Method for detecting aging of electrical breaking capacity of C4F7N / CO2 mixed gas

Abstract

The invention discloses a method for detecting aging of electrical breaking capacity of C4F7N / CO2 mixed gas. The method comprises the following steps: taking a proper amount of sample gas to be detected after the C4F7N / CO2 mixed gas is subjected to multiple arcing breaking through a ring main unit; carrying out gas chromatography-mass spectrometry detection on the sample gas to obtain a mass spectrum of the sample gas; analyzing and determining a decomposition product in the sample gas and the peak area of each product in the mass spectrum; when the number of arcing times is small, the aging degree of the mixed gas is judged according to the types of the generated products, and when the number of arcing times is large, the aging degree of the mixed gas is judged according to the change of the proportional relation between the peak areas of the products in the mass spectrum. According to the method, gas aging judgment is performed in a product proportion form, so that the accuracy of gas aging judgment is improved.

Description

Technical Field

[0001] The present invention relates to the research field of environmentally friendly insulating gases, and in particular to a method for detecting aging of the electrical breaking capacity of a C4F7N / CO2 mixed gas. Background Art

[0002] Perfluoroisobutyronitrile (C4F7N) gas is a promising SF6 alternative. The first 220 kV C4F7N environmentally friendly gas-insulated equipment has been put into operation. C4F7N gas decomposes under high temperatures and electric fields, producing various decomposition products that affect the electrical performance of C4F7N and its gas mixtures. With increasing interruption cycles and accumulated arcing time, the insulation and arc-extinguishing capabilities of C4F7N and its gas mixtures decrease, indicating that the gas's electrical performance deteriorates over extended periods of operation.

[0003] C4F7N gas has a complex molecular structure, a wide variety of decomposition products, and few practical applications. Therefore, research on the electrical performance degradation of C4F7N and its gas mixtures is still in its early stages, with limited research and methods for determining the extent of degradation. Accurately determining the aging of C4F7N and its gas mixtures is crucial for the engineering application of C4F7N to replace SF6, improving the service life of environmentally friendly gas-insulated equipment, and ensuring safe power grid operation. Summary of the Invention

[0004] The object of the present invention is to provide a method for judging the degradation of the electrical properties of a C4F7N / CO2 mixed gas.

[0005] In order to achieve the above object, the present invention mainly focuses on judging the aging degree of C4F7N / CO2 mixed gas in a 12kV ring main unit, and establishes a method for judging the aging degree of the environmentally friendly insulating gas C4F7N / CO2 mixed gas breaking capacity in a medium voltage ring main unit, which includes:

[0006] S1: In the laboratory equivalent circuit, use a ring main unit to conduct multiple arcing and interrupting experiments on the C4F7N / CO2 mixed gas, and record the number of arcing times and interrupting voltage;

[0007] S2: taking a small amount of sample gas to be tested from the ring main cabinet, sending it to a gas chromatograph-mass spectrometer and analyzing the mass spectrum of the sample gas to determine the product type and peak area of ​​each product;

[0008] S3: Analyze whether the product contains C5F 12 , if it does not contain C5F 12 The sample gas is judged to be slightly aged. If it contains C5F 12Then calculate the peak area ratio between the peak areas of each product in the mass spectrum of the sample gas;

[0009] S4: If the peak area ratio of CF4 / C3F5N is between 6 and 8 and the peak area ratio of C3F8 / C3F5N is between 0.4 and 0.6, the gas is in a moderately aged state. If the peak area ratio of CF4 / C3F5N is between 6 and 8 and the peak area ratio of C3F8 / C3F5N is between 0.4 and 0.6, the gas is in a severely aged state and it is necessary to consider replacing the gas in time.

[0010] In the preferred method, there are 9 kinds of fixed products of C4F7N / CO2 mixed gas, namely CF4, C3F8, C2F3N, C3F6, C4F 10 、C3F5N、C4F8、C2F2、C5F 12 .

[0011] In a preferred embodiment, the molar ratio of the C4F7N / CO2 mixed gas is 15% C4F7N / 85% CO2.

[0012] In a preferred embodiment, the ring main unit is a 12kV arc extinguishing grid type ring main unit, and the gas chromatography-mass spectrometry instrument model is gas chromatography 6890N-mass spectrometry 5975.

