A study on assessment of a fatigue life for a dropper in high-speed overhead line

초록

The main problems of increasing the speed of electric railways are related with tracks, vehicles, and overhead contact lines. Overhead contact lines compose the main interface to supplying power to vehicles through pantographs installed above the roof of electric trains. Specifications are maintained during the design process by considering electrical power supply capability and mechanical properties. Overhead contact lines are consisted of contact wires that supply power to vehicles by direct contact with a pantograph, messenger wires that suspend contact wires using droppers, hinged brackets that support messenger wires, and other supporting structures. Tensile load is constantly applied to droppers due to mass of contact wires. As a vehicle passes through points where droppers are installed, droppers are slackened because of uplift caused by pantographs lifting up contact wires. After pantographs pass by, droppers are tightened again by contact wires' fluctuation load. Since droppers are exposed to fluctuation load, fracture problems occur. About 55 sites had problems caused by dropper damage during the last 4 years starting from the opening of the Kyungbu High-speed Railway which is operated with speeds of 300km/h. Therefore, estimating and assessing the fatigue lifetime of high-speed railway droppers is essential. In this research, a P-N curve was obtained by conducting fatigue tests of the droppers used on the Kyungbu High-speed Railway with a developed fatigue tester. Fluctuation load applied to droppers with conditions of span length and vehicle speed was also estimated through a developed overhead contact line / pantograph simulation program. Then the estimated fluctuation force was simplified by rainflow cycle counting. The fatigue life of Kyungbu High-speed Railway droppers was assessed by applying the simplified force and the acquired P-N curve to Miner's rule.