SF6 gas-insulated ring main units eta solid-insulated ring main units-en konparaketa

Sarrera​
Unean, SF6 gas-insulatut erloju-unitateak (hurrengoan "SF6 RMUs" bezala) merkatua kontrolatzen dute. Hala ere, SF6 gasa mundu osoan ezagutzen da hainbat gas estufatzailerrentzako bat gisa. Ingurumen babesa eta emisioen murrizketa lortzeko, haren erabilera murriztu eta murriztu behar da. Insulazio solidoarekin erloju-unitateen (RMUs) agertzeak SF6 RMUekiko arazoak ebazteko batera, eta ezaugarri berri ugari sartu ditu.

​1 Erloju-unitateen (RMUs) jario sistema eta erloju-unitateak (RMUs)​​
"Hirigintzan" prozesuan, indarraren banaketarako fidagarritasuna eskatzen duen beharra handitu egiten da. Erabiltzaile gehien bat (edo gehiago) iturburu elektrikoko jario behar duten. "Jario erradiala" sistemari esker, kableen instalazioa, arazoak aurkitzea eta sarearen egokitzapena eta zabaldua konplexuak izan daitezke. Berriz, "erloju-unitateen jarioa" modu erraztan bi (edo gehiago) iturburu elektriko jarri daitezke beharrezko karguenentzat, banaketa-liniek sinplifikatu, kableen marrazkia erraztuta, kontaktoreen beharra murriztuta, huts eguneroko txikituta eta arazo-puntuen identifikazioa erraztuta.

​1.1 Erloju-unitateen jario sistema​
Erloju-unitateen jario sistema bi (edo gehiago) iturburu desberdinetatik ateratako liniek elkar lotzen ditu jarioa egiteko. Bere abantailak hauek dira: banaketa-ebaki bakoitza bere ezkerraldeko edo eskubideko nagusira iturburua hartu dezake. Honek esan nahi du, baldin nagusi baten arazo bat gertatzen bada, beste aldetik jarioa jarraitu dezake. Ez denorako jario bakarra baita, banaketa-ebaki bakoitzak duala jarioaren oso baliokidea izango du, fidagarritasuna handituz. Txinako normenak esan ohi dute, hiri nagusietan "N-1 segurtasun kriterioa" bete behar dela. Honek esan nahi du, linean N kargu badira, kargu bat arazo bat izanik, sistema beste "N-1" karguak jario segurua mantentzeko onartu dezake, isiltasuna edo kargu-kontsultatzea ekiditez gero.

​1.2 Erloju-unitateen konektatze-moduak​

• ​Estandar erloju-unitateen konektatzea:​​ Iturburu bakarrarekin, kableei buruzko erloju unitatea sortzen da, zati baten kableak hutsegitean beste guztien jario fidagarria garantizatzen duela.
• ​Erloju-unitateen konektatzea barrutietatik:​​ Bi iturburu ditu, arrunta ireki gisa erabiltzen da, jario fidagarritasuna handiagoa eta operazio-flaxutasuna handiagoa eskaintzen du.
• ​Erloju-unitateen konektatze bakarra:​​ Iturburuak substazio desberdinetatik edo bi barrutietatik hartzen dira. Sarea mantentzean, kableen zati batetan ez da kargu orok bat hutsetzen.
• ​Erloju-unitateen konektatze bikaina:​​ Kargu bakoitzak independentzia erloju-unitateen saretik jarioa jaso dezake, fidagarritasuna handia eskaintzen du.
• ​Bi iturburu bikaina "T" konektatzea:​​ Bi kable-sistema barrutietatik ateratzen dira. Kargu bakoitzak bi kableetatik jarioa jaso dezake. Modu honetan, bi iturburu dituzten erabiltzaileentzat hutsegitea gertatzen ez da, eta kasu batzuetan erabiltzaile kritikoentzat oso egokia da.

​1.3 Erloju-unitateak (RMUs) eta ezaugarriak​
RMUak erloju-unitateen jario sistema erabiltzeko kontsolak dira. Kontsol motak kargu-aktuatzaileak, kontaktoreak, kargu-aktuatzaile + fusible kombinazioak, konbinazio-tresnak, barruti-konexioak, neurgailuak, tensio-transformatorrek (VTs), etabaita, edo horren konbinazio edo luzapena direla.

