Vibrations and oscillations caused by laminar wind flow may occur on overhead transmission lines and can lead to damage to conductors, conductor fittings or towers. In order to reduce these vibrations and oscillations to a non-critical level, vibration damping systems are installed on transmission lines.
STOCKBRIDGE 4-R vibration dampers
These vibration dampers are used to suppress wind-induced vibrations, known as Kármán or aeolian vibrations. Depending on the type of conductor or ground wire, various damper models are available and, upon customer request, can be supplied with hot-dip galvanized or stainless steel messenger cables, hot-dip galvanized or stainless steel bolts, with or without breakaway heads.
Spacer dampers
Spacers maintain the required distance between bundled conductors. When both wind-induced vibrations (aeolian vibrations) and oscillations of conductors within the bundle are expected, spacer dampers must be used to reduce vibration amplitudes. In this context, various spacer damper models are available (bolted clamp type, Nutcracker type) with different conductor bundle spacings.
Long-wavelength oscillations, i.e. conductor galloping, may particularly occur in winter due to the formation of ice crystals on conductors. When such ice begins to melt or shed, differential tensile forces are created in the conductors, resulting in galloping oscillations with amplitudes of several metres. For this reason, interphase spacers must be installed to prevent conductors from colliding with each other, which, in the case of conductors of different phases within a span, could lead to severe and costly outages. Interphase spacers therefore ensure continuous and reliable power transmission without failures. They are installed in overhead line spans where there is a risk of conductor galloping. Essentially, interphase spacers are available for single conductors, as well as for bundles consisting of two, three, four or more conductors.
BRETELLE (BATE) dampers
These aeolian vibration dampers consist of a defined length of conductor (similar to the main conductor) installed within the span below the suspension strings and connected by so-called Bretelle clamps to each adjacent span. For large spans, such as river and fjord crossings, so-called FESTOON systems are used, consisting of multiple interconnected Bretelle dampers and extending over more than 50 metres of the span. We manufacture forged Bretelle clamps for phase conductors and ground wires, in both open and closed designs.
Interphase spacers
One of the key functions of conductor fittings on overhead lines is the long-term protection of conductors and ground wires. Airflow acting on conductors can induce vibrations which, in the worst case, may cause conductors to collide, resulting in short circuits that can severely damage overhead line conductors.