The causes for this failure mode are different. It has three typical origins
- Electrical – switching of currents (e.g. loop current) – at higher currents the arc burns on a specific spot and increases the resistance locally. With more switching operations, the contact surface will be more worn and its resistance will be increased.
- Mechanical – The major cause of mechanical ageing is abrasion due to vibrations caused by wind.
- Environmental – corrosion (includes also oxidation of aluminum, copper and steel).
This pic shows a deteriorated flexible joint(primary contacts of center break disconnector). The origin of the failure can be directed to improper welding of aluminum belts, which suggests manufacturing deficiency. The
environmental stresses lead to corrosion of the external belt. In combination with mechanical stresses (switching operation), the belt material at welding experiences significant material fatigue leading to breaking of aluminum blades.