Compact ring main units (RMUs) are widely used in urban areas, roads, residential communities, and other ring network distribution systems, as well as in industrial and mining enterprises for transmitting power to load centers. The hand-in-hand power supply method ensures continuous power supply. In gas-insulated RMUs, the high-voltage live parts are either completely sealed in gas-insulated chambers with IP67 protection or fully encapsulated by metal shielding and touchable solid insulation. As a result, except for the operating mechanism and secondary control protection equipment, the units are entirely unaffected by environmental conditions. The operating mechanism and secondary system compartments are sealed with high IP protection ratings, or their components are encapsulated using environmentally resistant materials, making them suitable for outdoor applications.
Outdoor Ring Main Unit
In many cases, RMUs are deployed outdoors. The conventional approach involves installing RMUs in separate outdoor enclosures, which increases both cost and dimensions. Unlike air-insulated switchgear, where live circuits are exposed to the atmosphere, gas-insulated RMUs only require protection for the secondary control system to be suitable for outdoor environments.
Compact outdoor RMUs integrate ring main unit components and outdoor protection into a unified structure. They feature a compact design with two incoming lines on both sides and outgoing lines in the middle.
Typical Configurations: Two Incoming + One Outgoing, Two Incoming + Two Outgoing
These configurations are particularly suitable for industrial and mining enterprises, tunnels, ships, and other demanding environments. Key advantages include:
Simple structure and small footprint
Easy installation and maintenance
IP54 protection rating, enabling operation in harsh environments
Reduced risk of internal arc faults
Simplicity and Cost-Effectiveness
The IP54-rated enclosure allows operation in the most severe conditions, eliminating the need for additional outdoor enclosures and reducing costs compared to traditional solutions.
All medium-voltage contacts are sealed in permanently airtight SF6 gas chambers with IP67 protection, ensuring a nearly maintenance-free design.
The compact structure simplifies installation in confined spaces such as narrow tunnels and underground elevator shafts, while the lightweight design enhances portability.
Additionally, according to IEEE C37.20.2 standards, outdoor switchgear can be categorized into two types: with or without maintenance corridors. Units without maintenance corridors achieve outdoor suitability by reinforcing side panels with necessary protections.
General Outdoor Application Solutions for RMUs
A simplified and cost-effective approach to outdoor applications involves upgrading indoor RMUs by protecting the control, protection, and mechanical operation components. This method reduces design complexity and costs while ensuring outdoor functionality.
In fact, outdoor switchgear does not necessarily require indoor switchgear combined with an outdoor enclosure. A more straightforward and integrated approach offers easier implementation, lower costs, reduced weight, and better meets customer needs. Compact outdoor RMUs are flexible, reliable, and ideal for deployment near load centers. Designed with a maintenance-free primary system and remotely operated secondary and automation systems, they eliminate the need for traditional outdoor enclosure concepts. Instead, they emphasize economic efficiency, environmental sustainability, space savings, reduced steel usage, and digitalization of switchgear. These features enable more flexible and efficient power distribution, faster equipment replacement and expansion, and plug-and-play functionality without system redesign or debugging.
The adoption of environmentally friendly insulating gases and air-tight sealed RMUs further supports green and low-carbon initiatives. With miniaturized sensors, low-energy microcomputer protection systems, and reduced power consumption, power distribution becomes safer and more reliable. Compact outdoor RMUs embody miniaturization, intelligence, and environmental sustainability, offering long service life, high reliability, minimal maintenance, and low operational costs. These advantages make them a preferred choice for enterprises and municipal engineering projects.
