... be designed to 30'', 15'', 7.5'', for rectification of 6-phase, 12-phase, 24-phase and 48-phase. A Model ... Cooling Device: Natural Cooling, Air Cooling F, Water Cooling S5. Way of Oil Circulations: Natural Circulation, Force Oil Circulation P6 ... . Way of voltage regulation: No-excitation regulation or without voltage regulation, ...