IEEE Power & Energy Magazine - May/June 2015 - 51

The Great East Japan Earthquake
Japan is sadly familiar with earthquakes and the tsunamis
they cause. Nonetheless, the horrific events beginning at
14:46 local time (2:46 UTC) on 11 March 2011 were truly
catastrophic, prompting a profound reassessment of the
country's perspective on resilience, public safety, and energy
supply. With an estimated moments magnitude according to
the U.S. Geological Survey of 9.0, its epicenter was off the
Tohuku coast of northeast Hokkaido, 70 km east of Onagawa and 20 km north of Sendai. This intense event was also
relatively shallow (approximately 30 km) and lasted a long
time (about 6 min). Accelerations between 1 and 2 g were
measured at coastal areas east of Sendai and inland around
the town of Furukawa, although these were not representative of the typical shaking experienced across most of the
area. A study from the Technical Council of Lifeline Earthquake Engineering group of the American Society of Civil
Engineers reports that the median acceleration was about
0.55 g along the Tohoku coast and approximately 0.3 g in
downtown Sendai. The GEJE caused a major tsunami that
arrived at the easterly Sanriku coast about a half hour after
the earthquake struck. The wave reached at least 10 m high
at most locations along about 400 km off the Tohoku coast,
from Soma in Fukushima Prefecture to Kuji in Iwate Prefecture, according to estimates by the Ministry of Land, Infrastructure, Transport, and Tourism of Japan. In several towns
along this portion of the coast, the tsunami was estimated
at 20-25 m high. Despite the massive defenses in place, the
resulting devastation was horrific, causing almost 20,000
fatalities and massive physical damage.

Japan's Megagrid
Megagrid Description
At the time of the GEJE, Japan's mainland summertime peak
demand was about 187 GW divided in two major, plus a third
smaller, grids. One main grid operates at 60 Hz and covers
all the islands of Kyushu and Shikoku plus about half of the
island of Honshu west of Tokyo. The second main grid is
a 50-Hz power system that spans the remaining half of the
island of Honshu and includes two investor-owned utilities: Tohoku Electric Power Company (ToPo) with a summertime peak demand before the GEJE of 15.2 GW and the
huge (64.3 GW) Tokyo Electric Power Company (TEPCo),
Japan's largest utility. A high-voltage dc link connects this
grid to the island of Hokkaido, which also operates at 50 Hz
with a 5.1 GW peak.
Three frequency conversion stations with a total capacity
of 1,200 MW connect the two main power grids in central
Honshu. In 2011, Japan had a total generation capacity of
286 GW, 65% of which was fossil fuel fired, and the 49 GW of
installed nuclear capacity represented a further 17%. Almost
all of the remaining capacity was hydro and some modest PV
and wind sources. These resources considered in aggregate
may be misleading because, in reality, the three main power
may/june 2015

table 1. Roppongi Hills microgrid assets.
(Source: Cogeneration Plan and Design Manual 2005,
Japan Industrial Publishing, p. 161, 2005.)
Equipment

Capacity

Generators
-Gas turbine generators
-Steam turbine generator

38,660 kW
6,360 kW X 6
500 kW X 1

Steam absorption chillers

73,340 kW

Steam boilers
Exhaust heat boilers

79.6 t/h
77.76 t/h

grids are weakly connected and should be assessed separately. ToPo controlled just over 18 GW, divided into 12 GW
thermal, 2.5 GW hydro, 3.3 GW at the Higashidori and Onagawa nuclear stations, and a relatively small PV and wind
contribution. Also in the eastern power grid of Honshu's
island, TEPCo operated just under 39 GW of thermal generation, 9 GW hydro, and 17 GW nuclear, including 4.6 GW at
the six reactor Fukushima nuclear station. Hence, it is important to highlight that without considering electric ties with
the other two power grids and the contribution of PV, wind
and other nonhydroelectric sources, the summertime reserve
margin was just about 4%, and nuclear contributed almost a
quarter of the total capacity. In general, reserve margins are
low in Japan compared to other developed economies.

Megagrid Resilience Performance
One of the most significant effects of the GEJE was the loss of
about 14 GW of generation in eastern Honshu, 6 GW nuclear
and almost all of the rest thermal. This loss was mostly due to
tsunami damage but some was caused seismically. The most
well-known damage occurred to the Fukushima #1 Power
Plant, where the tsunami surpassed the seawall and damaged
critical plant components, notably the cooling emergency diesel generators. Buildings housing reactors 1-4 were significantly damaged, leading to radiation leaks to the atmosphere
and sea and requiring evacuation of the area. The Onagawa

figure 9. An impression of Tokyo's Roppongi Hills development. (Source: Tokyo Gas.)
ieee power & energy magazine

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