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.