Pag-analisis sa mga Karaniwang Daganan sa Pagdumog sa Gas sa SF6 Circuit Breakers sa mga Substation ug Pagtungha sa mga Pamaagi sa Pagdetektar

Human sa pagkamalikhain sa teknolohiya ug sa pagpahigayon sa lebel sa produksyon, ang kalihukan ug kalidad sa SF₆ circuit breaker equipment adunay patulob-on nga gibag-o, ug ang mga produkto adunay lubong gipagtumong sa mga customer. Pero, human sa iyang layo nga paggamit, ang bilang sa mga sayop usab nagdaghan. Ang mga dahon sa mga sayop kasagaran mao ang mga isyu kauban ang design principles, manufacturing processes, ug material selection. Pinaagi sa pag-investigate ug statistics sa mga dahon sa mga sayop, gitukod nga 20%-30% sa mga problema gikan sa leakage sa SF₆ gas. Ang gas leakage detection usa ka mahimongon ug dili mapugos nga punto sa panahon sa electrical installation stage.

1 Main Causes

Ang leakage usa ka labi ka ordinaryong sitwasyon. Ang mga problema sa leakage makita kung asa may pagkakaiba sa content, temperature, ug pressure. Dapat mag-adopt og siyentipikong remedio alang sa uban-uban nga leakage phenomena, ug dapat ma-discover ang pinaghugnohan sa leakage sa wala pa mobati.

1.1 External Leakage of Hydraulic Machines

Alang sa uban-uban nga hydraulic machines, ang mga posisyon ug sitwasyon sa leakage mao ang nagkalain-laing. Kasagaran, ang mga ordinaryong posisyon sa leakage mao ang:

• Valves, seals, ug gaskets. Three-way switches, oil drain switches, primary switches, secondary switches, protection valves, etc. Ang mga dahon sa leakage kinahanglan ang improper closure sa valve core, uneven contact surface tungod sa insufficiency sa production precision; sand holes sa valve body, unsealed position, ug loose gas release bolts.

• Ang mga connection positions sa pressure gauges ug electromechanical equipment. Ang mga sealing gaskets sa kini nga mga joints mao ang uneven o nawala sa elasticity, na labi ka probable nga mag-result sa leakage.

• Ang mga sealing surfaces sa operating cylinder piston ug accumulator cylinder piston nga gihatag sa manufacturer. Tungod kay ang mga seals ug gaskets sa kini nga mga posisyon kasagaran molihok, sila prone sa deformation, deterioration, o damage.

Ang mga resulta sa leakage sa hydraulic machines labi ka serius. Ang minor leakage dili lamang maghatag ug epekto sa cleanliness sa equipment apan usab nagresulta sa repeated pressurization sa oil pump ug long pressure replenishment cycle. Ang massive oil leakage sa valve body magresulta sa pressure loss problem. Kung ang hydraulic oil mopasok sa accumulator cylinder, ang pressure sa gas side magpadayon nga madagan, resulta sa emergency repairs, misoperation, ug equipment defects, nga maghuhadlok sa safe operation sa equipment.

1.2 External Leakage at the Main Body and Connection

•  Welds. Tungod sa dako nga current sa panahon sa welding, ang welds mahimong maburn-through, resulta sa micro-leakage. Human sa pipila ka tuig, ang amount sa leakage magpadayon nga madagan. Sa mga posisyon sa welding sa duha ka ibang materyales, tungod sa taas nga local stress, ang weld cracks usab magresulta sa leakage. Pinaagi sa pag-improve sa manufacturer's manufacturing technology, ang probability sa kini nga panghitabo sa on-site installation ug operation stages kasagaran gamay na.

• Ang connection position tali sa supporting porcelain bushing ug flange. Tungod sa taas nga pressure sa kini nga posisyon, ang leakage probable kung ang sealing dili tight, sama sa rough manufacturing sa porcelain bushing joint surface, uneven joint surface, ug uneven o unstable bonding sa seal ring.

