Modern Designs
Modern designs use metal bell-shaped weights rather than Stockbridge's concrete blocks. The bell is hollow and the damper cable is fixed internally to the distal end, which permits relative motion between the cable and damping weights. To provide for greater freedom of motion, the weights may be partially slotted in the vertical plane, allowing the cable to travel outside the confines of the bell. In some installations, the weights are unequal, allowing damping over a greater frequency range. More complex designs use weights with asymmetric mass distribution, which enables the damper to oscillate in several different frequency modes.
The most vulnerable section of the cable is where it is clamped to the end of an insulator string, so dampers are typically installed at the nearest anti-nodes (points of maximum oscillation) either side of the clamp. There are thus normally two dampers per span, though more can be installed if necessary on longer spans.
Overhead transmission lines form a catenary for which vibration is predominately in the vertical plane. When more than one plane of vibration is anticipated, Stockbridge dampers may be mounted at right angles to each other. This is common when the cable runs in a vertical or off-horizontal plane, for example in cable-stayed bridges or radio mast guy-wires.
Read more about this topic: Stockbridge Damper
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