Selection of insulating materials used in SF6 circuit breakers

This presents a method and the results of evaluations of insulating materials for SF6 circuit interruption to be built under a "Single Pressure SF6 Interrupter Research" project sponsored by the Electric Power Research Institute (EPRI). In view of the high interrupting and continuous current ratings involved, selected insulating materials were tested in 135°C and 500 psig arced SF6 gas environments. The finally selected materials showed no measurable leakage current during a 300 hour exposure test and they all withstood a surface voltage stress in excess of 85 kV/inch. These tests, therefore, demonstrated that SF6 is a viable insulating medium for even higher temperature and pressure, permitting higher performance and lower costs in future switchgear applications.