Extreme bending of composite insulators on 750 kV compact transmission lines

In designing and constructing the first 750 kV double-circuit compact transmission line, much pioneering work is necessitated in the choice of tower, insulator strings and phase-to-phase spacers. In this paper the mechanical characteristics of three possible phase-to-phase composite spacers for such compact transmission lines are considered in respect of very large bending of the spacer. A large deflection theory is introduced to calculate the lateral deflections and longitudinal compressions caused by applied axial loads and these are compared with the results of tests on three spacers of different lengths and diameters. Agreement between calculation and test results was good and the necessity for the larger diameter demonstrated. No permanent damage due to the extreme bending was found and two of the spacer samples were found to be suitable for use in the compact transmission lines with a good safety margin in respect of such bending.