A solid-insulated ring main unit (RMU) is a main unit switch with solid composite insulation used in medium-voltage power distribution networks.

In the same power supply unit of a solid-insulated ring main unit, the three phases (A, B, C) are composed of three independent modules, which can provide multiple combinations for the power distribution network. The composite insulation system includes load switches and circuit breakers, with various operating functions such as manual and electric operation. By selecting and equipping various intelligent controllers such as FTUs (Feeder Terminal Units) and other related equipment, different levels of control, measurement, and protection functions can be realized.

Solid-insulated ring main units feature flexible combination. Users can configure optional control equipment in phases according to different investment stages, offering strong upgrade capability and investment savings. The operating mechanisms of composite insulated load switches and circuit breakers are a combination of independent quick-closing/quick-opening manual operating mechanisms and mechanically driven motor closing/opening operating mechanisms. The electric operating mechanism of the load switch achieves closing by directly releasing the stored energy through electric energy storage, thus maintaining the same simplicity and reliability as the manual mechanism under any circumstances.

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