[0013] The beneficial effects of the present invention are as follows: the present invention uses the product ratio to judge gas aging, which not only improves the accuracy of gas aging judgment, but also allows for horizontal comparison under different experimental conditions; this conclusion can provide product optimization solutions for the practical application and service life of C4F7N / CO2 mixed gas in 12kV arc extinguishing grid ring network cabinets. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram illustrating the detection process of the present invention;

[0015] Figure 2 The peak area ratio change curve of CF4 and C3F8 of the present invention;

[0016] Figure 3 This is a curve showing the change in the peak area ratio of C3F8 to C3F5N of the present invention;

[0017] Figure 4 It is the experimental equivalent circuit diagram of the present invention;

[0018] Figure 5 This is a schematic diagram of the retention time of the decomposition products of the present invention. DETAILED DESCRIPTION

[0019] Example 1:

[0020] The present invention uses gas chromatography-mass spectrometry to detect insulating gases and their decomposition components with different arcing times. The aging degree of the C4F7N / CO2 mixed gas is determined by detecting the types of decomposition products and the proportional relationship between different decomposition products. The electrical interruption performance of the mixed gas is directly related to the aging degree of the mixed gas. This method is not only applicable to arc interruption experiments in medium-voltage ring network cabinets, but can also be used by analogy to determine the aging degree of the C4F7N / CO2 mixed gas under other working conditions. Figure 1 As shown, the method for detecting aging of the electrical breaking capacity of the C4F7N / CO2 mixed gas comprises:

[0021] S1: Build the experimental circuit and gas detection platform. Fill a 12kV arc-extinguishing grid-type ring main unit (RMU) with a C₄FₐN / CO₂ mixture (molar ratio: 15% C₄FₐN / 85% CO₂), maintaining a slightly positive pressure of 0.14 MPa. Before each filling, wipe the RMU chamber walls, grids, and moving and static contacts several times with anhydrous alcohol and allow them to air dry. Place desiccant inside the chamber, package, and seal. After sealing, let the chamber rest for 2 hours, and then check the airtightness of the rubber seal. After confirming that the air tightness is good, wash the air. First, pump the air pressure in the air chamber of the ring main cabinet to vacuum, that is, <0.01MPa, and then fill it with high-purity CO2 gas as background gas to a slightly positive pressure and let it stand for 1 hour. The purity of CO2 is 99.99%, so that the residual impurity gas in the box is fully mixed with the background gas, and the water vapor in the box is fully eliminated. Then the gas in the air chamber is pumped out and the air pressure is pumped to vacuum. Repeat this 3 times. The washing is completed and the C4F7N / CO2 mixed gas is ready to be filled. When filling, according to Dalton's law of partial pressure, the proportion of the mixed gas is determined by the partial pressure ratio. To ensure the accuracy of the mixed gas mixing ratio, first fill it with C4F7N gas with a smaller mixing ratio, and then fill it with CO2 gas according to the partial pressure ratio. After filling, let it stand for 12 hours to allow the two gases to be fully mixed, and use a desiccant to eliminate the influence of water vapor. Repeat the same operation when ventilating.

[0022] S2: Before starting the experiment, close CB1 and the RMU. During the test, close CB2 to introduce a current source, generating a test current in the loop. Then, open the RMU and CB1 in sequence, causing the ring main unit to arc and break. The arcing duration is adjusted by controlling the timing of the opening command signal. A Rogowski coil is used to measure the test current, with a peak value of 1000A. A high-voltage probe is used to measure the arc voltage. Repeat this operation to perform multiple arcing experiments. Allow at least 5 minutes between each arcing experiment to allow the gas in the chamber to fully mix.

[0023] S3: Take a small amount of approximately 100 ml of sample gas from the ring main unit and send it to a gas chromatography-mass spectrometer for gas chromatography-mass spectrometry analysis. The chromatographic column model is GS-GASPRO 30m×0μm×0.32mm, and the splitless flow mode is used. Before each sample gas is drawn, it is allowed to stand for 30 minutes to allow the gas in the gas chamber to be fully mixed. The gas is collected using an aluminum-plastic composite film gas sampling bag.

