A solid-insulated ring main unit (RMU) is a type of ring main unit that uses solid insulating materials (such as epoxy resin) to completely encapsulate or seal the main live components. It possesses core characteristics such as full insulation, complete sealing, maintenance-free operation, miniaturization, and environmental friendliness.
Compared to conventional ring main units (typically referring to air-insulated ring main units), they differ significantly in technical principles, structural design, and application characteristics. The table below clearly summarizes the core differences between the two:
| Comparison dimensions | Solid insulated ring main unit | Standard ring main unit (air-insulated ring main unit) |
|---|---|---|
| Insulating materials | Solid composite insulation (such as epoxy resin) completely seals the entire main electrical circuit. | The insulation is primarily air-based, with live components exposed to the air inside the enclosure, and insulation is achieved through air gaps and insulators. |
| Personal safety and protection | Fully insulated and fully sealed. There is no risk of electric shock upon contact, and it has a high protection rating (usually IP67), allowing for operation even when submerged in water. | There are exposed live parts or only insulating barriers present, requiring sufficient safety distance. The protection level is low and it is not waterproof or moisture-proof. |
| Environmental impact | It is largely unaffected by environmental factors, resistant to condensation, dirt, salt spray, high altitude, and small animals, making it suitable for harsh environments. | Highly susceptible to environmental factors, dampness, dirt, and condensation can lead to reduced insulation and even short circuits. |
| Dimensions and footprint | It features a compact structure and small size, saving space and facilitating miniaturized layouts. | Sufficient air insulation distance is required, resulting in a relatively large size. |
| Maintenance requirements | Maintenance-free or requiring minimal maintenance. The sealed structure eliminates the need to deal with condensation or dust inside the enclosure. | Regular maintenance is required, including cleaning dust, checking for condensation, addressing rust, and preventing small animals from entering. |
| Environmental friendliness | It does not use SF₆ gas, resulting in no greenhouse gas emissions, and is in line with environmental protection trends. | SF₆ gas is commonly used as an arc-extinguishing or insulating medium (in SF₆ ring main units), but it poses a potential risk of greenhouse gas leakage. |
| Cost | The initial procurement costs are higher, but the overall life-cycle costs may be lower due to reduced maintenance requirements. | The initial purchase cost is low, but the long-term maintenance costs and potential risk of malfunctions may increase. |
| Main application scenarios | This is suitable for applications requiring high reliability and environmental adaptability, such as coastal areas, rainy and humid environments, severely polluted areas, high altitudes, confined urban spaces, rail transit systems, and data centers. | This refers to typical power distribution locations with favorable environmental conditions, ample space, sensitivity to cost, and ease of maintenance. |
Definition of "Conventional Ring Main Unit"
The term "conventional ring main unit" usually refers to:
Air-insulated ring main units: These rely on air gaps for insulation, have a simple structure and low cost, but are large in size and susceptible to environmental influences.
SF₆ gas-insulated ring main units: These use SF₆ gas as the insulating and arc-extinguishing medium. They are smaller than air-insulated units, but there are environmental concerns regarding potential SF₆ gas leakage (SF₆ is a potent greenhouse gas).
Solid-insulated ring main units are a new generation of products developed to overcome the shortcomings of the above two types of products (poor environmental adaptability and the use of SF₆ gas).
Summary
The essence of solid-insulated ring main units (RMUs) is to "integrate switches and high-voltage live parts into a single module using solid insulating materials," achieving high safety, high reliability, maintenance-free operation, environmental friendliness, and miniaturization.
Conventional ring main units (represented by air-insulated and SF₆ gas-insulated types) still have advantages in terms of cost and economic efficiency, but they have shortcomings in safety, environmental adaptability, and environmental protection.
Development trend: With increasing environmental requirements and the growing demand for reliable urban power distribution, solid-insulated ring main units and more advanced atmospheric pressure sealed air-insulated ring main units (such as "fully insulated and fully enclosed air-insulated ring main units") are gradually becoming the mainstream choice, especially since the use of SF₆ ring main units in new projects has been strictly restricted.
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