Kurum-kurum na Ring Main a Gas-Insulated SF6 da Solid-Insulated Ring Main Units

Introduction​
A tushen, SF6 gas-insulated ring main units (RMUs) na da shiga yawan market. Amma, SF6 gas ya zama daya daga cikin manyan greenhouse gases a duniya. Don in gina hanyar tsakiyar kasa da ƙarin hankali ga mafi girman tsaro, ana bukata a ɗauki da kuma rage ƙarin bayarwa. An samu solid-insulated ring main units (RMUs) don in gina abubuwan da ke faruwa game da RMUs na SF6, ta haka wanda ake iya haɓaka wasu abubuwan da suka faru.

​1 Ring Mains Power Supply and Ring Main Units (RMUs)​​
Tushen "urbanization" na yi lalacewa da tsari mai kyau a kan tsakar kasa. Masu amfani sun buƙata masu biyu (ko kadan) na noma na kasa. Idan a yi "radial power supply" system, za a iya kasance matsala a kan rike kable, daɗi ƙananan, da kuma matsala a kan ƙarin da ƙoyarwa. Ba tare, "ring mains power supply" na iya ba da noma na biyu (ko kadan) daidai don muhimmin magana, yana ƙara tsarin kasa, yana ƙara rike kable, yana ƙara sauran switchgear, yana ƙara ƙananan, da kuma yana ƙara inganci a kan ƙananan.

​1.1 Ring Mains Power Supply​
Ring mains power supply yana nufin system da biyu (ko kadan) na noma da take kusa da substation ko busbar daɗinsu a kan substation ɗaya, ta haka don in gina loop don noma. Abubuwan da suka faru sun hada da: har daidai na distribution branch na iya ci noma daga noma na farko zuwa ƙarfafarko. Yana nufin idan an yi ƙananan a nan noma, noma na iya haɗa da duk daidai. Kamar yadda ake iya ɗaukan noma, har daidai na distribution branch na iya samun fa'idoda mai ƙarin hankali. A China, an gudanar da "N-1 Security Criterion" don main ring mains connection. Wannan yana nufin idan akwai N loads a nan, idan akwai ƙananan a nan load, za a iya haɗa da duk "N-1" loads da suka fi sanya, bila da ƙananan ko koyarwa.

​1.2 Ring Mains Connection Methods​

• ​Standard Ring Connection:​​ An ci noma da source ɗaya, ta haka don in gina ring through the cables themselves, yana ƙara tsari mai kyau a kan duk loads ɗaya idan kable ɗaya ya ƙananansa.
• ​Ring Connection from Different Busbars:​​ Wannan connection na da biyu na noma, ake amfani da open-loop, yana ƙara tsari mai kyau da kuma ƙara yin ƙarin.
• ​Single Ring Connection:​​ Noma suna ci daga substation daɗinsu ko biyu na busbar. Idan an yi ƙarin a kan section ɗaya a nan network, ba za su ƙananansa ko koyarwa.
• ​Double Ring Connection:​​ Har daidai na load na iya ci noma daga independent ring network, yana ƙara tsari mai ƙarin.
• ​Dual Source Double "T" Connection:​​ Biyu na cable circuits suna ci daga busbar daɗinsu. Har daidai na load na iya ci noma daga biyu na kable. Wannan ƙarfin na iya ƙara tsari mai ƙarin da kuma yana daidai masu amfani mai muhimmanci.

​1.3 Ring Main Units (RMUs) and Their Features​
RMUs suna nufin switchgear cabinets da ake amfani don ring mains power supply. Cikin cabinet types, akwai load switches, circuit breakers, load switch + fuse combinations, combination apparatus, bus couplers, metering units, voltage transformers (VTs), ko kuma any combination or extension thereof.

RMUs suna da structure mai ƙaramin, space mai ƙaramin, cost mai ƙaramin, easy installation, da kuma short commissioning times, wanda ke tabbatar da "equipment miniaturization". Suna da amfani a kan residential complexes, public buildings, small & medium enterprise substations, secondary switching stations, compact substations, da kuma cable junction boxes.

​1.4 RMU Types​

• ​Air-Insulated RMUs:​​ An amfani da air as the insulation medium. Suna da space mai yawa da volume, da kuma suna da ƙananan da ya faru saboda environment.
• ​SF6 RMUs:​​ An amfani da SF6 gas as the insulation medium. Main switch yana cikin sealed metal shell filled with SF6 gas, operating mechanism yana cikin barka. Saboda enclosure mai ƙaramin, ba su ƙananansa saboda environment. Volume su na ƙaramin da air-insulated RMUs, don haka suna da amfani da ma'a ƙarin a yanzu.
• ​Solid-Insulated RMUs:​​ An amfani da solid insulation materials as the main insulation medium. Switch da all live parts suna cikin insulating materials like epoxy resin. Saboda safe phase-to-phase and phase-to-ground insulation distances inside the switch, size da volume su na ƙaramin da SF6 RMUs. Suna da ƙananan da ya faru saboda SF6 emissions, da kuma suna ƙara maintenance-free operation.

​2 Usage Limitations of SF6 RMUs​
SF6 yana ƙara greenhouse effects a duniya. Amma, SF6 na da electrical properties mai ƙaramin (excellent insulation, arc-quenching, and cooling performance), strong electronegativity, good thermal conductivity and stability, reusable, insensitive to ambient conditions (humidity, pollution, high altitude), and enables compact cabinet designs. Saboda haka, an amfani da shi da ma'a ƙarin a kan electrical equipment. SF6 consumption na da ma'a ƙarin a kan power industry; statistics indicate that 80% of the SF6 gas produced annually is used in electrical equipment.

United Nations Intergovernmental Panel on Climate Change (IPCC) da US Environmental Protection Agency (EPA) suna ƙara SF6 as an extremely harmful and impactful greenhouse gas. EU F-Gas Regulation (2006) yana gudanar da: except for power switchgear where no viable alternative exists, the use of SF6 is prohibited in most fields.

Duk da haka, SF6 RMUs suna da ƙananan da ya faru saboda complexity and require substantial investment, necessitating many auxiliary devices:

• ​Purchase SF6 Leakage Monitoring Equipment:​​ An amfani da shi don 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.​​

Idan ake amfani da SF6 RMUs, ya kamata:

• ​Minimize SF6 Leakage:​​ SF6 RMUs use 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.