Shinkansen substations receive a three-phase current power supply and convert it into two single-phase AC currents (phase A and phase B) with a 90-degree phase difference using feeding transformers before supplying power to EMUs. At sectioning posts, in order to make a distinction between different power sources from two substations, these sources have to be insulated, though the voltage difference between them is as low as about 10 kV or less, as power supplies of the same phase are supplied to the section between substations.

For this purpose, changeover sections are installed at substations and SPs where the power source is switched from one to the other, sandwiching a 0.3-second interruption time, when a train passes. At this power source changeover, however, an excessive surge voltage or rush current is generated, which adversely affects the main circuit components and transmits noise to the low-voltage control circuit.

To suppress these drawbacks, the RTRI has developed a parallel power source switchover system to temporarily connect power sources 1 and 2 when a train passes the SP (Fig. 1). This system continuously monitors the voltage difference between the two power sources, estimates the current that will emerge at parallel changeover, and implements parallel power source changeover only when the estimated current is 1,200 A (the rated current of the changeover switch) or less and moreover, the power sources are switched using the conventional method when the estimated current is over 1,200 A, thereby ensuring safe and uninterruptible changeover. Through field tests, the RTRI has confirmed that surge voltages do not emerge under this system.