Ring Main Unit

CCC, ISO9001
Shell Material
Stainless Steel
Voltage Level
Medium Voltage
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The RMR series is completely insulated SF6 Ring Main Unit, This product is in conformity with the standards the GB/IEC standard and the design of a high safety combined switch cabinets. One of the main components of circuit breaker and load break switch, high technical level, superb technology, stable performance, safe and reliable operation.

RMR series SF6 Ring Main Unit will take several functional units and connecting busbar assembly in sealed SF6 gas box, without any live parts exposed, with advantages completely insulated. Live parts maintenance free, small volume, compact structure,  convenient operation etc. . The stainless steel plate of cabinet with 3.0mm thick , which can effectively prevent moisture, corrosion caused by salt spray; Products passed the breaking and making test, dynamic thermal stability test, sealing test and mechanical test etc, the maximum guarantee the safety of persons and equipment. The cabinet is suitable for indoor and outdoor installation, and it is not affected by the external environment, with high performance of anti harsh environment

RMR series SF6 Ring Main Unit is widely used in industrial and civil ring network distribution system and power supply terminal, especially suitable for small Secondary distribution substation, urban residential district, and other places

Standards and specifications

Switchgear manufacture

The switchgear complies with the following specifications in accordance with relevant IEC publications:

----IEC62271-200 ----IEC62271-100

----GB3804-2004 ----GB3906-1991

----GB16926-1997 ----GB/T11022-1999


Normal operating conditions Design to relevant standard, with the following limit values:
a)Air temperature: ±40℃; Daily average ≤25°C
b)Altitude above sea level: Maximum installation altitude: 4000m c)Wind: less than 35m/s;
d)Earthquake intensity: no more than 8 degrees;

Main new advantages of RMR

3.1Main new advantages of RMR


Ring Main Unit

RMR use SF6 – gas (Sulphur hexafluoride) as insulation and quenching medium.


Ring Main Unit

The SF6 is contained in a welded stainless steel tank, which is sealed for life.The pressure system is defined as a sealed for life system with an operating life time exceeding 30 years. The leakage rate is less than 0.1% per year. In order to ensure a reliable and tight welding, all welding work is carried out by computer controlled robots. Electrical and mechanical bushings penetrating the tank are clamped and sealed to the tank by high quality O-rings. The mechanical bushing has in addition a rotating shaft which connects the shaft of the switch to the corresponding shaft of the mechanism. The rotating shaft is sealed by a double set of gas seals. All SF6-tanks have to pass a leakage test before gas fill-ing. Leakage test and gas filling are done inside a vacuum chamber. The first step in the leakage test is to evacuate all air inside both SF6-tank and vacuum chamber simultaneously. Then the SF6-tank is filled with Helium. Due to the characteristics of Helium this test will detect all possible leakages. If the SF6-tank passes this test, the Helium will be evacuated and replaced by SF6.The SF6-tank has a degree of protection of IP65 and can be immersed into water and still maintainable functions in a satisfactory way.

Switch Device

Wide selection of reliable quality switching products are avaiable,the load break switch,vaccum circuit breaker.

4.1 Load break switch

The load break switch is a 3-position switch disconnector and earthing switch using SF6 gas as an arc quenching meduim,the switch positioning is close-open-earthed. In the open position the switch satisfies the disconnector requirements

3-position load break switch (closed,open,and earthed)

Spring mechanism consists of single spring

action, double spring operating mechanism. Among

them, the double spring operating mechanism used in

switchgear unit, can realize the automatic tripping trip.

Ring Main Unit

4.2 Vacuum circuit beaker

RMR Vacuum circuit breaker has vacuum bottles as

interrupters of the current.In series with the

circuit-breaker main circuit is connected a 3-position

disconnector/earthing switch. The operation between

vacuum circuit breaker and disconnector/earthing

switch is mechanically interlocked.

Compact, simple structures and safe operation.

Ring Main Unit

4.3 Fuse

By means of tripping device it operates as a switch-fuse combination. Two earthing switches are equipped in both sides of the fuse-links in order to ensure the personal safety of operators.

Both earthing switches are operated in one operation.

The switch-fuse and earthing switch is mechanically

interlocked to prevent unauthorized access to the


The lower cover which gives access to the fuse-link is

also mechanically interlocked with the earthing switch.

The fuse holder is sealed tightly,so it is anti electirc dust

and moisture.

Ring Main Unit

Note: Fuse selection for transformer protection selection refer to IEC fuse standard.

The accessories

5.1Gas pressure/density meter

Ring Main Unit

Ring Main Unit

Density meter with Low voltage pressure alarm

General density meter

Each tank of RMU is equipped with density meter to monitor the gas pressure inside. The pointer of the meter is in the green area, that means the normal pressure in the gas tank, if the pointer is in the red zone, it means the pressure of the tank is low. It is required to periodically inspect the density meter, to ensure the pressure in the normal range. Additionally, density meters with low pressure alarm is also available as an option. The meter is provided as the customer specified.


Type C Bushing

Type C Bushing

The connection of the HV-cables is made by cable Type C bushings. See right side pictute. The Type C bushings are made of cast resin epoxy with moulded-in conductors.This C type is used together with full-screened elbow cable connectors which is an ideal solution for areas with humidity or condensation problems is achieved

Ring Main Unit

Voltage indicator

Each unit is equipped with voltage indicator with phase check outlet,which feature:Stable performance,High brightness, Wide viewing angle,long life.

Ring Main Unit

Fault indicator

Fault indicator is provided as an option Fault indicator for detection of a short circuit, single phase earth fault. Accurate detection and clear indication.

Ring Main Unit

Above components of RMU is standard equipped, any special requirement pls consult us.


CT/Zero sequence CT

CT/Zero sequence CT are provided according to the customer’s requirement. a.Installed on external bushings when need.CT should be earthed reliable,and open circuit of secondary side is not allowed,or it will lead to severe damage to the equipment and even dangers to the individuals.

Ring Main Unit


Elbow cable connector and relevant accessories

-Frontal Elbow Cable connectors
-Copper conductors
-Press cores
-Copper lugs
-Additional back cable connector optional

-Additional elbow connector type surge arrester

Ring Main UnitRing Main Unit

Ring Main Unit

Operating Handle

The operating handle has two sides,for both Load break switch,circuitBreaker,and earthing switch manual operation,

Ring Main Unit


Protection relay

RP260 protection device is numerical protection relay
with self-powered.
-OC/EF protection
-Fault report
-UV/OV protection
-Frequency protection
-Other required is discussable

Ring Main Unit

Dimension of Outdoor application RMU

Ring Main Unit

Ring Main Unit

Above is dimension for three unit combination, all the dimension about CCC, FFF,CCV, VVV,CVV, CFV, FFV, CCF is same.

Extension way by top connection

Ring Main Unit

For normal Ring main unit combined by three unit together, above picture reference is shown us.If special required more, pls consult us.



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