Seismic risk mitigation of cylindrical electrical equipment with a novel isolation device

Cylindrical electrical equipment is common in substations and vulnerable in earthquakes. Isolation technique, as an important method to mitigate seismic demand, has attracted less attention in electrical substation. This study aims at filling the knowledge gap by introducing a novel isolation device for cylindrical electrical equipment. The device is a combination of circularly arranged lead alloy isolator units installed at the bottom of equipment. A 1000 kV capacitor voltage transformer is adopted as specimen, and both non-linear time history analysis and shaking table test are incorporated in examining seismic mitigation effect. Probabilistic seismic demand analysis is carried out with two set of ground motions: recorded ground motions with spectral acceleration's corner periods around 0.85 s and scaled ground motions with corner periods around 1.7 s. Results show that for recorded ground motions, the failure probabilities on both flexural moment and displacement demand are lowered significantly; for scaled ground motions, the mitigation on flexural moment demand is significant but the effect on displacement demand is negligible, revealing that mitigation effect on displacement demand is promising but more conditional on properties of input. In shaking table test, a code spectrum compatible wave is adopted as excitation, and results show that the device is successful to reduce the acceleration, displacement and stress responses by more than 50% under a 1.4 x 0.5 g PGA input. Besides mitigation effects on earthquake induced flexural moment and displacement, the isolation device also avoids residual deformation after shaking and does not increase vibration amplitudes under wind. Numerical model of the isolation device is proposed with a validation by shaking table test result, providing a useful tool for parameter design of the device. The isolation technique and device in this paper offer an important option for seismic enhancement of cylindrical equipment in substations.