• Pipeline joints, density relay equipment interfaces, ang ends sa pressure gauges, ang cover sa three-way box, ug uban pang mga posisyon. Kini nga mga posisyon ang labi ka ordinaryong areas alang sa connections, closures, ug welding, ug sila ang difficult ug weak points sa sealing, may taas nga probability sa leakage.

Alang sa SF₆ gas, ang sealing surface sa anaa nga posisyon kinahanglan mas maintain sa very clean. Kon dili, mao lang usa ka gamay nga amount sa foreign matter nga nakapuyo sa sealing surface mao ang mag-increase sa leakage rate sa order sa 0.001MPa.M1/s, nga dili acceptable para sa equipment. Kaya, human sa installation, ang sealing surface ug gasket kinahanglan maputli sa white cloth ug high-quality toilet paper nga nanginat-an sa alcohol, ug gibuhat ang detailed inspection. Ang assembly mao lang mahimo human sa confirmation nga walay problema. Gisundan, ang dust sa flange, bolt holes, ug connecting bolts kinahanglan maputli aron masayran ang pagpasok sa sealing surface, lalo na sa panahon sa installation sa vertical seal.

2 SF₆ Circuit Breaker Leakage Detection Methods
2.1 Liquid Surface Tension Method

Ang basic principle mao ang liquids sama sa soapy water nga may strong surface tension, ang bubbles mahimong magpakita sa posisyon sa leakage kon ang gas mogawas. Ang detection method mao ang apply sa soapy water ug uban pang substances sa outer shell sa SF₆ circuit breaker ug possible leakage points.
Disadvantages: Taas nga requirements sa smearing, unable to detect minor leaks, ug ang uban nga mga posisyon dili mahimo mosmear.
Advantage: Intuitive.

2.2 Qualitative Leakage Detection

Ang basic principle mao ang SF₆ may strong electronegativity. Sa epekto sa pulsed high voltage, ang continuous discharge effect magpakita, ug ang SF₆ gas mag-change sa performance sa corona electric field, resulta sa detection sa presence sa SF₆ gas sa site. Kini naglakip sa determination sa relative degree sa leakage sa SF₆ circuit breaker equipment, pero dili sa actual leakage rate. Ang qualitative leakage detection naglakip sa sumala nga mga methods:

• Vacuum pumping detection. Pump the vacuum to 133Pa, keep pumping for more than 30 minutes, stop the pump, read the value A after observing for 30 minutes, and then read the value B after observing for 5 hours. If 67Pa > B - A, it can be determined that the sealing is good.

•  Foaming liquid detection. Kini usa ka simple nga qualitative leakage method nga maka-identify accurately sa leakage point. Ang foaming liquid mahimo mapreparar pinaagi sa pag-add og neutral soap sa two parts sa tubig. Apply the foaming liquid to the position to be detected for leakage. If bubbles appear, it indicates leakage at this position. The more and more urgent the bubbles are, the more serious the leakage is. This method can roughly find the leakage position with a leakage rate of 0.1ml/min.

•  Leakage detector detection. Ang leakage detector detection mao ang move the probe of the leakage detector along the surface of each connection of the circuit breaker and the surface of the aluminum casting, and determine the leakage situation according to the reading of the leakage detector . When using this method, the following techniques should be mastered: First, the movement speed of the probe should be slow to prevent missing the leakage due to too fast movement. Second, the detection should not be carried out in a strong wind to prevent the leakage from being blown away and affecting the detection. Third, a leakage detector with high sensitivity and low response speed should be selected. Generally, the minimum detectable amount of the leakage detector is that the leakage rate is lower than 10-6, and the response speed is lower than 5s, which is more appropriate.

• Segmentation and positioning method. This method is suitable for circuit breakers with three-phase SF₆ gas circuit connections. If leakage is determined but it is difficult to locate, the SF₆ gas structure can be divided into several parts for detection, thereby reducing blindness.

• Pressure reduction method. This method is applicable when the leakage amount of the equipment is large.

