v_vista-C (kV) 4.0 0.0 -4.0 Fault Is Applied Fault Is Cleared by C1 and C2 i_fault (kA) 30 (kA) 20 10 0 -10 -20 20 10 0 -10 -20 20 10 0 -10 -20 Fault Is Cleared by C3 i_fault (kA) 30 (kA) -4.0 Fault Is Applied (kA) 0.0 20 10 0 -10 -20 (kA) (kV) -30 v_vista-C 4.0 (kA) 20 10 0 -10 -20 (kA) -30 20 10 0 -10 -20 x i_grid i_gen 2.90 3.00 3.10 3.20 x 3.30 i_relay-C1 i_relay-C2 i_grid i_gen 2.90 3.00 (a) 3.10 3.20 3.30 (b) Figure 11. The simulation results when P SG = 4 MW in case A1. (a) The fault is cleared by the load-way PD. (b) The load-way PD failed to clear the fault, which was cleared by the backup protection provided by loop PDs. v_vista-C 4.0 (kV) (kV) 4.0 -4.0 v_vista-D (kV) 4.0 Fault Is Cleared by Fault Is POTT Applied (D2-C1) -4.0 Fault Is Applied 0.0 -4.0 30 Fault Is Isolated by Backup (D2-C2) Fault Is Fed Through Vista C i_fault (kA) 20 10 0 -10 -20 -30 i_relay-C1 20 10 0 -10 -20 (kA) (kA) 20 10 0 -10 -20 (kA) -30 x v_vista-D (kA) i_fault (kA) 30 0.0 -4.0 (kV) 4.0 v_vista-C 20 10 0 -10 -20 i_relay-D2 0.90 1.00 1.10 1.20 1.30 x (a) i_relay-C1 D2 Tripped; C1 Failed i_relay-D2 0.90 1.00 1.10 1.20 1.30 (b) Figure 12. The simulation results when the synchronous generator is disconnected in case A2. (a) The fault is cleared by the POTT scheme. (b) The fault is isolated by the backup loop PDs once the POTT scheme has failed. 76 I E E E E l e c t r i f i c ati o n M agaz ine / MARCH 2014