Patented thermosyphon & Field-proven P&O™ bushings has two series --Type P&O™ I & II according to rated current. The current rated at 8000A and below is called Type P&O I, the current rated above 8000A is called Type P&O II. These two type bushings have thermosyphon design with heat exchange with main oil tank to dramatically reduce hotspot temp rise without any condenser paper but porcelain.

ZDVolt_P&O_II_Patent_2009