2.3 Quantitative Leakage Detection

Kini mao ang detection sa leakage rate sa SF₆ circuit breaker, ug ang judgment standard mao ang annual leakage rate dili mogawas sa 1%. Ang specific methods mao ang (1) Local Wrapping Method: Use a plastic film with a thickness of 0.01 cm to wrap around the geometric shape of the density position for one and a half circles, with the joint facing upwards. Try to form a circular or square shape, and seal it with adhesive tape after shaping [3]. There should be a certain gap, approximately 0.05 cm, between the plastic film and the object being measured. After wrapping, detect the content of SF₆ gas in the wrapped cavity after 24 hours, and select the average value of four points at different positions. The leakage rate of this sealing process can be calculated using the following formula:F=ΔC⋅(V−ΔV)⋅P/Δt(MPa⋅m3/s)

 Where:

• F: Absolute leakage rate, leakage amount per unit time (MPa⋅m³/s).

• Δ C: Average value of the detected leakage content (ppm).

• ΔV: Volume between the object being measured and the plastic film (m³).

• Δt: Time interval for detecting ΔC(s).

• P: Absolute atmospheric pressure, which is 0.1MPa.

• V: Volume of SF₆ gas in the gas chamber (m³).

The annual leakage rate Fy of each gas chamber is calculated as follows: Fy=F⋅31.5×10−6/V⋅(Pr+0.1)⋅100% (per year) Where Pr is the specified SF₆ gas pressure (MPa).

When starting the above calculations, the following parameters are difficult to determine:

• Δ V: Since the volume between the object being measured and the plastic film has an irregular shape, its volume cannot be directly calculated. Experimental methods can be adopted, such as injecting other gases and liquids through a flowmeter into the wrapped cavity to collect volume information.

• V and W: The gas volume and mass of SF₆ in the gas chamber. This information is not provided by the manufacturer. You can require the manufacturer to provide accurate information in the order technical documents, or use a metering method during gas filling to obtain more precise information.

Hanging Bottle Detection Method: Hang a bottle at the detection hole of the insulator. After a few hours, use a leakage detector to detect whether there is leaked SF₆ gas in the bottle.

2.4 Infrared Detection

Ang infrared detection method mainly uses the strong infrared absorption property of SF₆ gas. SF₆ gas has the strongest absorption of infrared rays with a wavelength of 10.6um. Common infrared detection methods include the infrared laser method and the passive detection method.
The working principle of laser infrared detection is that an incident infrared laser is transmitted by the laser transmitter, and the backscattered laser enters the laser camera imaging platform through reflection. If the incident laser encounters leaked SF₆ gas, some of its energy will be absorbed, resulting in differences in the backscattered laser in the case of leakage and no leakage, and finally, different laser imaging can be used to detect the presence of SF₆ gas leakage. The passive detection method does not actively transmit laser light but detects the slight differences caused by the absorption of infrared rays in the atmosphere by SF₆ gas to detect the presence of SF₆ gas.

The refrigeration quantum well detector selected for foreign scientific products can determine a temperature difference of 0.03°C, and the minimum detectable gas volume is 0.001ml/s of SF₆ gas. Both of the above methods use an imaging viewfinder to display the image, making the invisible SF₆ gas visible. On the viewfinder display, the leaked SF₆ gas can be seen as a dynamic black cloud, which is clearly visible in a static environment. By carefully observing the position where the cloud emerges, the leakage source can be quickly and accurately located. The speed and size of the cloud reflect the leakage rate.

The infrared detection method of SF₆ gas can remotely detect the leakage position without power outage, ensuring personal safety and improving the stability of power supply. It is the most scientific detection method at present.

Strengthening the prevention of SF₆ circuit breaker leakage is a key supervision point to ensure the safe, economical, and reliable operation of substations. By analyzing the causes of SF₆ circuit breaker leakage, the theoretical level of preventing and dealing with SF₆ circuit breaker leakage problems can be continuously improved, and the ability to deal with SF₆ leakage accidents can be enhanced. Among various detection methods, infrared imaging detection is a new technical method for the condition-based maintenance of SF₆ circuit breakers and is the mainstream development trend in the future.