Metal Ring Main Unit

A Ring Main Unit (RMU) is a totally sealed, gas-insulated compact switchgear unit. The primary –switching devices can be either switch disconnectors or fused switch disconnectors or circuit breakers. Different combinations of these primary switching devices within the unit are In case a circuit breaker is the switching device, it is also equipped with 'protective relaying, either with a very basic self-powered type or a more advanced one with communication capabilities. The rated voltage and current ranges for RMUs typically reach up to 24 kV and 630 A respectively. With many of the manufacturers of RMUs, the basic construction of the unit remains the same for the whole of the voltage range. The increase in rated voltage is handled by an increase in the insulating gas pressure.