Please view the main text area of the page by skipping the main menu.

Mysteries still abound 1 week after quake-triggered blackout in Hokkaido

Hokkaido Electric Power Co.'s Tomato-Atsuma thermal power plant in the Hokkaido prefectural town of Atsuma is pictured from a Mainichi Shimbun aircraft on Sept. 6, 2018. (Mainichi)

SAPPORO/TOKYO -- Overdependence on a major power plant and bad timing were behind an unprecedented complete blackout in the northernmost prefecture of Hokkaido after a strong earthquake on Sept. 6, according to industry officials, but many mysteries still surround the power outage one week later.

The central government plans to launch an investigation into factors behind the blackout shortly, including the initial response to the earthquake taken by Hokkaido Electric Power Co., the major utility firm in the prefecture.

The power supply to all 2.95 million households in Hokkaido was cut at around 3:25 a.m. on Sept. 6 -- 17 minutes after the quake that measured a full 7 on the 7-point Japanese seismic intensity scale shook the southwestern part of the prefecture. The blackout was triggered by the emergency shutdown of the Tomato-Atsuma Thermal Power Plant in the town of Atsuma, near the epicenter. The facility's three generators act as the main power source in Hokkaido.

At 3:08 a.m., one minute after the earthquake hit, operators on night watch were surprised by abnormal readings on the indicator for electricity supply and demand. The No. 2 and No. 4 generators, which have production capacity of 600,000 kilowatts and 700,000 kilowatts, respectively, shut down automatically in response to the quake, and the crucial power source that was covering 40 percent of the then 3.1-million-kilowatt demand for electricity was gone in an instant.

A major blackout occurs when the balance between power supply and customer demand is disrupted. As the Tomato-Atsuma plant went down, a "load shedding" program kicked in to curb demand by shutting down power to certain areas. Meanwhile, power diversion from the country's main island of Honshu to the island prefecture reached full capacity of 600,000 kilowatts at around 3:11 a.m., and the power balance appears to have been restored momentarily.

However, at 3:25 a.m., the No. 1 generator at Tomato-Atsuma, with a 350,000 kilowatt capacity along with four other Hokkaido Electric thermal power plants -- those in Date, Shiriuchi, Naie and Mori -- came down simultaneously, spreading a prefecture-wide power outage for the next 10 1/2 hours or longer. It is still not clear if the blackout was triggered by the stoppage of the No. 1 generator or other factors were behind the shutdown. Hokkaido Electric Vice President Ichiro Sakai only said that the company "would like to examine data in detail."

The big question is if Hokkaido Electric was ready. The utility assumed that 1.29 million kilowatts of its power production capacity, or some 25 percent of the peak demand, could be lost in the event of accidents and natural disasters, and made preparations accordingly. However, President Akihiko Mayumi said they "did not imagine a scenario where three generators (at the Tomato-Atsuma plant) would fail all at once," which is what happened this time.

An individual connected to Tokyo Electric Power Co. (TEPCO), a major power supplier in Tokyo and surrounding areas, questioned Hokkaido Electric's premises, saying that after the 2011 Great East Japan Earthquake, the Tokyo utility made preparations "based on a possibility that nearly half of TEPCO's production capacity could be lost."

One of the focal points of future investigation should be how prepared Hokkaido Electric was for an all-out generator failure at the Tomato-Atsuma plant when the island depended so much on the facility's production to power the island.

Another factor potentially behind the blackout is the tough business environment for Hokkaido Electric. Following the 2011 earthquake in northeastern Japan, the company was forced to suspend its Tomari Nuclear Power Plant with a total capacity of 2.07 million kilowatts, and then in 2016, retail electricity sales became completely liberalized, triggering fierce price competition. A senior executive at a major power utility said Hokkaido Electric expected to resume operations at the Tomari plant earlier and to "cut back on investments in existing facilities, and failed to be sufficiently prepared" for a contingency such as the Sept. 6 quake. The utility's understanding of the balance between cost-effectiveness and stable supply is likely to be questioned in the future.

Meanwhile, bad luck did seem to have also played a role in the blackout. During the summer, when power demand is less than 4 million kilowatts -- far lower than the winter peak of 5 million or more -- many of Hokkaido Electric power plants are shut down for inspections. Nobuyuki Yamaguchi, a lecturer at Tokyo University of Science who specializes in power system operation, said that power companies prepare their production capacity to meet the peak demand, and "they were probably not prepared enough for low-demand situations."

(Japanese original by Hiroshi Nohara, Hokkaido News Department, Takayuki Hakamada and Daisuke Oka, Business News Department)

Also in The Mainichi

The Mainichi on social media