A method for detecting defects in high-voltage XLPE cable buffer layer based on characteristic gas

Abstract

The present invention relates to a method for detecting defects in a high-voltage XLPE cable buffer layer based on characteristic gas, comprising the following steps: S1: collecting buffer layer gas using a high-voltage cable buffer layer gas extraction device; S2: analyzing the components and relative concentrations of the collected buffer layer gas, the analysis method being gas chromatography-mass spectrometry (GC-MS); S3: detecting aldehyde gases in the collected buffer layer gas using a phenol reagent method; S4: judging whether the buffer layer has defects based on the analysis of step S2 and the detection of step S3. The present invention can detect defects in the cable buffer layer relatively directly, is more economical and simpler than existing detection methods, and belongs to the technical field of cable defect detection.

Description

Technical Field

[0001] The invention relates to the technical field of cable defect detection, and in particular to a method for detecting buffer layer defects of a high-voltage XLPE cable based on characteristic gas. Background Art

[0002] The buffer layer defect of high-voltage XLPE cable is a new type of cable defect that has appeared in my country in recent years. The buffer layer defect will further lead to the destruction of the outer insulation semi-conductive shield, and eventually cause the basic failure of the cable body, endangering the safe operation of the cable. At present, the detection methods for buffer layer defects mainly include partial discharge detection method and X-ray imaging method. The current detection methods have the following problems:

[0003] (1) Regarding the method of using the partial discharge method to detect the defect status of the buffer layer, the biggest difficulty in diagnosing whether partial discharge occurs inside the cable on site is not the lack of knowledge of the type of discharge spectrum, but the fact that on-site detection is easily interfered by the noise of surrounding power equipment. At the same time, the partial discharge signal inside the cable is very weak and lasts for a very short time, so it is very likely to miss the discharge signal during detection, resulting in very high difficulty in diagnosing the ablation defect of the buffer layer through partial discharge detection.

[0004] (2) The X-ray imaging detection method is affected by many factors such as X-ray exposure parameters, shooting angle, and X-ray image processing. In practical applications, it cannot effectively determine the location of buffer layer defects. In addition, X-rays can cause radiation damage to the human body and cannot be used in power systems for a long time and on a large scale. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a high-voltage XLPE cable buffer layer defect detection method based on characteristic gas, which can detect the defects of the cable buffer layer more directly and is more economical than the existing detection methods.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for detecting buffer layer defects of a high-voltage XLPE cable based on characteristic gas comprises the following steps:

[0008] S1: Collecting buffer layer gas using a high voltage cable buffer layer gas extraction device;

[0009] S2: analyzing the components and relative concentrations of the collected buffer layer gas by gas chromatography-mass spectrometry;

[0010] S3: using a phenol reagent method to detect the aldehyde gas in the collected buffer layer gas;

[0011] S4: Based on the analysis in step S2 and the detection in step S3, it is determined whether the buffer layer has defects.

[0012] Preferably, in step S1, the gas extraction device includes a gas sampling device, an air pump, an air valve, a gas collecting pipe and a gas collecting module; the gas sampling device, the air pump, the air valve, the gas collecting pipe and the gas collecting module are connected in sequence, and the gas collecting module is installed on the aluminum sheath of the cable.

[0013] As a preferred embodiment, in step S1, the method for collecting the buffer layer gas is: first remove the outer sheath of the cable with a length of L to expose the corrugated aluminum sheath of the cable, and then cut a notch with an area of ​​S in the cable aluminum sheath, and the gas collection module covers the notch and seals it at the same time; the gas collection module controls the opening and closing of the gas collection channel by a valve, and the valve is in a closed state during the installation of the gas collection module; the external gas valve and the gas collection module are respectively connected by a gas collection pipe, and the gas valve, air pump and gas sampling instrument are connected in turn through pipelines; when the gas extraction starts, the gas valve is opened first, and then the valve in the gas collection module is opened; when the gas extraction ends, the valve in the gas collection module is closed first, and then the gas valve is closed.

