A method for detecting the sealing performance of an oil-paper capacitor bushing

Abstract

An oil-paper capacitor bushing sealing performance detection method, characterized in that comprising the following steps: S100, placing the oil-paper capacitor bushing filled with tracer gas pre-pressurized in an environmental test chamber; S200, setting the temperature of the environmental test chamber, so that the oil-paper capacitor bushing in the environmental test chamber is subjected to the influence of high temperature and low temperature; S300, after completing the cold and hot cycle, the oil-paper capacitor bushing is placed in a sealed container, the pressure is maintained for a time t, and the gas content in the sealed container is detected again to judge the leakage of the oil-paper capacitor bushing; the tracer gas is SF6 and N2 mixed gas, or SF6 and dry air mixed gas. The purpose of the present application is to provide an oil-paper capacitor bushing sealing performance detection method, which can be applied to routine test sealing test of the bushing, and can also be applied to sealing test of the bushing with defects after repair.

Description

Technical Field

[0001] This invention relates to power equipment sealing performance testing technology, and in particular to a method for testing the sealing performance of oil-paper capacitor bushings. Background Technology

[0002] Bushings are critical components used to lead current-carrying conductors out of the transformer equipment. Oil-paper capacitor bushings are currently the most widely used type of transformer bushing. Sealing failure, leading to moisture ingress or dampness, is one of the main causes of bushing failures. Therefore, performing sealing checks on bushings to improve sealing reliability is of significant engineering importance. Currently, the factory testing method for the sealing of oil-paper capacitor bushings used in transformers is the liquid-filling and pressure-holding method (Method 1, see GB / T 4109 "Insulating Bushings with AC Voltage Higher than 1000V"). The specific steps involve filling the bushing with a high-temperature (75℃) liquid, applying an additional pressure 0.1 MPa higher than the maximum operating pressure, holding the pressure for 12 hours, and visually inspecting for leaks to determine the sealing performance. Alternatively, the bubble test method (Method 2) can be used. This involves filling the bushing with dry air, applying an additional pressure 0.1 MPa higher than the maximum operating pressure, immersing the entire bushing in a water tank, and observing for bubbling phenomena to determine the sealing performance. Alternatively, a gas pressure holding method can be used, which is method three. Dry air is filled into the casing, a pressure gauge is installed at the interface, and an additional pressure of 0.1 MPa higher than the maximum operating pressure of the casing is applied. After a predetermined time, the pressure gauge reading is checked to determine whether the airtightness has dropped.

[0003] Method 1 is a coarse leakage detection method for seepage fluid, with low sensitivity and a minimum detectable leakage rate of 10-6 Pa·cm3 / s. The test uses the method of filling with high-temperature liquid to improve the assessment margin, but does not take into account the phenomenon of alternating hot and cold in actual operation of the casing. For example, under high load rate operation in hot weather, the equipment is cooled down by rain, and the different expansion coefficients of different parts of the casing lead to sealing failure.

[0004] Method 2 is a coarse leak detection method for gas leaks. It has low sensitivity and can detect a minimum leak rate of 10⁻⁶ Pa·cm³ / s.

[0005] Method 3 is a coarse leak detection method for gas leaks. It has low sensitivity, and the minimum detectable leak rate is 10⁻⁶ Pa·cm³ / s. It is also difficult to pinpoint the specific leak location.

[0006] In addition, some patent documents and papers disclose a method of pre-pressurizing the interior of a tracer gas. This type of test method belongs to the category of fine leak detection methods for sealed containers, and has high sensitivity, with a detectable leak rate of approximately 10⁻⁶ Pa·m³ / s to 10⁻¹² Pa·m³ / s. Specifically, tracer gas is introduced into the sealed container or electrical equipment, and the leak location is located using an ultrasonic locator based on the turbulence caused by the escape of the leaking gas.

[0007] In summary, existing tracer gases mainly include helium, helium / air mixtures, nitrogen / methane, SF6, and C4F7N. Helium is relatively expensive, and SF6 is a greenhouse gas, requiring strict emission control; therefore, its use should be approached with caution. Furthermore, the aforementioned patents do not provide a method for accurately locating leaks; they can only determine whether a container is present or a leak point in a specific area. They cannot accurately locate pinhole leaks caused by poor manufacturing processes in equipment. Summary of the Invention

[0008] To address the aforementioned deficiencies, the present invention aims to propose a method for testing the sealing performance of oil-paper capacitive bushings. This method can be applied to routine bushing sealing tests as well as to sealing tests after repairing bushings with potential defects.

