We performed an electrical equipment inspection with blackout of KAGRA on March 4th, 2026.
Timeline of the blackout is as follows,
8 AM, Morning meeting with company members and start preparation works before the black out.
10:12, Blackout.
13:21, Notification of power outage start at 13:30 from Hokuriku Electric Power company (Reconstruction work of the electric pole used by KAGRA, etc.)
16:19, Notification of completion of construction from Hokuriku Electric Power
16:56, Re-electricity. Start of recovery work.
(1) The dehumidifier at the Mine entrance could not be operated after switching the generator. →Wiring error was found.
(2) The voltage of the generator was too high and the UPS of the PHS was malfunctioning → Lowering the output voltage of the generator to respond.
(3) Discovered burned parts in Yend cubicle →Reconfirmed by Miyoki, Kimura, and Furuyado.
Traces of burning were found on the control circuit board of the No. 1 conductor contact point in the capacitor bank for power factor improvement of 3 systems (No.1~No.3) installed in the Y-end receiving panel.
Countermeasures: Since the capacitor bank for power factor improvement(力率改善) of N0.1 and No.2 usually works, it was decided to replace the No.3 and No.1 conductor contacts for the time being and operate it with a capacitor bank for power factor improvement of the 2 systems. In addition, the operation of the conductor contact of No.3 was manually turned off. The No.1 conductor contact was taken back to the contractor factory and requested to replace the control circuit board and perform an operation test. After adjusting the schedule, it was decided to reinstall the No. 1 conductor contact that had completed the repair into the empty slot of the No. 3 conductor contact. In addition, it was confirmed that there was no need for a power outage when reinstalling.
We asked Nakai-denki company to check the number of operations of the capacitor bank at monthly inspection.
(4) The company members moved in the EYC booth and maybe in EYA. (I have not instructed that Do not walk in the clean booth. I am so sorry.)
(5) The monitoring system for fire alarms and so on, at the mine entrance and Xend, has not been recovered due to a broken media converter.
The monitoring system for the mine entrance has recovered by changing the AC adapter for the media converter.
We will try to recover the monitoring system for Xend tomorrow. Until the recover, entering the Xend area is prohibted.
(6) Two oil heters in EYC did not worked after the blackout.
About the (5) issue.
We recovered the monitoring system of Xend by changing the AC adpter for the media converter in the morning on March 5, 2026.
We tried to start the BS-C and SR-C Daikin coolers. However, we could not operate the BS-C Daikin cooler in the cooling mode, but only in the air flow mode. We started the IYC-C Daikin cooler, instead. We need a repair for the BS-C Daikin cooler.
I guess the malfunction of two Sunrise heaters is related to changes in thermal conditions after several years of continuous operation at ~1kW. This means that the inner circuits of heaters are baked at high temperature ( < ~60 °C: this is normal according to the manual) for several years. The circuits inside the heaters might have cracked during the cooling period of the power outage.