Galloping Control Permits Tower Head Compaction and Line Upgrading

Abstract

Galloping of overhead lines due to ice and wind often results in damage and power interruptions. Control devices are being evaluated in field trials in many utilities world-wide and data based on performance have accumulated to the point where control is verified for some devices. This paper describes approaches to modifying existing transmission tower head design methods to incorporate the benefits of these controls. This allows use of longer spans and shorter towers, reducing the cost of new lines. It also provides opportunities to upgrade existing lines by retrofitting the control devices. The data from galloping observations with no controls, combined with records of actual outage rates, permit better quantification of reliability associated with line exposure and clearance between phases. Where existing practice is shown to be conservative, savings are possible in future lines through smaller clearances, even with no controls. Incorporation of controls will then offer even further savings. The field data indicate that bundle conductors are much more likely to gallop at maximum amplitude than single conductors. Consequently, there is a need to rationalize the galloping ellipse sizes so that there is a similar level of reliability on the two types of lines. An example is included where a line is built to present clearance standards but future higher security operation can be assured through add-on galloping controls.