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Blackout linked to fire damaging main power cable sending electricity to Tokyo

A TEPCO representative shows a power cable that runs underground, the same type as the one that caught fire, during a news conference at TEPCO headquarters on Oct. 12, 2016. (Mainichi)

A fire that broke out in an underground tunnel of Tokyo Electric Power Company Holdings Inc. (TEPCO) in Niiza, Saitama Prefecture, on the afternoon of Oct. 12, damaged the main power cable connecting power plants and substations that send electricity to Tokyo, causing a large-scale blackout in the capital.

The temporary power outage hit a total of 11 Tokyo wards, including business and shopping hubs in Chiyoda and Shinjuku wards, at around 3:30 p.m. on Oct. 12, affecting up to around 580,000 households. Prior to the blackout, a fire broke out at around 2:50 p.m. at TEPCO's underground tunnel and a utility official said at a news conference later that day that power transmission was partially cut off due to the fire. The Metropolitan Police Department said there were no reports of injuries.

According to TEPCO, power was resumed in all affected areas by 4:25 p.m. The Ministry of Economy, Trade and Industry demanded TEPCO Power Grid, in charge of power transmission and distribution, investigate the cause of the fire.

TEPCO told a news conference that the power cable that caught fire was 13 centimeters in diameter with a metal conductor in the middle. The conductor with 275,000 volts of electricity was wrapped by layers of paper dipped in insulator oil. The utility explained that there is a possibility of a malfunction with the paper such as a rip that triggered a short circuit, creating a spark, with which the oil caught fire.

The underground tunnel connects the Niiza power substation and two substations in Tokyo. The cables are buried 7.5 meters underground and have not been renewed since they were installed about 35 years ago. TEPCO says no defects were detected during an inspection in June this year and explained that there is no unified lifespan for the cables.

According to the Tokyo Fire Department, calls for help from those trapped inside elevators in Suginami, Toshima, Bunkyo, Minato and Nerima wards poured in after the blackout. Traffic lights failed at some 200 locations and the Seibu Ikebukuro and Seibu Shinjuku lines suspended operations for about 90 minutes from around 3:30 p.m., affecting some 91,000 passengers.

The fire was put out in the wee hours of Oct. 13, about 9 1/2 hours after it broke out. At around 9:30 a.m. firefighters dressed in protective gear went underground via a ventilation hole as officials from Saitama Prefectural Police, fire departments and TEPCO gathered at the site. Police said those entering the tunnel need to wear masks due to high levels of asbestos around the hole.

Police officers inspect the ventilation hole at the underground tunnel in Niiza, Saitama Prefecture, on Oct. 13, 2016. (Mainichi)

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