[0014] As a preferred embodiment, L is 15cm and S is 10cm*8cm.

[0015] As a preferred embodiment, in step S2, the components of the buffer layer gas are determined by searching a spectral library based on the detection results of the chromatogram and the mass spectrum.

[0016] As a preferred embodiment, the relative concentration of the buffer layer gas is calculated by the peak area in the chromatogram. There are n mass spectrometry results obtained by analysis, and the relative content η of the kth group of substances is calculated. k The calculation formula is:

[0017]

[0018] In the above formula, Ai represents the chromatographic peak area of ​​the i-th group of mass spectrometry results.

[0019] As a preferred embodiment, in step S3, the chemical name of the phenol reagent used is: 3-methyl-2-benzothiazolone hydrazone hydrochloride hydrate, and the phenol reagent reacts with the aldehyde group R-CHO in the aldehyde gas of the buffer layer gas to generate a blue-green compound, and colorimetric quantification is performed according to the color depth.

[0020] As a preferred embodiment, in step S4, the specific method for determining whether the buffer layer has defects is: determining the presence of characteristic gas in the collected gas by the GC-MS method, and determining the presence of aldehyde gas after testing the gas with a phenol reagent. If the collected gas contains characteristic gas and aldehyde gas, then the buffer layer is determined to be in a defective state; otherwise, the buffer layer is not defective.

[0021] As a preferred embodiment, the gas collection module includes a base and a ventilation valve, the base is connected to the aluminum sheath, the base is provided with a gas channel, the ventilation valve is installed in the gas channel, and the gas channel is connected to the gas collection pipe.

[0022] As a preferred embodiment, the gas sampling apparatus is a gas sampling bag or a gas sampling tank, and the inlet and outlet of the gas sampling bag or the gas sampling tank are both provided with valves.

[0023] In general, the present invention has the following advantages:

[0024] 1. The present invention can detect the defects of the cable buffer layer relatively directly. Compared with the existing detection methods, it is more economical and simple. The change of the gas composition of the buffer layer is a direct reflection of the state of the buffer layer. The buffer layer defect state detection method based on characteristic gas can reduce interference problems such as partial discharge detection.

[0025] 2. Compared with partial discharge detection and X-ray detection, the buffer layer defect state detection scheme based on characteristic gas of the present invention is convenient to sample, has low gas testing cost, and is more economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a flow chart of a method for detecting buffer layer defects of high-voltage XLPE cables based on characteristic gas.

[0027] Figure 2 Schematic diagram of a gas extraction device extracting gas from a cable.

[0028] Among them, 1 is a gas collecting pipe, 2 is a gas valve, 3 is an air pump, 4 is a gas sampling bag, 5 is a gas collecting module, and 6 is an aluminum sheath of the cable. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with specific implementation methods.

[0030] A method for detecting buffer layer defects of a high-voltage XLPE cable based on characteristic gas comprises the following steps:

[0031] S1: Collecting buffer layer gas using a high voltage cable buffer layer gas extraction device;

[0032] S2: analyzing the components and relative concentrations of the collected buffer layer gas by gas chromatography-mass spectrometry (GC-MS);

[0033] S3: using a phenol reagent method to detect the aldehyde gas in the collected buffer layer gas;

[0034] S4: Based on the analysis in step S2 and the detection in step S3, it is determined whether the buffer layer has defects.

[0035] In step S1, the gas extraction device includes a gas sampling device, an air pump, an air valve, a gas collecting pipe and a gas collecting module; the gas sampling device, the air pump, the air valve, the gas collecting pipe and the gas collecting module are connected in sequence, and the gas collecting module is installed on the aluminum sheath of the cable. When the gas extraction starts, the gas valve is opened first, and then the valve in the gas collecting module is opened; when the gas extraction ends, the valve in the gas collecting module is closed first, and then the gas valve is closed.

