Saman sem SF6 loftunareiningar og fastloftunareiningar

Yfirlit​
Nú er SF6-gasinsuláð raunverulega hringnet (RMU) á markaði. SF6-gas er þó orkugert sem eitt af helstu loftslagsgjafgöngum. Til að ná umhverfisvaram og dreifa minna, verður að takast við notkuninni. Þegar fastinsuláð hringnets (RMU) koma fram, hefur það leyst vandamál sem tengjast SF6-RMU með mörgum nýjum eiginleikum.

​1 Hringnetrafur og hringnet (RMU)​​
Ferli "borgaræðingar" leggja stærri kröfur á áreiðanlegu rafbannsdeild. Fleiri notendur biðja um tvö (eða fleiri) orkurafur. Notkun "radial rafbannsdeildar" getur valdið vandræðum við setningu snúrs, vandamál við leiðréttingu og óþægileika við uppgraderingu og útfærslu nets. Á móti því, "hringnetrafur" getur auðveldlega veitt tvö (eða fleiri) orkurafur fyrir mikilvæg lausn, einfaldrað rafbannslínu, auðveldara snúrasetningu, lágmarkað switchgear kröfur, lækkað misfallshlutfall og gert leiðréttingu auðveldari.

​1.1 Hringnetrafur​
Hringnetrafur merkir kerfi þar sem tveir (eða fleiri) útflutningar frá mismunandi spennustöðum eða mismunandi busbarum í sama spennustöð eru tengdir saman til að mynda hring fyrir rafbannsdeild. Fyrirlefnin hans innihalda: hver deild getur fengið rafbann frá hægri eða vinstri hringnum. Þetta þýðir að ef villur kemur upp í einhverju hringnum, getur rafbann verið farið frá öðrum hringnum. Þrátt fyrir að það sé eitt kerfi í raun, fær hver deild förmenn eins og tvö kerfi, sem bætir áreiðanleika. Reglugerðir í Kína segja að aðal hringnet tengsl í borgum fylgi "N-1 Öryggisreglu". Þetta þýðir að ef það eru N lausnir á línu, þá getur kerfið tekið yfir lausnar þegar ein villa kemur upp, en sýnir að "N-1" lausnir halda áfram að fá örugg rafbannsdeild án aukalegra kostnaðar eða lausnargjafa.

​1.2 Hringnet tengslamöguleikar​

• ​Staðlað hringtengsl:​​ Gefið af einni upprunaa, formar hring með snúrum, tryggir örugg rafbannsdeild fyrir allar aðrar lausnir þegar hluti af snúri misskötnar.
• ​Hringtengsl frá mismunandi busbörum:​​ Þessi tengsl hefur tvö orkurafur, venjulega virkuð í opinn hring, bætir áreiðanleika og mun fléttu aðgerða.
• ​Einfalt hringtengsl:​​ Orkurafur taka frá mismunandi spennustöðum eða tveim busbörum. Þegar einhver hluti af netinu er í viðhaldi, missir engin lausn rafbannsdeild.
• ​Dubbelt hringtengsl:​​ Hver lausn fær rafbann frá sjálfstæðu hringnetkerfi, gefur mjög áreiðanlegt kerfi.
• ​Tvöfaldur "T" tengsl:​​ Tveir snúrar tengd frá mismunandi busbörum. Hver lausn getur fengið rafbann frá báðum snúrum. Þessi aðferð bætir áreiðanleika fyrir tvöföld orkurafur og er sérstaklega passandi fyrir nokkrar mikilvægar lausnir.

​1.3 Hringnet (RMU) og eiginleikar þeirra​
RMU merkir skáp fyrir hringnetrafur. Skáp tegundir innihalda aflskiptingar, strykspennu, aflskipting + fús, sameiningarapparat, bus couplers, mælingar, spennubreytir (VT), o.fl., eða hvaða sameining eða útvíkkun þeirra sem er.

RMU hafa smá skipulag, litla svæði, lág kostnað, auðvelda setningu og stuttan keyrslutíma, uppfylla kröfur fyrir "minnkað tæki". Þau eru víðtæklega notaðir í býilag, opinberum byggingum, smám & miðstærðum viðskiptafyrirtækjum, sekundari skiptistöðum, kompakta spennustöðum og snúraskiptingarskrifum.

