SF₆ Insulated Ring Main Unit (RMU)

In a distribution network,SF₆ Insulated Ring Main Unit (RMU) play a vital role in establishing connections. They create a loop by linking feeders, overseeing and identifying any faults or malfunctions at both feeder and distribution transformer ends. This ensures a seamless and uninterrupted power supply to the utility with minimal voltage drop, guaranteeing a reliable source of electricity.

Ring Main Unit (RMU) Definition

The RMU (Ring Main Unit) cabinet, also known as a medium voltage cabinet, is a comprehensive electrical apparatus designed to interconnect, measure, and incorporate a fixed-type breaker with transformer protection capabilities.

These cabinets are characterized by their compact size, high dependability, safety features, ease of maintenance, and straightforward replacement and expansion options. Depending on specific needs, RMUs are offered in various voltage configurations, catering to both indoor and outdoor installation requirements.

Structure of a Ring Main Unit (RMU)

The RMU cabinet is structured with distinct output and input cable compartments, which are linked by isolating breakers and cables extending to transformers through the use of load breakers and protective fuses.

Essentially, the switch components, which include load breakers, cutting machinery, ground knives, busbars, and terminals, are securely housed within an SF6 gas tank constructed from a material highly resistant to environmental factors like dirt, oil, and grease, ensuring corrosion prevention.

RMU cabinets are designed with separate compartments that are both interconnected and divided. These cabinets adhere to RMU standards, available in configurations with two, four, or six compartments, depending on the specific requirements outlined by the customer.

Historically, the prevailing approach to safeguarding medium/low voltage transformers in distribution grids involved the common combination of fuses and cutter knives. This method was known for its simplicity and cost-effectiveness. Conversely, circuit breakers were typically reserved for high/medium voltage (HV/MV) stations, rather than being extensively utilized in medium/low voltage (MV/LV) stations.

Some features of RMU switch gears are as follows:

– Compact and sealed, it features a small footprint with insulation for enhanced safety.

– Designed for 11KV/33KV systems, typically rated at 630 A with a 21KA interrupting rating.

– Equipped with three insulation options: oil, air, and widely adopted SF6 gas insulation.

– Typically configured with two incoming and one outgoing lines, and vice versa.

– Includes distinct protective and measuring devices for added functionality.

– Suitable for both indoor and outdoor applications, providing versatility in installation.

– Mitigates fire-related hazards, prioritizing safety in operation.

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