At 3:08 am on September 6, 2018, an earthquake with a maximum seismic intensity of 7 occurred in the Hokkaido Iburi region, Hokkaido Electric Power Tomato Atsuma Thermal Power No. 1 (350,000 kW), No. 2 (600,000 kW), No. 4 (700,000 kW) generators (total 1.65 million kW) were stopped in an emergency. As a result, the frequency suddenly decreased, the power plants in electric power system stopped generating electricity, and it became an unprecedented situation where all Hokkaido power outages occurred.
Upon this event, the physical reason that the frequency decrease due to the emergency stop of one power station leads to the whole power failure is a major concern. Recently, there was an example in Tokyo Electric Power Company during the Great East Japan Earthquake on March 11, 2011 avoiding the whole power blackout, partial power outage has been done, and we are interested in what is different from such past examples.
It seems that this event was an unavoidable situation for Hokkaido Electric Power.
Frequency is the turbine rotation speed per 1 second (in the case of 50 Hz, the turbine rotates 50 per second). Supply power is the power to rotate the turbine. It balances supply and demand, and maintains a certain frequency by stabilizing the turbine rotation (when demand outweighs supply, the turbine speed decreases and the frequency decreases).
If the frequency drops due to a decrease in power supply due to power plant stoppage etc., the protection device (UFR = Under Frequency Relay) operates, and the demand is partially cut off (= power outage) to recover 50 Hz. TEPCO at the time of the Great East Japan Earthquake avoided the whole blackout by UFR operation.
It takes a certain time for UFR operation. If the frequency drops suddenly, demand cutoff can not be made in time so that frequency recovery becomes impossible. If this situation is left unchecked, the connected generator will cause unstable blurring on the turbine shaft and it will be damaged. In such situations they protect the generation system by removing the generator from the system (= disconnection).
Let’s look back on the supply power of Hokkaido Electric Power Company at the time of the earthquake. The total demand in Hokkaido was 2.92million kW(3:00～3.05am). The output of the Tomato Atsuma Power Station is 1.65 million kW, so the supply capacity of more than half of the grid has been lost due to the earthquake.
The frequency should have decreased in milliseconds. It is thought that UFR’s operation can not be done in time for this kind of decay, and it is considered that other generators were disconnected at almost the same time (Hokkaido Electric Power will analyze and publish details).
It can not be thought that Hokkaido Electric Power Company could do something to avoid all-way blackouts. Although it can only be said that the occurrence of an earthquake hit the Tomato Atsuma power plant was unfortunate, if it is dare to say, if the Tomari Nuclear Power (total of 2,070 MW) had been operating, there was a possibility that the whole power failure could be avoided.
At the time of preparing this paper, It recovered the supply capacity of 3.15 million kW on all roads, and it seems that the power was almost recovered except for the damaged parts of distribution facilities. This recovery is the best possible result. Press media officials should report such circumstances (eg by organizing special feature at NHK Special).
Although it is speculation, I think that there is a high possibility that the planned blackout can be avoided. I express my respects from the heart for the efforts of Hokkaido Electric Power.
Thank you very much!