​1.4 RMU tegundir​

• ​Loftinsuláð RMU:​​ Notar loft sem insuláð meðal. Þeir hafa stór svæði og rúmmál, og eru ávallt ávirkandi á loftslagi.
• ​SF6 RMU:​​ Notar SF6-gas sem insuláð meðal. Aðal streymi er lokkur í sealed metal shell full af SF6-gas, með virkni utan skeljarinnar. Vegna lokkuðs skeljarinnar, er hann ekki ávirkandi á loftslagi. Rúmmál þeirra er stórlega minna en staðlað loftinsuláð RMU, sem gerir það mest notað tegund núna.
• ​Fastinsuláð RMU:​​ Notar fast insuláð efni sem aðal insuláð meðal. Streymi og allir lifandi hlutar eru lokkar eða potter með insuláð efni eins og epoxy resin. Vegna lágri öruggu fjarlægðar milli fás og jörðar innan streymis, er stærð og rúmmál þeirra svipað sem SF6 RMU. Þeir búa ekki til SF6 útskot og ná raunverulega viðhaldsfrjáls virkni.

​2 Notkunarrök fyrir SF6 RMU​
SF6 er mikilvægur bidragandi til loftslagsgjafganga. En SF6 hefur frábær rafbannseiginleikar (frábær insuláð, bogabréf og kælingar), sterka elektrónégatívit, góða hitaveitu og öruggu, er endurnotuð, óviðmótmælt loftslagi (fukt, órensku, hátt hæð), og leyfir smá skáp hönnun. Því er hann víðtæklega notaður sem insuláð og bogabréf meðal í rafbannstæki. SF6 notkun er hæsta í rafbannsvísindum; tölfræði sýna að 80% af SF6-gas sem búið er til árslega er notað í rafbannstæki.

Samstarfsráð UN Intergovernmental Panel on Climate Change (IPCC) og US Environmental Protection Agency (EPA) báðir dæmi SF6 sem mjög skemmtilegt og áhrifsemi loftslagsgjafgas. EU F-Gas Regulation (2006) segir að: nema fyrir rafbannsskiftistæki þar sem engin hæfileg viðbót er, er notkun SF6 bannað í möstum sviðum.

Að auki, SF6 RMU eru flóknar til notkunar og krefjast stórra fjárhagslega fjárfestingar, með mörgum hjálpar tæki:

• ​Kaufa SF6 Leakage Monitoring Equipment:​​ Notuð fyrir SF6 gas leak detection, monitoring SF6 concentration and oxygen content, detecting trace moisture, etc.
• ​Equip SF6 Recovery Units:​​ By-products like SF4 are generated within the gas compartment during the SF6 arc-quenching process. Therefore, at end-of-life, not only must the remaining SF6 gas be recovered, but the residual toxic by-products require special treatment.
• ​Configure SF6 Gas Purification Equipment:​​ To purify and recycle the SF6 gas.
• ​Install Ventilation Equipment in Substations.​​

Þegar SF6 RMU eru notuð, er mikilvægt að:

• ​Minimize SF6 Leakage:​​ SF6 RMU notar pressurized sealed cavities, but gas leakage is unavoidable. Performing switching operations when SF6 pressure is low results in low reliability, directly threatening operator safety and reducing equipment lifespan.
• ​Before workers enter the substation, forced ventilation must be performed first, and they must wear special protective gear.​​
• ​Operations and procedures are complex, requiring repeated training for relevant personnel.​​

​3 Characteristics and Applications of Solid-Insulated RMUs​
The potential environmental threat of SF6 RMUs limits their further development. Finding alternatives to SF6 has been a subject of research worldwide. Solid-insulated RMUs were first developed and introduced by Eaton Corporation (USA) in the late 1990s. During operation, they do not generate any toxic or harmful gases, have no environmental impact, offer higher reliability, and achieve true maintenance-free operation.

Solid-insulated RMUs refer to systems where primary conductive circuits—such as the vacuum interrupter, disconnector, earthing switch, main busbar, branch busbar—are individually or in combination enclosed with solid insulation materials like epoxy resin. They are encapsulated within fully insulated, sealed functional modules that can be further combined or expanded. Exterior surfaces of the modules accessible to personnel are coated with a conductive or semi-conductive shielding layer and can be directly and reliably earthed.

