iUnswitch Air Insulation Ring Main Unit

Air Insulation Ring Main Unit

Air Insulation Ring Main Unit

Medium Voltage Switchgear

Model Number: UN-Panel

Up to 24 kV-1250A-25kA

Product Description

Air Insulation Ring Main Unit

RMU, the light flexible switchgear developed as a modular, simple to apply design, with fewer components, providing a high reliable, quality and safe product for you, our Customer. By reducing the number of components, utilising modern materials correctly, we have developed an environmentally and user friendly product. The simple design and construction of will stand the test of time for generations to come.
RMU, is an air insulated (AIS), metal enclosed, switchgear cubicle design of the next generation developed through continuous innovation and vision to meet the changing market needs.
RMU, provides long-term technical solutions for various applications. Safety, user friendliness and environmental con- cerns have been the driving force in the development of the switchgear.



RMU, product provides our Medium Voltage Customer with the best solution for heavy duty switchgear in a size only a little than a single tank Ring Main Unit while including:

  • the flexibility in meeting our Customers specification and accomodating on future change and upgrading
  • the options include complete control, measuring and protection systems

RMU, Air Insulation Ring Main Unit Construction

Metal enclosed switchgear

iUniswitch Air Insulation Ring Main Unit

RMU, Air Insulation Ring Main Unit

  • Busbar compartment

The busbar compartment is located on the top of the cubicle. This compartment contains the main busbars that intreconnect between switchgear cubicles.

  • Switching compartment

A 3-position SF6 switch disconnector with epoxy cast resin housing is provided with inspection windows and available also with gas density indicator.

  • Cable compartment

75 % of the space in the switch disconnector cubicle is reserved for power cable connection making it possible to use both 1- and 3-phase cables with most simple unscreened terminations. Space is also adequate for cubicle accessories such as surge arresters, current transformers, second earthing switch etc. The door has an inspection window and safety interlocking as standard. For cable entry there are 3 individual cable gland plates in the bottom with support for a suitable dimensioned cable clamp. The bottom and the threshold of the cubicle can be removed for ease of cable installation.

  • Mechanism, interlocking and low voltage compartment

Behind a hinged door (which serves as control panel) are located the spring operating mechanism with position indicator and the mechanical interlocking unit. There are also facilities for cubicle accessories such as: auxiliary contacts, tripping coil, emergency tripping mechanism, capacitive voltage presence indicating system, key interlocks and motor operating device. Space is also provided for control circuits and measuring instruments as well as a protection relay. In the 750 wide cubicles there is also a second indentical compartment for further accessories.


The upper part of the cubicle, including the busbar compart- ment, the switch disconnector and the mechanism and low voltage compartment is separated from the lower part and the cable compartment. Because of this it is possible to carry out maintenance, repair and upgrading of the unit in the lower module while the switchgear is in service.


RMU, Air Insulation Ring Main Unit Construction


Top unit

  • 3-position switch disconnector
  • Operating mechanism with mechanical position indication
  • Enclosure of busbar compartment
  • Integrated low voltage compartment for secondary components
  • Interlocking unit
  • Busbars
  • Control cable ducts

Bottom unit

  • Enclosure
  • Circuit breaker (fixed version)
  • Current transformers
  • Earthing switches
  • Voltage transformers
  • Cable entry with cable support

Cubicle Types / Cubicle Program

  • Switch Disconnector Cubicle, type SDC
  • Switch Disconnector with Fuse, type SDF
  • Circuit Breaker Cubicle, type CBC
  • Withdrawable Circuit Breaker cubicle, type CBW
  • Sectionalising Cubicle, type SEC
  • Bus Riser Cubicle, type BRC
  • Sectionalising cubicle with Fuse, type SEF
  • Sectionalising Breaker Cubicle, type SBC
  • Direct Busbar connection Cubicle, type DBC
  • Sectionalising Withdrawable Breaker cubicle, type SBW
  • Sectionalising Metering cubicle with Disconnector, type SMD
  • Bus Metering Cubicle, type BMC
  • Sectionalising Metering Cubicle, type SMC
  • Universal Metering Cubicle, type UMC

Air Insulation Ring Main Unit Technical data

Rated voltage Ur kV 12 24
BIL common value kV 75 125
across the isolating distance 85 145
AC withstand voltage common value kV 28 1) 50
across the isolating distance 32 1) 60
Rated frequency Hz 50/60 50/60
Rated current busbar A 630/1250 630/1250
feeder A 630/800/1250 4) 630/1250 4)
Rated short-time withstand current main circuit kA 25 20
earthing circuit kA 25 20
Rated peak withstand current kA 65 50
Rated duration of short circuit s 1 1
Arc-fault current, 1s kA 20 20
Degree of protection, enclosure IP2XC IP2XC
Degree of protection, partitions IP2X IP2X
Ambient temperature maximum value [oC] 40 40
maximum value of 24 h-mean +35 35
minimum value -5 3) -5 3)
Altitude above sea level [m] <1000 2) <1000 2)

1) Higher values in accordance with national standards on request

2) Adjustment is necessary for greater altitudes

3) Lower ambient temperature on request.

4) 1250 A = CBW, SBW, BRC, DBC