected to the detection interface to pump the escaped gas inside the protective copper shell into the photoacoustic pool. The solenoid valve is connected between the detection interface and the air pump to control the flow direction and switch of the escaped gas. The FPGA core control and demodulation system is used to control the opening and closing of the light source, the opening of the solenoid valve, and the opening and closing of the air pump.

[0008] It also includes an AD conversion module, which is connected between the detection module and the FPGA core control and demodulation system and is used to process the type and concentration information of the escaping gas to obtain a digital signal.

[0009] The display analysis module compares the concentration of each type of gas escaping from the high-voltage cable joint with the corresponding gas threshold. If the concentration of the gas of this type is greater than or equal to the gas threshold, it is determined that the high-voltage cable joint is defective.

[0010] Types of gases emitted include CO2, CO, CH4, C2H2, C2H4, C2H6, H2O.

[0011] The gas ratios between various gas types are calculated according to the concentration of each gas type in the escaping gas: R1 = CO concentration / CO2 concentration, R2 = C2H2 concentration / C2H4 concentration, R3 = C2H2 concentration / CH4 concentration, R4 = C2H6 concentration / C2H2 concentration and R5 = CO2 concentration / H2O concentration. The defect type of the high-voltage cable joint is judged according to the range of the gas ratios between various gas types. R1 to R5 are the first gas ratio, the second gas ratio, the third gas ratio, the fourth gas ratio and the fifth gas ratio, respectively.

[0012] The defect types mentioned include overheating, partial discharge, arc faults and moisture.

[0013] If R1>K 1high , R2<K2, R3<K3, R4>K4, it is judged as overheating defect;

[0014] If R1<K 1low, R3<K3, R4>K4, it is judged as a partial discharge defect;

[0015] If K 1low ≤R1≤K 1high , K 2low ≤R2≤K 2high , R3 ≥ K3, R4 < K4, it is judged as an arc fault defect;

[0016] If K 1low ≤R1≤K 1high , R4≥K4, R5≤K5 is judged as moisture defect;

[0017] Among them, K 1low is the lower limit of the first setting range, K 1high The upper limit of the first setting range; K 2low is the lower limit of the second setting range, K 2high is the upper limit of the second setting range; K2 is the second setting value; K3 is the third setting value; K4 is the fourth setting value; K5 is the fifth setting value.

[0018] A method for detecting gas escaping from a high-voltage cable joint, comprising:

[0019] The light source emits a light beam with a characteristic wavelength and irradiates the gas escaping from the high-voltage cable joint stored in the photoacoustic cell, receives the excited escaping gas to generate a photoacoustic signal, determines the type and concentration information of the escaping gas based on the photoacoustic signal, processes the type and concentration information of the escaping gas to obtain a demodulated digital signal, and analyzes the demodulated digital signal to determine whether the high-voltage cable joint has defects and the type of defects.

[0020] The concentration of each type of gas escaping from the high-voltage cable joint is compared with the corresponding gas threshold. If the concentration of the gas of this type is greater than or equal to the gas threshold, it is determined that the high-voltage cable joint has a defect.

[0021] Types of gases emitted include CO2, CO, CH4, C2H2, C2H4, C2H6, H2O.

[0022] The gas ratios between various gas types are calculated according to the concentration of each gas type in the escaping gas: R1 = CO concentration / CO2 concentration, R2 = C2H2 concentration / C2H4 concentration, R3 = C2H2 concentration / CH4 concentration, R4 = C2H6 concentration / C2H2 concentration and R5 = CO2 concentration / H2O concentration. The defect type of the high-voltage cable joint is judged according to the range of the gas ratios between various gas types. R1 to R5 are the first gas ratio, the second gas ratio, the third gas ratio, the fourth gas ratio and the fifth gas ratio, respectively.

[0023] The defect types mentioned include overheating, partial discharge, arc faults and moisture.

[0024] If R1>K 1high , R2<K2, R3<K3, R4>K4, it is judged as overheating defect; if R1<K 1low , R3<K3, R4>K4, it is judged as a partial discharge defect; if K 1low ≤R1≤K 1high , K 2low ≤R2≤K 2high , R3 ≥ K3, R4 < K4, it is judged as an arc fault defect; if K 1low ≤R1≤K 1high , R4 ≥ K4, R5 ≤ K5 is considered as a moisture defect, where K 1low is the lower limit of the first setting range, K 1high The upper limit of the first setting range; K 2low is the lower limit of the second setting range, K 2high is the upper limit of the second setting range; K2 is the second setting value; K3 is the third setting value; K4 is the fourth setting value; K5 is the fifth setting value.

