On May 17, 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.                 (already announced on May 18)

Following the instruction, TEPCO has implemented survey for the 
transmission lines consisting the trunk transmission system and for the 
protection equipments of substations and switching stations connected to 
the transmission line to the nuclear power plants and reprocessing 
facilities. TEPCO reported the survey result to NISA yesterday. 

Attachment
"Report regarding inspection of protection equipments of transmission lines 
at substations, etc"(PDF 20.2KB)

*"Regarding inspection of protection equipments of transmission lines at 
substations, etc. (Instruction)" [May 16, 2011  NISA No.4]

Due to the earthquake occurred at off 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.