Switchgear Versus Ring Main Unit

Both switchgear and Ring Main Units (RMUs) are vital for electric power systems, and their distinctive functions are often referred to incorrectly due to all the similarities they share. In this article, we will look at what the different types of equipment are and answer frequently asked questions related to switchgear and RMUs to provide a comprehensive overview of the role of RMUs within the overall development of switchgear as well as their advantages and contribution for reliable power distribution.

How are Switchgear and Ring Main Unit Defined?

Any electrical device used to control, isolate, or protect electrical equipment can be categorized as part of the broader umbrella of Switchgear. The most common types of switchgear include circuit breakers, disconnect switches, and fuses, which help ensure a safe and reliable transmission of electricity. These electrical devices also come in both high voltage and medium voltage configurations, so they can be used at many different sites, such as generating plants and industrial facilities.

A Ring Main Unit (RMU) is one type of switchgear device that performs a single function in the medium voltage range of 11kV to 36kV. The reason it is called a “ring main unit” is that the devices are linked to create an electrically looped (or “ringed”) network in a manner that creates redundancy for electrical supply. RMUs provide uninterrupted electricity delivery even when parts fail within the loop. This redundancy in distribution systems is especially important in urban settings or industrial operations where constant reliability is critical.

Differences Between Switchgear vs. Ring Main Unit

RMUs fall under the umbrella of switchgear as a type of product, but there are major differences between switchgear and RMUs in application, design, and function.

1. Function: The purpose of switchgear is to provide several different functions, including protection, isolation, and control of the power being distributed. The primary purpose of RMUs is to provide distribution of power using a ring network configuration, allowing the network to provide service continuously in the event of a fault in the distribution system.
2. Industries/Applications: Switchgear is used in a variety of industries, including electricity generation, transmission, and end users of electricity, such as factories, while RMUs are more prevalently used in the distribution aspect of an electrical system, commonly found in secondary substations for an electricity distribution system.
3. Design: RMUs are designed to be compact and modular to facilitate installation in very limited space, such as in urban substations. In contrast, traditional switchgear products are typically bulkier and do not lend themselves to installation in limited spaces.
4. Voltage: While switchgear operates on both high- and low-voltage systems, RMUs generally are manufactured for the medium voltage range (11kV RMU or 3-way RMU).

Benefits of a Ring Main Unit

The amount of RMUs being manufactured and sold continues to grow daily because of the specific advantage they provide to the electricity distribution system. Benefits:

• Small Size: RMUs are designed to be compact, modular units that can be easily installed in very limited spaces, e.g., urban substations.
• Reliability of Continued Supply of Electricity: The redundancy of the ring network is provided for by using a ring network to connect all of the RMUs attached to the same section of the distribution system.

The RMU allows electricity to continue flowing around the network in an alternative way, should a section of the network (ring) experience a fault.

RMUs provide greater ease of maintenance, as RMUs do not require as much ongoing maintenance as traditional switchgear; the ability to locate faults quickly and resolve issues rapidly with no downtime is also factored into the ease of maintenance of RMUs.

As RMUs are a contained system, there are fewer safety risks associated with using them by operators and maintenance personnel.

Frequently Asked Questions (FAQ)

What are the differences between Ring Main Units and Switchgear?

The term Switchgear refers generally to all of the devices that control, protect and isolate circuits within an electrical system; Ring Main Units (RMUs) are a specific type of switchgear that is used specifically for the purpose of delivering power within a ring network, emphasizing availability (redundancy) and reliability for medium-voltage power applications.

Are RMUs Classed as a Type of Switchgear?

Yes, RMUs are classed as medium-voltage switchgear as they have the specific function of delivering continuous power within ring distribution systems.

What are Ring Main Unit Switchgears?

As a compact RGB system (part of the secondary distribution system operating at a Medium Voltage of either 11 kV), Ring Main Unit Switchgears are typically located at a substation or an industrial facility to provide an uninterrupted power supply with a high degree of reliability.

When Should You Use a Ring Main Unit?

If you have any of the following requirements for medium voltage power distribution in an urban area or a factory or industrial sites that require reliability and redundancy; you should consider RMUs as they offer many advantages over traditional switchgear in terms of compactness and high performance, particularly when used in secondary substation facilities. Additionally, RMUs provide safety and require minimal maintenance in systems designed to use RMUs.

Conclusion

The difference between Switchgear and Ring Main Units (RMUs) should provide you with a solid foundation for making an informed purchase decision relative to your power distribution requirements. All RMUs are switchgear; however, they offer significant advantages in the area of reliability, redundancy and compact size in a median voltage application of typically at or around 11kV networks and the installation and operations of a substation or urban grid. In summary, when considering the requirements of your facility or active urban grid (i.e. RMUs) for operational efficiency and maintenance & safety savings are worth evaluating.