[0024] S4: After the sample test is completed, analyze the mass spectrum of the sample gas; compare the retention time of each product to determine the type of product produced by the mixed gas contained in the sample after discharge decomposition. The molecular formula and retention time of each decomposition product are as follows: Figure 5 As shown. At the same time, determine the peak area corresponding to each type of product;

[0025] S5: After the sample is tested, the mass spectrum of the sample gas is analyzed; the types of products produced by the mixed gas contained in the sample after discharge decomposition are determined by comparing the retention time of each product;

[0026] S6: Analyze whether the product contains C5F 12 , if it does not contain C5F 12 The sample gas is judged to be slightly aged. If it contains C5F 12 Calculate the peak area ratio between the peak areas of each product in the mass spectrum of the sample gas; if the peak area ratio value of CF4 / C3F5N is between 6 and 8 and the peak area ratio value of C3F8 / C3F5N is between 0.4 and 0.6, the gas is in a moderately aged state; if the peak area ratio value of CF4 / C3F5N is between 6 and 8 and the peak area ratio value of C3F8 / C3F5N is between 0.4 and 0.6, the gas is in a severely aged state and timely replacement of the gas is required.

[0027] The present invention mainly utilizes the principle that under arc-breaking conditions, the types and rates of products generated by a C4F7N / CO2 mixed gas vary with the accumulation of interruption times to judge the aging of the electrical interrupting capacity of the C4F7N / CO2 mixed gas. The present invention mainly includes an experimental module, a detection module, and an analysis module; the experimental module includes a ring main unit and a synthetic circuit that can generate a voltage of 12kV and a current of 1000A; the detection module includes a gas chromatograph-mass spectrometer and a corresponding gas chromatograph-mass spectrometer.

[0028] like Figure 4As shown, the present invention uses a laboratory equivalent circuit to simulate the high voltage and large current generated in actual working conditions; uses a 12kV arc-extinguishing grid ring main unit structure to conduct arc interruption experiments on a C4F7N / CO2 mixed gas; and uses gas chromatography-mass spectrometry technology to detect the decomposition components of the mixed gas. The detection instrument is a gas chromatography-mass spectrometer model 6890N-mass spectrometer 5975 produced by Agilent Corporation of the United States. Based on the mass spectrum of the mixed gas sample produced after the experiment, the types of decomposition products and their quantitative relationships are calculated. The experimental equivalent circuit is as follows: Figure 1 As shown, C i 、L i The capacitor and inductor are the current source, which can generate power frequency current as the breaking current. CB1 is the auxiliary switch, CB2 is the input switch, RMU is the ring main unit, and Rog is the Rogowski coil.

[0029] The present invention comprehensively evaluates the aging degree of the C4F7N / CO2 mixed gas based on the number of arcing times and the breaking voltage, wherein:

[0030] Mild aging: If the C4F7N / CO2 gas mixture has a small number of arcing events (less than 40 times) under arcing conditions, generates a small number of products, and its maximum withstand breaking voltage drops by less than 10% compared to the standard gas at 0 arcing events, the gas mixture is described as "mildly aged".

[0031] Moderate aging: If the C4F7N / CO2 gas mixture arcs a large number of times (about 40 to 100 times) under discharge arcing conditions, the types of products generated are fixed, and the maximum breaking voltage that can be tolerated is reduced by 10 to 20% compared to the standard gas at 0 arcing times, then the gas mixture is described as "moderately aged" and should be used with caution.

[0032] Severe aging: If the C4F7N / CO2 gas mixture arcs frequently (over 100 times) under discharge arcing conditions, generates a fixed type of product, and the maximum withstand breaking voltage drops by more than 20% compared to the standard gas at 0 arcing times, the gas mixture is considered "severely aged" and should be replaced with a new gas mixture.

[0033] The present invention utilizes the principle that, under arcing interruption conditions, the types and rates of products generated by a C4F7N / CO2 mixed gas vary with the accumulation of interruption times to determine the aging of the electrical interrupting capacity of the C4F7N / CO2 mixed gas, which is analogous. The standard used in the present invention below is applicable to the experimental conditions of a 15% C4F7N / / 85% CO2 mixed gas in a 12kV arc-extinguishing grid ring main unit. This method can be used to measure standards under other experimental conditions in a similar manner.

[0034] The present invention has 9 kinds of C4F7N / CO2 mixed gas fixed products, namely CF4, C3F8, C2F3N, C3F6, C4F 10 、C3F5N、C4F8、C2F2、C5F 12 The ion peak area is the relative area of ​​the graph formed by the ion peak representing each product and the horizontal axis of the coordinate in the mass spectrum of the sample gas measured by the gas chromatography-mass spectrometry.

