New Ultra Fast Earthing Switch (UFES) device based on the vacuum switching principle

In the low and medium -voltage range the vacuum interruption principle has been well established since 30 years in series production. Based on this experience a new application of vacuum technology is being introduced for use in the medium voltage range. This paper presents the design principle and the performance of the Ultra Fast Earthing Switch (UFES) based on a vacuum insulation device. The UFES design consists of two main sections: The vacuum device and the corresponding drive section to close the vacuum device. The vacuum device is divided into two separate ultra high vacuum zones to create at the one hand a double gap between both contacts in order to enhance the dielectric performance significantly, and on the other hand to obtain redundant vacuums. The two vacuum zones are separated by applying a closed membrane between both contacts which can be opened by activating the plug contact side and breaking through the membrane to close the self-blocking contact system within less than 1.5 ms. The UFES system was developed for medium voltage application up to 40.5 kV and the short circuit current up to 63kA. Both ratings are tested in accordance to the standard IEC 62271-102 at the KEMA laboratory. Furthermore the short-circuit rating can be extended in the short-time-current (STC) of up to 3 s. The design, test results and the application in commercial solutions are being presented.