For a 75/95 MVA transformer rated 220/110-70/15 kV, the typical vacuum level during insulation drying is usually in the sub-millibar range, around 0.2-0.5 mbar, and in many procedures it is kept below 1 mbar depending on temperature and moisture condition. During oil processing and degassing, vacuum oil purification units normally operate at a slightly higher level, commonly around 1-3 mbar, which is sufficient to efficiently remove dissolved gases and moisture from transformer oil.