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In power distribution systems, reliability and safety are paramount, and ring main units (RMUs) are the equipment responsible for ensuring these aspects. An RMU is a compact switchgear primarily used in secondary distribution networks to manage current flow while protecting the system during faults. Numerous RMU types are available on the market, with different models suited for varying requirements. This guide will introduce common RMU types, helping you understand their features and applications.
Electrical RMUs are a critical component within medium-voltage secondary distribution networks. They are compact, factory-preassembled switchgear units that undergo type testing, typically incorporating load switches, circuit breakers, and fuses.
They primarily serve three functions:
Load Management: RMUs support flexible network configurations such as “ring networks” or “loops.” Even if a section of the network fails, power can be rapidly redistributed to ensure uninterrupted customer service, significantly enhancing system reliability.
Protection: It safeguards cables, transformers, and other equipment from damage caused by overcurrent or short circuits.
Safety: By isolating the faulty section, the RMU provides a safe and convenient operating environment for maintenance and repairs.
The insulation medium is one of the most critical factors that determines an RMU‘s design, safety, and performance.
A Gas-Insulated RMU uses an inert gas, typically sulfur hexafluoride (SF6) or an alternative eco-friendly gas, as the insulating and arc-quenching medium. The main components are sealed in a compact, gas-tight tank.
An Air-Insulated RMU uses ambient air as the primary insulating medium. The busbars and switchgear components are open and accessible inside an enclosure.
This type uses a solid dielectric material, such as epoxy resin, for insulation. The live parts are completely encapsulated within this solid medium.
A Hybrid RMU combines features from both GIS and AIS technologies. It might use gas insulation for the main busbar and switches, while the cable compartments are air-insulated.
The number of “ways” or feeder connections an RMU has determines its functional configuration and is a key factor in network design.
The most basic configuration, it typically includes two load break switches for “in” and “out” connections, allowing for a simple loop-in, loop-out setup.
This is a common configuration that adds a third way, usually a fused switch or circuit breaker, to connect a transformer. This is ideal for distributing power from a ring network to a single substation.
Expands on the 3-way by adding another feeder. It’s used for more complex distribution points where power needs to be fed to multiple transformers or different sections of the network.
Provides even greater flexibility for complex networks, allowing for connections to multiple transformers or network branches from a single point.
The installation location is another crucial consideration.
Indoor RMU is designed for installation inside substations or buildings. They are protected from the elements and do not require special weatherproofing.
Outdoor RMU is built to withstand harsh weather conditions, including rain, sun, dust, and extreme temperatures. They feature robust, weather-resistant enclosures.
Selecting the right RMU requires consideration of specific application scenarios, budget, and environmental conditions. Chuanli offers a complete range of high-quality RMU products, including gas-insulated, air-insulated, and solid-insulated models, with configurations ranging from 2 to 5-way options. Our experts can provide professional guidance to help you find a reliable and cost-effective power distribution solution that meets diverse power distribution needs.
What is the main difference between an RMU and a switchgear?
An RMU is a specific type of compact switchgear designed for secondary distribution networks, typically in a ring configuration, while “switchgear” is a broader term for a wide range of devices used to control, protect, and isolate electrical circuits.
Are SF6-free RMUs becoming the standard?
Yes, due to increasing environmental regulations and concerns over the high global warming potential of SF6 gas, there is a growing trend towards using SF6-free alternatives like solid-insulated or eco-friendly gas-insulated RMUs.
What factors affect the cost of an RMU?
The cost is primarily influenced by the type of insulation medium (GIS is generally more expensive than AIS), the number of ways, the rated voltage, and the inclusion of advanced features like remote monitoring capabilities.
Understanding different types of Ring Main Units (RMUs)—whether by insulation method, functional configuration, or installation environment—is crucial for building efficient, flexible power distribution networks. Choosing the right RMU not only enhances system safety and reliability but also delivers greater value for your investment. Explore our full range of innovative RMU products to find the optimal solution for your project.
