Completely insulated SF6 Ring Main Unit 12kV 24kV 40.5kV

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