Influence of Irons on Magnetic Field Characteristics of Vacuum Interrupter with Cup type Axial Magnetic Field Contacts

Magnetic field characteristics of vacuum interrupter with cup type axial magnetic field (AMF) contacts where an iron ring is introduced are investigated by three dimensions finite element method. The results show that 1) Axial magnetic flux density at current peak increases greatly on iron area, while it decreases slightly on center area. With increase of gap distance, AMF keeps unchanged on non-iron area, while it decreases greatly on iron area. 2) Axial magnetic flux density at current zero increases greatly on iron area. With increase of gap distance, it decreases greatly. Influence of irons on AMF only takes place on iron area. 3) Phase shift time between AMF and source current becomes higher all over the contact area including iron area and non-iron area