Gas-Insulated Ring Main Unit (GIS RMU) and Solid-Insulated Ring Main Unit (SIS RMU) are two common power distribution equipment, mainly used for power distribution and protection in medium voltage distribution networks (such as 10kV, 20kV, etc.). They have significant differences in insulation media, structural design, application scenarios, etc. The following is a detailed comparison of the two:
1. Insulation medium
| Type | Insulation Medium | Features |
| Gas insulation | Sulfur hexafluoride (SF₆) or other environmentally friendly gases (such as dry air, N₂) | SF₆ gas has excellent insulation performance, but there is a greenhouse effect problem (high GWP) |
| New environmentally friendly gases (such as N₂ or mixed gases) are gradually replacing SF₆ | ||
| Solid insulation | Solid materials such as epoxy resin and silicone rubber | No risk of gas leakage, environmentally friendly. |
| After the insulation material is cured, it forms an integral structure with high mechanical strength |
2. Structure and design
| Type | Structural features |
| Gas insulation | High air tightness requirements, need to seal the pressure system. |
| Relatively small size, suitable for space-constrained scenarios. | |
| Internal components (such as circuit breakers, disconnectors) are immersed in gas. | |
| Solid insulation | Modular design, all live parts are wrapped with solid insulating materials. |
| No pressure vessel is required, simple structure. | |
| The volume may be slightly larger than the gas insulated cabinet. |
3. Environmental protection
| Type | Environmental issues |
| Gas insulation | The global warming potential (GWP) of SF₆ is 23,500 times that of CO₂ and requires strict recycling. |
| New environmentally friendly gases (such as g₃ and AirPlus) can reduce environmental impact. | |
| Solid insulation | No greenhouse gases, the material is recyclable. |
| The production process may involve environmentally friendly disposal of epoxy resin. |
4. Reliability & Maintenance
| Type | Reliability | Maintenance requirements |
| Gas insulation | High reliability, but depends on gas tightness. | Gas pressure and purity need to be checked regularly. |
| SF₆ leakage will lead to reduced insulation performance. | Maintenance is complex and requires professional equipment. | |
| Solid insulation | No risk of leakage, strong weather resistance. | Maintenance-free or low-maintenance. |
| Long life (up to 30 years). | No gas management required. |
5. Application scenarios
| Type | Applicable scenarios |
| Gas insulation | High load density areas (such as city centers, underground distribution rooms). |
| Harsh environments (humid, dirty, high altitude). | |
| Where compact design is required. | |
| Solid insulation | Regions with strict environmental protection requirements (such as Europe and Japan). |
| Suitable for both indoor and outdoor use, especially for occasions with frequent operations. | |
| Scenarios with high requirements for maintenance convenience. |
6. Cost comparison
| Type Initial cost Long-term cost | Initial cost | Long-term cost |
| Gas insulation | Higher (SF₆ gas handling costs) | Higher (gas detection, replenishment, recovery). |
| Solid insulation | Moderate or slightly higher | Low (maintenance-free, no gas management costs) |
7. Development trends
Gas insulation: transition to environmentally friendly gases (e.g., N₂/SF₆ gas mixtures, dry air), reducing SF₆ use.
Solid insulation: increasing technology maturity and market share growth, especially in new infrastructure and smart grid applications.
Summary of selection recommendations
Choose gas insulation: if you need high insulation performance, compact design, and can properly handle gas management (such as SF₆ recycling).
Choose solid insulation: if you value environmental protection, maintenance-free, long-term cost savings, or deploy in variable environments indoors and outdoors.
If you would like to know more, please contact:pannie@hdswitchgear.com.
