Axial magnetic field strength needed for a 126kV single break vacuum interrupter

The objective of this paper is to investigate how strong the axial magnetic field (AMF) is needed for a 126kV vacuum interrupter at different contact gaps. The AMF was generated by a pair of 2/3 coil AMF contacts. First, the accuracy of the three-dimensional finite element simulation of AMF was validated by an AMF measurement at contact gap 30mm. After that high-current switching experiments with the AMF contacts were carried out at different contact gaps of 20mm and 50mm at 40kA rms. Then the AMF at the contact gaps of 20mm and 50mm was simulated to analyze the interrupting experimental results. The results showed that there was a successful interruption at 40kA with an AMF of 235mT at contact gap 20mm. And current interruption failures occurred with an AMF of 146mT at contact gap 50mm.