The Nuclear and Industrial Safety Agency, still the one and only regulatory agency for the nuclear power plants in Japan, disclosed it during the press conference in Ooi-cho on June 24. Plant operator KEPCO says that happens all the time, nothing to worry about.
And the famous last word, "It won't have any effect", on the restart.
Sankei Shinbun (6/24/2012) reported:
Alarm sounded 26 times at the power transmission line to Ooi Nuke Plant
Alarms sounded 26 times total, at two monitoring facility locations for the power transmission lines between KEPCO's Ooi Nuclear Power Plant (Ooi-cho, Fukui Prefecture) and the power transmission facilities in Kyoto City from midnight on June 23 till June 24 morning. KEPCO and the Nuclear and Industrial Safety Agency (NISA) announced the incident in the press conference held in Ooi-cho on June 24
According to KEPCO, alarms also went off 32 times at 5 power transmission facilities located in southern Fukui and northern Kyoto Prefectures between KEPCO Takahama Nuclear Power Plant and the power transmission facilities, due to the unstable atmosphere.
In all, 58 alarms sounded between 6:41PM on June 23 and 8:12AM on June 24. There was no actual problem at the power transmission facilities themselves, and [KEPCO and NISA says] the alarms were due to the wireless signals for monitoring were cut off by the atmospheric disturbances.
KEPCO explained it was "a phenomenon that happens often, due to the weather conditions", and said there would be no effect on the work to prepare for the restart of the plant.
It may be that such an incident is very common and very minor, and is usually not reported at all. But now that NISA and the electric power companies in Japan have lost credibility, whenever they do report an incident it is immediately upgraded to something that could be a major problem in the minds of the general public. When KEPCO says there will be no effect, people simply hear the echo of then-Chief Cabinet Secretary Yukio Edano in March 2011.
These alarms are connected to the carrier relays, and use microwave for communication. Because of the bad weather in June 23 and 24, the atmospheric disturbances caused the phenomenon called "fading", according to Kaden Watch News.
KEPCO's press release has this diagram: