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Submission of "Report on Equipment Damage of 275-kV Nos. 1 and 2 Koto Lines due to Contact by Floating Crane and Failure of Koto Substation and Other Power Supply Troubles" and "Report on Electricity-Related Failures"

As for the state of affairs following blackout accident due to a floating crane *1 that contacted transmission lines on August 14, 2006, Tokyo Electric Power Co. (TEPCO) announced that the company was given directions on the same day by the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry concerning "early and complete restoration," "thorough investigation of the cause," and "necessary measures to prevent the same accident from happening again based on the investigation of case." In response, TEPCO produced a "report on equipment damage of 275-kV Nos. 1 and 2 Koto Lines due to a hit by a floating crane and a failure of Koto Substation and other power supply troubles" and a "report on electricity-related failures," and submitted them today to the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry.

TEPCO has investigated the blackout in detail. As a result, the following facts are confirmed:
  • At about 7:38 a.m. on August 14, 2006, a raised construction crane on a barge hit TEPCO's extra-high voltage transmission lines (275,000 volts) called the "Koto Lines" that run across the Old Edo River flowing between Minami-Kasai in Edogawa ward, Tokyo, and Urayasu in Chiba.
  • The transmission lines were damaged and power transmission was stopped. As a result, about 1,217,000 households and offices in the central part of Tokyo, northern part of Yokohama and western part of Kawasaki in Kanagawa prefecture, Ichikawa and part of Urayasu in Chiba prefecture were hit by blackout *2.
    Then, power transmission was resumed in sequence. At 7:58 a.m., however, Shinagawa Thermal Power Station that continued to supply power to some areas *3 was automatically shut down because the balance between the supply capability and demand was lost due to increased demand in the morning, and about 174,000 households and offices were blacked out (a total of about 1,391,000 TEPCO customers were suffered from the blackout *4).
  • Then, power supply was resumed in sequence. After 59 minutes at 8:37 a.m., all substations were restored and resumed power transmission.
    At this point in time, electricity supply to about 1,376,000 out of a total of 1,391,000 households and offices hit by the blackout was resumed, and the number of those customers hit by the blackout decreased to about 15,000 *5.
  • As for about 15,000 households and offices mentioned above, the power supply to them was interrupted by malfunctions of TEPCO's power distribution equipment *6, which were triggered by the floating crane that contacted the transmission lines. As a result of resolution of these malfunctions, the number of TEPCO customers suffered from the blackout decreased to about 200 at 10:44 a.m. After four hours and forty-two minutes from the occurrence of the accident, power supply was fully restored at 12:20 p.m.

Although the blackout was caused by contact of a floating crane as negligence of a third party, TEPCO would like to sincerely apologize for the inconvenience and trouble to its customers and other people in general.

TEPCO always keep in mind stable electricity supply to customers in its service area. TEPCO will continue to try to prevent blackout accidents, and make further efforts to realize faster restoration activities at the time of disasters.

*1 Floating crane possessed by Mikuniya Kensetsu

*2 Blackout of about 1,217,000 households and offices
  • Central part of Tokyo: about 800,000
  • Northern part of Yokohama and western part of Kawasaki in Kanagawa prefecture: about 220,000
  • Ichikawa and part of Urayasu in Chiba prefecture: about 197,000
*3 Continued power supply to some areas
After the accident, Shinagawa Thermal Power Station continued to supply electricity to some areas in Chuo, Koto, Shinagawa, Meguro and Shibuya wards, and contributed to reduction in the area of the blackout.
*4 Blackout of about 1,391,000 TEPCO customers
  • Central part of Tokyo: about 974,000
  • Northern part of Yokohama and western part of Kawasaki: about 220,000
  • Ichikawa and part of Urayasu: about 197,000
*5 Decrease to about 15,000 TEPCO customers
  • Summary of the blackout at 8:37 a.m.
    The number of households and offices hit by the blackout: about 15,000 Areas blacked out: Koto, Shinjuku, Shinagawa, Shibuya, Minato, Setagaya, Edogawa, Chuo and Ota wards, and Urayasu.
    * Part of each administrative district.
  • Summary of the blackout at 10:44 a.m.
    The number of households and offices hit by the blackout: about 200 Areas blacked out: Chuo and Ota wards, and Urayasu.
    * Part of each administrative district.
*6 Malfunctions of power distribution equipment
The functions to control switches of distribution lines (systems from distribution substations to customers) do not work mainly because of damage or faulty settings of equipment.
(Reference) Notice given on August 14:
At about 7:38 a.m. on August 14, 2006, a floating crane contacted TEPCO‘s extra-high voltage transmission lines called “Koto Lines” (275,000 volts) that run across the Old Edo River flowing between Minami-Kasai in Edogawa ward, Tokyo, and Urayasu in Chiba prefecture.
The lines were damaged and power transmission stopped. As a result, a total of about 1,391,000 households and offices in the central part of Tokyo, northern part of Yokohama and western part of Kawasaki in Kanagawa, and Ichikawa and part of Urayasu in China were suffered from the blackout.
TEPCO immediately started trying to restore power supply. As a result, electricity supply to all TEPCO customers, except for two high-voltage customers, was restored at 9:55 a.m. Electricity supply to the two high-voltage customers was also restored at 10:44 a.m.
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