Evaluation of the effect of pressurized bushings on seismic qualification of SF6 circuit breakers

It is noted that the verification of the seismic performance of power system equipment should be performed simulating the conditions experienced by the equipment when in service. Stresses on the porcelain of high-voltage switchgear under seismic vibration are statically biased by internal pressure; however, restrictions from the seismic test facility pose some difficulties in implementing practical procedures of testing with pressure. The authors discuss the effect of pressure on the strain and propose an equivalent test method to simulate a pressurized condition without actually filling the SF₆ gas to the operating pressure. The equivalent nonpressurized test simulating the pressurized condition is possible by increasing the input motion amplitude by a small amount. The increase of the input motion amplitude is determined by the required increase in the total strain to simulate the static strain caused by the gas pressure