Stockbridge Damper - Wind-induced Oscillation

Wind-induced Oscillation

Wind can generate three major modes of oscillation in suspended cables:

• gallop has an amplitude measured in metres and a frequency range of 0.08 to 3 Hz;
• aeolian vibration (sometimes termed flutter) has an amplitude of millimetres to centimetres and a frequency of 3 to 150 Hz;
• wake-induced vibration has an amplitude of centimetres and a frequency of 0.15 to 10 Hz

The Stockbridge damper targets oscillations due to aeolian vibration; it is less effective outside this amplitude and frequency range. Aeolian vibration occurs in the vertical plane and is caused by alternating shedding of vortices on the leeward side of the cable. A steady but moderate wind can induce a standing wave pattern on the line consisting of several wavelengths per span. Aeolian vibration causes damaging stress fatigue to the cable and represents the principal cause of failure of conductor strands. The ends of a power line span, where it is clamped to the transmission towers, are at most risk. The effect becomes more pronounced with increased cable tension, as its natural self-damping is reduced.