[0036] In step S1, the method for collecting the buffer layer gas is as follows: first remove the outer sheath of the cable with a length of L to expose the corrugated aluminum sheath of the cable, and then cut a notch with an area of ​​S in the cable aluminum sheath, and the gas collection module covers the notch and seals it at the same time; the gas collection module controls the opening and closing of the gas collection channel by a valve, and the valve is in a closed state during the installation of the gas collection module; the external gas valve and the gas collection module are respectively connected with the gas collection pipe, and the gas valve, air pump and gas sampling device are connected in turn through pipelines; when the gas extraction starts, the gas valve is opened first, and then the valve in the gas collection module is opened; when the gas extraction ends, the valve in the gas collection module is closed first, and then the gas valve is closed.

[0037] L is 15cm and S is 10cm*8cm.

[0038] In step S2, the components of the buffer layer gas are determined by searching a spectral library based on the chromatogram and mass spectrum detection results.

[0039] The relative concentration of the buffer layer gas is calculated by the peak area in the chromatogram. There are n mass spectrometry results obtained by analysis. The relative content η of the kth group of substances is calculated. k The calculation formula is:

[0040]

[0041] In the above formula, Ai represents the chromatographic peak area of ​​the i-th group of mass spectrometry results.

[0042] The buffer layer material is mainly composed of polyester fiber (PET). According to the thermal cracking mechanism of polyester fiber, when the detected gas components include dibutyl phthalate, cinnamaldehyde, 4-ethylbenzoic acid and formaldehyde, and the relative content is above 5%, it can be judged that the buffer layer is in a defective state.

[0043] In step S3, the chemical name of the phenol reagent used is: 3-methyl-2-benzothiazolone hydrazone hydrochloride hydrate. The phenol reagent reacts with the aldehyde group R-CHO in the aldehyde gas of the buffer layer gas to generate a blue-green compound, and colorimetric quantification is performed according to the color depth.

[0044] Buffer layer: A structural layer in high-voltage AC XLPE cables that absorbs thermal expansion, mechanical stress, and has water-blocking and buffering effects. XLPE: Cross-linked polyethylene, GC-MS: Gas chromatography-mass spectrometry, phenol reagent:

[0045] In step S4, the specific method for judging whether the buffer layer has defects is: judging the presence of characteristic gas in the collected gas by GC-MS method (gas chromatography mass spectrometry), and the presence of aldehyde gas after testing the gas by phenol reagent. If the collected gas contains characteristic gas and aldehyde gas, the buffer layer is judged to be in a defective state; otherwise, the buffer layer is not defective. The detection of characteristic gas by GC-MS can indicate the presence of defects, and the degree of defects can be further judged by detecting aldehyde gas. Because of the limitation of GC-MS's detection ability for different gases, further verification needs to be combined with aldehyde.

[0046] For the gas sample in the same air bag, if GC-MS detects characteristic gas components such as dibutyl terephthalate, there must be aldehyde gases present. This can be deduced based on the thermal cracking mechanism of PET materials. It's just that GC-MS (to be precise, the chromatographic column of the detection instrument does not support the detection of aldehydes, and you can also find GC-MS instruments that can directly detect aldehydes) cannot directly detect aldehyde gases.

[0047] The gas collection module includes a base and a ventilation valve. The base is connected to the aluminum sheath. The base is provided with a gas channel. The ventilation valve is installed in the gas channel. The gas channel is connected to the gas collecting pipe. The ventilation valve of this embodiment adopts a one-way stop valve structure, and the valve is only conductive to the outside during the extraction process. During construction and installation, first remove about 15 cm of the outer sheath of the cable to expose the corrugated aluminum sheath, and then cut a gap of about 10 cm*8 cm in the aluminum sheath of the cable. The base of the gas collection module is connected to the gap and sealed with lead. The gas collection channel of the gas collection module is controlled by a valve, and the valve is in a closed state during the installation of the gas collection module.

[0048] The gas sampling apparatus is a gas sampling bag or a gas sampling tank, and both the inlet and outlet of the gas sampling bag or the gas sampling tank are provided with valves.

