On criteria of optimized application of AMF- and RMF-contact systems in vacuum interrupters

In case of interrupting high AC-currents in vacuum, a metal vapour arc burns between the separating contacts, till the next current-zero. However, if the current exceeds the range of approximately 10 kA the arc will pinch due to its own magnetic field. In order to avoid a local contact overheating there are two possibilities: movement of the constricted arc on the contact surface by a radial magnetic field (RMF); and prevention of arc constriction by an axial magnetic field (AMF). In this short overview the functional principles and physics of RMF and AMF are given. Pros and cons of RMF versus AMF with regard to interrupting capability, electrical resistance, tubes dimension and production costs are compared for the low, medium and high voltage range