[0025] The mechanism of gas generation in the high-voltage cable joint of the present invention is: when the high-voltage cable joint has local discharge defects, overheating defects, and the materials in the joint are damp and aged, the cable and the joint components will undergo pyrolysis reaction and release gas products. XLPE is a macromolecular polymer composed of carbon chains of different lengths. The carbon chains will break to different degrees at different temperatures, and eventually various small molecular hydrocarbons will be generated. The pyrolysis reaction equation can be expressed as formula (1):

[0026]

[0027] When the pyrolysis area contains a certain amount of oxygen (such as a small amount of oxygen molecules adsorbed in the amorphous area of ​​the polymer, oxygen and water molecules in the porous structure of the water-blocking buffer layer, etc.), CO and CO2 will also be generated, and their output mainly depends on the amount of oxygen. Therefore, when there are defects in the cable joint, acetylene, ethane, methane, ethylene, carbon monoxide, carbon dioxide, water and other escaped gases will be produced.

[0028] The gas detection principle of the present invention is: the escaped gas is stored in a closed photoacoustic cell, and when the light beam of a specific infrared band irradiates the escaped gas molecules, the escaped gas molecules choose to absorb the light energy of a part of the band. After absorbing the incident light, the escaped gas molecules in the photoacoustic cell are excited from a low energy state to a high energy state, and then return to the low energy state in the form of spontaneous radiation transition and radiationless transition. In the radiationless transition process, its energy is converted into the translational kinetic energy and rotational kinetic energy of the escaped gas molecules, so that the temperature of the escaped gas increases. When the volume of the escaped gas remains unchanged, the temperature increases and the pressure increases. If the incident light is modulated in intensity or wavelength, the temperature of the escaped gas will change at the same frequency, resulting in periodic changes in the pressure of the escaped gas. If the modulation frequency is within the acoustic frequency range, the periodic change in the pressure of the escaped gas will generate a photoacoustic signal. The photoacoustic signal is detected by the detection module, and information on the type and concentration of the escaped gas can be obtained.

[0029] The present invention realizes distributed perception and alarm of local discharge defects, overheating defects and aging of materials in high-voltage cable joints, and realizes low cross-sensitivity, high sensitivity, high resolution and anti-electromagnetic interference detection of gas escaping from high-voltage cable joints, thereby improving the safe operation level of cable lines.

[0030] The implementation of the present invention has the following beneficial effects: the gas detection device for escaping from high-voltage cable joints has the characteristics of high sensitivity, high reliability and high defect detection rate, and can identify the insulation state and defect type of the cable joints, effectively improve the lean management level of the cable lines, and reduce the occurrence of cable joint failures. The joint state monitoring and early warning capabilities of high-voltage cable lines are greatly enhanced, and the safe operation level of the equipment is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flow chart of the detection method;

[0032] Figure 2 It is a structural block diagram of a gas detection device for escaping from a high-voltage cable joint of the present invention;

[0033] Figure 3 It is a schematic diagram of the structure of the photoacoustic sensor of the TU-type micro-cantilever structure of the present invention;

[0034] Figure 4 It is a structural block diagram of another embodiment of a device for detecting gas escaping from a high-voltage cable joint;

[0035] Figure 5 Schematic diagram of the protective copper shell structure. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments to facilitate a clear understanding of the present invention, but they do not constitute a limitation on the present invention.

[0037] Embodiment 1:

[0038] like Figure 2 As shown, the present invention provides a gas detection device for escaping from a high-voltage cable joint, comprising a photoacoustic cell 4, a detection module 5, a light source 7, an FPGA core control and demodulation system 8 and a display analysis module 10.

[0039] In the above technical scheme, the photoacoustic pool 4 is used to store the gas escaping from the high-voltage cable connector A, the light source 7 is used to emit a light beam with a characteristic wavelength and irradiate the gas escaping from the high-voltage cable connector A stored in the photoacoustic pool 4, the detection module 5 is used to receive the excited escaping gas to generate a photoacoustic signal, and determine the type and concentration information of the escaping gas according to the photoacoustic signal, the FPGA core control and demodulation system 8 is used to process the type and concentration information of the escaping gas to obtain a demodulated digital signal, and the display analysis module 10 is used to analyze the demodulated digital signal to determine whether the high-voltage cable connector A has defects and the type of defects.

