Study of the effectiveness of steel cable dampers for the seismic protection of electrical equipment

This paper deals with the problem of the seismic protection of high voltage electrical equipment by using steel cable dampers (wire-ropes). The wire-rope isolators, often used in shock and vibration problems, are here proposed as seismic isolation devices. The main results concerning an experimental campaign devoted to the identification of the mechanical characteristics of these devices, are illustrated and discussed. In particular, experimental tests, carried out on six different isolators and consisting of imposed harmonic displacements, have shown an asymmetric behaviour of the devices along the vertical direction (tension-compression) and a symmetric behaviour along the main horizontal directions (Shear, Roll). Moreover, the cycles are independent of excitation frequency and fully dissipative, which corresponds to have high values of damping ratio. Subsequently, using the classical Bouc-Wen model properly modified, the cycle behaviour of the isolators has been modeled and the relative parameters have been identified. Finally, the seismic response of a 420 kV circuit breaker, equipped with four wire-rope isolators, has been evaluated: the results confirm the high efficiency of the wire-rope as base isolation system.