A swivel joint symmetrical about a longitudinal axis has an outer housing around a stacked connector, and has a cylindrical wall, a bottom wall, and a top wall. The swivel connector terminals are connected to the top and bottom walls. A second wall having a bottom and a top is placed around the inner wall.
There is no oil in the space defined between the walls. In the wall, a plurality of holes of the rotary joint are provided to be closed by a blasting disc, which bursts when the pressure increases in a space defined by the wall. When the pressure in the space in the inner wall rises sharply due to a short circuit, the blasting disc will burst from the hole so that oil can flow into the space between the inner wall and the outer wall. Therefore, the risk of hot oil spraying from the rotary joint container and explosive gas from the rotary joint is drastically reduced, and the operational safety of the rotary joint is increased.