IEEE Electrific ation Magazine / d ec em be r 2 0 1 3 17 Voltage in Thousands (V) -200 09:52:51.453 -100 0 100 200 300 400 500 600 3.25 09:52:51.726 3.3 3.35 3.4 3.45 3.5 3.55 3.6 3.65 3.7 09:52:53.453 09:52:53.726 09:52:55.453 09:52:55.726 09:52:59.726 (b) 09:52:57.453 Time (s) 09:52:59.453 Current Increasing (a) 09:52:57.726 Time (s) Voltage Drop Figure 4. The evolution of railway power line (a) voltage and (b) current, determining the flywheel operation modes. Current (A) 09:53:01.453 09:53:01.726 09:53:04.252 09:53:03.726 09:53:04.766