Understanding Ring Main Unit (RMUs): A Comprehensive Overview

A Ring Main Unit (RMU) is a compact, gas-insulated switchgear unit designed for secondary power distribution systems. Its sealed design ensures reliability and efficiency, making it a key component in ensuring uninterrupted power supply and transformer protection.

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Main Switching Devices in an RMU

The switching devices in an RMU can be configured as:

• Fused switch disconnectors
• Switch disconnectors

These configurations allow RMUs to provide critical functionality in secondary distribution systems, safeguarding the connected transformers from transient currents and ensuring uninterrupted power flow.

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Key Features and Components of an RMU

1. Transformer Protection
   • Depending on the load conditions and application, an RMU can use:
     • Circuit breakers
     • Switch-fuse combinations
   • The transformer connected to these devices is referred to as the Tee-off.
2. Load Break Switches
   • Typically, load break switches are installed on either side of the Tee-off.
   • These switches serve as isolators that can break the circuit under load conditions.
3. Feeders
   • RMUs consist of incomer feeders and outgoing feeders:
     • Incomer Feeder:
       • Equipped with either an SF6 or vacuum circuit breaker.
       • Includes an associated earth switch and disconnect switch.
       • Provides a protruding connection point for supply cables.
     • Outgoing Feeder:
       • Contains load break switches, earth switches, and disconnect switches.
       • Includes provisions for cable connections.
4. Gas-Insulated Design
   • Both incomer and outgoing feeders are enclosed in an SF6-insulated environment, ensuring a compact and efficient design.
   • RMUs are equipped with instruments to monitor SF6 gas pressure, featuring scales categorized into zones (green for safe pressure, red for critical).
5. Mechanical Indicators
   • The RMU panel displays mechanical indicators for:
     • Earth switch status
     • Disconnect switch status
     • Circuit breaker status
6. Current Transformers (CTs)
   • A current transformer with the desired ratio is installed in the incomer feeder.
   • Its secondary output connects to a self-powered relay, which offers essential protections like:
     • Overcurrent protection
     • Earth fault protection
7. Self-Powered Relay
   • A microprocessor-based numerical relay with a user interface is integrated for efficient operation.
   • Manufacturers may offer customized protection features based on user specifications.

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Applications and Advantages of RMUs

1. Ease of Installation
   • RMUs come as a complete package, requiring only cable connections and installation.
   • This design minimizes commissioning time, making deployment faster and more convenient.
2. Distribution Network Use
   • RMUs are widely used in underground cable distribution networks, particularly at:
     • Junction points
     • Load connection points of a ring-type distribution network
3. Versatile Applications
   • RMUs are ideal for various environments, including:
     • Small industries
     • Renewable energy plants (solar and wind power)
     • Compact secondary substations
     • Critical infrastructure such as:
       • Airports
       • Hospitals
       • Shopping centers
       • Business centers
       • Residential complexes
       • Hotels

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Why Choose an RMU? An RMU, or Remote Monitoring Unit, offers numerous advantages. From real-time monitoring to proactive maintenance, an RMU ensures seamless operations. With its advanced technology and extensive capabilities, an RMU is a reliable choice for optimizing efficiency and maximizing productivity.

Ring Main Units offer a complete, compact solution with a wide range of capabilities. Their reliability, ease of installation, and versatility make them the go-to choice for efficient power distribution across diverse applications.

Professional RMU supplier and manufacturer 

1. 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 
2. 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.