This standard defines the requirements for operation and design of three-phase and single-phase liquid immersed subsea power transformers (including auto transformers) with at least one winding with rated voltages in the range 3.6 kV Um to 145 kV Um and with rated power in the range 50 kVA to 100 MVA. The intention is to specify additional requirements that are not covered by IEC 60076 and ANSI/IEEE C57.12 series.