New seismic qualification methods for class IE switchgear and equipment

The paper describes a testing program employing biaxial, single and multi-frequency excitation to qualify metalclad switchgear following procedures recommended in IEEE 344-1975. By testing at high g levels and for a series of different RRSs immediate and future specifications are covered. Low level impedance tests were performed to gain a better understanding of the dynamic behavior of the equipment. Mechanical Impedance Modeling is used to create a mathematical model based directly on results obtained from full-scale tests, it is shown that the model accurately predicts the response Of the equipment for a multiaxis Seismic excitation. The predicted device mounting-location time-histories can be used in device testing of separate instruments. Aspects of the qualification process are Critically reviewed in the paper. These considerations are broadly applicable to all Class IE equipment.