Vulnerability of Centralized Power Systems as Evidenced by the Area-Wide Outage in the Hokkaido Earthquake

Hiroshi Takahashi, Professor, Tsuru University

7 September 2018

in Japanese

A large-scale outage occurred throughout the prefecture of Hokkaido due to an earthquake on 6 September 2018, with a maximum seismic intensity of 7. According to Hokkaido Electric Power Co., Inc., the situation is the first since its founding as a company in 1951, and restoration of service will take at least one week. While hopes are pinned on the efforts of concerned personnel working for normalization as early as possible, unfortunately the fact that this could happen could have been foreseen. The real cause is the vulnerability of the centralized power system.

Cause of the Area-wide Outage in Hokkaido

The area-wide outage was caused by earthquake-induced damage to boilers and other equipment of the Tomato-Atsuma coal-fired thermal power plant, which consequently suspended operation. Installed with three units for a total capacity of 1.65 GW, the plant is a huge one that supplied about half of the demand for power throughout the prefecture before the earthquake. The power system needs to match demand and supply at every instant, and falls into a situation of large-scale outage when this breaks down. The shutdown of the Tomato-Atsuma plant greatly upset the supply-demand balance. As a result, other power plants were forced to shut down in succession, and the outage spread over the entire supply area.
When there is a shortage of supply in the area, one response is to procure power from outside the area. This is referred to as "wide-area" (cross-regional) system operation. Hokkaido is connected to the system in Honshu by the transmission network, but the capacity of the interconnection lines between the two is limited to 600 MW. In addition, a technical problem was involved: because the power plants in the area had shut down completely, they were unable to convert the direct-current transmission from Honshu into an alternating current.
In short, the area-wide outage in Hokkaido was provoked by the high risk of power source failure due to the concentrated siting of centralized power sources. The situation was aggravated by the imperfect provisions for wide-area operation that could have compensated for the failure. This is what I mean by the "vulnerability of centralized power systems."

Reform for a Shift to a Distributed Power System

What can be done to avoid such situations? A primary solution is the dispersed siting of distributed power sources. While large-scale power plants must have a centralized configuration, smaller ones must necessarily be dispersed. With power plants dispersed in various sites in the area, disasters will have only a minor impact on the entire area even if they stop the operation of a few plants. As long as about half of the supply power in the area is not lost, there is a higher possibility that the supply-demand balance can be maintained.
The major candidate for distributed power sources is renewable energy systems. Hokkaido has an abundance of wind, sunlight, biomass, and other renewable energy resources. Aside from these, there are good prospects for the use of on-site power generation and CHP (Combined Heat and Power) systems, and, farther on, storage batteries (including electric vehicles), fuel cells, and demand response as demand-side adjustment power. In other words, what is needed is a flexible combination of supply or adjustment capacities with diverse characteristics in various areas instead of dependence on large-scale power sources in a particular area.
A second course of action is to promote wide-area operation by strengthening interconnection lines between supply areas. According to the reports, the Hokkaido-Honshu interconnection was not usable on 6 September, the first day of the outage, but was placed into operation beginning on 7 September. As its capacity is 600 MW, the line is not fully adequate, but it can still play a certain role. If it is bolstered and more lines are constructed, they could form a more resilient network. Hokkaido is situated at the northern end of Japan, and the idea of connecting with systems in other countries could also be explored.
To this end, it is necessary to promote neutral, the inter-regional transmission sector in addition to dispersing and diversifying the generation sector. This agenda, in turn, entails power sector liberalization and unbundling to separate the generation and transmission sectors.
In this way, the power system can make the transition to a distributed network consisting mainly of distributed power sources. A certain cost will arise in the process, and questions such as how to distribute the cost burden and the length of time needed to make the transition will require full discussion. Nevertheless, in Europe at least, this general approach is shared, and steps are in fact being taken toward the large-scale input of renewable energy and augmentation of international interconnection lines.

Toward the Achievement of Power System Reform

Based on the bitter experience of the 2011 disaster, presumably the Japanese government also shares the basic approach of reformation to shift from a centralized system to a distributed one. One indication is the power system reform it has been promoting since 2012. It is supposedly targeting the "further use of diverse distributed power sources” “including renewable energy" and the "preparation of transmission and distribution networks that are interconnected between regions” “for wide-area use of supply power" (quoted from the "Report of the Expert Committee on Electricity Systems Reform," February 2013). In reality, over the last six years, the installed capacity of photovoltaic power generation systems has increased more than 7 times, and work to increase the capacity of the Hokkaido-Honshu interconnection to 900 MW is moving ahead.
Over the last few years, however, the approach of reform seems to be in a process of significant change. In the Basic Energy Plan, for example, centralized power sources in the form of nuclear power and coal-fired thermal power are being maintained, while transmission networks are not being fully opened to new power sources such as renewable energy, and wide-area system operation is not making much progress either. In Europe, by contrast, base-load power sources (i.e., centralized ones) are being perceived as behind the times because of the lack of flexibility for adjusting output and their high business risks. This is precisely why there is a movement away from nuclear power and coal-fired thermal power.
In fact, Hokkaido Electric Power has a power source on a larger scale than the Tomato-Atsuma power plant: the Tomari nuclear power plant. This consists of three units with a combined capacity of 2.07 GW, but discontinued operations in 2012. If it had been in operable condition at the time, it may have been able to prevent the outage. However, I want to emphasize that this is not a reason to hasten the operational resumption of nuclear power plants, which would not be a genuine solution. In the final analysis, as long as areas depend on centralized sources, they cannot avoid the associated risks. The very fact that the Tomari power plant has not been operating for a remarkable six years underscores the risk of concentrated sources.
According to news reports, the executives of Hokkaido Electric Power said that they "had not foreseen a major accident" of the sort that would put all three units at the Tomato-Atsuma power plant out of operation. Over the coming years, Japan will probably continue to be visited by disasters and other "unforeseen" events. For this very reason, it needs distributed systems that disperse various risks and enable a more flexible response. I earnestly hope that the authorities will learn the lessons from the outage and fully achieve this kind of genuine power system reform.

<Related Links>
More Thoughts on the Hokkaido Blackout: Can the Lessons Learned be Applied?
(22 October 2018)

External Links

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