1.Basic information
Conductor/Cable Type: AAAC FLINT
Outer diameter (mm): 25.16
Weight (kg/km): 1035.0
Rated Tensile Strength (kg): 11068
Stockbridge damper: FR-3
Maximum span length (m): 512.97
Wind speed (m/s): 8.6
Anunal average temperaature (°C): 25
2.Damping concept
Each damper is capable to transform a certain amount of vibration energy into heat, without being overloaded. As the vibration energy is increasing with the length of the span, for longer spans several vibration dampers have to be installed. In special cases, as for example river crossings, additional damping has to be provided inside the span. The damping concept gives information about the damper location, the necessary quantity of dampers considering the length of the span and the type of damper (for example messenger wire made of stainless steel, clamping range etc.) The damping concept is developed with a computer vibration study. Given the conductor and damper properties, for every installation-arrangement and span-length it is proven that the strain of conductors or optical fiber aerial cable (admissible bending strain ≤ ±150 ε/10-6) and vibration dampers remains uncritical and will not cause fatigue breakages.
3. Tronco Electric vibration dampers-effective protection against conductor vibrations
A dreaded phenomenon in overhead transmission lines is the occurrence of high-frequency, short-wave vibrations in conductors, shield wires and aerial telecommunication cables due to natural wind flow. This is caused by the periodic shedding of vortices on the downstream side of the conductors, which induces vibrations in the conductor transverse to the direction of wind flow. The frequencies are in the range from 5 to 120 Hz with amplitudes up to 1 x conductor diameter. These vibrations cause alternating bending strains in the conductor, which are superimposed on the static tensile and bending strains. This can result in conductor damage at the clamping points, ranging from fatigue breakages in single wires to breakage of the complete conductor. The vibrations spread via the suspension and tension fittings to the mast and lead to problems such as shaking out of joints to breakage of mast struts. These wind-induced vibrations cannot be prevented. Tronco Electric vibration dampers remove the wind energy from the conductor and reduce vibration stresses sufficiently to ensure a long life for the overhead transmission lines.
4.Selection of vibration damper clamp
The selection of a suitable vibration damper clamp occurs after selection of the vibration damper
type. The suitable clamp prevents excessive strain of optical fibers in a cable. For aerial cables additional protection rods are necessary. When determining the vibration damper clamp the total diameter resulting out of the aerial cable diameter plus two times the rod diameter of the protection rods has to be considered. By means of clamping tests the optimal clamp size and recommended tightening torque of the bolt are determined.
5.Selection of vibration damper
The vibration damper, i.e. it´s mechanical properties (impedance), must fit for the conductor or optical fiber aerial cable. If not, either the damper can cause damages at its clamp on the conductor or aerial cable, or the damper itself can be destroyed. The damper selection is based on the conductor size, which determines its vibration frequency range, including characteristic impedance Z
Z= SQRT(TM)
T: Everyday stress on conductor(EDS:15%-25%RTS)（N）
M: Weight per unit length（kg/m)
6.Calcalation of vibration damper
After the selection of vibration damper, we calculation the most economical damper quantity for different span length according the cable specification and normal local climatic conditions.
At the same time, in order to simplify the design and construction, we summarize a number of vibration damper for the largest span length
Fig.1 Bending strain(ε) of cable without damper at fixed point for conductor
Fig.2 Bending strain(ε) of conductor with 2 dampers at fixed point for Conductor
Fig.3 Bending strain(ε) of conductor with 4 dampers at fixed point for Conductor
Fig.4 Placement of vibration damper on Conductor
Fig.5 Installation position scheme
Span length 0-350m. Qty of damper: 1pc
Span length 350-700m.Qty of damper: 2pcs
Span length of 700-1000m.Qty of damper: 3pcs
S=1.41m. Tolerances: S±30mm
