Several oscillatory phenomena are induced by the wind in the electric and telecommunication overhead lines. Aeolian vibration is the most known of them because it is the most frequent (every overhead line is more or less affected), and because, being of relatively high frequency, without proper protection, problems of fretting-fatigue and even breakages could appear in the conductor and/or fittings.
Aeolian vibration is induced in the conductor by resonant excitation by the wind. Therefore its amplitude is governed by the balance between the wind power imparted to the conductor and the power dissipated by it, controlled by the conductor damping (selfdamping), that, in a stranded conductor, decreases with the tensile load. This is the reason why vibration is more severe (higher amplitude and frequency range) in a highly tensioned overhead line.
SAPREM ́s Stockbridge damper
IEC describes the Stockbridge damper as a system consisting of a messenger cable with two masses at its ends and a clamp that supports them; this clamp is attached to the conductor or earthwire with the purpose of reduction of the aeolian vibration on the conductor. Sure enough, starting from a messenger cable optimised for maximum dissipation with an appropriate stiffness at which ends are attached masses designed with a shape so as to obtain an inertia moment and centre of gravity such that, when vibration is induced to the clamp, modes at conveniently distributed frequencies within the frequency range of the damper design will be excited, that is, within the range of dangerous frequencies of a range of overhead line conductors. It happens that, with a high damping the resonance peaks flatten, lowering the levels and widening their frequency coverage, resulting in a wide and uniform frequency response, both in magnitude an phase, e. i., a response of maximum energy dissipation that could be adapted to the needs of any cable size and tensile load.
So can be said of SAPREM’’D5s vibration dampers whose drawings and data follows. They are asymmetrical, Stockbridge type, dampers with four resonance modes, of his own design and development. With this aim suitable laboratories were set up at his premises, with equipment for damper response research and a 40 m inside test span, fully equipped with specific instruments, even measurement of attenuation in optical fibres, for vibration testing on cables and fittings. These laboratory facilities were primarily intended for the development and performance control of our vibration dampers but they are also at the entire disposal of customers for specific testing programs.
This damper is especially designed for installation with ADSS fibre optic cables, improving the performance of the conventional stockbridge vibration damper when used with this kind of cables. It is a damper with eight frequencies,with less mass than in comparison with the conventional models and with a clamping system without bolts that minimises stress concentration. The damper is normally installed on the armour rods of the suspension clamp or the protection splice of the dead end tension set. When the damper has to be positioned directly on the cable, it is needed a set of armour rods provided on demand. It is also recommended for OPGW cables with overall diameter from 8 to 14 mm.
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