Mechanism and Novel Elimination Method of Delayed Current Zero for Fault Current fed by High-Capacity Synchronous Generator

The unique delayed current zero (DCZ) exists in fault current fed by high-capacity synchronous generator (HSG). As current zero is the pre-condition for current interruption, DCZ must be eliminated within 1∼2 power cycle to realize rapid fault interruption. Existing method is using SF6 arc resistance to eliminate DCZ, meaning SF6 interrupter is the inevitable choice for high-capacity generator circuit breaker (GCB). To promote the replacement of SF6 interrupter by vacuum interrupter (VI), mechanism of DCZ is revealed, and novel elimination method of DCZ without using SF6 arc resistance is proposed. Contributions of this paper are: First, based on the existing recognition that different time constants lead to DCZ, it is found the magnetic coupling effect between stator winding and damping winding is the fundamental reason for DCZ, and the stronger the coupling effect is, the more severe the DCZ is. Second, the key constraint of eliminating DCZ is revealed. Instead of using large SF6 arc resistance, changing the material of damping winding can also satisfy the constraint, and eliminate DCZ within 1∼2 power cycles, providing technical premise for the replacement of SF6 interrupter by VI in high-capacity GCB. All these findings are validated by simulations based on finite element method (FEM).