This standard prescribes insulation levels and dielectric test requirements for power transformers where: (1) The transformer insulation levels and dielectric test requirements are explicitly specified to be in accordance with this standard. (2) The transformers are to be operated at system voltages from 115 kV through 230 kV. (3) The transformer has a rating, eithere single-phase or three-phase, equal to or greater than 30000 kVA self-cooled or 50000 kVA forced cooled.