[0049] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for detecting defects in a high-voltage XLPE cable buffer layer based on characteristic gas, characterized in that: The following steps are involved: S1: Collecting buffer layer gas using a high voltage cable buffer layer gas extraction device; S2: analyzing the components and relative concentrations of the collected buffer layer gas by gas chromatography-mass spectrometry; S3: using a phenol reagent method to detect the aldehyde gas in the collected buffer layer gas; S4: judging whether the buffer layer has defects according to the analysis in step S2 and the detection in step S3; In step S3, the chemical name of the phenol reagent used is: 3-methyl-2-benzothiazolone hydrazone hydrochloride hydrate. The phenol reagent reacts with the aldehyde group R-CHO in the aldehyde gas of the buffer layer gas to generate a blue-green compound, and the colorimetric quantification is performed according to the color depth; In step S4, the specific method for judging whether the buffer layer has defects is as follows: judging whether the collected gas has characteristic gas by combining gas chromatography-mass spectrometry, and whether aldehyde gas exists after testing the gas by phenol reagent. If the collected gas has characteristic gas and aldehyde gas, it is judged that the buffer layer is in a defective state, otherwise the buffer layer is not defective; the characteristic gas is dibutyl phthalate; The buffer layer material is mainly composed of polyester fiber PET.

2. A method for detecting defects in a high-voltage XLPE cable buffer layer based on characteristic gas according to claim 1, characterized in that: In step S1, the gas extraction device includes a gas sampling device, an air pump, an air valve, a gas collecting pipe and a gas collecting module; the gas sampling device, the air pump, the air valve, the gas collecting pipe and the gas collecting module are connected in sequence, and the gas collecting module is installed on the aluminum sheath of the cable.

3. A method for detecting defects in a high-voltage XLPE cable buffer layer based on characteristic gas according to claim 2, characterized in that: In step S1, the method for collecting the buffer layer gas is as follows: first remove the outer sheath of the cable with a length of L to expose the corrugated aluminum sheath of the cable, and then cut a notch with an area of ​​S in the cable aluminum sheath, and the gas collection module covers the notch and seals it at the same time; the gas collection module controls the opening and closing of the gas collection channel by a valve, and the valve is in a closed state during the installation of the gas collection module; the external gas valve and the gas collection module are respectively connected with the gas collection pipe, and the gas valve, air pump and gas sampling device are connected in turn through pipelines; when the gas extraction starts, the gas valve is opened first, and then the valve in the gas collection module is opened; when the gas extraction ends, the valve in the gas collection module is closed first, and then the gas valve is closed.

4. A method for detecting defects in a high-voltage XLPE cable buffer layer based on characteristic gas according to claim 3, characterized in that: L is 15cm and S is 10cm*8cm.

5. A method for detecting buffer layer defects of high-voltage XLPE cables based on characteristic gas according to claim 1, characterized in that: In step S2, the components of the buffer layer gas are determined by searching a spectral library based on the chromatogram and mass spectrum detection results.

6. A method for detecting defects in a high-voltage XLPE cable buffer layer based on characteristic gas according to claim 5, characterized in that: The relative concentration of the buffer layer gas is calculated by the peak area in the chromatogram. There are n mass spectrometry results obtained by analysis. The relative content of the kth group of substances is calculated. The calculation formula is: In the above formula, Ai represents the chromatographic peak area of ​​the i-th group of mass spectrometry results.

7. A method for detecting defects in a high-voltage XLPE cable buffer layer based on characteristic gas according to claim 3, characterized in that: The gas collection module comprises a base and a ventilation valve, the base is connected to the aluminum jacket, the base is provided with a gas channel, the ventilation valve is installed in the gas channel, and the gas channel is connected to the gas collection pipe.

8. A method for detecting defects in a high-voltage XLPE cable buffer layer based on characteristic gas according to claim 2, characterized in that: The gas sampling apparatus is a gas sampling bag or a gas sampling tank, and both the inlet and outlet of the gas sampling bag or the gas sampling tank are provided with valves.

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