The impact of cap orientation on mechanical strength of high voltage devices and a novel design for improvement

Porcelain insulators are extensively used in South Korea to support and electrically isolate components in transmission lines. In this study, 58 porcelain insulators were collected from several transmission lines in South Korea and conducted to mechanical and electrical load tests. The results showed significant variation of failure loads from 154.8 to 171.6 kN and displacements ranged from 6.76 to 20.42 mm. 88% of the samples broke on the cap part. Anderson–Darling test indicates that the failure loads due to fracture in the cap follow a normal distribution. We presumed that some of the caps experienced deterioration during their service time through work hardening of iron, crack nucleation, and propagation. Localized plastic deformation was detected right on the cap-pin contact region through finite element modeling. Hardness test results also showed strong evidence of strain hardening of the cap. An average of 390 Vickers was found in the pin-cap contact region, whereas an average of 261.33 Vickers was found in other regions. According to the Soderberg diagram, stress amplitudes above 60 MPa for 30 kN load and 9 MPa for 45 kN load induces fatigue cracking. According to numerical analysis results, the critical crack length for the 45, 60, and 75 kN tensile load cases is on the order of 1.14, 0.9, and 0.71 mm, respectively. We proposed a new pin design that would increase the pin-cap contact area by 54%, reducing the level of stresses on the cap by 35% and extending the lifetime of the porcelain insulator.