I recently spotted an arrangement of wires on a lightning arrester on top of a power line. The power line is IIRC a 110 kV, 16.7 Hz, two phase line for railway systems.
The lightning arrester is of a linear type on top of the power line arrangement.
The device attached to the lightning arrester seems to consist of two short pieces of rigid wire wound around the lightning arrester itself. They form a helix with increasing radius to the middle of the arrangement. Between the ends of the helices there is a distance of perhaps 10 cm I think.
The helices seem to be fixed to the arrester just by their winding radius at the outer ends.
It might be that these devices may perform a similar task as a stockbridge damper, but this doesn't explain why only the lightning arrester is equipped with them.
There were three or four of these mysterious wire couples between two power poles.
On the picture you can see the lightning arrester on top with one of these arrangements and one power line (much thicker) below.
What could be the purpose of these devices?
Best Answer
These devices appear to be for gallop arresting. Long wire/cables (even structures) are subject to high-amplitude, low frequency vibrations that can cause self-destruction. These vibrations occur in the presence of generally gentle winds of just the right velocity.
Factors such as the cable length, material, jacketing can affect its sensitivity to this affect.
My guess, in your case, was the engineering analysis indicated the lightning arresting cable was of a design that was subject to this gallop effect, while the power lines were not.