What is a Ring Main Unit (RMU)? Key Components and Working Principle

Power outages are one of the major issues both at home and for businesses. Power is required to be supplied continually without fail, and that is what an RMU does for you. An RMU helps keep the system secure and uninterrupted, no matter the size of the enterprise. Understanding how RMUs function protects your critical assets from faults. In this blog, we will explore the ring main unit thoroughly, covering its functions, applications, key components, types, working, and much more. So, keep reading!

1) What is an RMU?

The RMU is a type of electrical switchgear that serves as a critical part of the electrical distribution network. Its use encompasses the management of electricity distribution in medium voltage systems. The RMU is integrated into a loop or ring network. This allows power to be supplied in multiple directions. Consequently, in case of some failure to a part of the system, alternative routes from other sides can ensure a continuous supply of electricity to consumers.

An RMU or Ring Main switchgear is used all over the world at 11 kV substations and switch stations. With the help of the RMU network, it is possible to change feeder substations or incorporate transformer substations in a ring fashion. The effective applicability of RMUs is evident in its components, which include circuit breakers, load break switches, and fuses. These ensure that the network is safeguarded from faults and overloads. Reliability alongside savings in costs and space makes installation seamless in rural and urban areas alike.

Functions of RMU

Ensuring safety and smooth power flow are basic areas that an RMU focuses on. These include controlling the distribution of electricity and flawlessly maintaining the flow while at the same time, minimizing outages. Besides the above, here are more pointers that elaborate on the function of an RMU:

• Power Switching: Routing power and switching it with different network parts is another function an RMU performs. This ensures that there is no disruption in the power supply.

• Fault Isolation: Detecting faults and isolating the sections of the network are areas where the RMU shows its efficacy. Well, this guarantees minimal damage across areas of the network.

• Load Management: Redistributing and balancing the electrical load to avoid the overloading of parts within the system is one of the most vital tasks an RMU tackles..

• Backup Power: The RMU serves as a prospective measure in the event that one section in a network fails. The RMU ensures the switches keep running even when there is a failure in parts of the system.

• System Protection: RMUs have built-in circuit breakers and fuses that disconnect power automatically at the moment when specific fault conditions are sensed. This assists lessen system damage.

• Remote Monitoring and Control: The majority of the new RMUs have remote monitoring features that enable operators to evaluate system health and control the unit from a distance.

• Maintenance Isolation: RMUs allow for the isolation of certain parts of the network for maintenance purposes without disrupting the operation of the system.

• Safety: RMUs provide innovative safety features to the power distribution network by protecting it from electrical faults such as short circuits.

Applications of RMU

Ring circuit Units are utilized in numerous applications, particularly where uninterrupted and reliable power distribution is essential. Some common applications include:

• Urban Power Networks: RMUs are widely used in metropolitan areas for the efficient control of power distribution of electricity.

• Industrial Plants: They are used in factories and plants to provide power to the machinery and production processes.

• Commercial Buildings: Other shopping malls, office buildings and commercial establishments depend on RMUs to guarantee reliable power for lighting, elevators and HVAC systems.

• Transportation Networks: RMUs are important in airports, metros, and train stations for sustaining power to Thameslink lighting and signalling systems.

• Underground Power Systems: In addition, RMUs can be found in underground electrical systems because of their small size and environmental durability.

• Remote Areas: These places are considered power deserts, lacking proximity to energy. In such regions, RMUs are essential to ensure dependable power in off-grid systems.

2) RMU Key Components

Well, an RMU includes a number of components that are critical for the command and protection of an electrical distribution system. Below are the basic elements of an RMU:

i) Circuit Breakers: To shield the system from electrical faults, circuit breakers are a must. They discontinue the power link automatically in case of a short circuit or overload to protect against damage to the network.

ii) Load Break Switches: The switches serve to disconnect regions of the grid. As they are capable of breaking the circuit while under load, they can disconnect the power safely even when current is present.

iii) Fuses: Fuses offer additional protective coverage for system components. They protect wires from prolonged bursts of high current. Disconnecting the overload once a set threshold is reached limits added damage.

iv) Busbars: Busbars are big electrical conductors that are used to link various components of the system. Busbars permit electrical energy to move from one portion of the RMU to another. Busbars also allow the network to balance the electric load for each part of the system.

v) Protection Relays: Protection relays are designed to avoid or stop adding or posing damage to a system that has electrical components and would suffer from detecting a malfunction or faulty part in the network. They send an alert or signal to the circuit breaker/load break switch to isolate the parts with issues.

vi) Gas Insulation: RMUs are normally sealed with SF6 to protect the inside parts.

vii) Terminal Connectors: The terminal connectors connects the electric RMU with external cables or other components of the electrical network. They must guarantee the flow of current with no interruptions.

viii) Control Panel: The control panel has the functionality for an operator to manage and view the functionality of the RMU. It's a control switch that has adequate information regarding the entire system and provides hands-on commands for switches whenever the situation necessitates it.

