Optimization of Axial Magnetic Field Characteristics of Slotted Horseshoe Type Contacts for 126 kV Vacuum Interrupters

The objective of this paper is to optimize a design of a slotted horseshoe type axial magnetic field (AMF) contacts, which is used for 126 kV vacuum interrupters (VIs). Through Box-Behnken Design method and finite element calculation, the AMF characteristics and loop resistance of the contact system with seven design parameters were obtained. Seven contact parameters included the outer diameter of the iron plates ( $D$ ), the inner diameter of the iron plates ( $d$ ), the height of iron plates ( $h$ ), the slot angle of iron plates ( $\theta$ ), length of the slope on iron plates ( $s$ ), the height of chamfer on the tip of iron plates ( $h_{t}$ ), the height of chamfer on the back side of iron plates ( $l$ ). Three optimization objectives were chosen as follows: the maximum axial magnetic flux density at current peak ( $B$ ), the maximum area of “effective region” ( $S$ ), and the minimum loop resistance of contact system ( $R$ ). Based on the simulation results, the equations of AMF characteristics and loop resistance of the contact system were determined. Then the AMF characteristics were optimized by multi-objective optimization. The optimum values of $D, d, h, \theta, s, h_{t}$ , and $l$ were determined as 92 mm, 72 mm, 59 mm, 104.6°, 70 mm, 0 and 20 mm, respectively, which achieved the optimal performance. The optimized $B, S$ and $R$ were 186.2 mT, 2766.9 mm2, and $7.7 \mu\Omega$ , respectively. After optimization, $B$ increased 45.47%, $S$ increased 81.28%, $R$ decreased 54.50%.