Fatigue Fracture of the Copper Bridge in a Medium Voltage Make Switch

The case of damage presented here relates to the switching bridge of a medium voltage switch, a so-called make switch. Such assemblies are used for fast high current switching operations in medium voltage technology. The copper switching bridge failed due to low-cycle fatigue fractures symmetrically initiated where the transition radius between the copper bridge and the shaft was too sharp. The primary cause of the damage was the fact that the design principle of avoiding too sharp transition radii was needlessly violated where there were no apparent structural limitations. It is remarkable that, time and again, the violation of the same simple design rules causes component damages. The respective simple principles of good design practice thus violated are the same in virtually any mechanical engineering sector.