​3.1 Characteristics of Solid-Insulated RMUs​

• ​Eco-Design:​​ Does not use SF6 as insulation or switching medium. Instead, vacuum is used as the arc-quenching medium for switches, and environmentally friendly materials with no environmental impact (and which are recyclable) are used as the main insulation medium. Furthermore, the number of components is minimized to ensure low energy consumption during operation and fewer potential failure points.
• ​Truly Maintenance-Free:​​ Solid-insulated RMUs eliminate the SF6 pressure vessel. The internal insulation and arc-quenching of the switch body utilize a vacuum medium; external insulation uses solid dielectric materials like insulating cylinders. The insulating cylinder employs solid-casting technology, integrating the vacuum interrupter, main conductive circuit, and insulating supports into a single unit, sealed within a metal enclosure, unaffected by the external environment. Due to the fully insulated and sealed overall structure, and the absence of issues like SF6 leak detection, refilling, and waste disposal, true maintenance-free operation is achieved.
• ​High Cost-Effectiveness:​​ Although the initial investment for solid-insulated RMUs is slightly higher than for SF6 RMUs, the total life-cycle cost is significantly lower, as shown in Table 1. User considerations are increasingly comprehensive, encompassing not only the initial purchase price but also overall life-cycle costs, including safety risks, grid quality, cost control, and sustainability. The costs required for maintaining, refilling gas, handling leaks, and final recovery of SF6 RMUs during their lifespan are almost equivalent to the purchase cost. In contrast, solid-insulated RMUs involve one initial investment with essentially no subsequent costs. Therefore, from a long-term perspective, the economic efficiency of solid-insulated RMUs is far superior to that of SF6 RMUs.

​Table 1: Life-Cycle Cost Comparison between SF6 RMUs and Solid-Insulated RMUs​

• ​Compact Structure:​​ Designed to be as compact as possible while ensuring cabinet safety and ease of operation. Their footprint and volume are even smaller than SF6 RMUs, helping users save space and providing direct economic benefits.
• ​Internal Arc-Resistant Design, Safer and More Reliable:​​ For primary and secondary switchgear, significant damage due to internal arcing occurs at least once annually. Most solid-insulated RMUs incorporate internal arc-resistant design. When an internal arc occurs, its impact on the RMU is minimized as much as possible, ensuring safer and more reliable equipment operation.
• ​Visualized Isolation Gap:​​ Features a visual observation window for easily checking the contact status of the internal triple-position disconnector, providing visible isolation on-site and enhancing operator safety.
• ​Smart Capabilities:​​ Easier to implement distribution automation compared to SF6 RMUs. After installing a Distribution Terminal Unit (DTU) and communication devices, functions like status data acquisition and monitoring, "Four-Remote" functions (remote signaling, remote measurement, remote control, remote regulation), communication, self-diagnosis, and logging/reporting can be readily achieved.

​3.2 Application Status​
Currently, the widespread adoption of solid-insulated RMUs is constrained by their relatively higher price and complex manufacturing processes. Their process requirements exceed those of SF6 gas-insulated RMUs. If process techniques are inadequate, insulation risks, failure probabilities, and hazards may be higher than SF6 RMUs, necessitating strict quality control of raw materials and craftsmanship. Additionally, the wiring flexibility of solid-insulated RMUs can be limited, particularly for functional units like PT (VT) cabinets and metering cabinets, offering fewer connection options and limiting user choice, which also somewhat restricts the application and development of solid-insulated RMUs.

With continuous optimization of production structures and increasing standardization in product manufacturing, the product quality of solid-insulated RMUs is becoming more stable, and prices are gradually decreasing. Some countries offer incentives of 5%~10% for products that do not use SF6, to reduce its usage and emissions. This means users don't solely consider purchase costs in decision-making. We can also learn from international practices: prioritize the use of solid-insulated RMUs in environmentally sensitive projects and new projects (e.g., residential communities, public buildings, municipal construction), while gradually phasing out SF6 RMUs. Phase out and replace aging or operational SF6 RMUs according to their manufacturer-promised lifespan and provide subsidies to users adopting eco-friendly solid-insulated RMUs to support such products. As user environmental awareness grows and life-cycle cost considerations increase, the prospects for solid-insulated RMUs are broad.

​4 Conclusion​
Solid-insulated RMUs are technically equivalent to SF6 RMUs and possess some features that SF6 RMUs lack, such as no harmful gas emissions, true maintenance-free operation, and lower total life-cycle cost. They are increasingly garnering user attention and preference.