A third-party panel investigating the massive blackout that occurred in Hokkaido following last month’s powerful earthquake plans to propose an increase to Hokkaido Electric Power Co.’s preset quota for forced shutdowns as a measure to prevent a similar large-scale power failure, it was learned Tuesday.

Electricity supply and demand need to be balanced to ensure stable power supply. In the event there is a sharp decline in supply, power companies need to reduce demand through forced shutdowns to maintain the balance and prevent additional damage to the grid.

Following the 6.7-magnitude earthquake in the early hours of Sept. 6, all three units of the regional power supplier Tomato-Atsuma shut down, causing the company’s power supply capacity to decline substantially.

The plant in the town of Atsuma is the biggest thermal power station in Hokkaido, with the three units’ combined capacity standing at 1.65 million kilowatts.

Meanwhile, Hokkaido Electric had a preset forced shutdown quota of only 1.46 million kW at the time, and the firm was thus unable to keep supply and demand balanced and failed to prevent the massive blackout as a result, according to the panel under the Organization for Cross-regional Coordination of Transmission Operators or OCCTO.

The panel is poised to propose a hike in the quota by about 350,000 kW to over 1.8 million kW until March 2019, when the firm’s capacity is slated to rise thanks partly to the launch of a liquefied natural gas-fired power plant, sources said.

The proposal will be included in the panel’s interim report, expected to be compiled within this month, the sources said.

Forced blackouts are considered to be the last resort for preventing a massive power outage. Hokkaido’s September quake, which measured up to 7 on the Japanese earthquake intensity scale, led to blackouts across the prefecture.

At its meeting Tuesday, the panel concluded that the massive blackout in September occurred because of “multiple factors,” including damage caused by the quake to power grids in the eastern area of Hokkaido and the halting of operations at the Tomato-Atsuma plant, which supplied roughly half of the prefecture’s electricity needs before the quake.

It was also disclosed at the meeting that Hokkaido Electric failed to restore electricity in its first attempt soon after the disaster.

At 4 a.m. on Sept. 6, or 35 minutes after the blackout happened following the pre-dawn quake, the company tried to restore power by restarting operations at the No. 1 unit at its Takami hydroelectric power plant in the town of Shinhidaka.

But the Takami plant was shutdown again due to a large current surge that occurred at a facility related to Hokkaido Electric’s Tomari nuclear plant in the village of Tomari, forcing the company to try to restart another power station, according to the panel.

Because of the failed first attempt, electricity restoration might have been delayed by two-and-half hours, a senior OCCTO official said.

The failure of the first attempt delayed the full restoration of external power sources at the Tomari plant to 1 p.m. on Sept. 6, according to the panel.

The massive blackout was almost fully resolved by 12:13 a.m. on Sept. 8, or about 45 hours after the start of the outage.

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