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Failure to balance power supply, demand soon after quake led to Hokkaido blackout

Hokkaido Electric Power Co.'s Tomato-Atsuma thermal power station in the Hokkaido town of Atsuma is seen here from a Mainichi Shimbun aircraft on Sept. 12, 2018. (Mainichi/Naotsune Umemura)

TOKYO -- Data released on Sept. 19 by the Ministry of Economy, Trade and Industry (METI) and other bodies has shown that the failure to maintain balance between power supply and demand following the massive quake that hit Hokkaido in the wee hours of Sept. 6 contributed to a prefecture-wide blackout.

The data that was released included the shifts in electrical frequency in the 18 minutes between the quake and the blackout within the area covered by Hokkaido Electric Power Co.

Power companies keep electrical frequencies stable by balancing electricity supply and demand, since dramatic changes in frequencies can overload power stations, increasing the risk of blackouts on a massive scale.

According to data released by METI and other bodies, operation of the No. 2 and No. 4 generators at the Tomato-Atsuma thermal power plant, which have a maximum output of 600,000 kilowatts and 700,000 kilowatts, respectively, came to an emergency halt immediately after the earthquake struck at 3:07 a.m. on Sept. 6. Because the power supply suddenly plunged, electrical frequency, which is normally stabilized at 50 hertz in eastern Japan (60 hertz in western Japan), dropped rapidly. A chain reaction resulted in wind power generators and hydraulic power generators also coming to a stop. It is believed that within a minute, nearly half the 3.1 million kilowatts of power in overall demand prior to the quake was lost, with electrical frequency falling at one point to 46.13 hertz.

Hokkaido Electric's "load-shedding" measures -- forced blackouts in certain areas -- kicked in automatically to reduce the demand for power, and the utility also worked to maintain balance between supply and demand through the accommodation of approximately 600,000 kilowatts of electricity from utilities in Japan's main island of Honshu. This allowed Hokkaido Electric to regain a frequency of around 50 hertz, and it appeared as though the crisis had passed.

What happened next was unexpected. In areas that had not lost power, residents who were woken up by the temblor turned on lights and televisions, suddenly increasing demand for electricity. This then began to lower electrical frequency, to which Hokkaido Electric responded by increasing its electrical output. By around 3:20 a.m., output of the No. 1 generator at Tomato-Atsuma power station, which has a maximum output of 350,000 kilowatts, had dipped. A second round of load shedding kicked in.

Tomato-Atsuma power plant's No. 1 generator came to a stop soon after frequency levels recovered. The third round of load shedding was also unsuccessful in stopping frequency levels from dropping, leading to a chain reaction that stopped three other thermal power stations -- causing a prefecture-wide blackout at 3:25 a.m.

The majority of measures taken by Hokkaido Electric, including load shedding, are automated, and METI said it did not believe that the trouble was due to human error.

The METI data highlighted the extreme difficulty of balancing power supply and demand in the 18 minutes after the quake. However, several questions remain, such as: "Why wasn't Hokkaido Electric able to stop the dip in frequency?"

The Organization for Cross-regional Coordination of Transmission Operators, Japan, a METI-approved body, founded a third-party panel on Sept. 19 to investigate the cause of the problems that triggered the blackout and draft preventative measures.

"Output and demand of individual power sources, and voltages of electrical grids are intricately intertwined," says Kazuhiko Ogimoto, a project professor at the University of Tokyo's Institute of Industrial Science. "So there's a need to further inspect the situation using more detailed data without letting preconceived notions get in the way."

(Japanese original by Daisuke Oka, Takayuki Hakamada and Kenji Wada, Business News Department)

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