Currently, there are various types of ring main unit (RMU) products available, such as the HK-10, MKH-10, 8DH-10, XGN-15, and SM6 series.
A ring main unit is a type of electrical equipment consisting of a set of high-voltage switchgear installed in a steel plate metal cabinet or configured as an assembled compartmentalized ring network power supply unit. Its core components include load switches and fuses, featuring advantages such as a simple structure, small size, low cost, improved power supply parameters and performance, and enhanced power supply safety. It is widely used in power distribution stations at load centers (e.g., urban residential districts, high-rise buildings, large public buildings, factories and enterprises) as well as in box-type substations.
Ring Main Units
Ring main units are generally classified into three types based on insulation medium: air-insulated, solid-insulated, and SF₆-insulated. They are used to switch load current, interrupt short-circuit current and transformer no-load current, and charge current of overhead lines and cable lines over a certain distance. Serving control and protection functions, they are key switchgear for ring network power supply and terminal power supply.
In the cabinet:
●  Load switches with air insulation mainly include gas-generating, air-blast, and vacuum types.
●  Load switches with SF₆ insulation are SF₆-type; since SF₆ gas is sealed in the cabinet, the isolated breakpoints formed are invisible.
Load switches in RMUs generally require three positions: cutting off load current, isolating the circuit, and enabling reliable grounding. Gas-generating, air-blast, and SF₆-type load switches can easily achieve these three positions. However, vacuum arc-extinguishing load switches can only interrupt current but cannot isolate the circuit. Therefore, vacuum load ring main switchgear is generally equipped with an additional isolating switch before the load switch to form an isolated breakpoint.
This article is compiled and edited by DAYA Electric Group Co., Ltd. (https://www.hygraphics.com/). Please indicate the source when reprinting.