A Quadrupole Longitudinal Magnetic Field Electrode Structure Of Vacuum Interrupter Development

The constriction performance of vacuum arc at high current levels depends on the contact material and its structure. Axial magnetic field (AMF) contacts within vacuum interrupters can prevent the vacuum arc from constriction. The diffuse arc results in a reduced energy impact on the electrodes. Therefore, AMF contacts provide an excellent behavior of breaking short-circuit current. Depending on the contact design the axial field distribution is different. For single-pole contact the direction of the AMF is the same within the whole inter-electrode gap. For multiple-pole contact, the polarity of the AMF changes.In this paper a new quadrupolar axial magnetic field contact design and its characteristics are presented. The quadrupolar AMF contact not only can generate very strong AMF but also has low circuit resistance. It is applied within the vacuum interrupter especially in case of high rated short-circuit breaking current, high rated current and small clearance between open contacts. In the paper the basic operational principle of the new contact design is studied. The contact design provides four areas with nearly the same axial magnetic flux density distribution (by amount), i.e. four areas with equal conditions are given. By arranging two iron cores after two contact plates respectively, a magnetic circuit is built up. The lines of magnetic induction are forced to penetrate four times the plain between the two contacts. The AMF is generated by a hybrid principle. The first contribution is produced by a magnetic circuit, the second one by slots incorporated into the electrodes.In this paper three-dimensional field simulation analyses are performed with the aid of Finite-Element-program software. The magnitude of the axial magnetic flux density, the effect of eddy current and the current flow within the contact plate are investigated during arcing. The AMF distribution on middle plain within inter- contact gap and contact surface are calculated when the current is at peak. The calculation of the eddy current and the AMF on contact surface and middle plain in contact gap are carried out respectively while the current is at zero. Also, the hysteresis time of the AMF is caculated when the current is at zero. The result of the simulation analyses indicate that...