RELIABILITY AND LONG TIME BEHAVIOUR OF MV-DISTRIBUTION SWITCHGEAR IN SEVERE ENVIRONMENTAL CONDITIONS - EXAMINATION OF SF{sub}6-INSULATED RING MAIN UNITS (RMU) UP TO 20 YEARS IN SERVICE

摘要

SF{sub}6 insulated RMUs are designed and tested for operation in severe environmental conditions and have proven its reliability on thousands of units in service since 1983. International standards give only limited recommendations of how to test switchgears for special and severe environmental conditions and which risks have to be considered for an expected life time of more than 30 years. To accumulate field experience, tests are carried out on switchgears which were operated up to 20 years in different regions in the world. Such tests include e.g. dielectric tests, mechanical tests or dew point measurements inside the SF{sub}6 compartments. One of the examined 24kV-RMU was in service continuously from 1985 to 2000 on the south west coast of Norway with salty atmosphere and has been used since 2000 also in sandy and traffic atmosphere after moving in a substation for temporary installation.