Disconnector switching in GIS: Three-phase testing and phenomena

Certification tests in accordance with the requirements of the recent IEC 6 1259 standard for switching of bus-charging current by disconnecters of a ( three-phase enclosed) 145 kV gas insulated switchgear (GIS) are described. These tests are primarily aimed at verifying that the discharge between the disconnector contacts does not introduce internal are faults. Special emph asis is given to the high-frequency measuring system, used to verify a suff iciently severe waveshape of switching transients in the MHz range. Three-p hase tests were performed, showing phenomena that were not demonstrated in practice before: First, it was shown that phase-to-phase voltage transients with a higher am plitude than the phase-to-ground values do actually occur. Second, the phas e-to-phase capacitive coupling of the busbar system could raise the trapped charge, left after at the load side of the installation after disconnectio n, to values above 1 pu. In addition, measurements of induced voltages in the secondary system are r eported.