[0009] To achieve this objective, the present invention adopts the following technical solution: A method for testing the sealing performance of an oil-paper capacitor bushing includes the following steps: S100, place the oil-paper capacitor sleeve pre-pressurized with tracer gas in the environmental test chamber; S200 allows for variable temperature settings in the environmental test chamber, subjecting the oil-paper capacitor bushing inside the chamber to the effects of high and low temperatures. S300: After completing the hot and cold cycle, the oil-paper capacitor bushing is placed in a sealed container and kept under pressure for a continuous time t. The gas content in the sealed container is then detected to determine the leakage of the oil-paper capacitor bushing. The tracer gas is a mixture of SF6 and N2, or a mixture of SF6 and dry air.

[0010] Preferably, step S200 further includes the following steps: Step S211: Set the environmental test chamber temperature to 90℃ for 12 hours and -20℃ for 12 hours for cycling. Step S212: After setting the temperature of the environmental test chamber, personnel will evacuate the environmental test chamber and begin the hot and cold cycle test.

[0011] Preferably, step S200 further includes the following steps: Step S221: Set the temperature of the environmental test chamber to 90℃ for 12 hours and start the high-temperature test; Step S222: After the high-temperature test is completed, spray the high-temperature sleeve with rain mist for 2 hours.

[0012] Preferably, step S300 further includes the following step: S310, drain the insulating oil from the oil-paper capacitor bushing before or after oil filling, and let it stand to dry for 12 hours. S320, tracer gas is introduced into the oil paper sleeve at a pressure of 0.2~0.3MPa; S330, the sleeve filled with tracer gas is placed in a sealed container of a defined volume, the volume of the sealed container being Vm, and the gas concentration of the tracer gas in the sealed container or soft cover at the initial moment is measured as C0; S340, after the tracer gas is filled into the bushing and held under pressure for a time t, the concentration of SF6 gas C1 in the sealed container or hood is detected; Calculate the casing leakage rate using the following formula: In the formula, R is the leakage rate, and the unit is Pa·m 3 / s;V m For volume measurement, the unit is m. 3 t represents the pressure holding time interval, in seconds (s). The initial and pressure-held gas concentrations of the tracer gas are given in cm³. 3 / m 3 k represents the volume fraction of SF6 gas in the tracer gas; p e This represents the pressure on the outer surface of the sample, in units of 10. 5 Pa; S350, based on the calculated casing leakage rate R, a preliminary judgment is made as to whether leakage exists. If the leakage rate R is less than 10... -6 Pa·m 3 If the value is / s, the casing sealing test is considered qualified.

[0013] Furthermore, it also includes step S400, which uses an SF6 leakage detection probe to manually inspect each connection point from the tail of the oil-immersed capacitor bushing, including the lower porcelain bushing and the lower terminal block, the lower porcelain bushing and the flange, the upper porcelain bushing and the flange, the upper porcelain bushing and the bushing oil conservator, and the bushing oil conservator and the terminal block. A 360° surround inspection is performed on each sealed joint surface. For example, if the SF6 leak detection probe detects an SF6 leak rate in the air greater than 10... -6 Pa·m 3 A leak is determined to exist at this location if the leak rate is less than 10%. -7 Pa·m 3 / s indicates that the seal is good.

[0014] Furthermore, the leakage detection component includes an arc-shaped ultrasonic detection array sensor, a relay and a signal amplifier, a high-pass filter and a microcontroller. The signal output terminal of the arc-shaped ultrasonic detection array sensor is connected to the acquisition terminal of the relay, the output terminal of the relay is connected to the acquisition terminal of the signal amplifier, the output terminal of the signal amplifier is connected to the signal acquisition terminal of the high-pass filter, and the output terminal of the signal amplifier is connected to the microcontroller. Furthermore, the ultrasonic detection array sensor with an arc-shaped fan surface consists of multiple flexible acoustic-electric conversion units evenly arranged on the arc-shaped fan surface.

