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Ring Main Unit
Keywords:
A Ring Main Unit (RMU) is a set of high-voltage switchgear equipment housed within metal or non-metallic insulated enclosures, or configured as modular, prefabricated ring-network power supply units. Its core components consist of load switches and fuses. The RMU boasts advantages such as simple structure, compact size, low cost, improved power supply parameters and performance, and enhanced supply safety. It is widely used in distribution substations and packaged substations located at load centers—including urban residential communities, high-rise buildings, large public buildings, and industrial enterprises.
A ring network refers to a ring-shaped power distribution system in which the main power supply lines form a closed loop. The power source supplies electricity to this ring-shaped main line, and from the main line, power is distributed outward through high-voltage switches, one branch at a time. The advantage of this configuration is that each distribution branch can draw power from both the left-hand and right-hand sections of the main line. If the left-hand section experiences a fault, the branch can continue to receive power from the right-hand section; similarly, if the right-hand section fails, the branch can still draw power from the left-hand section. In this way, although the overall power supply is single-source, each distribution branch effectively enjoys a dual-power-supply-like reliability, thereby significantly enhancing the overall reliability of the power supply.
The so-called “ring main unit” refers to a switchgear installed for each distribution branch circuit (outgoing feeder switch). switchgear cabinet), the busbar of this switchgear cabinet is simultaneously part of the ring main. In other words, the ring main is collectively formed by connecting the busbars of each outgoing feeder cabinet. Each outgoing feeder cabinet is referred to as a “ring network cabinet.” In fact, if you take just one ring network cabinet out by itself, you wouldn't be able to discern the meaning of “ring network.”
The rated currents of these ring main units are not high; therefore, the high-voltage switches in ring main units typically do not employ complex circuit breakers but instead use simple high-voltage load switches equipped with high-voltage fuses. In other words, the high-voltage switches in ring main units are generally load switches. The load switch is used to operate normal currents, while the fuse is employed to interrupt short-circuit currents. Together, these two components effectively replace a conventional circuit breaker. Of course, this approach is limited to a certain capacity range.
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