A ring main unit (RMU) is a set of electrical equipment used for power distribution, primarily in high-voltage systems. Its working principle is based on the design of a ring distribution network, where the power supply mainline forms a closed loop. The power source feeds into this loop, and the power is distributed outward through high-voltage switches. This design ensures that each distribution branch can draw power from either side of the mainline, thus enhancing the reliability of the power supply. The core components are primarily load switches and fuses, offering advantages such as simplicity, compact size, low cost, improved electrical performance, and enhanced safety.

In a ring network power supply system, the primary function of the RMU is to connect the ring network lines and enhance the reliability of the supply by supporting operations like loop closure or load transfer. The RMU contains different types of switches for various purposes, such as switches that connect to loads or provide power to distribution transformers.

Because RMUs generally operate at lower rated currents, the high-voltage switches typically use load switches with high-voltage fuses instead of more complex circuit breakers. This allows load switches to handle normal currents, while fuses interrupt short-circuit currents, effectively replacing circuit breakers.

There are several types of arc-extinguishing methods used in RMUs, such as direct air blast, rotating air blast, magnetic arc quenching, arc chutes, and sand-filled arc extinguishers. Different models and series of RMUs may vary in design and functionality to accommodate specific environments and needs.

Main Advantages of RMUs:

Excellent Protection: RMUs offer high protection levels, effectively preventing dust, moisture, and other external contaminants from entering the equipment. This ensures safe operation and minimizes the risk of electrical shock to operators, improving overall safety.

High Reliability: RMUs are modular in design, with fault diagnostics and online monitoring capabilities, making maintenance easier. The internal layout is spacious and wiring is simple, making repairs and maintenance more convenient.

Compactness: RMUs utilize SF6 gas, which has excellent insulation properties, allowing for a smaller, more lightweight, and compact enclosure that saves space.

Advanced Flexibility: RMUs are designed with international standards and use advanced production and testing methods. The simplified product structure, flexible operation, and reliable interlocks make it easy to use. The integration of advanced sensors and microprocessor-based protection devices further enhances their functionality.

High Safety: RMUs are designed to prevent operational errors. For instance, when a vacuum load switch is opened, the isolation switch automatically disconnects, creating a visible disconnection that ensures the safety of both personnel and equipment. Additionally, the visibility of the switch's position enhances safety.

Strong Weather Resistance: The stainless steel enclosure of RMUs allows for full insulation and sealing, enabling them to operate reliably in harsh outdoor environments. They have strong flood resistance and are suitable for a wide range of challenging locations.

Ease of Maintenance: RMUs are relatively simple in structure compared to other electrical equipment, making installation easier. After being put into operation, they require minimal maintenance, with some even offering maintenance-free operation.

High Performance Parameters: Both vacuum and SF6 RMUs feature vacuum and SF6 load switches that offer repetitive control, with the capability to close rated active loads up to 100 times. Their breaking performance is excellent, making them highly reliable.

Smart Operation and Expandability: As operational experiences improve, expandable outdoor RMUs are gradually replacing older, fully enclosed RMUs.

In conclusion, RMUs play a crucial role in enhancing the reliability, safety, and cost-effectiveness of power distribution systems.