Analyzîna Sêbêjên Cih û Terkîyên Gasê dîsa SF6 da Breakerên Circuit a Stasyonên Elektrik û Lêtina Kurdiya Xebitandinên Pêşkeftin

Têkhnîyên piştguh û pêşketinên cihazan SF₆ circuit breaker hatine çêker kirin, û performansa û nîveta cihazan di rastiyê de hatine bêr nehat. Lekin, bi serkarîn vê cihazan, piranîya serkarîyan da ku ji bo hûn re hatine girêdaya. Sereka serkarîyan ji bo qadên dizayn, prosesên destpêk û hilbijartina materyalan ne. Li gorî têkildana û herkirinan ser sereka serkarîyan, dixwaza ku 20%-30% serkarîyan ji bo xerabkirina SF₆ gas e. Têkildana xerabkirina gas yek demeke yên wan û nekin e leser asta.

1 Serekan Serek

Xerabkirina yek demeke yên wan e. Xerabkirina li jêr her tiştê ku di navbera naverok, derexa û presiyonê de ye. Divê rêzeyên zanistî yên serbexer bikin ji bo xerabkirina yên din, û xerabkirina divê bi tevahî bibîne.

1.1 Xerabkirina Daraftina Mekanîkî

Ji bo her tişt mekanîkî, cihan û wateya xerabkirina hatine vin. Gerota, cihan yên xerabkirina yên dema hene:

• Valves, seals, û gaskets. Switches ê sazan, oil drain switches, primary switches, secondary switches, protection valves, û bini. Sereka xerabkirina ji bo nederdina valve core, navendekirina nederdina ji bo kêmîna zanistîna destpêk; sand holes di valve body de, navendekirina nekabîn, û bolts ê gaz release loose.

• Navendekirina pressure gauges û electromechanical equipment. Seals û gaskets di navendekirina yên din de dikare navendekirina nekabîn an elasticitiya bibînin, ku divê xerabkirina bibîne.

• Sealing surfaces ya piston û accumulator cylinder piston ê manufacturer provided. Ji ber ku seals û gaskets di navendekirina yên din de her tişt li ser tarakirina friction dibin, dikarin deform bînin, deteriorate, an damage bînin.

Natajeya xerabkirina dar mekanîkî yên dema hene. Xerabkirina kecil dikare navendekirina cleaniness û cihazan bide û derbasdar bike ku pumpa oil dikare pressurize bike û cycle ê pressure replenishment long be. Xerabkirina malpera oil di valve body de dikare problem ê pressure loss bide. Ji bo her tişt ku oil hydraulik enter accumulator cylinder, pressure ê gas side dikare increase bike, ku dikare repair emergency, misoperation, û defects ê cihazan bide, ku dikare safe operation ê cihazan bipekerbike.

1.2 Xerabkirina Daraftina Main Body û Connection

•  Welds. Ji ber ku current ê mezin di welding de ye, welds dikare burn through bike, ku dikare micro-leakage bide. Piştî demekî, amount ê xerabkirina dikare increase bike. Di navendekirina welding ê materialên din de, ji ber ku stress ê local mezin ye, weld cracks dikare xerabkirina bide. Bi pêşketina teknolojî ê manufacturer, probability ê vê şeviya di stage ê on-site installation û operation de ye.

• Navendekirina supporting porcelain bushing û flange. Ji ber ku pressure ê mezin di navendekirina din de ye, xerabkirina dikare bike ji bo sealing ê nekabîn, mînace manufacturing ê rough û joint surface ê uneven, û seal ring ê uneven or unstable bonding.

• Pipeline joints, density relay equipment interfaces, ends ê pressure gauges, cover ê three-way box, û navendekirina din. Navendekirina din navendekirina yên dema hene connections, closures, û welding, û navendekirina yên difficult û weak ê sealing, ku dikare xerabkirina bide.

Ji bo SF₆ gas, sealing surface di her navendekirina de hewce ye ku very clean be. Ji ber ku even small amount ê foreign matter stuck di sealing surface de dikare leakage rate increase bike to 0.001MPa.M1/s, ku nederdî ye ji bo cihaz. Ji ber vê yekê, piştî installation, sealing surface û gasket divê carefully wiped bikin bi white cloth û high-quality toilet paper dipped in alcohol, û detailed inspection bikin. Assembly dikare bike piştî confirming ku no problems ne. Her du, dust di flange, bolt holes, û connecting bolts de dikare wiped bikin ji bo prevent it from entering the sealing surface, especially during the installation of the vertical seal.

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

Prinsîpê asayî ya ku liquids ê strong surface tension, mînace soapy water, bubbles dikare appear bike di navendekirina xerabkirina de. Rêzê detection ê ku apply soapy water û other substances di outer shell ê SF₆ circuit breaker û possible leakage points de.
Rojilat: High requirements for smearing, unable to detect minor leaks, and some positions cannot be smeared.
Advantage: Intuitive.

2.2 Qualitative Leakage Detection

Prinsîpê asayî ya ku SF₆ electronegativity ê mezin ye. Under the influence of pulsed high voltage, a continuous discharge effect occurs, and the SF₆ gas will change the performance of the corona electric field, thereby detecting the presence of SF₆ gas on-site. This is only to determine the relative degree of leakage of the SF₆ circuit breaker equipment, rather than detecting its actual leakage rate. Qualitative leakage detection includes the following 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. This is a relatively simple qualitative leakage method that can accurately find the leakage point. The foaming liquid can be prepared by adding a neutral soap to two parts of water. 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. The leakage detector detection is to 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

This is to detect the leakage rate of the SF₆ circuit breaker, and the judgment standard is that the annual leakage rate does not exceed 1%. The specific methods are as follows: (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

The 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.