Abstract
The malfunction of induction disk type relays under earthquake conditions is caused by rotation of the disks induced by seismic excitation. The rotation of the disk results from torques generated by friction forces between the thrust bearing supporting the pivot at its bottom and the lower end of the pivot whirling in the bearing due to seismic excitation. This mechanism of malfunction was revealed by the authors and analysed in the former paper. In this paper, modification of the shapes of the bearing and the lower end of the pivot is proposed, to reduce the torques. The effectiveness of the modification was verified by both excitation tests and theoretical analysis. Furthermore the maximum accelerations of seismic excitation inputs having various dominant frequencies which did not cause the malfunction were investigated by analysis, and it was shown that an improvement of 1.3∼2.0 times in the maximum accelerations was obtained by the modification.
