Experimental studies of fatigue strength and surface electrical resistance of aluminum wire of overhead power transmission lines

Abstract

The effect of wind on the wires of overhead transmission lines leads to their vibration, as well as oscillations of different amplitudes. At places where the wire is suspended, damage to the metal structure of the fatigue type occurs. This is an excessive number of vacancies, dislocations, grain boundaries and blocks compared to the equilibrium one. The defective structure degrades in the direction of the formation of micro-gaps and cracks. The generation and development of the damage zone occurs from the surface of the wire. To prevent a rupture, it is necessary to monitor the development of this zone during the operation of the line without dismantling the wire. To improve the accuracy of assessing the level of accumulation of fatigue damage, the limiting states of the wire, it is recommended to develop methods based on measuring the electrical resistance of the wire material during the development of fatigue damage. A method for monitoring the state of the surface layer by measuring electrical resistance at high frequencies is proposed. The thickness of the controlled layer is determined by the frequency of the measuring signal due to the presence of a surface effect. For effective control, the depth of penetration of the field into the conductor must be commensurate with the thickness of the defective layer. For experimental research, samples were taken of a new wire and wires after various periods of operation on existing lines. According to the results of static tests, the tensile strength and the degree of nonlinearity of the tensile curve were determined. The results of experimental studies of fatigue strength and surface electrical resistance of a separate aluminum wire of A50 conductor are presented. The samples were tested for fatigue under loads close to the conditional endurance limit. The surface resistance of the wires was measured before and after fatigue tests in the frequency range 200 Hz – 2 MHz. The studies have shown the dependence of surface resistance on the degree of development of fatigue damage, which can be used to diagnose the accumulation of fatigue damage.