Design of an Integrated Mechanical Fatigue Test Apparatus for S-Bend Busbar

An integrated test apparatus was designed and constructed in a cryostat in order to qualify the performance of high-voltage (HV) insulation on a mockup ITER TF feeder S-bend (S-shaped) busbar after mechanical fatigue tests at room temperature and low temperature, respectively. The force generator was designed and developed with a hydraulic cylinder as a source of cyclic load. The traveling distance of the hydraulic cylinder can be adjusted between 10 and 100 mm in order to meet different displacement requirements. The fatigue tensile load is transmitted by a reciprocating ball-end shaft at the free end of the S-bend. Welded diaphragm bellows was applied as a flexible vacuum envelope for the transmission rod. The fatigue test displacement and the stretching frequency were set according to the theoretical analysis result. The leakage current in the hipot test of the S-bend busbar after thermal and mechanical cycles was 13.7 μA at 30-kV dc, less than the ITER requirement of 60 μA. The integrated test apparatus has been fully commissioned and is ready for the qualification tests of the HV insulation of the ITER S-bend busbar affected by mechanical and thermal fatigue loads.