[0015] Furthermore, the flexible acoustic-electric conversion unit adopts polymer piezoelectric materials such as polyvinylidene fluoride (PVDF); Alternatively, a flexible acoustic-to-electric conversion unit may be used, employing a higher voltage-voltage polyvinylidene fluoride (PVD-TrFE) binary copolymer, preferably in a quantity of 32 units.

[0016] Furthermore, the arc-shaped fan surface serves as the base for fixing the flexible acoustic-electric conversion unit.

[0017] Furthermore, the relay is electrically connected to each of the flexible acoustic-electric conversion units.

[0018] One of the above technical solutions includes the following beneficial effects: Furthermore, this invention uses SF6 / N2 or SF6 / dry air as the tracer gas, which is low-cost, reduces the amount of SF6 gas used, and is readily available to power companies and power equipment manufacturers; This invention uses tracer gas to detect bushing sealing performance, enabling both coarse and fine positioning, with a measurement sensitivity of up to 10⁻⁶ Pa·m³ / s, significantly superior to existing testing methods; This invention proposes alternating hot and cold testing conditions, which are more suitable for the service conditions of oil-immersed bushings, providing a more comprehensive and rigorous assessment of bushing sealing reliability. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the leakage detection component of the present invention.

[0020] The components include: 1. Acousto-electric conversion unit; 2. Arc-shaped fan surface; 3. Relay; 4. High-pass filter; 5. Microcontroller; 6. Acoustic pulse array; 7. High-frequency ultrasonic signal; 8. Signal amplifier. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0022] like Figure 1 As shown, 1. A method for testing the sealing performance of an oil-paper capacitor sleeve, characterized by comprising the following steps: S100, place the oil-paper capacitor sleeve pre-pressurized with tracer gas in the environmental test chamber; S200 allows for variable temperature settings in the environmental test chamber, subjecting the oil-paper capacitor bushing inside the chamber to the effects of high and low temperatures. S300: After completing the hot and cold cycle, the oil-paper capacitor bushing is placed in a sealed container and kept under pressure for a continuous time t. The gas content in the sealed container is then detected to determine the leakage of the oil-paper capacitor bushing. The tracer gas is a mixture of SF6 and N2, or a mixture of SF6 and dry air.

[0023] To address the issues of low sensitivity, high cost of tracer gas, and inability to detect and accurately locate slow, minute leaks in existing casing sealing test methods, an improved casing sealing test method is proposed. This improved method can be applied to routine casing sealing tests (factory delivery) as well as to sealing tests after repair of casings with potential defects.

[0024] Furthermore, this invention uses SF6 / N2 or SF6 / dry air as the tracer gas, which is low-cost, reduces the amount of SF6 gas used, and is readily available to power companies and power equipment manufacturers. The invention uses tracer gas to detect bushing sealing performance, enabling both coarse and fine positioning, with a measurement sensitivity of up to 10⁻⁶ Pa·m³ / s, significantly superior to existing testing methods. This invention also proposes alternating hot and cold testing conditions, which are more suitable for the service conditions of oil-immersed bushings, providing a more comprehensive and rigorous assessment of bushing sealing reliability.

[0025] Step S200 further includes the following steps: Step S211: Set the environmental test chamber temperature to 90℃ for 12 hours and -20℃ for 12 hours for cycling. Step S212: After setting the temperature of the environmental test chamber, personnel will evacuate the environmental test chamber and begin the hot and cold cycle test.

[0026] Step S200 further includes the following steps: Step S221: Set the temperature of the environmental test chamber to 90℃ for 12 hours and start the high-temperature test; Step S222: After the high-temperature test is completed, spray the high-temperature sleeve with rain mist for 2 hours.

[0027] Step S300 further includes the following steps: S310, drain the insulating oil from the oil-paper capacitor bushing before or after oil filling, and let it stand to dry for 12 hours. S320, tracer gas is introduced into the oil paper sleeve at a pressure of 0.2~0.3MPa; S330, the sleeve filled with tracer gas is placed in a sealed container of a defined volume, the volume of the sealed container being Vm, and the gas concentration of the tracer gas in the sealed container or soft cover at the initial moment is measured as C0; S340, after the tracer gas is filled into the bushing and held under pressure for a time t, the concentration of SF6 gas C1 in the sealed container or hood is detected; Calculate the casing leakage rate using the following formula: In the formula, R is the leakage rate, and the unit is Pa·m 3 / s;V m For volume measurement, the unit is m. 3 t represents the pressure holding time interval, in seconds (s). The initial and pressure-held gas concentrations of the tracer gas are given in cm³. 3 / m 3 k represents the volume fraction of SF6 gas in the tracer gas; p e This represents the pressure on the outer surface of the sample, in units of 10. 5 Pa; S350, based on the calculated casing leakage rate R, a preliminary judgment is made as to whether leakage exists. If the leakage rate R is less than 10... -6 Pa·m 3 If the value is / s, the casing sealing test is considered qualified.

