Comprehensive Guide to Ring Main Units (RMU)
A Ring Main Unit (RMU) is a compact, fully enclosed, and gas-insulated switchgear system used in secondary distribution networks. It serves as a critical component for managing medium-voltage power distribution by ensuring reliable switching and protection of electrical circuits.
Key Components of an RMU
An RMU integrates different types of switching devices, including:
- Switch Disconnectors
- Fused Switch Disconnectors
- Circuit Breakers (often combined with protective relays, either self-powered or advanced versions with communication features)
These units generally operate at voltage levels up to 24kV and current ratings up to 630A. The core structure remains similar across different voltage ranges, with higher voltage levels requiring increased gas pressure for insulation.
Types of Ring Main Units
1. Classification by Insulation Type
A. Gas-Insulated RMU (GIS RMU)
Gas-insulated RMUs (rated up to 36kV) are widely used in secondary distribution systems due to their compact design and robust performance in various environments, including wind farms, transformer substations, and industrial facilities.
Key Features:
✅ Compact & Space-Saving: Designed for both indoor and outdoor installations.
✅ High Operator Safety & Reliability
✅ Resistant to Pollution, Humidity, and High Altitude
✅ Low Maintenance & Long Service Life
✅ Expandable Design: Can be extended on one or both sides.
✅ Remote Monitoring & Control
✅ Compliance with IEC & EN Standards
B. Oil-Insulated RMU
This type of RMU is ideal for harsh and corrosive environments, such as oil fields and mining applications. It features a compact yet expandable design with modular ring switches and fused circuit breakers.
Key Features:
✅ Robust, IP54-Rated Enclosure: Withstands extreme temperatures (-10°C to 55°C) and 100% humidity.
✅ Flexible Installation: Side and rear cable termination for easy commissioning.
✅ SCADA Compatibility: Can be integrated into remote monitoring systems.
✅ Safety Mechanisms: Equipped with interlocking and padlocking for secure operation.
✅ Voltage & Current Ratings: 15.5kV, 630A, 50Hz.
C. Air-Insulated RMU (AIS RMU)
Air-insulated RMUs are metal-enclosed switchgear commonly used in residential complexes, high-rise buildings, factories, and businesses. They feature a vacuum load switch as the primary switch.
Key Features:
✅ Environmentally Friendly & High Insulation Strength
✅ Modular Design: Easy to install and operate.
✅ Reliable Performance: Built for harsh operating conditions.
✅ Strong Interlocking System: Ensures safety and compliance with protection standards.
✅ Cost-Effective & Compact
2. Classification by Installation Location
A. Outdoor RMU
Outdoor RMUs (typically rated 13.8kV) are widely used in urban and rural power distribution for utilities, commercial buildings, hospitals, airports, and metro systems.
Key Features:
✅ Vacuum Circuit Breaker for High Durability
✅ Maintenance-Free & Pedestrian-Safe (No exposure to active parts)
✅ Integrated Safety Interlocks
✅ Remote Monitoring & Control Support
✅ Eco-Friendly & Recyclable
B. Indoor RMU
Indoor RMUs are SF6-insulated switchgear designed for secondary distribution networks. They are compact, easy to install, and require minimal maintenance.
Key Features:
✅ Fully Insulated with SF6
✅ Available with Switch Disconnectors, Fuses, and Circuit Breakers
✅ Rated Voltage: 12kV, 17.5kV, 24kV
✅ Rated Current: 630A
✅ Remote Monitoring Capabilities
3. Classification by Application
- Utility Distribution Networks
- Industrial and Commercial Power Systems
- Smart Grid & Substation Automation
- Rural Electrification Projects
4. Classification by Voltage Rating
🔹 Below 15kV
🔹 16kV – 25kV
🔹 Above 25kV
5. Classification by Structure
🔹 Extensible RMU: Can be expanded to meet growing power demands.
🔹 Compact RMU: Space-efficient, designed for fixed configurations.
6. Classification by Insulation Material
🔹 Air-Insulated Cabinet
🔹 Vacuum-Sealed Insulation Cabinet
🔹 SF6 Gas-Insulated Cabinet
Operation of a Ring Main Unit
The RMU switchgear is designed to connect and protect distribution systems by isolating faults and ensuring the safe transfer of electricity.
✅ How It Works:
- The RMU is connected through circuit breakers between input and output cable compartments.
- It contains load break switches, circuit breakers, earthing switches, busbars, and interconnections.
- Most RMUs are hermetically sealed in SF6 gas for enhanced insulation and protection.
- They are divided into compartments, typically two, four, or six, based on the customer’s requirements.
Modern RMUs are also integrated with SCADA systems for remote monitoring and automation, improving efficiency in smart grids.
Global Market Trends & Demand for RMUs
The demand for RMUs is steadily growing, particularly in developing countries like China, India, Japan, and South Korea, where urbanization, industrialization, and infrastructure expansion are driving power sector investments.
🔹 Key Growth Factors:
- Expansion of power grids and increased electricity consumption
- Rural electrification programs
- Adoption of smart grids & substation automation
- Need for reliable, compact, and eco-friendly power distribution solutions
Conclusion
RMUs are a vital component of modern power distribution networks, offering safety, reliability, and flexibility in various applications. With advancements in smart grid technology, remote monitoring, and eco-friendly insulation, RMUs continue to play a crucial role in efficient electricity distribution.
For those looking to optimize their power distribution infrastructure, choosing the right RMU type and configuration is key to ensuring long-term performance and cost efficiency.
Professiona Switchgear supplier and manufacturer
- Zhejiang GONGSHUN Electrical Co.,Ltd (electricgs.com), Our company was founded in the late 1990s, specializing in the production of inflatable cabinets, SF6 inflatable cabinets, and various high and low voltage complete sets of electrical equipment. It has multiple subsidiaries under its jurisdiction, including high-voltage load switch branch, high-voltage circuit breaker branch, high-voltage fuse branch, and technology development branch.Our technical expertise, comprehensive product portfolio and long-term rich experience are helping many customers in need to solve their power problems. We’re happy to help at any time. Whether you need application product advice or technical assistance, our global service team is committed to providing you with the right support. For more technical information about medium voltage earthing switch, feel free to contact us, send an email to gongshun@electric-cn.com
- Our company specializes in producing 12KV-40.5KV series high-voltage electrical products: FZN58, FLN48, FLN36, FZRN25, FZN21, FN18, ZFN16, FN12, FN8, FN7, FN5, XRNT, XRNP, VS1, ZN28, ZW8, ZW32, JN15, GN19, GN22, GN24, GN30, CLXGN15-12, HXGN □ -12, DXG-12 (L), DFW □ -12 high-voltage cable branch box, CLXGN □ -12 (SF6) series inflatable cabinet 12KV and 35KV cable accessories, etc; CLVXP-12 indoor AC high voltage fixed switchgear, CL-SIS-12 compact solid insulated ring main unit, professional assembly Schneider SC6 (SF6) series load switchgear, ABB produced SFG (SF6) series load switchgear and other series products; Distribution and agency of high-voltage load switches and inflatable cabinets produced by Schneider Electric and ABB; Siemens produces the 3AJ1 series of indoor medium voltage vacuum circuit breakers and other related products. The company has a complete range of products and has been operating safely on domestic and international power grids for a long time, receiving unanimous praise from both new and old users. Among them, multiple products such as FZRN25, FN12, FLN36-12, XRNT-12 have been exported to various countries and regions in East Asia, South Asia, Southeast Asia, Africa, and the United States.