Pagkumpara sa IEE-Business SF6 Gas-Insulated Ring Main Units ug Solid-Insulated Ring Main Units

Introduksyon​
Karon, ang gas-insulated ring main units nga gipangita og SF6 (sumala sa pagtumong "SF6 RMUs") adunay kontrol sa merkado. Apan, ang gas nga SF6 gitawag og usa ka primary na greenhouse gas sa internasyonal. Aron makuha ang proteksyon sa kinatibuk-ang kalibutan ug pagbawas sa pagpuno, ang paggamit nini kinahanglan maputli ug mahimong limitado. Ang pagpakita sa solid-insulated ring main units (RMUs) natugot sa problema nga gihatag sa SF6 RMUs ug adunay daghan pa ka mga bag-ong feature.

​1 Ring Mains Power Supply ug Ring Main Units (RMUs)​​
Ang proseso sa "urbanization" naghatag og padayon nga pagtaas sa demand sa reliability sa power distribution. Mas daghan nga users nagkinahanglan og dual (o multiple) power source supplies. Ang paggamit sa "radial power supply" system mahimong magresulta sa kalisud sa pag-install sa cable, troubleshooting challenges, ug inconvenience sa pag-upgrade ug pag-abroad sa grid. Sa kabalaka, ang "ring mains power supply" makapaborable nga maka-provide og dual (o mas daghan) power sources para sa critical loads, simplifies distribution lines, facilitates cable routing, reduces switchgear requirements, lowers failure rates, ug mas madali sa pag-identify sa fault point.

​1.1 Ring Mains Power Supply​
Ang ring mains power supply nagrefer sa usa ka sistema diin duha (o mas daghan) outgoing lines gikan sa lain-laing substations o lain-laing busbars sa sama nga substation gibag-oan sa loop aron makapagtubig og power. Ang iyang mga advantage kinahanglan: ang bawg distribution branch makapangita og power gikan sa main feeder sa wala o main feeder sa hiru. Kini nagpasabot kon may fault sa bisan asa main feeder, ang power makapadayon sa pagtubig gikan sa uban nga bahin. Bagamaog single-circuit power supply sa esensya, ang bawg distribution branch nakakamata sa benefits similar sa dual-circuit supply, sigurado nag-improve sa reliability. Ang regulasyon sa Tsina nagtumong nga ang main ring mains connection sa mga lungsod sumala sa "N-1 Security Criterion". Kini nagpasabot kon may N loads sa line, kon may fault ang bisan asa load, ang sistema makapagaccept sa transferred load, sigurado ang remaining "N-1" loads makapadayon sa pagtubig og safe power supply walay brownout o load shedding.

​1.2 Ring Mains Connection Methods​

• ​Standard Ring Connection:​​ Supplied by a single source, forming a ring through the cables themselves, ensuring reliable power supply to all other loads when a section of cable fails.
• ​Ring Connection from Different Busbars:​​ This connection has two power sources, typically operated in open-loop, offering higher supply reliability and greater operational flexibility.
• ​Single Ring Connection:​​ Power sources are taken from different substations or two busbar sections. When any cable section in the network is under maintenance, it does not cause any load outage.
• ​Double Ring Connection:​​ Each load can receive power from an independent ring network, providing very high reliability.
• ​Dual Source Double "T" Connection:​​ Two cable circuits are connected from different busbar sections. Each load can draw power from both cables. This method essentially achieves no outage for dual-source users and is particularly suitable for certain critical users.

​1.3 Ring Main Units (RMUs) ug Kanilhang Features​
Ang RMUs nagrefer sa mga switchgear cabinets nga gigamit sa ring mains power supply. Ang mga cabinet types kasagaran load switches, circuit breakers, load switch + fuse combinations, combination apparatus, bus couplers, metering units, voltage transformers (VTs), o bisan unsang kombinasyon o extension niini.

Ang RMUs adunay compact structure, small footprint, low cost, easy installation, ug short commissioning times, satisfying the requirement for "equipment miniaturization". Giwide use sila sa residential complexes, public buildings, small & medium enterprise substations, secondary switching stations, compact substations, ug cable junction boxes.

​1.4 RMU Types​

• ​Air-Insulated RMUs:​​ Use air as the insulation medium. They have a large footprint and volume, and are susceptible to environmental influences.
• ​SF6 RMUs:​​ Use SF6 gas as the insulation medium. The main switch is enclosed within a sealed metal shell filled with SF6 gas, with the operating mechanism located outside the shell. Due to the sealed enclosure, they are unaffected by the external environment. Their volume is significantly smaller than standard air-insulated RMUs, making them the most commonly used type currently.
• ​Solid-Insulated RMUs:​​ Use solid insulation materials as the main insulation medium. The switch and all live parts are encased or potted with insulating materials like epoxy resin. Because the safe phase-to-phase and phase-to-ground insulation distances inside the switch are reduced, their size and volume are similar to SF6 RMUs. They produce no SF6 emissions and achieve true maintenance-free operation.

​2 Usage Limitations of SF6 RMUs​
Ang SF6 adunay dako nga kontribusyon sa atmospheric greenhouse effects. Apan, ang SF6 adunay ideal electrical properties (excellent insulation, arc-quenching, ug cooling performance), strong electronegativity, good thermal conductivity ug stability, reusable, insensitive sa ambient conditions (humidity, pollution, high altitude), ug enables compact cabinet designs. Konsekwentemente, giwide use siya isip insulation ug arc-quenching medium sa electrical equipment. Ang consumption sa SF6 ang pinakadako sa power industry; statistics indicate nga 80% sa SF6 gas nga giproduce annually gigamit sa electrical equipment.

Ang United Nations Intergovernmental Panel on Climate Change (IPCC) ug ang US Environmental Protection Agency (EPA) parehas gitawag ang SF6 isip extremely harmful ug impactful greenhouse gas. Ang EU F-Gas Regulation (2006) nagtumong: except for power switchgear diin walay viable alternative, ang paggamit sa SF6 prohibited sa majority sa fields.

Sa labaw pa, ang SF6 RMUs komplikado sa paggamit ug nanginahanglan og dako nga investment, nanginahanglan og daghan pa ka auxiliary devices:

• ​Purchase SF6 Leakage Monitoring Equipment:​​ Used for 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.​​

Kon magamit ang SF6 RMUs, importante nga:

• ​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​
Ang potential environmental threat sa SF6 RMUs naglimit sa ilang development. Ang paghunahuna sa alternatibo sa SF6 usa ka subject sa research sa buhat-buhat sa mundo. Ang solid-insulated RMUs unang gidevelop ug introduced ni Eaton Corporation (USA) sa late 1990s. During operation, sila wala mogenerate og toxic or harmful gases, wala sa environmental impact, mas taas sa reliability, ug achieve true maintenance-free operation.

Ang solid-insulated RMUs nagrefer sa mga sistema diin ang primary conductive circuits—such as the vacuum interrupter, disconnector, earthing switch, main busbar, branch busbar—individually or in combination enclosed with solid insulation materials like epoxy resin. Sila 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​
Karon, ang widespread adoption sa solid-insulated RMUs limited sa ilang relatively higher price ug complex manufacturing processes. Ilang process requirements exceed those of SF6 gas-insulated RMUs. Kon ang process techniques wala maayo, ang insulation risks, failure probabilities, ug hazards mas taas kay sa SF6 RMUs, nanginahanglan strict quality control sa raw materials ug craftsmanship. Additional, ang wiring flexibility sa solid-insulated RMUs limited, lalo na sa functional units like PT (VT) cabinets ug metering cabinets, offering fewer connection options ug 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.