[0028] In addition, step S400 is included, which uses an SF6 leakage detection probe to manually inspect each connection point from the tail of the oil-immersed capacitor bushing, including the lower porcelain bushing and the lower terminal block, the lower porcelain bushing and the flange, the upper porcelain bushing and the flange, the upper porcelain bushing and the bushing oil conservator, and the bushing oil conservator and the terminal block. A 360° surround inspection is performed on each sealed joint surface. For example, if the SF6 leak detection probe detects an SF6 leak rate in the air greater than 10... -6 Pa·m 3 A leak is determined to exist at this location if the leak rate is less than 10%. -7 Pa·m 3 / s indicates that the seal is good.

[0029] like Figure 2 As shown, the leakage detection component includes an arc-shaped ultrasonic detection array sensor, a relay 3 and a signal amplifier, a high-pass filter 4 and a microcontroller 5. The signal output terminal of the arc-shaped ultrasonic detection array sensor is connected to the acquisition terminal of the relay, the output terminal of the relay is connected to the acquisition terminal of the signal amplifier, the output terminal of the signal amplifier is connected to the signal acquisition terminal of the high-pass filter, and the output terminal of the signal amplifier is connected to the microcontroller. This method utilizes the turbulence generated by gas leakage at the leak point, which emits high-frequency ultrasound. An ultrasonic detection array sensor with an arc-shaped fan-shaped surface is proposed. This sensor is characterized by multiple flexible acoustic-to-electric conversion units evenly arranged on the arc-shaped fan-shaped surface. Each acoustic-to-electric conversion unit converts the high-frequency ultrasonic signal into an electrical signal, generating a set of electrical pulse signals. Each acoustic-to-electric conversion unit is connected to a signal amplifier via a relay. A high-pass filter is then used to filter out low-frequency noise from the signal. A microcontroller calculates the electrical pulse signals, determining the leak location based on the amplitude, frequency, and time delay of the electrical pulse signals. This invention proposes an ultrasonic array sensor for precise leak location, enabling accurate leak localization.

[0030] Furthermore, the ultrasonic detection array sensor with an arc-shaped fan surface consists of multiple flexible acoustic-electric conversion units 1 evenly arranged on the arc-shaped fan surface 2.

[0031] Furthermore, the flexible acoustic-electric conversion unit uses polymer piezoelectric materials such as polyvinylidene fluoride (PVDF). Alternatively, a flexible acoustic-to-electric conversion unit may be used, employing a higher voltage-voltage polyvinylidene fluoride (PVD-TrFE) binary copolymer, preferably in a quantity of 32 units.

[0032] In addition, the arc-shaped fan surface serves as the base for fixing the flexible acoustic-electric conversion unit.

[0033] The leaked ultrasonic signal spreads outward in a fan shape. Using an arc-shaped fan can increase the probability of receiving high-frequency ultrasonic signals.

[0034] Furthermore, the relay is electrically connected to each of the flexible acoustic-to-electric conversion units.

[0035] To control the reception of sound signals from different directions.

[0036] The signal amplifier is used to amplify the weak voltage signal output by the acoustic-to-electric conversion unit, preferably with an amplification factor of 60dB.

[0037] The high-pass filter is used to filter out low-frequency noise in the signal, and the preferred cutoff frequency is 5kHz.

