Eswari Electricals Private Limited

Pro Plus SF6 Ring Main Units

Eswari PRO PLUS gas insulated Ring Main Unit (RMU) incorporates the most modern technology which are best suitable for secondary distribution network applications up to 24kV.

Pro Plus RMUs are available in multirange such as.

Extensible/non-extensible type.


non-automation/ automation compatible/ smart RMU.

indoor and outdoor applications.

The automation compatible units are now readily available with Remote terminal Units (RTU) for integration with the existing smart grid and automation systems.

Standards – Pro Plus SF6 RMU

IEC 62271 – 100 Alternating current circuit breakers.

IEC 62271 – 102 Alternating current disconnectors and earthing switches.

IEC 62271 – 103 Switches for rated voltages between 1kV and 52kV.

IEC 62271 – 200 AC metal enclosed switchgear and control gear.

Types of RMUs

Oil Ring Main Units.

Air insulated Ring Main Units (Conventional).

SF6 insulated Ring Main Units.

Solid Ring Main Units.

Why SF6 gas preferred ?

Due to SF6 gas high dielectric strength it is best to use as an insulating medium in MV and HV switchgears.

It insulates 2.5 times better than air (N2),

Its over 100 times better arc quenching capability than air (N2).

Its has better heat dissipation than air.

SF6 insulation ensures complete freedom from oxidation of components.

For MV equipment sealed for life no replenishment is necessary because of the SF6 unique quality that no degradation occurs under normal operating conditions.

SF6 gas hazardous ?

Pure SF6 is physiologically completely harmless for humans and animals. It’s even used in medical diagnostic.

According to clause 7.1 of IEC 60480: “In principle a mixture of 20% of oxygen and 80% SF6 can be inhaled without adverse effect. Concentrations above 20% would cause suffocation due to lack of oxygen.

If larger quantities are inhaled directly may irritate the lungs causing coughing and/or shortness of breath.

Legislation for chemicals does not categorise SF6 as a hazardous material.

Benefits – Pro Plus SF6 RMU

Local operator safety

The total enclosure of all live parts provides immanent protection against electric shock and minimises the risks associated with human errors.

Very high operational reliability

The conducting parts are insensitive to the outside environment.

SF6 insulation ensures complete freedom from oxidation for the contacts and screwed joints, which means that there is no gradual reduction in the current carrying capacity of the equipment as it ages.

Important contribution to the security of supply

Gas- insulated switchgear completely eliminates this possibility of contamination, e.g. dust from industry or agriculture or saline deposits in coastal areas throughout the whole service life of an installation.

In contrast to air insulation, whose insulating capacity reduces with increasing altitude, SF6-insulated switchgear retains its full insulating capacity regardless of height above sea level.

Distinct economic benefits

Minimal maintenance expenditure due to maintenance-free, gas-tight enclosures.

RMUs are the prerequisite for remote control and automation of power networks.

Small Space requirement

Due to the high dielectric strength of the gas, the switchgear is compact with space requirements minimised.

In several cases SF6 switchgear is the only possible solution: for wind power plants (offshore), for large generator circuit-breakers, and for extensions of existing installations.

Ecological and economic benefits

Minimum transmission losses as a result of placing equipment close to load centres.

Reduced primary energy consumption and emissions contribute to economically optimised power supply systems.

Long service life of SF6 switchgear also contributes to the conservation of resources.

Aesthetic benefits for rural and city landscapes

Integrated seamlessly in any landscape or architecture of towns, cities or countryside.

Reclamation of areas previously taken up by conventional substations.

Applications – Pro plus SF6 RMU

Secondary distribution lines & compact substations.

Solar & wind power plants.

Commercial and residential buildings.

Industries such as mining, steel, cement, petroleum, etc.,

Airports & Underground metro railways.

Eswari Electricals Private Limited

Salient Features – Pro Plus SF6 RMU

Easy installation and commissioning.

Simple operation & maintenance.

Three position switch (ON, OFF & Earth).

Single stainless-steel tank up to 5 switching functions.

Space saving spatial footprint.

Scada/Distribution automation ready units.

Broader cable compartments facilitate dual cable terminations.

Hermetically sealed SS tank insensitive to outside environment.

Enhanced arc test 21kA/3sec rated for AFLR (operator safety from the front, side and rear protection).

Long service life .

Voltage presence indicator.

Padlocking facility for all operations.

Market – SF6 RMU

Although overhead power lines are typically more economical, they are susceptible to damage from wind-borne tree branches, debris, high wind and extreme weather conditions. The damages can cause extended power outages that in extreme cases cannot be restored for days. The cost for repairing the physical damages can be very high.

These tangible and intangible impacts makes the electric utility industry’s to move for underground cable in secondary distribution networks.

Overhead power lines are easily tapped, rerouted or modified to serve customers. To achieve the same in UG installations Ring Main Units plays the vital role.

As most of the proposed distribution networks are UG and there are many utilities now converts their existing overhead to UG wherever possible, the RMUs are going to be the essential equipment in the electrical network.

RMU manufacturers in Indian Market

Eswari, Schneider, Siemens, Lucy, C&S, ABB, Eaton (new comer),


For decades, the unique properties of sulfur hexafluoride (SF6) have made it popular as an insulation and switching medium for electrical switchgear. However, SF6 is a potent greenhouse gas.

Henceforth the alternatives may arise such as solid RMUs or Airplus (fluroketone gas mixture) RMUs which are in pilot studies in the future.

But as of now

”A combination of extraordinary electrical, physical, chemical and thermal properties makes SF6 a unique and indispensable material in electric power equipment for which there is no functionally equivalent substitute.”