On May 17th, 2011, TEPCO received documents titled "Regarding inspection
of protection equipments of transmission lines at substations, etc.
(Instruction)"* from Nuclear and Industrial Safety Agency, Ministry of
Economy, Trade and Industry.
Hereafter, following this instruction, TEPCO will inspect protection
equipments of trunk transmission systems and those which at substations
and switching stations which are connected to the transmission lines which
are connected to nuclear power stations and reprocessing facilities, and
will report the results of such inspections and measures to be taken, etc.
to Nuclear and Industrial Safety Agency, Ministry of Economy, Trade and
Industry.
*"Regarding inspection of protection equipments of transmission lines at
substations, etc. (Instruction)" [May 18th, 2011 NISA No.4]
Due to the earthquake occurred at off coast of Miyagi Prefecture on April
7th, 2011 (hereinafter referred to as the "Earthquake"), blackouts
occurred in wide-spread area supplied by Tohoku Electric Power Company,
Incorporated. Also, due to these blackouts, off site powers were lost
temporarily at Higashidori Nuclear Power Station of Tohoku Electric Power
Company and Rokkasho Reprocessing Plant of Japan Nuclear Fuel Limited.
In response to this, May 16th, 2011, Nuclear and Industrial Safety Agency
(hereinafter referred to as this "Agency") received a report regarding the
cause of such wide-spread blackouts from Tohoku Electric Power Company.
According to this report, one of the main causes of such wide-spread
blackouts was failure in actuation of a protection equipment of 270,000
Volts transmission line when many earth faults and short circuits occurred
at a same time because of the Earthquake. The isolation function of such
protection equipment could not be restored because the lost of the
isolation function was not sensed because the protection equipment failed
to display its status although isolation function of such protection
equipment had been lost. Because of it, due to the actuations of
protection equipments of some transmission lines, etc. around such broken
protection equipment, some transmission lines, etc. around it were cut off.
In response to this, to prevent occurring same type of wide-spread
blackouts in the area where electricity is supplied by Tohoku Electric
Power Company and other general electric utilities, this Agency instructs
general electric utilities, etc., in addition to taking measures described
below, to report the result of it to this Agency by each dead line.
1. Inspect protection equipments of trunk transmission systems and those
which at substations and switching stations which are connected to the
transmission lines which are connected to nuclear power stations and
reprocessing facilities of each general electric utilities, etc.
regarding the possibility of occurrence of the condition that the
function to display the status of the protection equipments does not
work although the isolation function of such protection equipments is
lost (hereinafter referred to as the "Non-display Condition"), and if
there is a possibility that the Non-display Condition may occur, the
function to display the disorder of such protection equipment shall be
repaired by June 8th, 2011. Further, prevent such protection equipments
from occurring of Non-display Condition by checking such protection
equipments regularly.
2. As to the protection equipments that are discovered to be having
possibilities to be the Non-display Condition as a result of the
inspection described 1 above, take permanent measures to prevent such
protection equipments from being the Non-display Condition. Also,
develop a permanent measures implementation plan by June 8th, 2011.