Yadda Yana Lafiya Na Gasar SF6 Tushen Gida?

1. Karamin Kirki SF6 da Masu Amfani Da Oil Leakage a Relays na Tsakar Kirki SF6

Yanzu ana amfani da karamin kirki SF6 da yawa a cikin gaban karkashin kuli da kuma tattalin arziki, wanda ya yi tasiri mai yawa a fannin karkashin kuli. Wani abu mai kirki da kuma tsakar harshe a wannan karamin da ke cikin gas sulfur hexafluoride (SF6), wanda ba zai iya ci gaba ba. Idan ci gaba, za su iya dogara aiki da kyau da kuma inganci a cikin karamin. Saboda haka, ya danganta a nemi tsakar gas SF6. Yanzu ana amfani da relays na tsakar mechanical pointer-type don haka. Waɗannan relays za su iya haɓaka shiga da kuma alama a lokacin da ci gaba ta faru, sannan kuma za su iya bayyana tsakar a cikin yanayi. Don samun yadda ake sauya, waɗannan relays suna da oil silicone.

Amma, a cikin yanayi, masu amfani da relays na tsakar gas SF6 suna da muhimmanci wajen ci gaba. Wannan matsalai suna da shi a dukkan ofisuna na karkashin kuli a kasar. Wasu relays suna da ci gaba a lokacin da suka yi aiki ne mafi yawan shekaru ɗaya. Amsa, masu amfani da relays na tsakar gas SF6 suna da muhimmanci wajen ci gaba, wanda ya zama abu mai karfi da yawa.

2. Dabba na Ci Gaba a Cikin Relays na Tsakar

Kamar yadda ake sani, relays na tsakar SF6 suna da electrical contact na spring-type, wanda ake taimaka da magnetic assist mechanism don in ba da aiki da kyau. Amma, force na contact (don alarm ko lockout) suna da shi a kan force mai girma na spring. Hatta da taimakawa magnetic, force ya zama mai girgirsa, wanda ya ba contacts da shi a kan vibration. Don samun yadda ake sauya, oil silicone suna da shi a cikin relay. Idan ci gaba ta faru, za su iya ba da dabba ga karamin kirki SF6.

Dabba 1: Idan anti-vibration oil ta ci gaba duk, damping effect ya zama, wanda ya kawo tsari a kan yadda ake sauya a cikin relay. Ba da damar vibration mai karfi a lokacin da ake yi circuit breaker switching operations, pointer ya zama ita, contacts ya zama babu aiki (ko da ya zama baki a aiki), ko kuma measurement deviations ya zama mafi yawa da abubuwa.

Dabba 2: Saboda contacts na relays suna da taimaka magnetic da force mai girgirsa, idan a yi aiki ne mafi yawan lokaci, za su iya ba da oxidation a kan contact surfaces. Don relays wadanda suka ci gaba oil duk, contacts na magnetic assist suka zama direct a kan air, wanda ya ba su da shi a kan oxidation ko dust accumulation, wanda za su iya ba da poor contact ko complete failure.

Da ƙarin bayanai: A lokacin da utility na biyu ya yi ƙarin testing a cikin relays na tsakar SF6, an samu 196 units, kuma 6 (kusan 3%) suna da shi a kan unreliable contact conduction. Duk waɗannan relays da suka ci gaba oil duk. Idan density relay ta yi stuck pointer, failed contacts, ko unreliable conduction, za su iya ba da tsari ga grid safety. Amsa, idan SF6 circuit breaker ta ci gaba gas kuma ta zama bai da insulating medium, amma density relay ba ta haɓaka alarm ba saboda stuck pointer ko contact failure, idan breaker ya yi attempt to interrupt a fault current, za su iya ba da ƙasarai.

Kuma, oil ta ci gaba za su iya kudeta komponenton da suka da switchgear, wanda za su iya juye dust kuma yana ba da tsari ga aiki. Wasu units suna yi amfani da plastic bags don in ba ci gaba oil, kuma in ba juye dust. Kuma, substation na zaman na da design mai bai da oil; saboda haka, ci gaba oil ta zama defect wanda ya danganta a sake ƙara.

3. Tabbacin Dabba na Ci Gaba

Muhimman leakage points a cikin relays na tsakar suna da seal between terminal block and case, glass window and case, da kuma cracks a cikin glass itself. Na yi disassembly a cikin many leaking relays, an samu cewa primary cause of oil leakage ita ce seal failure at the terminal block-to-case and glass-to-case interfaces. Waɗannan ne initial identified reasons for seal failure.

