IEEE Power & Energy Magazine - May/June 2015 - 53

www.PowerStandards.com

50.200
(Hz)
50.000
(Hz)

(a)

49.800
00:00

02:00

04:00

IEC 61000-4-30

(c)

(b)
06:00

08:00

10:00 12:00
2011/03/11

Frequency (1-cyc)

14:00

48.730 Hz

16:00

18:00

49.998 Hz

20:00

22:00

23:59

50.120 Hz

figure 11. A Tokyo frequency trace, 11 March 2011. (Used with permission of Power Standards Lab, www.
PowerStandards.com.)

dwellings, as shown in Figure 9. The 724,500 m 2 total floor
space is located in the Roppongi embassy area of southwestern Tokyo. When opened in 2003, it was the largest
and most iconic element of the area's redevelopment. Both
electricity and heat are supplied by Roppongi Energy Service (RES), a "specified electricity utility," under Electricity Business Act Article 2 (vi), which defines a specified
electricity utility as "an entity which has obtained a license
under paragraph 1 of the next Article to conduct a Specified
Electricity Business." This status established in the Electricity Business Act is an entity that can supply electricity
in a defined area within the service territory of a traditional
electricity utility.
The energy system is shown in Figure 10 and described
in Table 1. Six natural-gas-fired turbines provide full-time
CHP service. Natural-gas-fired boilers and absorption chillers are also installed to supply steam and chilled water for
space heating and cooling. The electrical system and water
pipes are connected to neighboring buildings, and the development can island, making Roppongi Hills a true microgrid.
The energy system has reliability-enhancing redundancy
because the capacity of the CHP system exceeds the peak
electricity demand and megagrid imports are available.
Natural gas and electricity are supplied by Tokyo Gas and
TEPCo, respectively. The facility's medium pressure natural gas system is very robust and reliable, never having
been interrupted during Japan's past natural disasters. Additionally, the system includes kerosene storage for lifeline
generator backup. To improve resilience, redundancy is
incorporated into the supply path via two separate substation feeds.
may/june 2015

Roppongi Hills Resilience Performance
Following the GEJE, whereas TEPCo had inadequate supply capability and was forced to conduct rolling blackouts,
the RES was able to completely meet Roppongi Hills loads
and supply electricity to TEPCo. Interestingly, RES's
resilience was proven during that fateful day without any
blackout occurring in the area. In Figure 11, (a) shows
normal frequency variations around 50 Hz on 11 March
2011. The earthquake hit at (b), causing an instantaneous
frequency collapse to 48.73 Hz, which continued for a few
minutes and then recovered. This frequency excursion and
later variability at (c) caused the microgrid to island for
several hours.
Unless microgrids are powered exclusively from local
renewable sources paired with significant levels of energy
storage, during disasters, microgrids' resilience is affected
by the performance of their lifelines, infrastructures needed
for the operation of other systems. Natural gas infrastructure was a lifeline for Roppongi Hills, fueling its natural
gas turbines without interruption. As in Sendai, the medium
pressure network in Tokyo is designed to endure big earthquakes and was never critically damaged throughout the
GEJE crisis.

Sendai Microgrid
Project Description
The NEDO SM project was intended to demonstrate the
delivery of multiple power qualities to various circuits on the
small Tohuku Fukushi University campus and nearby Sendai municipal facilities, a school and a water treatment plant.
ieee power & energy magazine

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2015

IEEE Power & Energy Magazine - May/June 2015 - Cover1
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IEEE Power & Energy Magazine - May/June 2015 - Cover3
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