Influence of mechanical faults on electrical resistance in high voltage circuit breaker

•The resistance is influenced by the stress relaxation, the fatigue, and the mechanical wear.•The radial offset has a dramatic effect on contact force, which accelerates the fatigue fracture.•The metal on the dimples is mainly tungsten, and the fatigue fracture is mainly copper. The health of contact sets is one of the most critical factors for the breaking capacity of the high voltage circuit breaker. Dynamic resistance measurement is considered to be an effective method to assess the erosion degree of the contact sets. However, the electrical resistance may be influenced by many other mechanical faults which will cause the misdiagnosis of the contact sets. At present, the influence mechanism has not been clarified. Therefore, the influence mechanism and degree of mechanical faults (stress relaxation, fatigue, friction) of contact sets is studied in the present paper. Firstly, the accelerated stress relaxation experiments of CuW alloy, the fatigue experiments of contact sets, and the mechanical friction experiments are carried out to obtain the relationship between the fault degree and the electrical resistance. Secondly, the fatigue fracture, micromorphology, energy dispersive spectroscopy, and metal loss of the contact sets are investigated. Thirdly, the stress distribution and fatigue fracture of the contact finger is analyzed by the finite element method. Based on the above works, the fatigue damage, and the partial loss of the contact fingers are considered to be the most distinct influence on the electrical resistance curves.