3.1 Rubber Seal Aging

Yanzu, most density relays suna amfani da nitrile rubber (NBR) don oil-sealing O-rings. NBR ita ce copolymer of butadiene (CH₂=CH–CH=CH₂) and acrylonitrile (CH₂=CH–CN), wanda ake produce via emulsion polymerization. Ita ce unsaturated carbon-chain rubber. Acrylonitrile content yana taimaka NBR properties: higher content improves oil, solvent, and chemical resistance, increases strength, hardness, wear resistance, and heat resistance, but reduces cold flexibility, elasticity, and air permeability.

Rubber degrades during processing, storage, and use due to various factors, exhibiting discoloration, stickiness, hardening, and cracking—phenomena collectively known as rubber aging.

Factors contributing to NBR seal aging include internal and external causes.

3.2 Internal Causes

• Molecular Structure of NBR:
  NBR contains unsaturated double bonds in its polymer chain. Under heat and mechanical stress, oxygen reacts at these double bonds, forming peroxides that decompose into oxidative products, causing chain scission and cross-linking. This increases cross-link density, making the rubber harder and more brittle. Higher double bond content accelerates aging. Additionally, electron-donating substituents (e.g., –CH₃) in the molecular structure are easily oxidized.

• Effect of Rubber Compounding Agents:
  The choice of vulcanization system is critical. Higher sulfur content increases polysulfide cross-link concentration but accelerates aging.

3.3 External Causes

• Oxygen and Ozone:
  Oxygen is a primary aging factor, promoting chain scission and re-cross-linking. Ozone is even more reactive; it forms ozonides at double bonds, which decompose and break polymer chains. The seal is directly exposed to air, and trace amounts of oxygen and ozone dissolve into the oil, accelerating rubber aging.

• Heat:
  Heat accelerates oxidation—typically, a 10°C rise doubles the oxidation rate. It also accelerates reactions between rubber and additives or causes volatile components to evaporate, degrading performance and shortening service life.

• Mechanical Fatigue:
  Under constant stress (compression, torsion), rubber undergoes mechanical oxidation, accelerated by heat. Over time, elasticity diminishes—this is mechanical fatigue aging.

Aging of the rubber seal leads to seal failure, loss of sealing capability, and ultimately oil leakage.

3.4 Insufficient Initial Compression of the Seal

Rubber seals rely on compression deformation during installation to tightly fit against sealing surfaces and block leakage paths. Insufficient initial compression can lead to leaks. This can occur due to:

• Design issues: undersized seal cross-section or oversized groove;

• Installation issues: improper tightening of the cover (most relays rely on manual feel, making precise control difficult).
  Additionally, rubber has a cold-shrink coefficient over ten times that of metal. At low temperatures, the seal shrinks and hardens, further reducing compression.

3. Excessive Compression Rate

While compression is necessary for sealing, excessive compression is harmful. It may cause permanent deformation during installation or generate high von Mises stress, leading to material failure and reduced lifespan. Again, manual tightening often results in over-compression.

4. Surface Defects on Sealing Surfaces

Scratches, burrs, low surface roughness, or improper machining textures on sealing surfaces can create leakage paths.

5. Temperature Effects

At high temperatures, rubber softens and expands, potentially extruding and breaking the seal. At low temperatures, shrinkage and hardening can also cause leaks.

6. Improper Hardness Selection

If the rubber seal is too soft or too hard, it may fail to seal properly.

7. Rough Installation

Careless installation can damage the seal. For example, sharp edges or burrs may scratch the O-ring, creating invisible defects that lead to seal failure and oil leakage.Additionally, glass cracking can also cause oil leakage.

Causes include:
A) Uneven stress during installation, exacerbated by sudden changes in temperature or pressure;
B) Thermal shock causing the glass itself to crack. Cracks form leakage paths, resulting in oil loss.

Conclusion

In SF6 electrical equipment, SF6 gas serves as the primary insulating and arc-quenching medium. Its dielectric strength and arc-interrupting capability depend directly on gas density—higher density generally means better performance. However, due to manufacturing, operation, or maintenance issues, gas leakage is inevitable. A drop in density leads to two main risks: reduced dielectric strength and decreased circuit breaker interrupting capacity. Therefore, monitoring SF6 gas density is crucial for safe and reliable operation. This is typically achieved using SF6 density relays, which provide two-stage warnings—alarm and lockout signals—when density drops, enabling timely intervention.

Hence, on-site SF6 density relays must be reliable. Based on the above analysis, we conclude:

• Density relays exhibiting oil leakage must be promptly monitored and replaced.

• Newly installed relays should preferably be oil-free types with superior vibration resistance or improved gas-sealed designs.