Fatigue Failure of Vacuum Interrupter Bellows in Vacuum-type Metal-enclosed Gas-insulated Switchgear

Abstract

The bellows of a vacuum interrupter (VI) become the most vulnerable components when the VI is introduced to comprise a dead-tank fast vacuum circuit breaker (FVCB). However, there is no work revealing the optimal design of VI bellows subjected to high gas pressure and high operating velocity in achieving a high mechanical endurance. The objective of this paper is to confirm the optimum design parameters of bellow structure, which would be subjected to a high gas pressure and high operating velocity. We adopted a transient fluid-structure coupled simulation method, as well as a fatigue failure simulation method, to obtain the dynamic strain-stress distribution and the fatigue life of the bellows. The U-shaped VI bellows used in the simulation were kept the same as those in the FVCB, which was with stainless-steel. The compressed length of the bellows was configured to be 30.00 mm corresponding to the rated contact gap of 30 mm for the VI. The gas pressure was set as 0.50 MPa and the operating velocity was set as 5.00 m/s. The equivalent stress the U-shaped VI bellows’ first wave crest being suffered was changed as follows: it was reduced by 27.46% when the thickness was increased from 0.16 mm to 0.18 mm; when the wave height was decreased from 8.34 mm to 7.74 mm, it was reduced by 25.37%; as for the radius of curvature of wave crest and the radius of curvature of wave trough, the equivalent stress was reduced by 16.15%, 19.36% respectively when the first parameter was changed from 2.00 mm to 1.80 mm and the second one was changed from 2.00 mm to 2.20 mm. Excessive reduction of the wave height contributes to higher superimposed frequency of the stress waves, the preferred optimum parameters were as follows: the thickness was 0.18 mm; the wave height was 8.04 mm; the radius of curvature of wave crest was 2.00 mm; the radius of curvature of wave trough was 2.00 mm. Two whole bellow structure models were built to verify the optimum design parameters. The equivalent stress the U-shaped VI bellows’ first wave crest being suffered was reduced by 17.13% when the optimum design parameters of the bellow structure were adopted. The fatigue life of the improved model is 942 cycles while the initial model is 720 cycles with the operating speed of 5 m/s under the pressure of 0.50 MPa. The mechanical endurance of the bellows was increased by 30.83% when the optimum design parameters of bellow structure was adopted.