The subject invention is directed to a vibration dampener and a method of installing the same.
The invention is especially suited for use on electric power lines and will be described with particular reference thereto; however, as will become apparent, the invention is capable of broader application and could be used on a variety of aerial cables, quy wires and the like.
Under certain wind conditions, and especially when accompanied by icing, aerial electric power lines or cables are sometimes subjected to a phenomenon commonly called "galloping". Galloping is a low-frequency, high amplitude motion of the lines. When it becomes severe, it can cause damage to the electrical conductors, the supporting structures and support hardware.
A somewhat parallel phenomenon is known as aeolian vibration. This is a higher frequency, lower amplitude vibration than that generally associated with galloping. As a smooth stream of air passes over a cylindrical shape, such as a power line, alternating vortices are formed which create alternating pressures that tend to move the power line at right angles to the direction of air flow. It is this mechanism which causes aeolian vibration.
Aeolian vibration can, over a period of time, damage the system in somewhat the same manner as galloping. Consequently, there has been a constant and ongoing interest in developing methods and apparatus for suppressing both galloping and aeolian vibrations.
A device has recently been developed which suppresses galloping and significantly reduces aeolian vibrations. The device comprises a non-metallic rod having a length in a range of approximately 10 to 18 feet. Each end of the rod has a multiple turn, helically configured gripping section designed to tightly fit and grip a relatively narrow range of wire or cable diameters. The midsection of the rod between the helical end portions is generally straight.
In installing the device, the installer first wraps one helical end section into gripping relationship with the electrical cable. He then moves to the opposite end of the device and wraps the entire straight midsection of the rod at least twice around the cable to produce a long, slow helix wrap. Thereafter, the second helically configured end section is wound tightly into gripping relationship with the cable.
The long, slow helix wrapped midsection of the device acts to vary the aerodynamic profile of the cable and increases the aerodynamic stability of the cable. When the total cable span has the devices applied thereto, cable galloping and aeolian vibration are eliminated or significantly reduced.
Devices of the type discussed have proven highly desirable for the purposes described. However, one of the problems with the devices has been certain installation difficulties. Specifically, because of their significant length and relative flexibility, they are somewhat difficult to hold in position as the first gripping helix is wound in place on the cable. In addition, after the first end is installed, the entire rod dangles and swings as the installer moves to the second end to complete the wrapping and the attachment of the helically configured gripping section at that end. Since the installations are often made at substantial elevations using trolleys and personnel lift equipment, the dangling, swinging rod can present special problems and slows down the installation process.