The safe, uninterrupted, and controllable distribution of electrical energy is an indispensable requirement of modern infrastructures. In medium-voltage systems, one type of equipment that addresses this need is the Ring Main Unit (RMU) system. Thanks to their compact structure, maintenance-free design, and wide range of applications, RMU systems stand out, particularly in urban distribution projects.
What is an RMU cell?
RMU (Ring Main Unit) cells are compact switchgear used in medium voltage levels up to 36 kV. They are insulated with SF₆ gas, have a metal enclosure, and are usually factory-sealed. Although they appear small at first glance, an RMU cell contains critical functions such as:
Load disconnectors
Fused transformer protection units
Grounding disconnectors
Circuit breakers (optional)
Cable bushings
Pressure gauges.
All these components are protected in a hermetically sealed gas tank. This allows them to operate for many years without maintenance, unaffected by environmental factors.
What is the function of an RMU cell?
By operating the distribution network in a ring structure, it increases continuity. It provides input-output connections for transformer substations. It quickly isolates short-circuited and faulty lines. It makes it possible to transmit energy through an alternative path in case of maintenance or malfunction. In short, RMU cells create a ring structure in distribution systems, ensuring that even if an interruption occurs at one point, energy can be transmitted through an alternative path. Thus, the continuity of the electrical circuit is increased and service interruptions are minimized.
What are the advantages of RMU cells?
Compact and space-saving design
Maintenance-free gas-insulated system
High personnel safety – high internal arc resistance
Long service life (over 20 years)
Fast installation and commissioning
Suitable for outdoor operation (protection up to IP67)
Where are RMU cells used?
RMU systems are particularly preferred in areas with space constraints and high uptime requirements:
Urban substations
Concrete kiosk transformer systems
Shopping malls and hotels
Metro, tram and tunnel infrastructures
Organized industrial zones
Renewable energy projects (Solar and Wind Power Plants)
Mobile substation applications
RMU Cell Types
RMU cells can be offered in different configurations depending on their structure. Common types include:
Transformer Protection Unit with 2 Load Disconnectors + 1 Fused (2L+T)
1 Load Disconnector + 1 Circuit Breaker Unit (L+C)
Multiple combinations such as 2L+C, L+L+L, C+T
They can also be equipped with options such as motorized mechanisms, SCADA integration, and remote control.
What Standards Do RMU Cells Comply With?
RMU switchgear used in Turkey is manufactured in accordance with the TEDAŞ-MYD/95-002.B SF6 gas-insulated modular switchgear technical specifications and the international IEC 62271-200 standard. High-quality manufacturers ensure that RMU switches pass type tests, successfully completing all critical tests such as internal arc resistance, dielectric strength, and short-circuit tests.
RMU switchgear is an indispensable solution in projects where energy continuity is critical. Thanks to its compact structure, high safety level, and maintenance-free design, it is widely used in city networks, industrial zones, and infrastructure projects. Choosing the right RMU means not only ease of initial installation but also a reliable operating life of 20 years or more.