Live working on vintage 138 kV steel lattice structures

Live working on very old structures often poses unique challenges, such as dealing with the effects of are rings and the behavior of old insulators. T his paper presents the results of tests conducted for Public Service Electr ic & Gas to confirm that very old broken insulators can be replaced live on 138 kV double-circuit steel lattice structures with suspension I-strings. Each string had nine porcelain units and two large are rings with a clear a ir ring-toring distance of 1.07 m (42 "), Issues addressed in this paper in clude: The effects of broken and shorted insulators The effects of live working tools and workers The possibility of selective barehanding For the above-listed conditions, switching impulse tests were performed on a full-scale mockup of the structure. Actual hardware retrieved from servic e was used for the mockups, Workers were represented by mannequins, The pap er gives switching impulse test results for the outlined conditions. Test d ata suggest that there is little difference between broken and shorted insu lators in the tested cases, However, the CIGRE formula for calculation of t he effects of defective insulators is shown to be sufficiently conservative .