RMUek struktura trinkoa, espazio txikiak, kostu baxuak, instalazio erraza eta hasieratze-denbora laburra dituzte, "tresna miniaturizatze" eskaintzen dutelako. Orokorki erabiltzen dira etxe-buleguez, eraikinen publikotan, enpresen tamain txiki eta ertainen substazioetan, bigarren mailako aldaketa-gelak, substazio kompaktoetan eta kableen konexio-kaxetan.

​1.4 RMU motak​

• ​Insulazio airearekin RMUak:​​ Airea insulazio-medio bezala erabiltzen dute. Espazio handiak eta bolumen handiak dituzte, eta ingurumenaren eragina hartzen dute.
• ​SF6 RMUak:​​ SF6 gasa insulazio-medio bezala erabiltzen dute. Kontaktorea metalaren kutxan itxita dago, SF6 gasarekin beteta, eta aktuatzailea kanpoaldean dago. Itxi geratzen direlako, kanpoaldeko ingurumenarekiko independenteak dira. Bolumenei SF6 RMU arruntetatik txikiagoak dira, eta une honetan erabili beharrena dira.
• ​Insulazio solidoarekin RMUak:​​ Insulazio-material solidoen insulazio-medio bezala erabiltzen dute. Kontaktorea eta zati guztiak bizitako insulazio-materialen, adibidez epoxi-resina, barnean dituzte. Barneko kontaktoreen arteko eta kontaktorearen eta lurren arteko insulazio-distantei gutxitu direlako, tamaina eta bolumena SF6 RMUetatik antzekoak dira. Ez dute SF6 emisiorik eta mantentze-libreko funtzionamendua lortzen dute.

​2 SF6 RMUen erabilera-murrizketak​
SF6 atmosferaren gas estufatzailerrentzat eragin handiena duen bat da. Hala ere, SF6 elektrikoki idealeko ezaugarriak ditu (insulazioa, arkuen finizioa eta saihestea, eta termika ondoa), elektro-negatibotasuna handia, termika ondoa eta estabilitatea, erabilgarri dena, ingurumenarekiko (ilunpea, kontsultazioa, altuera handia) sentitzen ez dena, eta kontsol-tamain txikiak lortzeko. Hortaz, elektrikoki tresnen insulazio eta arkuen finizio-medio bezala erabili ohi da. SF6-en erabilera handiena industrian dago; estatistikak esan ohi dute, urtean sortutako SF6 gasaren %80 elektrikoki tresnetan erabiltzen dela.

Nazioarteko Estropadak (IPCC) eta Ameriketako Estatu Batuetako Ingurumen Agentziak (EPA) bi SF6-a gas estufatzailerrentzat oso arriskutsua eta eragile handia dituztela. EU F-Gasaren regulazioak (2006) esan ohi du: SF6-ren erabilera zabaltasunean, baina ez da alternatiborik badago, SF6-ren erabilera zabaltasunean debekatuta dago.

Gainera, SF6 RMUak erabilera konplexua eta investimentu handia eskatzen dute, tresna laguntzaile asko behar dituzte:

• ​SF6-leakage monitoring equipment purchase:​​ SF6 gasaren lekuko detektatzeko, SF6 konzentrazioa eta oxigeno-edukia monitorizatzeko, azken puntua garbitzeko, etabaita erabili ohi da.
• ​Equip SF6 Recovery Units:​​ SF4 produktu sekundarioak SF6 arkuen finizio-prozesuan sortzen dira. Beraz, amaieran, SF6 gasaren geratzen den atzeratzea, eta produktu toxiko sekundarioen tratamendu berezia behar da.
• ​Configure SF6 Gas Purification Equipment:​​ SF6 gasa garbitzeko eta errepikatzeko.
• ​Install Ventilation Equipment in Substations.​​

SF6 RMUak erabiliz, honek egin behar da:

• ​Minimize SF6 Leakage:​​ SF6 RMUak presio altuan itxita dagoen kontsolak erabiltzen ditu, baina gasaren lekua ezinezkoa da. SF6 presioa baxua denean, aktuazioa egiten denean, fidagarritasuna baxua da, zerbitzarien segurtasuna eta tresnen iraunkortasuna murriztuta.
• ​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.