Electrical Switching Life of Vacuum Circuit Breaker Interrupters

Experiments were performed to determine the electrical life of a vacuum interrupter as a function of current. The test currents ranged from the normal load currents of 630A (rms) to 3150A (rms) to higher currents of 20% to 100% of the rated short-circuit current. The two vacuum interrupter contact styles were evaluated: the transverse magnetic field (TMF) contact and the axial magnetic field structure (AMF). For the short-circuit current switching the AMF contact shows a longer electrical life, but the erosion may not be the only limitation on the life of the vacuum interrupter. The results will be discussed in terms of the expected performance of the two contact designs and on the operating life of a vacuum interrupter.