[0040] The above technical scheme also includes a detection interface 1, a solenoid valve 2, an air pump 3, an AD conversion module 6, a communication module 9 and a power supply 11. The detection interface 1 is used to connect to the detection hole C of the protective copper shell B of the high-voltage cable connector A. The air pump 3 is connected to the detection interface 1 to pump the escaped gas inside the protective copper shell B into the photoacoustic pool 4. The solenoid valve 2 is connected between the detection interface 1 and the air pump 3 to control the flow direction and switch of the escaped gas. The AD conversion module 6 is used to process the type and concentration information of the escaped gas to obtain a digital signal. The FPGA core control and demodulation system 8 is used to control the opening and closing of the light source 7, the opening of the solenoid valve 2, and the opening and closing of the air pump 3.

[0041] In the above technical scheme, the detection interface 1 is connected to the photoacoustic pool 4, the detection module 5 is arranged in the photoacoustic pool 4, the light source 7 is arranged outside the photoacoustic pool 4 and connected to the FPGA core control and demodulation system 8, and the detection module 5, the D conversion module 6, the light source 7, the FPGA core control and demodulation system 8, the communication module 9 and the display analysis module 10 are connected in sequence.

[0042] In the above technical solution, the solenoid valve 2 is arranged between the detection interface 1 and the photoacoustic cell 4 and connected to the FPGA core control and demodulation system 8 to control the flow direction and switch of the escaping gas.

[0043] In the above technical solution, the air pump 3 is arranged between the detection interface 1 and the photoacoustic cell 4 and connected to the FPGA core control and demodulation system 8, and is used to pump the escaped gas inside the protective copper shell B into or out of the photoacoustic cell 4.

[0044] In the above technical solution, the photoacoustic cell 4 is used to store the escaped gas to be measured.

[0045] In the above technical solution, the detection module 5 is used to detect the photoacoustic signal, and obtain the type and concentration of the escaping gas.

[0046] In the above technical solution, the AD conversion module 6 is used to convert the analog signal into a digital signal.

[0047] In the above technical solution, the light source 7 is used to provide light of a wavelength for detecting escaped gas in the photoacoustic cell 4 .

[0048] In the above technical solution, the FPGA core control and demodulation system 8 is used to control the working status and sequence of the light source 7, the solenoid valve 2, the air pump 3, the AD conversion module 6 and the communication module 9 and demodulate the digital signal.

[0049] In the above technical solution, the communication module 9 is used to transmit the demodulated digital signal to the display analysis module 10 .

[0050] In the above technical solution, the display analysis module 10 is used to determine whether the high-voltage cable connector A has a defect by comparing the type and concentration of the escaping gas with the gas threshold. If there is a defect, the defect type of the high-voltage cable connector A is determined and displayed according to the gas ratio.

[0051] In the above technical solution, the power supply 11 is connected to the FPGA core control and demodulation system 8 and the display analysis module 10 respectively, and is used to supply power to the FPGA core control and demodulation system 9 and the display analysis module 10 .

[0052] The display analysis module 10 compares the concentration of each type of gas escaping from the high-voltage cable connector A with the corresponding gas threshold value. If the concentration of the gas of this type is greater than or equal to the gas threshold value, it is determined that the high-voltage cable connector A has a defect.

[0053] Types of gases emitted include CO2, CO, CH4, C2H2, C2H4, C2H6, H2O.

[0054] The gas ratios between various gas types are calculated according to the concentration of each gas type in the escaping gas: R1 = CO concentration / CO2 concentration, R2 = C2H2 concentration / C2H4 concentration, R3 = C2H2 concentration / CH4 concentration, R4 = C2H6 concentration / C2H2 concentration and R5 = CO2 concentration / H2O concentration. The defect type of the high-voltage cable joint A is determined according to the range of the gas ratios between various gas types. R1 to R5 are the first gas ratio, the second gas ratio, the third gas ratio, the fourth gas ratio and the fifth gas ratio, respectively.

