Fatigue Failure of Insulator String of Overhead Transmission Line

Failures of insulator strings of overhead power‐transmission lines due to shearing of the ball from the pin shank have been reported. The origin of such failures has been traced to aeolian vibration of conductors. The dynamics of porcelain insulator string has been analytically studied in this paper. The results were compared with those of tests carried out. The comparison showed that under resonant vibration of the insulator, the alternating bending stresses were high enough to cause accelerated fatigue and shearing of the ball from the shank of the insulator, leading to an interruption to power transmission. Fatigue stresses in suspension insulator, though less than those in tension insulator string, are comparable to the latter. A few methods of enhancing fatigue life of insulator strings are discussed. The methods involve improving the flexibility of insulators by increasing the shank length without affecting the overall dimensions, bringing down the vibration level and the resulting fatigue stresses by damping the transmission‐line conductor.