3) Common types of RMU

There are numerous models of Ring Main Units (RMUs), meant for specific functions within a power network. Below are the most popular ones:

i) Gas-Insulated RMU

These RMUs use gas (normally SF6 or even air) as insulation. Gas is useful in restricting electrical arcing and assures safe functioning under tough conditions.

ii) Air-Insulated RMU

These units rely on air to act as the insulating medium. They tend to be less complicated and cheaper than their gas counterparts. Such units are mostly found in rural regions where the conditions are not as tough.

iii) Compact RMU

Compact RMUs serve as smaller-sized traditional units. They are built for areas where space is limited while still ensuring effective power distribution. They offer all required parts, including circuit breakers, load break switches, and others irrespective of their small size.

iv) Outdoor RMU

Outdoor RMUs can endure tough weather conditions since they have a weather-resistant casing. These are found in substations and other areas where there are chances of rain, dust, or poor weather conditions.

v) Indoor RMU 

These RMUs are utilized in a building's internal zones, which are temperature-controlled, for example, in commercial buildings or factories. They help in controlling the power distribution in such buildings.

vi) Single Busbar RMU

These RMUs are less complex and inexpensive for smaller uses since they make use of a single busbar.

vii) Double Busbar RMU

The use of two busbars gives these units more dependability. If one fails, the functionality will continue in the other busbar, thus the system is still able to work.

4) How RMU works

The RMU works by providing a dependable supply of electricity while simultaneously protecting from faults. You will basically find them in medium voltage distribution systems which are used mainly in urban areas.

The RMU works with the power supply in a “ring” configuration. This allows electricity in either direction. If a fault or maintenance is required in one section, the RMU automatically switches to another power path.

When an RMU identifies a fault, it responds in several ways:

• Isolation of Faulty Areas: The breakout box disconnects the affected area. To make it simpler, it would cease only the infected area and the remaining part of the system would function normally.

• Automatic Reconfiguration: This unit has the capability to automatically change the configuration of the network by reallocating the energy pathways for electric continuity.

• Monitoring and Protection: The system monitors the network without breaks. When voltage increases, the RMU takes corrective measures to avert damage to the system.

Depending on the configuration, the RMU can be controlled either manually or automatically. It helps control power failure and damage to the system by providing better fault isolation.

5) Delixi Ring Main Unit

Delixi Electric provides a variety of Ring Main Units (RMUs) for power distribution and system reliability. These are essential parts of medium-voltage networks for electricity distribution systems that require safety and reliability.

Product Range:

• XGN20-12L/630-25 Indoor Medium Voltage SF6 Ring Main Unit: This model uses SF6 load switches as the main switching device. It comes with modern sensor technology and relay protection elements, guaranteeing high-grade performance and safety.

• CDL8 Series Indoor Cubicle Type Gas Insulated Switchgear (C-GIS): This series design provides space-saving and sufficiency features for medium voltage use. It employs gas insulation technology, fortifying safety and performance.

• CDRM6-12/24KV SF6 GIS Metal Enclosed Switchgear: This versatile switchgear is designed for a wide range of uses in medium voltage systems and offers strong protection.

Key Features of Delixi RMUs:

• Enhanced Reliability: Delixi RMUs have been developed to improve power supply reliability by automating fault isolation and lessening service interruptions.

• Advanced Protection: These units have modern protection relays and sensors which enable them to locally and remotely detect and isolate virtually any fault.

• Compact Design: The use of sparing space in designing the RMUs allows for their installation in areas with spatial constraints which include cities and industrial plants.

• Flexible Applications: Delixi's RMUs are applicable for urban power distribution as well as for industries and commercial buildings.

Delixi Electric's quality and innovation guarantee that these RMUs are compliant with standards, thus ensuring credible power distribution solutions to the clients. For further information or to view the complete range, visit our products page.

6) How to choose the right RMU?

These guidelines will assist in choosing the best ring electrical circuit unit to effectively enhance smooth, reliable, and safe network power distribution:

• Type of Unit Application: Consider the location of the RMU. Indoors require a non-resistant complaint to the inner workings of the structure, weather resistant units incorporate outer shielding.

• Control Voltage Level: The regularly used tolerance limits for voltage supply are between 12kV to 24kV for medium voltage systems. Make sure that the RMU fits the voltage specification of your system.

• Unit Insulation Type: Each gas-insulated (GIS) and air-insulated (AIS) has its merits. While GIS performs better in challenging environments, compact size and lower cost go to AIS models.

• Current rating units: Select an RMU with a current rating that aligns with the operational power needs of your network to avoid underperformance.

• Protection Features: Always ensure the RMUs include advanced safety features. This helps you separate the faulted portion in the quickest time possible and guarantees the safety of the systems.

• Space Availability: Some of the RMUs are more compact, which makes them ideal for places with limited room, while some are larger and more suited for areas that are less restricted.

7) Conclusion

As stated above, Ring Main Units (RMUs) ensure the efficient performance of power distribution systems. If you fully understand the components and all the basics about RMU, you will be able to select the right one to enhance the safety and stability of your electrical network. The best thing is that Delixi has a variety of high-standard rated RMUs that can be used reliably in both industrial and commercial power systems. You can contact us right now!

8) FAQ

1.  Will the RMU's insulation performance be affected in high humidity/high altitude areas?

Yes, high humidity or altitude does affect insulation performance. However, gas-insulated RMUs can withstand these more demanding conditions and ensure dependable operation in tough environments.

2.  What is the frequency of routine maintenance of the RMU? Does it require a specialized team to operate?

Of course, both high temperature and high altitude can affect the insulation. On the other hand, gas-insulated RMUs have a better capability to withstand such conditions, which makes them perform in even the most difficult places.

3. Gas-insulated vs air-insulated RMUs key differences

Gas-insulated RMUs are more compact, offer greater protection, and work in harsh environments while air-insulated RMUs are easier to use and cheaper, though they are less suitable for more demanding applications.