Fracture Mechanism Analysis and Structural Improvement for 1000-kV UHV Shield Ring

Some fracture failures of multiple shield rings on a 1000-kV ultra-high voltage transmission line have been found in succession. The method of reinforcing and welding at the fracture site were used to avoid crack enlargement. However, the reinforced shield rings were damaged again after half a year's use. A new approach is proposed to extract the root cause. The finite-element method is employed to calculate the static performance of shield ring for determining that the cause of the crack is not the ultimate strength failure of the material. And after acquiring the wind vibration frequency by vibration image recognition method, the critical vibration wind speed is obtained by the vortex-induced resonance analysis. And based on the critical speed, the lift force function is formed. According to the historical load simulated by lift force function, the displacement and stress response under the vortex-induced resonance are acquired by transient dynamic calculation. With the regional meteorological data of the transmission line, the probability of the wind direction and velocity within the critical vibration wind speed range is calculated out. Then, with the probability, the displacement and stress response and the vibration frequency of shield ring, the fatigue life assessment is conducted. Inspired by the idea of the energy dissipation-seismic reduction, a new type shield ring is designed. After testing the mechanical and electrical performance, the new one runs perfectly without emerging crack from November 2016, that verified the effectiveness of the design scheme for the new type shield ring.