[0055] Defect types include overheating, partial discharge, arc faults and moisture.

[0056] If R1>K1high , R2<K2, R3<K3, R4>K4, it is judged as overheating defect; if R1<K 1low , R3<K3, R4>K4, it is judged as a partial discharge defect; if K 1low ≤R1≤K 1high , K 2low ≤R2≤K 2high , R3 ≥ K3, R4 < K4, it is judged as an arc fault defect; if K 1low ≤R1≤K 1high , R4 ≥ K4, R5 ≤ K5 is considered as moisture defect; among which, K 1low is the lower limit of the first setting range, K 1high The upper limit of the first setting range; K 2low is the lower limit of the second setting range, K 2high is the upper limit of the second setting range; K2 is the second setting value; K3 is the third setting value; K4 is the fourth setting value; K5 is the fifth setting value.

[0057] Preferably, a photoacoustic sensor with a TU-type microcantilever structure is designed as the detection module 5 for measurement. Figure 3 As shown:

[0058] Through theoretical analysis, the analytical formula of the first-order natural frequency of the TU-type microcantilever beam is obtained:

[0059]

[0060] Take the elastic modulus E = 1.124e + 011N / m 2 , mass density ρ = 2330 kg / m 3 , h = 0.01mm, b1 = 0.8mm, b2 = 1mm, b3 = 0.5mm, l1 = 0.8mm, l2 = 0.4mm, l3 = 1mm. Substituting the results, the first-order natural frequency is calculated to be f = 5257.39Hz.

[0061] The light source 7 is used to provide light of a wavelength for detecting the escaped gas. Preferably, a light source of mid-infrared wavelength is selected, and the light source characteristics corresponding to the gas are shown in Table 1.

[0062] Table 1 Light source characteristics of different escaping gases

[0063]

[0064] Preferably, a battery is used to power the device in the live detection working mode, and an AC power supply is used to power the device in the online monitoring working mode.

[0065] Embodiment 2:

[0066] like Figure 1As shown, the present invention provides a method for detecting gas escaping from a high-voltage cable joint, comprising: a light source 7 emits a light beam with a characteristic wavelength and irradiates the gas escaping from a high-voltage cable joint A stored in a photoacoustic cell 4, receives the excited escaping gas to generate a photoacoustic signal, determines the type and concentration information of the escaping gas according to the photoacoustic signal, processes the type and concentration information of the escaping gas to obtain a demodulated digital signal, and analyzes the demodulated digital signal to determine whether the high-voltage cable joint A has a defect and the type of defect.

[0067] Connect the detection interface 1 of the device to the detection hole C of the high-voltage cable connector A to form a closed gas circuit, turn on the air pump 3 to allow the gas to enter the photoacoustic pool 4; detect the type and concentration of gas escaping from the high-voltage cable connector in the photoacoustic pool 4 at different times to determine the defect type of the high-voltage cable connector A.

[0068] The identification method is:

[0069] Each gas threshold is used to determine whether there is a defect; the gas threshold is usually selected within ±30% of the value measured for the first time on the high-voltage cable connector A. Preferably, the data in Table 2 can be used. If the concentration of this type of gas is greater than or equal to the gas threshold, there is a defect. The types of escaping gas include CO2, CO, CH4, C2H2, C2H4, C2H6, and H2O.

[0070] Table 2 Thresholds of 7 characteristic gases in normal high-voltage cable joints

[0071]

[0072] Calculate the gas ratio and identify the defect type inside the high-voltage cable joint.

[0073] Preferably, the overheating, partial discharge, arc fault and moisture inside the joint are identified by using the values ​​of the gas ratios, (R1=CO concentration / CO2 concentration), (R2=C2H2 concentration / C2H4 concentration), (R3=C2H2 concentration / CH4 concentration), (R4=C2H6 concentration / C2H2 concentration) and (R5=CO2 concentration / H2O concentration). In this embodiment,

[0074] Table 3 Ratio diagnostic criteria

[0075] Defect Type R1 R2 R3 R4 R5 overheat ＞0.5 ＜0.75 ＜0.3 ＞0.4 / Partial Discharge ＜0.2 / ＜0.3 ＞0.4 / Arc Fault ≥0.2～≤0.5 ≥0.01～≤0.1 ≥0.3 ＜0.4 / Damp ≥0.2～≤0.5 / / ≥0.4 ≤0.05