[0035] By studying the peak area ratio of CF4 to C3F5N, and the peak area ratio of C3F8 to C3F5N, they show a good positive correlation with the number of arcing times, such as Figure 2 、 Figure 3 As shown, this discovery is the basic logic of the present invention.

[0036] Example 2:

[0037] A method for detecting aging of the electrical breaking capacity of a C4F7N / CO2 mixed gas, characterized in that it comprises:

[0038] S1: In the laboratory equivalent circuit, use a ring main unit to conduct multiple arcing and interrupting experiments on the C4F7N / CO2 mixed gas, and record the number of arcing times and interrupting voltage;

[0039] S2: taking a small amount of sample gas to be tested from the ring main cabinet, sending it to a gas chromatograph-mass spectrometer and analyzing the mass spectrum of the sample gas to determine the product type and peak area of ​​each product;

[0040] S3: Analyze whether the product contains C5F 12 , if it does not contain C5F 12 The sample gas is judged to be slightly aged. If it contains C5F 12 Then calculate the peak area ratio between the peak areas of each product in the mass spectrum of the sample gas;

[0041] S4: If the peak area ratio of CF4 / C3F5N is between 6 and 8 and the peak area ratio of C3F8 / C3F5N is between 0.4 and 0.6, the gas is in a moderately aged state. If the peak area ratio of CF4 / C3F5N is between 6 and 8 and the peak area ratio of C3F8 / C3F5N is between 0.4 and 0.6, the gas is in a severely aged state and it is necessary to consider replacing the gas in time.

[0042] There are 9 kinds of fixed products of C4F7N / CO2 mixed gas, namely CF4, C3F8, C2F3N, C3F6, C4F 10 、C3F5N、C4F8、C2F2、C5F 12 .

[0043] In the C4F7N / CO2 mixed gas, the molar ratio is 15% C4F7N / 85% CO2.

[0044] The ring main unit is a 12kV arc extinguishing grid type ring main unit, and the gas chromatography-mass spectrometry instrument model is gas chromatography 6890N-mass spectrometry 5975.

[0045] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for detecting the aging of the electrical breaking capacity of C4F7N / CO2 mixed gas, characterized in that: It includes: S1: In the laboratory equivalent circuit, use the ring main unit to conduct multiple arcing and breaking experiments on the C4F7N / CO2 mixed gas, and record the number of arcing and breaking voltage; S2: Take a small amount of sample gas to be tested in the ring main cabinet, send it into a gas chromatograph-mass spectrometer and analyze the mass spectrum of the sample gas to determine the product type and peak area of ​​each product; S3: Analyze whether the product contains C5F 12 , if it does not contain C5F 12 The sample gas is judged to be slightly aged. If it contains C5F 12 Then calculate the peak area ratio between the peak areas of each product in the mass spectrum of the sample gas; S4: If the peak area ratio of CF4 / C3F5N is between 6 and 8 and the peak area ratio of C3F8 / C3F5N is between 0.4 and 0.6, the gas is in a moderately aged state. If the peak area ratio of CF4 / C3F5N is between 6 and 8 and the peak area ratio of C3F8 / C3F5N is between 0.4 and 0.6, the gas is in a severely aged state and it is necessary to consider replacing the gas in time.

2. The method for detecting aging of electrical breaking capacity of C4F7N / CO2 mixed gas according to claim 1, characterized in that: There are 9 kinds of C4F7N / CO2 mixed gas fixed products, namely CF4, C3F8, C2F3N, C3F6, C4F 10 、C3F5N、C4F8、C2F2、C5F 12 .

3. The method for detecting aging of electrical breaking capacity of C4F7N / CO2 mixed gas according to claim 1, characterized in that: In the C4F7N / CO2 mixed gas, the molar ratio is 15% C4F7N / 85% CO2.

4. The method for detecting aging of electrical breaking capacity of C4F7N / CO2 mixed gas according to claim 1, characterized in that: The ring main unit is a 12kV arc extinguishing grid type ring main unit, and the gas chromatography-mass spectrometry instrument model is gas chromatography 6890N-mass spectrometry 5975.

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