Ring Main Unit

In an electrical power distribution system, a ring main unit (RMU) is a factory assembled, metal enclosed set of switchgear used at the load connection points of a ring-type distribution network. It includes in one unit two switches that can connect the load to either or both main conductors, and a fusible switch or circuit breaker and switch that feed a distribution transformer. This type of switchgear is used for medium-voltage power distribution, from 7.2kV to about 36kV volts.

Ring main units can be characterized by their type of insulation: air, oil or gas. The switch used to isolate the transformer can be a fusible switch, or maybe a circuit breaker using vacuum or gas-insulated interrupters. The unit may also include protective relays to operate the circuit breaker on a fault. lt is suitable for distribution systems, ring power supply and biradial power supply system in factories, workplaces, residential high-rise buildings, it possesses functions of receiving, distribution and protection. It can also be used in the prefabricated substation.