[0076] Embodiment 3:

[0077] like Figure 4 , Figure 5As shown, the present invention provides a method for detecting gas escaping from a high-voltage cable connector, comprising connecting a first detection interface 1-1 and a second detection interface 1-2 (there are two detection interfaces in this embodiment) of the device with a first detection hole C1 and a second detection hole C2 (there are two detection holes in this embodiment) of a protective copper shell B to form a closed gas path. The FPGA core control and demodulation system 8 controls the solenoid valves 2 (the first solenoid valve 2-1, the second solenoid valve 2-2) and the air pump 3 to open in sequence, and pumps the gas escaping from the high-voltage cable connector A in the protective copper shell B into the photoacoustic pool 4, and then controls the light source to emit a light beam with a characteristic wavelength. After the light beam enters the photoacoustic pool 4 and excites the escaping gas to generate a photoacoustic signal, which is received by the detection module 5, the digital signal is obtained through the AD conversion module 6 and transmitted to the FPGA core control and demodulation system 8 for real-time solution, and then uploaded to the display analysis module 10 through the communication module 9 for processing and analysis. The display analysis module 10 displays the type and concentration of gas escaping from the high-voltage cable connector A at the moment of detection. As shown Figure 4 As shown, the device power supply 11 is battery-powered, and the working mode is that the handheld device performs live detection on the high-voltage cable connector.

[0078] Table 4 Seven characteristic gases of high voltage cable joints in this embodiment

[0079]

[0080] The gas ratio is calculated to identify the defect type inside the high-voltage cable connector, R1=0.8, R2=0.2, R3=0.27, R4=0.75, R5=1. According to Table 3, the defect type is identified as overheating, and the defect type is displayed through the display analysis module 10.

[0081] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A gas detection device for escaping from a high-voltage cable joint, characterized in that: It includes a photoacoustic cell (4), a detection module (5), a light source (7), an FPGA core control and demodulation system (8) and a display analysis module (10). The photoacoustic pool (4) is used to store gas escaping from a high-voltage cable joint (A); the light source (7) is used to emit a light beam with a characteristic wavelength and irradiate the gas escaping from the high-voltage cable joint (A) stored in the photoacoustic pool (4); the detection module (5) is used to receive the excited escaping gas to generate a photoacoustic signal, and determine the type and concentration information of the escaping gas according to the photoacoustic signal; the FPGA core control and demodulation system (8) is used to process the type and concentration information of the escaping gas to obtain a demodulated digital signal; and the display analysis module (10) is used to analyze the demodulated digital signal to determine whether the high-voltage cable joint (A) has a defect and the defect type.

2. A gas detection device for escaping from a high-voltage cable joint according to claim 1, characterized in that: The invention also comprises a detection interface (1), a solenoid valve (2) and an air pump (3); the detection interface (1) is used to be connected to a detection hole (C) of a protective copper shell (B) of a high-voltage cable connector (A); the air pump (3) is connected to the detection interface (1) and is used to pump the escaped gas inside the protective copper shell (B) into a photoacoustic pool (4); the solenoid valve (2) is connected between the detection interface (1) and the air pump (3) and is used to control the flow direction and switch of the escaped gas; and the FPGA core control and demodulation system (8) is used to control the opening and closing of the light source (7), the opening degree of the solenoid valve (2), and the opening and closing of the air pump (3).

3. A gas detection device for escaping from a high-voltage cable joint according to claim 2, characterized in that: It also includes an AD conversion module (6), which is connected between the detection module (5) and the FPGA core control and demodulation system (8) and is used to process the type and concentration information of the escaping gas to obtain a digital signal.

4. A gas detection device for escaping from a high-voltage cable joint according to claim 1, characterized in that: The display analysis module (10) compares the concentration of each type of gas escaping from the high-voltage cable connector (A) with the corresponding gas threshold value, and if the concentration of the gas of this type is greater than or equal to the gas threshold value, it is determined that the high-voltage cable connector (A) has a defect.

5. A gas detection device for escaping from a high-voltage cable joint according to claim 4, characterized in that: Types of gases emitted include CO2, CO, CH4, C2H2, C2H4, C2H6, H2O.