[0038] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A method for testing the sealing performance of an oil-paper capacitor sleeve, characterized in that, Includes the following steps: S100, place the oil-paper capacitor sleeve pre-pressurized with tracer gas in the environmental test chamber; S200 allows for variable temperature settings in the environmental test chamber, subjecting the oil-paper capacitor bushing inside the chamber to the effects of high and low temperatures. S300: After completing the hot and cold cycle, the oil-paper capacitor bushing is placed in a sealed container and kept under pressure for a continuous time t. The gas content in the sealed container is then detected to determine the leakage of the oil-paper capacitor bushing. The tracer gas is a mixture of SF6 and N2, or a mixture of SF6 and dry air; Step S200 also includes the following steps: Step S211: Set the environmental test chamber temperature to 90℃ for 12 hours and -20℃ for 12 hours for cycling. Step S212: After setting the temperature of the environmental test chamber, personnel will evacuate the environmental test chamber and begin the hot and cold cycle test. Step S200 also includes the following steps: Step S221: Set the temperature of the environmental test chamber to 90℃ for 12 hours and start the high-temperature test; Step S222: After the high temperature test is completed, spray the high temperature sleeve with rain mist for 2 hours. Step S300 also includes the following steps: S310, drain the insulating oil from the oil-paper capacitor bushing before or after oil filling, and let it stand to dry for 12 hours. S320, tracer gas is introduced into the oil paper sleeve at a pressure of 0.2~0.3MPa; S330, the sleeve filled with tracer gas is placed in a sealed container of a defined volume, the volume of the sealed container is Vm, and the gas concentration of the tracer gas in the sealed container or soft cover at the initial moment is measured as C0. S340, after the tracer gas is filled into the bushing and held under pressure for a time t, the concentration of SF6 gas C1 in the sealed container or hood is detected; Calculate the casing leakage rate using the following formula: ； In the formula, R is the leakage rate, and the unit is Pa·m 3 / s;V m For volume measurement, the unit is m. 3 t represents the pressure holding time interval, in seconds (s). The initial and pressure-held gas concentrations of the tracer gas are given in cm³. 3 / m 3 k represents the volume fraction of SF6 gas in the tracer gas; p e This represents the pressure on the outer surface of the sample, in units of 10. 5 Pa; S350, based on the calculated casing leakage rate R, a preliminary judgment is made as to whether leakage exists. If the leakage rate R is less than 10... -6 Pa·m 3 If the value is / s, the casing sealing test is considered qualified.

2. The method for testing the sealing performance of the oil-paper capacitor sleeve according to claim 1, characterized in that, It also includes step S400, which uses an SF6 leakage detection probe to manually inspect each connection point from the tail of the oil-immersed capacitor bushing, including the lower porcelain bushing and the lower terminal block, the lower porcelain bushing and the flange, the upper porcelain bushing and the flange, the upper porcelain bushing and the bushing oil conservator, and the connection point between the bushing oil conservator and the terminal block. A 360° surround inspection is performed on each sealed joint surface. For example, if the SF6 leak detection probe detects an SF6 leak rate in the air greater than 10... -6 Pa·m 3 A leak is determined to exist at this location if the leak rate is less than 10%. -7 Pa·m 3 / s indicates that the seal is good.

3. The method for testing the sealing performance of the oil-paper capacitor sleeve according to claim 2, characterized in that, The leak detection probe includes an arc-shaped ultrasonic detection array sensor, a relay and a signal amplifier, a high-pass filter and a microcontroller. The signal output terminal of the arc-shaped ultrasonic detection array sensor is connected to the acquisition terminal of the relay, the output terminal of the relay is connected to the acquisition terminal of the signal amplifier, the output terminal of the signal amplifier is connected to the signal acquisition terminal of the high-pass filter, and the output terminal of the signal amplifier is connected to the microcontroller.

4. The method for testing the sealing performance of the oil-paper capacitor sleeve according to claim 3, characterized in that, The ultrasonic detection array sensor of the arc-shaped fan surface consists of multiple flexible acoustic-electric conversion units evenly arranged on the arc-shaped fan surface.

5. The method for testing the sealing performance of the oil-paper capacitor sleeve according to claim 4, characterized in that, The flexible acoustic-electric conversion unit uses polyvinylidene fluoride (PVDF) polymer piezoelectric material. Alternatively, flexible acoustic-electric conversion units, using polyvinylidene fluoride binary copolymer PVD-TrFE with a higher voltage constant, are available in quantities of 32.

6. The method for testing the sealing performance of the oil-paper capacitor sleeve according to claim 5, characterized in that, The arc-shaped fan surface serves as the base for fixing the flexible acoustic-electric conversion unit.

7. The method for testing the sealing performance of the oil-paper capacitor bushing according to claim 6, characterized in that, The relays are electrically connected to each of the flexible acoustic-to-electric conversion units.

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