The electrical industry is moving away from sulfur hexafluoride (SF6). Solid insulated ring main units are becoming a mainstream alternative. In addition, they offer the compactness of gas-insulated designs without the environmental concerns. This guide explains how solid insulated RMUs work and their key benefits. It also shows where they fit best.
1. What Is a Solid Insulated Ring Main Unit?
A solid insulated ring main unit uses solid insulation material around the live conductors. This material is typically epoxy resin. It replaces air or gas. In fact, the switching and protection functions are the same as any RMU. Load break switches, fuses or vacuum circuit breakers sit in a metal-enclosed unit. In addition, the insulation medium is solid. A leading example is the GSG2-12 Solid Insulated Ring Main Unit (RMU).
2. How It Works
Epoxy resin provides excellent dielectric strength in a small volume. The epoxy fully encapsulates the energized parts. This protects them from dust, moisture and pollution. The switching device still handles arc interruption. For example, many designs use a vacuum interrupter. The solid insulation is purely an insulation and encapsulation layer.
3. Benefits Over SF6 and Air Designs
- No greenhouse gas: eliminates SF6 and the associated monitoring, reporting and end-of-life handling
- Compact footprint: similar or smaller than gas-insulated units, ideal for space-constrained substations
- Low maintenance: no gas pressure checks, no gas refilling, fewer consumables
- Rugged: sealed encapsulation resists contamination, vibration and environmental aging
- Simpler logistics: no gas handling for transport or installation
4. Comparison with Other Technologies
| Feature | Solid Insulated | SF6 Gas | Air Insulated |
|---|---|---|---|
| Footprint | Compact | Compact | Larger |
| SF6-free | Yes | No | Yes |
| Maintenance | Low | Gas checks | Low |
| Pollution resistance | Excellent | Excellent | Moderate |
5. Where Solid Insulated RMUs Fit
Generally, solid insulated units suit many applications. For example, they fit urban distribution networks, commercial buildings and renewable energy projects. They also work on any site where SF6-free requirements or sustainability targets apply. They are especially attractive when a utility has committed to SF6-free procurement.
6. Frequently Asked Questions
Is a solid insulated RMU more expensive?
The first cost is comparable to gas-insulated units. Over the lifecycle, however, it can be lower. This removes gas management from the equation entirely.
Can solid insulated units be repaired?
Yes, to a degree. Technicians can replace switches and bushings. The encapsulated conductor assembly leaves the factory sealed. For the sealed section, whole-assembly replacement is the norm.
Are solid insulated RMUs available at 24 kV and above?
Yes. Solid insulation technology supports 12 kV, 24 kV and higher voltage classes. In general, it depends on the specific design.
How does a solid insulated ring main unit handle switching?
Switching is performed by the built-in load break switch or vacuum circuit breaker. This is independent of the insulation medium. The vacuum interrupter extinguishes the arc reliably. Meanwhile, the epoxy encapsulation insulates and seals the energized parts. In practice, solid insulated units offer the same switching performance as SF6 units. They do this without gas handling or greenhouse gas emissions.
Is retrofitting existing SF6 substations with solid insulated units difficult?
Retrofitting depends mainly on the panel footprint and cable entry positions. Solid insulated units are often similar in size to gas-insulated models. Many replacements are therefore straightforward. Always compare the dimensions and ratings against the existing installation before ordering.
7. Conclusion
Solid insulated RMUs deliver the compact, low-maintenance benefits of gas designs without SF6. As a result, they are increasingly the default choice for projects with sustainability requirements. For another example, see the GSG2-12 solid insulated ring main unit.
Electric-GS is a professional power and electrical equipment manufacturer in Yueqing, Zhejiang, China. The company produces solid insulated, SF6 and air-insulated ring main units. OEM and ODM support is available. For a quotation or technical consultation, contact info@electricgs.com or WhatsApp +86 135 8897 8050.
Related Products
GSG2-12 Solid Insulated Ring Main Unit (RMU)
GSRM6 Gas Insulated Ring Main Unit
GSM6-12~24 Air-insulated RMU (Fixed Type)