6. A gas detection device for escaping from a high-voltage cable joint according to claim 5, characterized in that: The gas ratios between various gas types are calculated according to the concentration of each gas type in the escaping gas: R1 = CO concentration / CO2 concentration, R2 = C2H2 concentration / C2H4 concentration, R3 = C2H2 concentration / CH4 concentration, R4 = C2H6 concentration / C2H2 concentration and R5 = CO2 concentration / H2O concentration. The defect type of the high-voltage cable joint (A) is determined according to the range of the gas ratios between various gas types. R1 to R5 are the first gas ratio, the second gas ratio, the third gas ratio, the fourth gas ratio and the fifth gas ratio, respectively.

7. A gas detection device for escaping from a high-voltage cable joint according to claim 6, characterized in that: The defect types mentioned include overheating, partial discharge, arc faults and moisture.

8. A gas detection device for escaping from a high-voltage cable joint according to claim 7, characterized in that: If R1>K 1high , R2<K2, R3<K3, R4>K4, it is judged as overheating defect; If R1<K 1low , R3<K3, R4>K4, it is judged as a partial discharge defect; If K 1low ≤R1≤K 1high , K 2low ≤R2≤K 2high , R3 ≥ K3, R4 < K4, it is judged as an arc fault defect; If K 1low ≤R1≤K 1high , R4≥K4, R5≤K5 is judged as moisture defect; Among them, K 1low is the lower limit of the first setting range, K 1high The upper limit of the first setting range; K 2low is the lower limit of the second setting range, K 2high is the upper limit of the second setting range; K2 is the second setting value; K3 is the third setting value; K4 is the fourth setting value; K5 is the fifth setting value.

9. A method for detecting gas escaping from a high-voltage cable joint, characterized in that: The method comprises controlling a light source (7) to emit a light beam with a characteristic wavelength and irradiating gas escaping from a high-voltage cable connector (A) stored in a photoacoustic pool (4), receiving and exciting the escaping gas to generate a photoacoustic signal, determining the type and concentration information of the escaping gas according to the photoacoustic signal, processing the type and concentration information of the escaping gas to obtain a demodulated digital signal, and analyzing the demodulated digital signal to determine whether the high-voltage cable connector (A) has a defect and the type of defect.

10. A method for detecting gas escaping from a high-voltage cable joint according to claim 9, characterized in that: The concentration of each type of gas escaping from the high-voltage cable joint (A) is compared with the corresponding gas threshold. If the concentration of the gas of this type is greater than or equal to the gas threshold, it is determined that the high-voltage cable joint (A) is defective.

11. A method for detecting gas escaping from a high-voltage cable joint according to claim 10, characterized in that: Types of gases emitted include CO2, CO, CH4, C2H2, C2H4, C2H6, H2O.

12. A method for detecting gas escaping from a high-voltage cable joint according to claim 11, characterized in that: The gas ratios between various gas types are calculated according to the concentration of each gas type in the escaping gas: R1 = CO concentration / CO2 concentration, R2 = C2H2 concentration / C2H4 concentration, R3 = C2H2 concentration / CH4 concentration, R4 = C2H6 concentration / C2H2 concentration and R5 = CO2 concentration / H2O concentration. The defect type of the high-voltage cable joint (A) is determined according to the range of the gas ratios between various gas types. R1 to R5 are the first gas ratio, the second gas ratio, the third gas ratio, the fourth gas ratio and the fifth gas ratio, respectively.

13. A method for detecting gas escaping from a high-voltage cable joint according to claim 12, characterized in that: The defect types mentioned include overheating, partial discharge, arc faults and moisture.

14. A method for detecting gas escaping from a high-voltage cable joint according to claim 13, characterized in that: If R1>K 1high , R2<K2, R3<K3, R4>K4, it is judged as overheating defect; If R1<K 1low , R3<K3, R4>K4, it is judged as a partial discharge defect; If K 1low ≤R1≤K 1high , K 2low ≤R2≤K 2high , R3 ≥ K3, R4 < K4, it is judged as an arc fault defect; If K 1low ≤R1≤K 1high , R4≥K4, R5≤K5 is judged as moisture defect; Among them, K 1low is the lower limit of the first setting range, K 1high The upper limit of the first setting range; K 2low is the lower limit of the second setting range, K 2high is the upper limit of the second setting range; K2 is the second setting value; K3 is the third setting value; K4 is the fourth setting value; K5 is the fifth setting value.

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