The 3rd tale: What is minimum amount of oil?
The photo shows a minimum-oil circuti-breaker at a nearby substation in Naganuma. The picture was taken 30 or so years ago. This one looks like already being replaced by GIS type long ago. Well, it is inevitable.


This is a product of T manufacturer under a licensed arrangement. Although I had seen many times the details starting from the assembly of the extiguishing chambers to the final operation tests at both factories in Sweden and T company, it was the first time for me to see the product installed in the actual substation.

The neighbouring place to the substation was a stone dealer. In ordert to take this picture, I was permitted to climb a stone lantern for sale.

In later years, I was given opportunities to see many substations in the U.S. It is at this time that I really understood the reason why the oil-minimum circuit-breaker is called in that way.

The typical oil circuti-breaker in the U.S. was none other than a gigantic steel tank which looks like the inverted body of "Tetujin 28 gou". The required oil quantity seemed an order or even 2 orders of mgnitude larger than that of oil-minimum CB.