Hokkaido's prefecture-wide blackout on Sept. 6 was caused by a failed emergency step that was designed to prevent exactly what it caused after the level 7 earthquake, a document has revealed.
The reason it failed was because the temblor triggered a bigger initial power loss than expected, the document said.
The document presented Friday to a government third-party committee looking into the causes of the blackout showed that Hokkaido Electric Power Co. had prepared emergency shutdowns to prevent a power outage from striking the entire prefecture on the assumption that any power loss would total less than half the island's total power supply.