Ring Main Unit (RMU)


Susol RMU (12/17.5/24kV)
Susol Ring Main Unit is a compact and comprehensive solution for secondary power distribution networks up to 24kV which leads numerous applications for wind power plants, small industries, buildings, mining, airports and underground installations where require only a little maintenance and minimum spaces.



  • Metal enclosed unit for indoor installation and type tested.
  • Insulated by SF6 gas.
  • Maintenance free and easy installation.
  • Independent of climate.
  • On-Off-Earth, three position load break switch.
  • Recyclable materials used.Safety
  • Approachable and operable safely in the presence of power in the cables.
  • Clear indication of operation status via mimic diagram on front panel.
  • Fully automatic interlocking system.
    • Operation is only possible in case door is totally closed.
    • Fuse compartment is only accessible when Load break switch is earthed.
    • Voltage detector to check whether cables are lined or not.
  • Rupture disk is designed to protect devices in case of emergency like gas expansion.
  • Internal arc withstand is tested for the operator safety in case of accident current occur. (21kA/1s,, without SF6 gas)

Durability and Usefulness

  • Metal enclosed tank is hermetically sealed. It means this is independent of environmental effects such as dirt, small insects, moisture and so on.
  • Load break switch operating is possible in the front of Ring Main Units.
  • All switching operations can be made safely to personnel because of interlocking system that operates automatically according to the switch position by the operator.
  • No requirement of recharging SF6 gas until its service life.
  • Remote operation available in case of using motor operating mechanism and FRTC.
  • HRC power fuse will trip the mechanism automatically by a fuse striker pin connected to mechanism in the event of fault happening.

Saving Cost

  • No maintenance is required other than replacement of HRC Power Fuse after installation.
  • Compact design that requires minimum spaces to install and operate locally is main advantage especially where the space is limited.
  • No additional costs for replacement because of long service life.
  • Materials can be recycled after the end of its service life.Characteristics


Compact LS Susol Ring Main Unit is designed compactly, which makes RMU operated easily.
Easy Access & Maintenance Every operation part is located at the front
Safety Mechanical automatic interlocking system is applied

Field application

Susol RMU is enable to install on medium voltage distribution network and is mainly used for protection of transformers in compact substations. It is used for medium voltage distribution in compact substations, small buildings, residential housing complex, large shopping malls, airports, subway stations, etc. comprising medium voltage networks.



Rated Voltage kV 12 17.5 24
Rated frequency Hz 50/60 50/60 50/60
Rated power frequency withstand voltage kV 28 38 50
Rated lightning impulse withstand voltage kV 75 95 125
Rated current main busbars A 630 630 630
Rated short-time withstand current (3s) kA 21 21 21
Rated short-circuit making current kA 54.6 54.6 54.6
Internal arc fault current (1s, AFAL) kA 21 21 21
Rated SF6 gas pressure Psi.G 5 5 5